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WHO/Hi???

This is to certify that the
thesis entitled

MODELING THERMAL AND MECHANICAL EFFECTS OF
EXTRUSION ON THIAMIN RETENTION IN EXTRUDED WHEAT
FLOUR

presented by
MARIA SUPARNO

has been accepted towards fulfillment
of the requirements for the

Master of degree in Biosystems and Agricultural
Science Engineerinl

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6/01 c:/ClRC/DateDue.p65-p.15

MODELING THERMAL AND MECHANICAL EFFECTS OF EXTRUSION ON
THIAMIN RETENTION IN EXTRUDED WHEAT FLOUR

By

Maria Suparno

A THESIS

Submitted to
Michigan State University
In partial fulfillment of the requirements
For the degree of

MASTER OF SCIENCE
Department of Biosystems and Agricultural Engineering

2004

ABSTRACT

MODELING THERMAL AND MECHANICAL EFFECTS OF EXTRUSION ON
THIAMIN RETENTION IN EXTRUDED WHEAT FLOUR

By

Maria Suparno

Average shear rate ( 7,) of a twin-screw co-rotating extruder was investigated to
calculate shear history- a factor to model the mechanical effect (Rs) of extrusion. Fluids
with different flow behavior indices, which represent different feed materials, were

extruded at degrees of fill ranging from 04-10. Using mixer viscometry assumptions, 7,,

was estimated and then modeled as a function of screw speed and degree of fill.

To calculate extrusion thermal effects on thiamin degradation (RB), kinetic
parameters were obtained by heating flour, mixed with thiamin, at temperatures>100°C
in a shearless environment. Two methods (atmospheric and controlled-pressure) to obtain
the parameters were compared. The results from the two methods were not statistically
different. The parameters obtained from the controlled-pressure method had lower
standard error; for 25% moisture content flour, activation energy was 121.0 kJ/g-mol and
reaction rate at 80°C was 9.69E—5 min".

For extrusion, the same thiamin flour mixture was extruded at screw speeds of
100-300 rpm at two temperatures profiles. R1; was calculated using the thiamin kinetic
parameters. Rs was calculated by mathematically removing R5 from the total thiamin
retention. At higher temperature, thermal effects predominated over mechanical effects
for thiamin loss, while at lower temperature, mechanical effects slightly prevailed over

thermal effects. Mechanical effects caused 28.9% to 64.5% of total thiamin loss.

DEDICATION

To my parents, Suparno and Tjhin Meliana, for their unconditional love, relentless word
of encouragement and faith in me. To my brothers, Robert, William and Jeffry, for

always looking out for me.

iii

SL‘

 

ACKNOWLEDGEMENT

Deepest gratitude for my major professor, Dr Kirk Dolan, for your excellent
guidance, encouragement and positive attitudes. Many thanks to my committee members,
Dr Perry Ng and Dr Bradley Marks, for your valuable inputs for my research. Special
thanks to Dr Perry Ng and Dr James Steffe for letting me use your laboratory facilities.

Special appreciation for Yoo Gi Chan and Edmund Tanhehco for your assistance
in extrusion experiments. Special thanks goes to Mr Richard Wolthuis for your technical
expertise.

I would also like to thank my close friends, for the many laughters and tears that
we shared together. Deepest thanks for the best lab 110 mates I could ever ask for; Kathy
Lai, Kay Sunthanont, Mitzi Ma, Monali Yajnik, Mavis Tan, Norm Matella and Shantanu
Kelkar, for your help and friendships. Lastly, many thanks to my brothers, Jeffry Suparno
and Rizal Prawira and my best fi'iends, Jimmy Pangestoe and Elvina Jonas for all your

support, care and prayers.

iv

TABLE OF CONTENTS

Pg

LIST OF TABLES .............................................................................. ix

LIST OF FIGURES ............................................................................. xii

INTRODUCTION .............................................................................. 1

CHAPTER 1. Literature Review .............................................................. 4

1.1. Food extrusion .................................................................... 4

1.2. Thiamin ............................................................................ 8

1.3. Thiamin analysis in wheat flour ................................................ 10

1.4. Thiamin stability .................................................................. 11

1.5. References ........................................................................ 13
CHAPTER 2. Average shear rate in a twin-screw extruder as a function of degree of

fill, screw speed and flow behavior index .................................. 15

2.1. Abstract ............................................................................ 15

2.2. Introduction ....................................................................... 16

2.3. Materials and Methods .......................................................... 19

2.3.1. Rheometer ............................................................... 19

2.3.2. Extruder .................................................................. 20

2.3.2.1. Hydraulic diameter and void volume ........................ 20

2.3.2.2. Energy balance in extruder .................................... 22

2.3.2.3. Extrusion run ................................................... 23

2.3.2.4. Degree of fill ................................................... 23

2.3.2.5. Estimation of average shear rate by matching viscosity. 25

2.4. Results and Discussions ......................................................... 27

2.4.1 . Rheometer ............................................................... 27

2.4.1.1. Newtonian fluid ................................................ 27

2.4.1.2 Non-Newtonian fluids ......................................... 29

2.4.2. Extruder .................................................................. 32

2.4.2.1. Degree of fill ................................................... 32

2.4.2.2. Estimation of average shear rate by matching viscosity. 32

2.4.2.3. Extruder constant ............................................... 35

2.4.2.4. Equation’s exponent (alpha) evaluation ..................... 40

2.4.3. Average shear rate model ............................................. 41

2.4.3.1. Fluid suitability ................................................. 43

2.5. Conclusions ....................................................................... 43

2.6. Future work recommendations ................................................. 44

2.7. Acknowledgment ................................................................. 44
2.8. Nomenclature ..................................................................... 45
2.9. References ........................................................................ 46

CHAPTER 3: Thermal kinetic parameters of thiamin in wheat flour at

temperatures >100°C ......................................................... 47
3. 1. Abstract ............................................................................ 47
3.2. Introduction ............. 48
3.3. Materials and Methods .......................................................... 53
3.3.1. Sample preparations .................................................... 53
3.3.2. Study la and 1b: Atmospheric Pressure heating ................... 54
3.3.2.1 Study 1a: Atmospheric pressure (AP)
— Constant-moisture ............................................ 55
3.3.2.1.1. Data analysis ................................... 55
3.3.2.2. Study 1b: Atmospheric pressure (AP)
— High-temperature ............................................ 57
3.3.2.2.1. Data analysis ................................... 57
3.3.2.3. Correction method for high-temperature reaction rate
constant .......................................................... 57
3.3.3. Study 2: Controlled Pressure heating ................................ 59
3.3.3.1. Data analysis .................................................... 61
3.3.3.1.1. Temperature calculation ...................... 61
3.3.3.1.2. Kinetic parameters estimation ............... 64
3.4. Results and Discussions ......................................................... 68

3.4.1. Study 1a. Atmospheric Pressure heating- Constant-moisture. . .. 69
3.4.2. Study 1b. Atmospheric Pressure heating

- High-temperature heating ........................................... 71

3.4.2.1. Corrected high-temperature reaction rate constant. . . . . 73

3.4.3. Study 2: Controlled Pressure heating ................................ 75

3.4.4. Comparison of the kinetic parameters obtained by two methods 81
3.4.4.1. Activation energy .............................................. 81

3.4.4.2. Reaction rate constant ......................................... 82

3.5. Conclusions ....................................................................... 86
3.6. Future work recommendations ................................................. 87
3.7. Acknowledgement ............................................................... 87
3.8. Nomenclature ..................................................................... 88
3.9. References ........................................................................ 90

vi

CHAPTER 4: Modeling thermal and mechanical effect of extrusion processing of

wheat flour on thiamin retention .............................................................. 93
4.1. Abstract ............................................................................ 93
4.2. Introduction ....................................................................... 95
4.3. Materials and Methods .......................................................... 98

4.3.1. Extrusion ................................................................. 98

4.3.1.1. Equipment specification ....................................... 98

4.3.1.2. Pre- extrusion preparation ........................................... 99

4.3.1.3. Extrusion processing .......................................... 100

4.3.2. Analysis .................................................................. 102

4.3.2.1. Residence Time ................................................ 102

4.3.2.2. Color-concentration calibration curve ....................... 103

4.3.2.3. Degree of fill ................................................... 103

4.3.2.4. Thiamin ......................................................... 104

4.3.3. Modeling ................................................................. 105

4.3.3.1. Thermal effect of extrusion on thiamin retention .......... 106

4.3.3.2. Mechanical effect of extrusion on thiamin retention ...... 107

4.3.3.3. Model validation ................................................ 108

4.3.4. Thiamin loss ............................................................. 109

4.4. Results and Discussions ......................................................... 110

4.4.1. Mean residence times .................................................. 110

4.4.2. Degree of fill ............................................................ 112

4.4.3. Effect of screw speed on thiamin retention ......................... 113

4.4.3.1. Condition 1, barrel temp = 50/85/ 1 15/ 130/ 155°C ......... ‘ 114

4.4.3.2. Condition 2a—e, barrel temp = 50/80/1 10/140/165°C. . 115

4.4.3.3. Condition 3, barrel temp = 50/80/1 10/ 140/ 165°C ......... 116

4.4.4. Effect of moisture content on thiamin retention .................... 118

4.4.5. Modeling thiamin mechanical retention at constant fill ........... 119
4.4.5.1. Combining data for model

development .............................................................. 120

4.4.5.2. Model development, Rs = f(screw speed) .................. 121

4.4.5.3. Model development, R3 = f(shear history) .................. 122

4.4.5.4. Model development, Rs = f(SME) ........................... 124

4.4.5.5. Model validation ...................................................... 124

4.4.6. Thiamin loss (thermal and mechanical) .............................. 126

4.4.7. Obtaining the moisture content parameter (b) in extrusion ....... 128

4.5. Conclusions ....................................................................... 129

4.6. Future work recommendations ................................................. 130

4.7. Nomenclature ..................................................................... 131

4.8. References ........................................................................ 132

vii

CHAPTER 5: Conclusions and Novelty of research ....................................... 133

Appendix 1. Thiamin analysis and standard curve .......................................... 136
LA. Thiamin analysis ................................................................ 137
IE. Standard Curve and Thiamin Calculation .................................... 140
Appendix 2. Extrusion data collection for Chapter 2 ....................................... 142
2.A. Data collection during extrusion run .......................................... 143
2.B. Average shear rates data ........................................................ 149
Appendix 3. Data and Figures for Chapter 3 ............ '- .................................... 151
3.A. Data for constant-moisture study (study 1a) ................................. 152
3B. Data for high-temperature heating at atmospheric pressure (study 1b)... 154
3C. Thiamin retention data from controlled-pressure heating (study 2) ...... 155
3D. Gauss-Legendre quadrature (Stasa 1985) .................................... 156
3.E. Plot of measured vs predicted center temperature for study 2 ............ 158
3.F. Plot of measured vs predicted thiamin retention in study 2 ............... 159
3.G. Confidence region for 28.2% MC flour 160
Appendix 4. Data from Chapter 4 ............................................................. 161
4.A. Color concentration curve ...................................................... 162
4B. Condition 1 extrusion data ...................................................... 163
4.C. Condition 2 extrusion data ...................................................... 165
4D. Condition 3 extrusion data ...................................................... 169

viii

 

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LIST OF TABLES

Chapter 1
Table 1.1 United States Food and Drug Administration standards for minimum
amount of vitamin B in mg/lb for cereal-grain products (1998) ..........................

Chapter 2
Table 2.1. Screw configurations and volume ................................................

Table 2.2. Extruder and screw flight data ...................................................

Table 2.3. Rheological properties of Com syrup based on the model a- = p7

Table 2.4. Rheological properties of 2.8% A40M Methycellulose based on the
model 0' = K 7" .................................................................................

Table 2.5. Rheological parameters of fluids used for extrusion and their
temperature and shear rate dependence ......................................................

Table 2.6. Equations correlating Power number and Reynolds number for corn
syrup at three different degrees of fill ........................................................

Table 2.7. Summary of regression analysis (extruder constant and alpha) ..............
Chapter 3
Table 3.1. Summary of the experiments conducted to obtain thermal kinetic

parameters of thiamin ...........................................................................

Table 3.2. Activation energy, reference rate constant and pre-exponential

constant generated from study 2 ...............................................................

Table 3.3. Statistic analysis from bootstrap results of 1,000 E, and k, values ..........

Table 3.4. Comparison of activation energies for MC (wb/db) = 25/33.3% flour. .

Table 3.5. Comparison of reaction rate constant for MC (wb/db) = 25/ 33.3% flour..

Table 3.6. Moisture content parameter b(-) based on two studies .........................

Table 3.7.Activation energy and rate constants for thiamin loss in food products. .

ix

Pg

21
21

28

29

31

33

35

67

78

78
81

82

83

85

Chapter 4
Table 4.1 Screw configuration for high shear extrusion ................................... 99

Table 4.2. Extrusion conditions ............................................................... 101

Table 4.3. Data for extrusion at barrel temperature 50/85/ 1 15/ 130/ 155°C and
50/80/ 1 10/ 140/ 165°C for 33.3% MC (db) dough .......................................... 111

Table 4.4. Data for extrusion at barrel temperature 50/80/ 1 10/ 140/ 165°C at 200
rpm for various moisture contents ............................................................ 111

Table 4.5. Visual observation of sectional degree of fill after dead-stop at 200
rpm ................................................................................................. 112

Table 4.6. The significance of the shear term on the thiamin mechanical retention,

Rs .................................................................................................. 119
Table 4.7. Thiamin loss during extrusion processing for 2 different days ............... 127
Table 4.8. Moisture content parameter b based on three studies ......................... 129
Appendix

Table 1.B.1. Amounts of reagents used to determine standard curve .................... 140
Table 2.A. 1. Data collection during extrusion run for corn syrup, n = 1.00 ............ 143
Table 2.A.2. Data collection during extrusion run for A40m, n = 0.24 .................. 145
Table 2.A.3. Data collection during extrusion run for A40m, n = 0.28 .................. 146
Table 2.A.4. Data collection during extrusion run for K99, n = 0.60 .................... 147
Table 2.A.5. Data collection during extrusion run for K99, n = 0.67 .................... 148
Table 23.1 Average shear rates data for non-Newtonian fluid ........................... 149
Table 3.A.1. Moisture content of flour mixture ............................................. 152

Table 3.A.2. Thiamin concentration value of 80°C heating for MC (wb/db)
= 5.8 / 6.15, 8.8 / 9.67 and 9.7 /10.7% ......................................................................... 152

Table 3.A.3. Thiamin concentration value of 80°C heating MC (wb/db) =14.7 /
17.2, 21.3 /27.0 and 26.9 / 36.9% ................................................................................ 153

Table 3.A.4. Regression analysis for constant-moisture study ........................... 153

Table 3.B.1. Thiamin concentration of 25% MC (wb)/ 33.3% MC (db) at
high-temperatures (Study 1b) .................................................................. 154

Table 3.B.2 Regression analysis of hi gh-temperature atmospheric
heating data (Study 1b) ......................................................................... 154

Table 3.C. Thiamin retention data from study 2 ............................................ 155

Table 4.B.1. Processing data for extrusion at condition 1 at constant degree of fill
(varying feed rate) .............................................................................. 163

Table 4.B.2. Calculated data for extrusion at condition 1 at constant degree of fill... 164

Table 4.C.1. Processing data for extrusion at condition 2a-e die temperature at
constant degree of fill ........................................................................... 165

Table 4.C.2. Calculated data for extrusion at condition 2a—e at constant degree of
fill ................................................................................................. 166

Table 4.C.3 Processing data for extrusion at varying moisture content (constant fill) 167
Table 4.C.4.Calculated data for extrusion at varying moisture content (constant fill) 168

Table 4D. 1. Processing data for extrusion at condition 3 at varying degree of fill
(constant feed rate) .............................................................................. 169

Table 4.D.2. Calculated data for extrusion at condition 3 at varying degree of fill. . .. 170

xi

LIST OF FIGURES

Pg
Chapter 1
Figure 1.1. Flow chart to describe the goal of this research ............................... 3
Figure 1.2. Chemical structure for thiamin (Ottaway 1993) .............................. 9
Chapter 2
Figure 2.1. Matching viscosity method to determine average shear rate ............... 26
Figure 2.2. Plot of Shear stress versus Shear rate for Corn syrup ....................... 27
Figure 2.3. Consistency coefficient versus reciprocal temperature for corn syrup... 28
Figure 2.4. Shear stress versus shear rate for 2.8% A40M Methycellulose. . . . . .. . 29
Figure 2.5. Consistency coefficient versus temperature for 2.8% A4OM
Methycellulose ................................................................................. 30
Figure 2.6. Plot of Power number versus measured degree of fill for corn syrup. . 32
Figure 2.7. Plot of Power number versus Reynolds number for corn syrup ............ 33
Figure 2.8. Plot of average shear rate versus screw speed for 2.8% A40M
Methycellulose (Curve equation = 7, = k'N“) ............................................ 34
Figure 2.9. Extruder constant (k') vs. screw speed of non-Newtonian fluids
with varying flow behavior index (n) at 1.0 degree of fill ................................ 36
Figure 2.10. Extruder constant vs. screw speed of non-Newtonian fluids with
varying flow behavior index (n) at 0.7 fill degree ......................................... 37
Figure 2.11. Extruder constant vs. screw [speed of non-Newtonian fluids with
varying flow behavior index (n) at 0.4 fill degree .......................................... 38
Figure 2.12. Effect of degree of fill on extruder constant ................................. 39
Figure 2.13. Effect of degree of fill on alpha ............................................... 40

xii

Figure 2.14. Predicted average shear rate versus the experimental average shear

rate data .......................................................................................... 42
Chapter 3

Figure 3.1. Steel cell for Atmospheric Pressure heating .................................. 54
Figure 3.2. Setup for Atmospheric Pressure heating ....................................... 54

Figure 3.3. Example plot of the moisture content effects on reaction rate
constant for thiamin ............................................................................ 56

Figure 3.4. Thermocouple was inserted into the center of can (left) so that the
geometric center temperature was recorded (right) ........................................ 59

Figure 3.5. Five—point Gauss-Legendre quadrature for off temperature
calculation for half-can ...................................................................... .. 64

Figure 3.6. Plots of flour center temperature versus time for study la and 1b. . . . . 68

Figure 3.7 . Semi-log plot of thiamin concentration versus heating time for
6.15, 9.67, 10.7% moisture content (db) flour heated isothermally at
80°C in an oil bath .............................................................................. 69

Figure 3.8. Semi-log plot of thiamin concentration versus heating time for
17.2, 27.0, 36.9% moisture content (db) flour heated isothermally
at 80°C in an oil bath ........................................................................... 70

Figure 3.9. Effect of flour mixture moisture content (db) on reaction rate constant
at 80°C heating ................................................................................. 70

Figure 3.10. Plot of Ln k versus MC % (db) of Hermann and Tunger (1966)
at 90 and 110°C and the present study ...................................................... 71

Figure 3.11. Possible reason for the difference between the result in
Hermann and Tunger (1966) and the present study ....................................... 72

Figure 3.12. Semi-lo g plot of thiamin concentration versus heating time for

flour mixture heated isothermally at 144.8, 159.2 and 170.6°C
average oil bath temperature .................................................................. 73

xiii

Figure 3.13. Plot of flour moisture content versus heating time during high
temperature heating in study 1b .............................................................. 74

Figure 3.14. Arrhenius plot for the corrected and uncorrected reaction rate
Constants ........................................................................................ 75

Figure 3.15. Plot of measured versus predicted center temperature for 33.3% (db)
MC flour in 201x211 cans heated at 129.4°C retort temperature ........................ 76

Figure 3.16. Plot of measured thiamin retention vs predicted thiamin retention for
33.3%MC (db) flour in 201x211 cans heated at 129.4°C retort temperature ........... 77

Figure 3.17. 3-D bivariate normal probability distribution
[90 & 95% confidence region] for estimated activation energy (kJ/g-mol)
and reaction rate constant k80 (min-l) for MC=33.3% flour from bootstrap data... 79

Figure 3.18. 90% and 95% joint confidence region for estimated activation
energy (kJ/gmol) and reaction rate constant (min'l) for MC=33.3% flour

from bootstrap data ............................................................................. 80
Chapter 4

Figure 4.1. Residence time distribution curves of flour extruded at

50/80/ 1 10/ 140/ 165°C barrel temperature at 100, 200 and 300 rpm ..................... 110

Figure 4.2. Pictorial view of an opened extruder barrel, showing the extruder
degree of fill at specific barrel sections opened after dead- stopping at 200 rpm. . 112

Figure 4.3. Thermal and mechanical effects on thiamin retention versus screw
speed for samples extruded at barrel temp 50/85/ 1 15/ 130/ 155°C (condition 1) ....... 114

Figure 4.4. Thermal and mechanical effects on thiamin retention versus screw
speed for samples extruded at 50/80/ 1 10/ 140/ 165°C (condition 2a-e) .................. 115

Figure 4.5. Thermal and mechanical effects on thiamin retention versus screw
speed for samples extruded at 50/80/ 1 10/ 140/ 165°C (condition 3) ..................... 116

Figure 4.6. Plot of measured thiamin retention for condition 2 at constant
degree of fill and condition 2 at varying degree of fill .................................... 117

Figure 4.7. Thermal and mechanical effects on thiamin retention versus moisture
content for samples extruded at 200 rpm and 50/80/ 1 10/ 140/ 165°C
barrel temperature .............................................................................. 1 18

xiv

Figure 4.8. Plot of thiamin mechanical retention versus screw speed for all data. .
Figure 4.9. Plot of thiamin mechanical retention versus shear history for all data. . ..

Figure 4.10. Plot of thiamin mechanical retention versus specific mechanical
energy for all data ..............................................................................

Figure 4.11. Plot of predicted measured retention versus experimental retention
for data from condition 3 and Schmid et a1. (2002) .......................................

Appendix
Figure LB. 1. Standard curve for fluorescence reading vs thiamin concentration
constructed in duplicate on two different days .............................................

Figure 3.E. 1. Plot of measured vs predicted center temperature for
19.1% MC (db) flour in 201x211 cans heated at 129.4°C retort temperature ..........

Figure 3.B.2. Plot of measured vs predicted center temperature for 28.2% MC (db)
flour in 201x211 cans heated at 129.4°C retort temperature ..............................

Figure 3.F. 1. Plot of measured vs predicted thiamin retention for 19.1% MC flour
in 201x211 cans heated at 129.4°C retort temperature ....................................

Figure 3.F.2. Plot of measured vs predicted thiamin retention for 28.2% MC flour
in 201x211 cans heated at 129.4°C retort temperature ....................................

Figure 3.G. 90 and 95% joint confidence region for estimated activation energy
(kJ/g-mol) and reaction rate constant k80 (min") for MC=28.8% flour obtained
from bootstrap data .............................................................................

Figure 4.A. Plot of Hunter b’ color units versus blue-dye concentration (%wb) of
flour extruded at 200 rpm at 160°C ..........................................................

XV

121

122

123

124

141

158

158

159

159

160

162

INTRODUCTION

Extrusion is growing as a processing technology for food products, due to its
ability to combine several processes such as mixing, cooking, shaping and texturizing in
one energy-efficient process. The list of food products being produced with extruders
includes ready-to-eat cereals, beverage powders, pasta and snack products.

When some food materials are processed in an extruder, they are subjected to high
temperature in combination with severe shear. These conditions can be beneficial for
denaturing anti-nutritional factors, but can also be undesirable, because nutrients are
degraded to varying extents (Harper 1973, ijrk and Asp 1983). Consequently, for a
heat-labile nutrient, fortifying food materials pre-extrusion is necessary. A model to
predict the effect of the many variables of the extrusion process on thiamin degradation
would be helpfirl for designing processes.

Few studies h ave reported the total thiamin d egradation in e xtruded wheat and
corn flour (Beetner et al. 1974, Guzman-Tello and Cheftel 1987, 110 and Berghofer 1998,
Schmid 2002). Some of these researchers have modeled thiamin retention or thiamin
degradation rate as a function 0 f b arrel temperature, 8 crew speed 0 r m oisture c ontent.
However, the proportionate effects of shearing and heating on degradation were
unknown. By quantifying these two effects (thermal and mechanical), the significance of
each could be evaluated and the processing variables could be chosen for an optimum
condition.

Mechanical effect of extrusion could be represented by shear rate or shear history.
Due to the complexity of mixing in twin-screw extruders, calculating the velocity profile

or local shear rates in the extruder is not feasible. Thus, the average shear rate was

calculated. Mohamed et a1. (1990) investigated average shear rate in an extruder at fully
filled extruder condition (1.0 degree of fill) using the mixer viscometry matching
viscosity assumptions. A more extensive study on average shear rate must be conducted,
because 0 ommercial twin-screw food extruders normally 0 perated at 0 .4-0.8 d egree o f
fill. Furthermore, their study only investigated one type of non-Newtonian fluid with flow
behavior index = 0.5. Thus, the first objective 0 f the present study was to investigate
average shear rate as a function of degree of fill, flow behavior index and screw speed.

To calculate the thermal effects of extrusion on thiamin, thiamin kinetic
parameters at high temperature must be available. To date, few studies have investigated
thiamin kinetic parameter in flour at high temperature. Hermann and Tunger (1966)
reported that moisture content of flour affected thiamin kinetic parameters. Therefore,
during high temperature heating, moisture content of flour must be maintained constant
to attain the correct kinetic parameter at the corresponding moisture content. Hence, the
second objective of this study was to determine thiamin kinetics parameters of thiamin in
wheat flour at temperature higher than 100°C.

Subsequent to quantifying the thermal and mechanical effects of extrusion on
thiamin retention, a model could be developed to predict thiamin retention in extruded
products. The model may save time and cost compared to trial-and-error experiments. In
addition, the m odel w ould b e u seful for s cale-up p urposes o r for o ptimizing e xtrusion
processing to achieve minimum thiamin degradation. Thus, the last objective was to
model the thermal and mechanical effects of extrusion on thiamin retention.

In summary, the objectives of this research were;

1) To model the average shear rate in the extruder as a function of screw speed, flow
behavior index and degree of fill (Chapter 2);

2) To determine the thermal kinetic parameters of thiamin in wheat flour at high
temperature (Chapter 3);

3) To model the thermal and mechanical effects of thiamin retention in the extrusion
process (Chapter 4).

Figure 1.1 summarizes the goal of this research.

 

 

Chapter 2:
Average shear rate in an extruder = f(screw speed, flow behavior index
and degree of fill)

 

 

 

 

Chapter 3:
Thiamin kinetics parameters:
' Reaction rate constant (k,)
I Activation energy (Ea)
j I Moisture content parameter (b)

I

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 4: Chapter 4:
Modeling the mechanical Modeling the thermal effect
effect of extruder of extruder
\ J
V

A model to predict thiamin retention in extruded wheat flour

 

 

 

Figure 1.1. Flow chart to describe the goal of this research.

Chapter 1. Literature review
1.1. Food Extrusion

The use of extruders has been increasing over the past several decades in many
areas such as the aluminum, plastic and food industries. Several different types of
extruders are on the market, e.g., dry extruders, interrupted-flight screw extruders, and
single and twin- screw extruders. For over 25 years, single-screw extruders were
primarily u sed for p roducts ranging fiom light density c om s nacks, to dense, p artially
cooked, and formed pasta. However, as demand for new and high quality products has
increased, single screw extruders were no longer adequate. Twin—screw technology thus
gained popularity in the food industry because of its ability to produce different Shapes,
colors, and textures. In food industry, the first application of using a cooking extruder
occurred in the mid- 19408 to produce an expanded cornmeal-based snack (Harper 1978).
Currently, cooking extruders are used for production of ready-to-eat cereals, snack foods,
beverage powders, soft/dry pet foods, pasta products, full or defatted soy flour, soup or
gravy bases, and confections.

Food extrusion, by the definition of Rossen and Miller (1973), is a process in
which a food material is forced to flow, under different conditions of mixing, heating,
and shear, through a die designed to form and/or puff-dry the ingredients. Extrusion has
been extensively used in the food industry because it offers several advantages over the
processes it replaces. Extruders mix, cook, texturize, and shape food material in one
continuous, fully automated, and energy efficient process. A variety of shapes, textures,
colors, and appearances can be produced just by changing the die shape, minor

ingredients, or processing variables. Examples of processing variables are feed

ingredients, the amount of water injected into the extruder barrel, raw material feed rate,
screw speed, and barrel temperature. These are the equipment-dependant variables.
Equipment-independent variables such as moisture content of extrudate, pressure, shear
rate, shear history, residence time, and product characteristics change as a result of
modifications made to equipment-dependant variables.

Heat e nergy during e xtrusion c omes from different 8 ources. O ne 0 f the energy
inputs comes from viscous dissipation, which is the energy dissipated in the form of heat
caused by shear or friction between rotating screws and feed materials. This is referred as
the shear energy or the mechanical energy (Mohamed et al. 1990). An extruder is
usually equipped with electrically heated rods or a steam injection mechanism for adding
another energy input, the thermal energy to the process, thus helping to heat feed
materials to a temperature of up to 200°C in the barrel. A barrel is divided into three
zones: the feeding, kneading and final cooking zone. As materials enter the feeding zone,
they are pre-heated and may be injected with water or steam. Water is typically added in
this zone to alter the texture or viscosity of the material. The screws compress the low-
density raw materials and convey them to the kneading zone. In the kneading zone,
compression continues to expel entrapped air with decreasing screw pitch. As
temperature increases in this barrel section, pressure begins to build. The shear rates,
pressure, and temperature are highest in the final cooking zone. In this zone, the screw
pitch is the lowest, 0 ompressing the material to the greatest d egree. At the end 0 f the
extruder barrel, the material exits through a die opening, where it expands rapidly as
pressure decreases. At this time, moisture in dough flashes off to steam, resulting in

product expansion. In these three zones, the combination of twin-lead screw, single-lead

screw, and kneading/mixing paddles determine the degree of conveying and compression.
Screws can be configured to create high shear or low shear. Assembling different screw
configurations varies products characteristics, thus creating potential for product
developments. Twin-lead s crews are u sually placed in the feeding 2 one, and u seful to
convey materials. Single-lead screws are used for compressing material and increasing
the degree offill in the extruder. The kneadingpaddles canbe set at 30°, 60° or90°
rotated fiom one another on the extruder shafts. The paddles are called forward kneading
paddles if they are set up in a way that the material will be moved towards the die
direction. Reverse kneading paddles will move the material away from the die direction,
thus increasing the degree of fill at that point. As raw materials moved towards the final
cooking zone, the screws are usually configured such that the degree of fill increases to a
maximum of 1.0.

In addition to its ability to manufacture a variety of foods in a continuous process,
an extruder is also effective in inactivating spoilage enzymes, trypsin inhibitors and
microorganisms (Harper 1981, Chefiel 1989). The intense thermal and mechanical energy
inputs during extrusion also trigger many chemical and nutritional changes, such as
starch gelatinization, protein denaturation, and degradation of vitamins, flavors, and
pigments (Bjc’irk and Asp 1983, Harper 1988, Killeit 1994). While starch gelatinization is
desirable for digestibility, degradation of vitamins is the undesirable side effect of
extrusion. In s ome food industry, to replenish vitamins d egradation, extrudates c an b e
sprayed with vitamins after extrusion. Maga (1989) summarized many of the problems
associated with this surface coating method. Some disadvantages are heterogeneous

distribution, loss due to dripping, additional processing cost and time, and increased

possibility of microbial contamination. Thus, the most common method implemented in
most food industry is to over-fortify the dry mix prior to extrusion (Ottaway 1993 and L.
Morel “pers com.”). A predictive model would be useful to determine the retention of
these compounds to calculate the amount of vitamins to be added prior to extrusion.
Using the model, the optimum conditions could be determined where minimum
degradation is achieved. The resulting generalized model for vitamins degradation would

be helpful to minimize experimental time and cost in extrusion process design.

II

 

1.2. Thiamin

Since 1943, all bread and grains products in the United States must be enriched
with iron and vitamin B complex (niacin, thiamin, and riboflavin) because these vitamins
are removed during flour milling. Folic acid (vitamin B9) fortification of grain products
was mandated in 1998. The minimum standard for vitamin B content was established by
the Food and Drug Administration (Table 1.1) and reported by Fortitech (2001).

Table 1.1 Federal enrichment standards of vitamin B in mg/kg for cereal-grain products
(1998)

 

Grain products Thiamin Riboflavin Niacin Folic acid
(Vitamin B.) (Vitamin B2) (Vitamin B3) (V itarnin B9)

 

 

 

 

 

 

 

 

 

 

Pasta products 8.83 — 11.0 3.75 -— 4.86 59.6 — 75.1 1.99 — 2.65
Bread, rolls, and buns 3.97 2.43 33.1 0.95 7
Commeal 4.42 — 6.62 2.65 — 3.97 35.3 — 52.9 1.55 — 2.21
Flour 6.40 3.97 52.9 1.55

Rice 4.42 — 8.83 2.65 — 5.30 35.3 — 70.6 1.55 — 3.09

 

Among these four water-soluble vitamins, thiamin is the most susceptible to
degradation by thermal processing. Thiamin, a water-soluble B-complex vitamin, is also
known as B]. It is necessary for normal functioning of the cardiovascular, nervous,
muscular, and gastrointestinal systems. The coenzyme thiamine pyrophosphate, the active
form of thiamin, participates in the breakdown of glucose and in the Kreb's cycle, the
central energy-yielding pathway 0 f the b ody. T hiamin also enhances blood circulation
and blood formation, and assists in hydrochloric acid production, which is necessary for
proper digestion. It also optimizes cognitive activity and brain function (Rindi 1996). In
addition, thiamin acts as an antioxidant by protecting the body from the degenerative
effects of aging, alcohol consumption, and smoking. A deficiency in thiamin results in a

disease called beriberi. This deficiency is common in Asia where rice is excessively

 

milled to create polished rice (Krishna 1999). Thiamin is mostly found in the rice bran,
which is removed during milling. Depending on the organ system affected by thiamin
deficiency, beriberi has been termed wet, dry or cerebral. Wet (cardiovascular) beriberi
symptoms include rapid heart rate, enlargement of the heart, severe swelling, difficulty
breathing, and ultimately congestive heart failure. The main features of dry (neural)
beriberi are abnormal reflexes, diminished sensation, and weakness in legs and arms. The
most severe deficiency in thiamin results in cerebral beriberi, also known as Wenicke-
Korsakoff syndrome. Symptoms are profound memory disorder, abnormal eye
movements and aphasia. A diet including thiamin is necessary to prevent beriberi. The
average dietary thiamin intake for young adult men and women is about 2 mg/day and 1.2
mg/day, respectively. The reference daily intake value recommended by the Food and
Drug Administration (1994) is 1.5 mg/day. Sources of thiamin are whole grain cereals,
legumes, nuts, lean pork, yeast, enriched bread and flour (Ottaway 1993).

Thiamin consists of pyrimidine and tlriazole rings, linked by methylene bridge

(Figure 1.2).

r CH3 N NH2 \

\ CH3
I / +/—1—CH2-CH2- OH x
N CH2 7N\_ s

J

 

 

K

Pyrimidine Thiazole

Figure 1.2. Chemical structure for thiamin (Ottaway 1993).
X = C1", HCl (Thiamin hydrochloride)

X = NO; (Thiamin mononitrate)

X = H3P205 (Thiamin pyrophosphate)

Thiamin occurs in natural foods either in its free form or in a combined form as a
protein complex: a phosphorus-protein complex or the pyrophosphoric acid ester: co-
carboxylase (thiamin pyrophosphate). Thiamin is commercially available for addition to

food in the form of thiamin hydrochloride and thiamin mononitrate.

1.3. Thiamin analysis in wheat flour

Techniques for analyzing thiamin in food products are well-documented. The
thiochrome method is the standard chemical method approved by the Association of
Official Analytical Chemists (AOAC, 1995) and the American Association of Cereal
Chemists (AACC, 2000). Results obtained by the thiochrome method are equally as
precise as those obtained by High Performance Liquid Chromatography (HPLC), which
is another accurate, rapid and sensitive method (Toma and Tabekhia 1979, Kamman et a1.
1980, Abdel 1992). In this study, the thiochrome method was chosen because of its
accuracy within 5% (Labuza and Riboh 1982), and because the necessary equipment was
readily available. The thiochrome method involves oxidation of thiamin to thiochrome by
adding an oxidizing agent such as potassium ferricyanide under alkaline conditions. In
the absence of other fluorescing substances, the thiochrome fluorescence under UV light
is linearly proportional to the amount of thiamin present following a standard curve.
McFarlane and Chapman (1941) stated that different grain products contain different
proportions of organic materials, thus making the optimal amount of oxidizing agent
unique to each grain product. An investigation of the thiochrome method for soft wheat
flour was recently published by Moore and Dolan (2003). They were the first to optimize

the protocol for soft wheat flour analysis. They found that the maximum level of

10

potassium fenicyanide added to aqueous thiamin-HCI extract was ranged from 4.84 to
100 pg per pg thiamin solution. A higher or lower amount of agent would decrease the
fluorescence reading. Therefore, for our study, a level of 37.28 pg potassium ferricyanide
per pg thiamin solution was chosen for optimal range. Another finding was that mixing
potassium ferricyanide with sodium hydroxide as oxidizing agent yielded a lower
experimental error than adding the potassium ferricyanide and sodium hydroxide

separately to the thiamin extract. Their improved, accurate, and optimized protocol for

sofi wheat flour analysis was followed in the present study.

1.4. Thiamin stability

Dwivedi and Arnold (1973) summarized the factors affecting thiamin degradation
in food products, which includes pH, temperature, oxidation-reduction potential of
systems, sulphites and bisulphites content, presence of aldehydes, amine and radiation. At
pH < 5 .0, thiamin is quite stable to h eat and o xidation; h owever above pH > 5.0, it is
easily destroyed by heat. In the presence of heat, thiamin degradation involves the
cleavage at the CH ‘bridge’ between the pyrimidine and thiazole molecules. Thiamin is
very sensitive to sulphites and bisulphites especially at high pH. This is the cause of most
thiamin degradation in vegetables blanched with sulphites and in meat products where
sulphites and bisulphites are usually used as preservatives. Van der Poel (1956) reported
that when thiamin was heated in a glucose solution, a brown discoloration and fluorescent
compound was produced, which resembled a Maillard reaction of sugars and amino
acids. Thiamin’s participation in Maillard reaction may be important in the loss of

thiamin during heat processing. Its participation is believed to be caused by its

11

nitrogeneousity (Van der Poel 1956, Hermann and Tunger 1966). The breakdown of
thiamin, especially during heating, release off-flavors and odors, some which are

unpleasant.

12

1.5. References

AACC. 2000. Association of Cereal Chemists Approved Methods, 10th edition, St. Paul,
Minnesota

Abdel KZM. 1992. Comparison of AOAC and high-performance liquid chromatographic
methods for thiamin determination in foods. Food Chemistry 43(5): 393-397

AOAC International. 1995. Official Methods of Analysis, 16th edition. AOAC
International, Arlington, VA.

Beetner G, Tsao T, Frey A and Harper J. 1974. Degradation of thiamine and riboflavin
during extrusion processing. Journal of Food Science 39(1): 207-209.

Bender DA. 1992. Nutritional biochemistry of the vitamins. Cambridge University Press.
Printed in Great Britain.

Bj6rk I and Asp Ng. 1983. The effects of extrusion cooking on nutritional value- a
literature review. Journal of Food Enginering 2:281-308. ‘

Cheftel JC. 1989. Flavor formation and retention during extrusion. Extrusion cooking
Chapter 15. American Association of Cereal Chemists, Inc. St. Paul, Minnesota.

Dwivedi BK and Arnold RG. 1973. Chemistry of thiamine degradation in food products
and model food systems: A review. Journal of Agricultural Food Chemistry 21(1): 54-60.

Guzman-Tello R and C hefiel JC. 1 987. Thiamine loss during extrusion c ooking as an
indicator of the intensity of thermal processing. International Journal of Food Science and
Technology 22:549-562.

Harper JM. 1978. Extrusion processing of food. Food Technology 32 (7)267-72.

Harper JM. 1981. Extrusion of foods. Volume 1. CRC Press. Boca Raton, Florida.

Harper JM. 1988. Extrusion processing. In nutritional evaluation of food processing, 3rd
edition. E. Karmas and RS Hanis. Van Nostrand Reinhold Company, New York.

Hermann F and Tunger L. 1996. Thermal loss of thiamin in relation to moisture content
of foods, with special reference to flour products. Nahrung 10(8): 705-712 (in German).

110 S and Berghofer E. 1998. Kinetics of therrnomechanical loss of thiamin during
extrusion cooking. Journal of Food Science 63(2): 312-316.

Kamman JF, Labuza TP and Warthesen JJ. 1980. Thiamin and riboflavin analysis by high
performance liquid chromatography. Journal of Food Science 45 (6): 1497-1499, 1504.

13

Krishna S. 1999. Thiamin deficiency and malaria in adults from Southeast Asia. The
Lancet, volume 353; pg 546-549.

Killeit U. 1994. Vitamin retention in extrusion cooking. Food Chemistry 49:149-155.

Labuza TP and Riboh D. 1982. Theory and application of Arrhenius kinetics to the
prediction of nutrient losses in foods. Food Technology 36(10): 68-70, 72, 74.

Maga JA. 1989. Flavor formation and retention during extrusion. Extrusion cooking
Chapter 13. American Association of Cereal Chemists, Inc. St. Paul, Minnesota.

McFarlene WD and Chapman RA. 1941. An improved thiochrome method for the
estimation of vitamin B1. Canadian Journal of Research 19: 136-142.

Mohamed IO, 0 foli RY, M organ R C. l 990. M odeling the average 3 hear rate in a c o-
rotating twin-screw extruder. Journal of Food Process Engineering 12:227-246.

Moore JC and Dolan KD. 2003. Optimization of oxidation steps used in fluorometric
determination of thiamin in soft wheat flour. Cereal Chemistry 80(2): 23 8-240. ‘

Ottaway PB. 1993. The technology of vitamins in food. Blackie Academic &
Professional, Chapman and Hall, G642NZ.

Rindi G. 1996. Thiamin. Present knowledge in nutrition. Washington DC: ILSI Press, pg
1 60-166.

Rossen JL and Miller RC. 1973. Food extrusion. Food Technology 47-52.
Schmid, Abigail H. 2002. The effect of extruding wheat at lower temperatures on thiamin
loss and physical attributes when using carbon dioxide gas as a puffing agent. Michigan

State University, East Lansing, MI

Toma RB and Tabekhia MM. 1979. High performance liquid chromatographic analysis
of B-vitamins in rice and rice products. Journal of Food Science 44(1): 263-266, 268.

Fortitech. 2001. Fortifacts. The world leader in nutrient systems.
http://wwwfortitech.com/news/01_0ct.pdf

Van der Poel, GH. 1956. Participation of B vitamins in non-enzymatic browning
reactions. International Chemistry Abstract 54:3770a.

14

Chapter 2: Average shear rate in a twin-screw extruder as a function of degree of
fill, screw speed and flow behavior index

2.1. ABSTRACT

Shear rate is critical in calculating viscous dissipation for cooking extruders.
Shear r ate p rofiles in twin-screw e xtruders are difficult to m easure and predict due to
extruder complexity and the changing rheological properties of the product. Altemately,

average shear rate (7', ) can be estimated using mixer viscometry assumptions.

Screw speed was varied at 50, 100, 200, 300, 400 rpm in a twin-screw extruder
for fluids with different flow behavior indices, which represent different feed materials.
Degree of fill was varied from 0.4-1.0. A modified matching viscosity technique was

used to estimate 70 .

Average shear rate was modeled as a function of extruder constant (k’), screw
speed and an empirical parameter alpha. Effect of degree of fill was significant on alpha
and extruder constant. Thus, both were incorporated in the average shear rate model. The
model predicted average shear rate well for average shear rate <200 s". The average
shear rate estimated with this method may be useful for model mechanical effects during

extrusion of cereal products.

15

2.2. INTRODUCTION

Shear rate in an extruder can be used to evaluate viscous dissipation, which is the
main source of energy to cook the material in the extruder (Mohamed et a1. 1990). The
shear rate term is also needed for calculation of shear history — a potentially useful
factor tracking the material process history during extrusion.

Quantifying shear rate in a twin-screw extruder is complex, because the screw
configuration usually varies along the barrel. As a result, shear rate also changes along
the extruder barrel. Another two factors which further complicate the calculation of local
shear rate are that two flows are present in a twin-screw extruder: drag flow, which is
proportional to screw speed, and pressure flow, which opposes the drag flow as a result
of high pressure at the die (Mohamed et a1. 1990). The opposing flows and the mixing
disrupt the velocity profile. Moreover, the local shear rates in each screw flight are
unknown because of the large clearance between the screw root and the barrel. Often, the
maximum shear rate is estimated as the screw tip velocity divided by the clearance.
However, this maximum shear rate could be much larger than the average shear rate.
Therefore, for approximations of shear rate in a twin-screw extruder, an average shear
rate term can be used.

Li et al. (1996) developed an analytical model for predicting shear rate of a twin-
screw extruder. Their approach was to treat the extruder as a mixer and the paddles as
non-circular shaped bobs. However, the raw material’s flow behavior index data must be
known for this model. For some fluids, flow behavior index is easily determined by
testing it in a rheometer. In contrast, when material such as flour is processed in an

extruder, its flow behavior index changes significantly as flour is transformed to dough.

l6

...I 5. II. .I. .IkaI

 

Therefore, an average shear rate model relatively independent of flow behavior index
(material rheology) would be more convenient.

The mixer viscometry method to determine average shear rate in a mixer has been
fully developed by Mackey et al. (1987), and has been used by many researchers (Rao
and Cooley 1984, Briggs 1995, Lai et a1. 2000). This technique involves comparing the
power consumption curves of a Newtonian fluid and a non-Newtonian fluid during
mixing in identical equipment. If both fluids require the same power, the Newtonian
viscosity (,u) must be equal to the non-Newtonian average apparent viscosity
(7]) (Metzner and Otto 1957). Apparent viscosity and average shear rate are related by an
appropriate m odel e quation for n on-Newtonian fluids. U sing the e quation, the average
shear rate in the mixer can be determined.

This technique has been used in evaluating performance of commercial
equipment, such as a scraped-surface heat exchanger (Steffe 1996). However, Mohamed
et al. (1990) presented the first study using the matching viscosity concept to calculate
the average shear rate in an extruder. They determined the average shear rate and
extruder constant (k’) in the twin-screw extruder using one non-Newtonian fluid for each
type of screw (single-lead, twin-lead and paddles) at 100% fill. Cha et al. (2003) applied
Mohamed’s method and conducted another extrusion study at 40% fill using a different
non-Newtonian fluid and a combination screw configuration. Both studies predicted

average shear rate and modeled it as a function of screw speed and constants.
7,, = k'N‘ll (2.1)
where 7', is the average shear rate (3"), k' (rev'l) is a constant unique for the given type

of geometry and mixer (extruder) and must be determined from experimental data, or is a

17

constant to account for material c onveying in the extruder, and N (rev/s) is the 5 crew
speed.

Degree of fill in an extruder is a measure of what proportion of the barrel void
volume is filled with raw material. Degree of fill ranges from O to 1.0. Mohamed et a1.
(1990) investigated the average shear rate in a 1.0 degree of fill extruder and provided a
range of average shear rates in the extruder. Since a commercial food extruder is
commonly operated at a range of 0.4-0.8 degree of fill, it is necessary to determine the
effect of degree of fill on average shear rate.

Lai et al. (2000) showed that k' in a mixer viscometer is virtually independent of
the flow behavior index above a certain minimum speed. The same advantage may apply
to extruders.

To date, no studies were found relating average shear rate in an extruder to degree
of fill and material rheology. Hence, the objectives of this research were

1) To develop a method to measure extruder degrees of fill;

2) To determine the average shear rate in an extruder at various screw speeds, flow
behavior indexes (material rheology) and degree of fill;

3) To determine the significance of screw speed, degree of fill and flow behavior
index on the extruder constant (k') and alpha (or);

4) To model the extruder constant and alpha as a function of the significant variables

in 3).

5) To determine the accuracy of the model.

18

2.3. MATERIALS AND METHODS
2.3.1.Rheometer

Fluids with flow behavior indexes (n) ranging from 0.2 to 1.0 were chosen. The
Newtonian fluid (n=1) was corn syrup (Sweetose 4300, AB Staley Mfg. Co. Decatur,
IL). The non-Newtonian fluids were two types of methylcellulose food gum (The Dow
Chemical Co., Midland, MI); 2.8% (w/w) A4OM Methylcellulose® and 8% (w/w) K99
Methylcellulose®.

The fluids were analyzed for their rheological parameters before they were
extruded. Plot of shear stress versus shear rate at three different temperatures were
obtained using a concentric cylinder Haake VT 550 rheometer (Haake, Paramus, NJ).
Using a power-law model,

0' = K 7" (2.2)
The effect of temperature on K was determined using the Arrhenius relationship,

13d
K = Koe RT (2.3)

For Newtonian fluids (n=1) the consistency coefficient is known as the

Newtonian viscosity (y). For non-Newtonian fluids, the apparent viscosity (7]) is,

77 = (i (2.4)

7’
Replacing the shear stress term (0') with Eq.(2.2), the viscosity becomes a

function of shear rate,

77 = K7“ (2-5)

19

2.3.2.Extruder

A laboratory scale twin-screw extruder with co-rotating, interrneshing screws
(model MPF-19, APV Baker, Grand Rapids, MI), 19-mm barrels, and 3-mm circular die
opening was used for the experiment. The barrel length:diameter ratio was 25:1. The
screws were configured to cause high shear by combinations of twin-lead, single-lead and
paddles (Table 2.1).
2.3.2.1 .Hvdraulic diametwd void volume

The hydraulic diameter was calculated as (Komolprasert and Ofoli 1990)

D, = 423K". /£Am., (2.6)

Wetted volume (Vw) and wetted area (Aw) for each screw type were calculated using

equations in Mohamed et al. (1990). The screw configuration used in this study was the
same as that in Cha et al. (2003). Their calculated hydraulic diameter of 2.25 mm for 0.4
degree of fill extruder was used in the present study. In the present study, calculation of
hydraulic diameter at different degree of fill was replaced with a more convenient and
straightforward method of plotting individual power consumptions lines for each degree
of fill.

Volume of screws (Table 2.2) was measured by water displacement. The void
volume (V0) of the extruder was calculated using equation:

V0 = Barrel volume + die volume + die plate volume - (2 7)
(total screws volume + end screws volume) O

20

Table 2.1. Screw configurations and volume

 

 

 

Screw configuration

Volume @m3)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Feed port 8D Twin Lead Screw 40.0
7x30° Forward Kneading Paddles 11.2

4D Twin Lead Screws 20.0

4x60° Forward Kneading Paddles 6.4

4x30° Reverse Kneading Paddles 6.4

2D Twin Lead Screws 10.0

6x60° Forward Kneading Paddles 9.6

4x30° Reverse Kneading Paddles 6.4

1D Single Lead Screw 5.9

V 7x90° Kneading Paddles 11.2
Die 2D Single Lead Screws 11.8
Total screws volume 138.9

 

Table 2.2. Extruder and screw flight data

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Variable Value
Twin-lead volume @m3) 2.5
Single-lead volume (cm3) 2.95
Paddles volume (cm3) 0.8
End screw volume (cm3) 0.574
Barrel length (cm) 1.9
Barrel surface area (cmz) 5.352
Barrel volume (cm3) 245.7
Die size (cm) 0.3
Die volume (cm3) 0.8
Die plate volume (cm3) 12.0
Void volume (cm3) 118.4

21

 

2.3.2.2.Energv balance in extruder
Total energy input generated by the extruder motor was separated into four energy
types (Harper 1981):

AB = AEH + AB, + AEp + AEk (2.8)
where AB is the mechanical energy input (J), AEH is the viscous energy dissipation in
channel, AB, is the viscous energy dissipation in flight clearance due to drag flow,
ABD is the pressure energy and AEk is the change in kinetic energy. Since change in

velocity in an extruder is small, AEk is assumed negligible (Harper 1981). Eq. (2.8)
become

AB = AlaH + AB, + 211-:p (2.9)
\_Y—J

total viscous dissipation

Eq. (2.9) can also be represented in rates by dividing each term by time:

Pw=Ev+(P*Q) (2.10)
where Pw is the power input (J/s) from the motor to the screw shafts, E, is the rate of
viscous dissipation and P*Q is the rate of pressure increase, where P is pressure (Pa) and
Q is volumetric flow rate (m3/s). Power input to the screws can also be calculated using
the measured torque value during extrusion runs and the manufacturer’s correlation.

PW = 2.64*(%L0ad —%Base Torque)* N (2.11)

Another form to present power consumption for mixers is by a dimensionless power

number:

N =————i— 2.12
Po pN3Dh5 ( )

22

2.3.2.3.Extrusion run

Fluid was prepared in batches of approximately 10 kg for each extrusion run.
Density was measured. The fluid extrusion was conducted at temperatures ranging from
10-25°C depending on the type of fluid. A water-cooling jacket around the extruder
barrel was utilized to cool the barrel when necessary. During extrusion runs for each
fluid, the temperature was maintained constant. After fluid flow output was at steady-
state, % torque (load and non-load), pressure at die, temperature of fluid at feed inlet and
at die outlet, and mass flow rate were measured. Die temperature was measured using a
handheld T-Type needle thermocouple (Cole-Parmer, Vemon-Hills, IL) inserted into the
die hole. The weight of the extruded fluid was measured for 30 seconds to obtain mass
output flow rate. The density of extruded fluid was measured. The fluid density and
temperature used for calculation were the averages between inlet and outlet fluid
densities and temperatures, respectively.

Data were collected at a set of five screw speeds of 50, 100, 200, 300 and 400 rpm
for each fluid. Duplicate experiments were conducted on different days.

2.3.2.4.Degnee of fill

To investigate the effect of degree of fill on k', fluid degree of fill was varied. For
each fluid, three ranges of degree of fill were chosen: 1.0, 0.7-0.9 and 0.4-0.6. The range
was approximated for degree of fill <1.0 because exact degree of fill could not be set

beforehand. However, exact degree of fill was measured at the end of each extrusion run.

Degree of fill of 1.0 (fill 1) was ensured visually as the fluid was poured manually
into the feed inlet. A funnel with a ball valve attached on top of the extruder feed inlet

was utilized to achieve degree of fill less than 1.0. The procedure to measure the exact

23

degree of fill was as follows: After measurements were recorded at one screw speed (N 1),
the ball valve was closed to stop feeding of fluid, and the screw speed was increased to
300 rpm to force the remaining fluid in the barrel out of the die. The fluid exiting the die
at this time was collected for 10 minutes and weighed (ml). The screw speed was then
increased from N1 to N2 for the next desired screw speed. At this time, the fluid feed rate
was arbitrarily increased to maintain a degree of fill approximately the same as at M. The
same procedure was repeated for each screw speed. At the end of the procedure for 400
rpm (N5), the barrel was opened, and the tared shafts with screws attached were removed
and weighed (mg) to obtain the fluid remaining on the screws. Fluid remaining on the

barrel was scraped and weighed (m3).
Measured degree of fill was calculated as follows:

n11 + m2 + m3
pV.

 

Degree of fill = (2.13)

Preliminary measurements taken at 50, 100, 200 and 300 rpm for corn syrup showed that
m2+m3 differ by only 5% over all screw speeds. Therefore, m2 and m3 were only
measured at the end of the set of 5 screw speeds (50, 100, 200, 300 and 400 rpm), rather

than after each screw speed.

For each screw speed, log Np, (calculated using Eq.(2.12)) was plotted versus
measured degree of fill to obtain a regression line. The regression equation was used to
interpolate Npo at an exact 0.4 and 0.7 degree of fill. Thus, fill 2 was established at 0.7

and fill 3 at 0.4.

24

2.3.2.5. Estimation of average shear rate by matching viscosity method (Mohgmed et al.

1990)
According to Metzner and Otto (1957) and Steffe (1996), when mixing a
Newtonian fluid in laminar flow (NR, < 63) and assuming that surface tension, elastic and

vortexing effects are insignificant, power consumption is inversely proportional to

 

 

Reynolds number.
A
N = 2.14
Po NR: ( ) ‘
where
Nh=lth ‘943
p

Mohamed et al. (1990) added another parameter to the general mixing model
(2.14) for twin screw extruders to account for the conveying and thorough mixing. Thus,

the model becomes

Na= ‘48 QJQ
(NRe)

 

where A and B are constants depending on the screw configuration. A and B were
determined using linear regression of log Np, with log NRe of the Newtonian fluid (com
www-

Once the power number of the non-Newtonian fluid was determined, the
correlated Reynolds number was calculated using the established regression equation

from Eq.(2.16). The matching viscosity method was applied,

fl=n=Kh"' 010

25

Finally, the average shear rate was calculated by solving for shear rate,

 

. 77 J—
n=( E,)n-l 01m
K027i?

The procedure is summarized in Figure 2.1.

 

1. Obtain Npo = f(NRe)

 

 

 

 

 

 

 

 

A Newtonian 3. Equate Npoofrom (2) to get the
log N” \ fluid corresponding NR, from (1).
V\ 4. Solve for Newtonian viscosity that
A Log NR: > would give the same power
3 consumption
‘ Non- Dh N ,0
Newtonian # = N
fIUld Re
10g N p0 \
Log Screw 5;“! 5. Match the viscosities
#=U=Kh””
2. Obtain Np, for non-Newtonian 6. Solve for average shear rate
fluid at certain screw speed ,7 "—1;
.. =6)

 

 

 

Figure 2.1. Matching viscosity method to determine average shear rate (Steffe 1996).
Once the average shear rate was calculated, the non-linear model (Eq.(2.1)) was
transformed to linear regression equation below to determine the extruder constant (k')
and 01. Regression analysis was done using Excel®.
log 70 = logk'+0tlogN (2.19)

Correlations between k' and the fluid’s flow behavior index, and k’ and degree of fill

26

were determined. The effects of degree of fill, screw speed and flow behavior index on k'

were analyzed using PROC REG in SAS software to determine each significance.

2.4. RESULTS & DISCUSSIONS
2.4.1. Rheometer
2.4.1.1. Newtonian fluid

Plots of shear stress versus shear rate for Corn syrup are presented in Figure 2.2
at temperatures of 24, 35 and 44°C. The graph shows that the viscosity of the fluid,
represented by the slope of the line, is constant with increasing shear rate. This verified
that corn syrup is a Newtonian fluid, with n z 1. Table 2.3 summarizes the results

obtained from regression analysis.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2000
1; 1500 ~
9:.
W
E a
.5 1000 « -— 0 AW -
5 35 c ”W4
“m: W’M

500 ~ WOW/1319*

wmww‘ 44°C
0 ‘ l l l 1 l
0 20 40 60 80 100 120 140 160
Shear rate (Us)
l

 

 

Figure 2.2 Plot of Shear stress versus Shear rate for Corn syrup.

27

Table 2.3. Rheological properties of Com syrup based on the model a = p}?

 

 

 

 

 

Temperature (°C) p (Pa 9 n R2
24 28.62 1.04 0.99
35 7.20 1.04 0.99
44 2.71 1.05 0.99

 

 

 

 

The temperature dependency of the viscosity was determined from regression

1:0 o o o
from Figure 2.3. The slope was T , and the lntercept was the log of reference VlSCOSlty.

The temperature dependence equation was

IIJIT

(2.20)

 

 

 

 

 

 

 

 

n = (1 .568*10-'5)e7—

4 M.
:4
a 2 *—
A

y= llll7x- 34.089
R2 > 0.99
0 T 1
0.003100 0.003200 0.003300 0.003400
l/T (l/K)

 

Figure 2.3. Consistency coefficient versus reciprocal temperature for corn syrup.

28

 

2.4.1.2 Non-Newtonian fluids

Plots of shear stress versus shear rate for one of the non-Newtonian fluids

(A40M) at temperatures of 25, 37 and 43°C are presented in Figure 2.4. The curved lines

on the graph show that the apparent viscosity changed with shear rate. Table 2.4

summarizes the data obtained by power-law fit.

 

 

 

 

 

 

 

 

 

 

__
{ 800
. 37°C

,3 600 " ‘* W gram-Wag

EL 1 W 43°C

0

5 400 ~-

in

8

.1:

m

200
O I I l r r T 1 l
0 20 40 60 80 100 120 140 160
Shear rate (l/s)

 

 

 

 

Figure 2.4. Shear stress versus shear rate for 2.8% A40M Methycellulose.

Table 2.4. Rheological properties of 2.8% A40M Methycellulose based on the model

 

 

 

 

 

0' = K 7"

Temperature (°C) K (Pa s") n R2
25 179.48 0.302 0.99
37 139.64 0.321 0.97
43 124.35 0.313 0.95

 

 

 

 

 

A plot of the consistency coefficient versus temperature is presented in Figure 2.5

E0 0
based on the Arrhenius relationship in Eq.(2.3). The slope was 7;— , and the 1ntercept

was the reference consistency coefficient. The complete equation was given by

29

1921.7

 

 

 

 

 

 

77 = (2.839 "'10“).e"7_y'"'1 (2.21)

l

5.5

5
y =1921.7x - 1.259
R2 >099
4.5 a 1
0.0031 0.0032 0.0033 0.0034
1/r (l/K)

L

 

 

 

Figure 2.5. Consistency coefficient versus temperature for 2.8% A4OM Methycellulose.

Table 2.5 summarizes the rheological parameters, temperature and shear rate
dependence of all fluids used for extrusion.

The rheological properties of the non-Newtonian fluids used in the present study,
especially those of type A40m were very difficult to reproduce when doing replicate
preparations. Slight differences in hydration and mixing procedures altered the
consistency coefficient and flow behavior index. Despite using similar gum
concentration, the rheological parameters were different, as seen in Table 2.5, and thus

the non—Newtonian fluids were not treated as replicates.

30

Table 2.5. Rheological parameters of fluids used for extrusion and their temperature and
shear rate dependence

 

 

 

 

 

 

 

 

Fluid Flow Consistency Temperature and shear rate dependance
behavior coefficient
Index (11) (K) at 25°C,
Pa 8“
2 8V A4OM L415
‘ ° =l.075*e T *‘H
Methylcellulose® 0'24 137-18 '7 7
2 8°/ A40M w
' ° = 2.839*10" *a r - ..-.
Methylcellulose® 0'28 ”9°48 ’7 ( ) 7
8? K99 335g 1
° = 1.098*10’2 *e r t
Methylcellulose® 0'60 42-19 ’7 ( ) 7
8°/ K99 5391-2
° = 1.785*10"' *e r * 71-1
Methylcellulose® 0'67 47'56 ’7 ( ) 7
4300 S t e® m
wee 0’ = 1.006*10"° *e r
Corn Syrup (Staley) 1'00 249 ,u ( )
ll.ll7
4300 Sweetose® = 1.568 * 1045 *eT
Corn Syrup (Staley) 1'00 29:04 ,u ( )

 

 

 

 

31

 

2.4.2. Extruder

All extrusion data can be found in Appendix 2.A.
2.4.2.1. Degee of fill

Dimensionless power number for all fluids was calculated using Eq.(2. 12). Figure
2.6 shows an example plot of power number versus measured degree of fill. The best fit
lines on the power number vs. degree of fill plot were linear for corn syrup with 0.63 S R2
50.88. Therefore, the relationship between log power number and degree of fill was
assumed linear in the range of 0.4 and 1.0 degree of fill for all fluids. Using linear
regression, trend lines were obtained for all screw speeds (Table 2.6). The trend lines

were then used to predict the power number at 1, 0.7 and 0.4 degree of fill.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

9.000
//8 o 50 rpm
8.500 ° D n
a n 100 rpm
5 D
a / A 200 rpm
En 8.000 / o 300 rpm
A
X /
7.500 /
x
7.000 t t t t . t
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Measured Degree of Fill

 

 

 

Figure 2.6. Plot of Power number versus measured degree of fill for corn syrup.

2.4.2.2. Estimation of average shear rate by matching viscosity method (Mohamed et al.
1990)

 

32

Figure 2.7 shows the plot of the Power number versus Reynolds number for
degree of fill of 1, 0.7 and 0.4 for Corn syrup. Table 2.6 summarizes the slopes (B) and

the intercept (A) obtained by linear regression.

 

 

 

 

 

 

 

 

 

 

 

9
o
A
O
on
g9 8 -—— —--——-—.__._-__--_-
...1
o 1.0 fill degree \
O 0.7 fill degree A
A 0.4 fill degree
7 f , I . I
-3-2 -3.0 -2.8 -2.6 -2.4 -2.2 -2.0
Log Re

 

 

 

 

Figure 2.7. Plot of Power number versus Reynolds number for corn syrup.

Table 2.6. Equations correlating Power number and Reynolds number for corn syrup at
three different degrees of fill

 

 

 

 

 

Degree of fill Equation N Pa = N:3 R2
1 N a. = [$2225 0.99
0.7 NP, =i—J—f’——) 0.99
0.4 NP, = $7,671,) 0.95

 

 

 

 

 

33

By assuming that at a constant speed, the power number would be the same for all
fluids during mixing if the fluid viscosities are the same, the Reynolds number for non-
Newtonian fluids could be calculated using the correlated equations in Table 2.6. Then,
the equivalent average shear rate was determined using Eq.(2.18). Figure 2.8 shows a plot

of average shear rate versus screw speed for one of the non-Newtonian fluids (A40m, n

=0.24).

I

§ ;

 

 

 

0 1.0 Degree offill

D 0.7 Degree offill

u—a

UI

O
l

 

 

A 0.4 Degree offill

 

 

 

U1
0

 

Average shear rate (l/s)
§

 

 

 

 

 

O T 1 l ‘l l l
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Screw Speed (rps)

 

Figure 2.8. Plot of average shear rate versus screw speed for 2.8% A4OM Methycellulose
(n=0.24)(Curve equation = 7‘ = k'N“).

All calculated average shear rates are given in Appendix 2.B. The results of linear

regression of Eq. (2.19) are displayed in Table 2.7.

34

2.4.2.3. Extruder constant

Table 2.7. Summary of regression analysis (Eq.(2.19)) (extruder constant and alpha)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Flow Overall extruder constant a Overall model
behavior Fill

index degree Log k' Std Error k' (rev") Value Std Error R2 Std Error
0.24 1.0 1.550 0.0355 35.52 0.747 0.0648 0.98 0.0476
0.24 0.7 1.267 0.0454 18.48 0.914 0.0830 0.98 0.0609
0.24 0.4 0.995 0.0848 9.89 0.936 0.155 0.92 0.0114
0.28 1.0 1.654 0.0587 45.13 1.048 0.107 0.97 0.0788
0.28 0.7 1.462 0.0574 28.98 1.410 0.105 0.98 0.0769
0.28 0.4 1.268 0.117 18.55 1.601 0.214 0.93 0.157
0.60 1.0 1.407 0.0412 25.52 0.671 0.0412 0.96 0.0552
0.60 0.7 1.132 0.0140 13.56 1.263 0.0257 0.99 0.0188
0.60 0.4 0.943 0.0299 8.77 1.736 0.0546 0.99 0.0400
0.67 1.0 1.557 0.0757 36.14 0.987 0.0757 0.94 0.101
0.67 0.7 1.239 0.0668 17.33 1.721 0.122 0.99 0.0896
0.67 0.4 0.753 0.0536 5.66 2.086 0.0979 0.99 0.0719

 

The value of k' shown in Table 2.7 was an “overall” k' for all screw speeds. An

 

increasing trend was observed with increased degree of fill. The regression results
showed an excellent fit for all the data with minimum R2 of 0.92. Alpha decreased with
degree of fill for all fluids. This result suggests that a low degree of fill allowed more
mixing of the fluid in the extruder, thus increasing the alpha value.

Research on mixer viscometry showed that speed did not affect the mixer constant
above a certain minimum speed (Castell-Perez and Steffe 1990, Mackey et al. 1987). Lai

et al. 2000) added that mixer constant was independent of flow behavior index also. To

35

investigate whether a similar trend would be observed for an extruder, R’ was calculated

at each screw speed using the known alpha obtained from regression analysis.

7'
k' = —a 2.22
N, ( )

Figures 2.9, 2.10, 2.11 show the relationship of k' and screw speed (rps) at fill degree of

1.0, 0.7 and 0.4 respectively.

 

6O

40 CR , L mm

. \I A
’ "‘ fi . -—D-—n=0.28‘
—<>— n=0.60

 

 

k!
>1

 

 

 

 

 

 

O l l T
0 2 4 6 8
Screw Speed (rps)

 

 

 

Figure 2.9. Extruder constant (k') vs. screw speed of non-Newtonian fluids with varying
flow behavior index (n) at 1.0 degree of fill.

 

Mohamed’s k' values for 1.0 degree of fill were 19.4 rev’1 for single-lead, 28.0
rev’l for feed-screws and 42.8 rev" for 30F paddles (Mohamed et al. 1990). In the present
study, the screw configuration was a combination of single-lead, twin-lead and paddles.
Figure 2.9 shows that most of the k' values fell in the range of 20-40 rev/s (within the
range of Mohamed’s results) afier screw speed of 1.667 rps (100 rpm) for 1.0 degree of
fill. A different trend is observed for n=0.28 where k' still increases after 3.33 rps (200

rpm). This inconsistency was caused by decreasingly small torque differences at higher

36

screw speeds. When the power number was low, the Newtonian viscosity was low. Thus,
average shear rate increased (Eq. (2.17)), and so did the extruder constant. A possible
reason for the drop in torque reading was that type A40m fluid’s texture was slippery and
slimy. Its slipperiness might act as a lubricant, yielding a lower torque difference at

higher screw speed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6O
40 “‘ @- n=0.24
:1 Cl _ \ —El— n=0.28
“u U,» “1:! —<>— n=0.60
20 LL LA\“\~—\L >43 5;“ ;;;_,Lo____, as? n=0.70
.3., _.:8:::’L o———<> ELL,
0 1 1 l
O 2 4 6 8
Screw Speed (rps)

 

Figure 2.10. Extruder constant vs. screw speed of non-Newtonian fluids with varying
flow behavior index (n) at 0.7 fill degree.

37

 

 

 

 

 

 

 

 

 

 

 

 

 

 

60
40 ' 7 w ""“” --O—n=0.24
- 1:1 —D—n=0.28
a: \ -~<>— n=0.60
20 ~ {3 -— LL_—L43. ‘\ —A—n=0.70
I /
0:8 \u
0L «’09: L‘:\L..L_ L:—-— _... . ;L&:——O’—_‘8
AL B38:
0 1 T 1
O 2 4 6 8
Screw Speed (rps)

 

 

Figure 2.11. Extruder constant vs. screw speed of non-Newtonian fluids with varying
flow behavior index (n) at 0.4 fill degree.

Very apparent trends are observed in Figures 2.10 and 2.11 where the k' is
relatively constant above screw speed of 1.667 rps (100 rpm). A different trend is
observed for n =0.28. The same justifications as mentioned above might cause this
behavior. For this reason, fluid of n = 0.28 was not included in fiirther calculation and
analysis.

These plots suggest that the average k' at screw speed above 1.667 rps (100 rpm)
for 1.0, 0.7 and 0.4 degree of fill was 32.23 i538, 16.49 i248 and 8.2 i215 rev'l,
respectively (excluding data of n=0.28).

Efl'ect of screw speed and flow behavior index on k’

Figures 2.9, 2.10 and 2.11 show that k' does not change significantly above screw
speed of 1.667 rps (100 rpm) for all fluids but one. This observation was confirmed by
statistical analysis (PROC REG in SAS) at 95% confidence level, which proved that

screw speed did not significantly affect k' (P = 0.902). Flow behavior index effect on k'

38

was also not significant (P = 0.426). These results were similar to those found in mixer
viscometers, where angular velocity and flow behavior index did not influence the mixer

constant.
Effect of degree of fill on k’

On the other hand, degree of fill affected k' significantly (P < 0.0001). Because
flow behavior index and screw speed were not significant factors affecting k’, all the k'
values were fitted as a function of degree of fill only. The best fit was a power law fit ( R2

= 0.86). Figure 2.12 shows that k' increased with degree of fill. The equation of the line

 

 

 

 

 

 

 

 

 

was
k' = 3039* Degree of fill"508 (2.23)
60
y = 30.39x"508 A
R2 = 0.857
A 40 LL —
'7:
b
' 8
x 20 A
O l l l l T
0 0.2 0.4 0.6 0.8 1 1.2
Degree of fill
L

 

 

 

Figure 2.12. Effect of degree of fill on extruder constant.

39

2.4.2.4. Evaluation of equaLion’s exponent (alpha)

Table 2.7 shows that alpha ranged from 0.671 to 2.086. Statistical analysis
showed that degree of fill and flow behavior index significantly affected alpha (P<0.01).
Alpha was fit using multiple linear regression as a function of degree of fill and flow
behavior index, yielding R2 of 0.79. Alpha increased with n and decreased with degree of
fill.

It was mentioned earlier that a model that was independent of flow behavior index
was preferred due to the difficulty in determining flow behavior index during extruder
cooking. Another alpha model was therefore proposed, where alpha was fitted with linear

regression as a function of degree of fill only (Figure 2.13, R2 = “0.457).

 

 

 

 

 

 

 

 

 

3
y = -1.308x + 2.145
R2 = 0.457
2
.2 ° A
E
< \\
1 0 O \‘3
. 8
O r l l 7 l
O 0.2 0.4 0.6 0.8 1 1.2
Degree of fill

 

 

 

 

Figure 2.13. Effect of degree of fill on alpha.

40

2.4.3. Average shear rate model
Two average shear rate models were developed following Eq.(2.1). For both

models, k' = 3039* Degree of fill"508 (Figure 2.12).

Model 1 incorporated the flow behavior index in alpha,

70 = k v N(-1.308 * degree offill + 1.471" n +1404) (224)
Model 2 accounted for degree of fill only,
ya = k ' N(-l.308 " degree offill + 2.144) (2.25)

A student t-test, paired with two-tailed distribution, was performed to determine if there
was significant difference between the two models. The result showed that inclusion of
flow behavior index did not change the predicted average shear rate model significantly
(P=0.03). Therefore, using the second model (Eq.((2.25)), average shear rate was
predicted at all points and then compared to the experimental average shear rate data

(Figure 2.14).

41

Figure 2.14 shows that the model predicted the average shear rates relatively well
for average shear rate <200 5". However, at higher average shear rates, the predicted
value underestimated the experimental value for fluid n=0.67. For fluid of n=0.67, the
alpha values obtained were higher than those of other fluids (Figure 2.13). Because the
model ‘averaged’ the k' and alpha values, the predicted average shear rate would be

underestimated.

 

 

400

 

 

 

 

 

 

 

 

 

 

 

3
CL
8
2 0 =024
,_ 300 L g n .
a
0
:1
:0
go 200 0 n=0.6
3 A
Q
g A n=0.67
.2 100 L
E
On

0 T T F 1*

O 100 200 300 400

 

 

Experimental average shear rate (l/s)

 

Figure 2.14. Predicted average shear rate versus the experimental average shear rate data.

42

2.4.3. 1. Fluid suitability

The most challenging task in this study was to find a non-Newtonian fluid
suitable for extrusion. This fluid must be thick enough to generate sufficient torque
response, and yet had to flow continuously without yield stress. In the present study, the
fluid concentration chosen for type A40M and K99 methylcellulose was at its maximum
allowable concentration. If the concentration was higher than 2.8% and 8.0%
respectively, the fluids would not flow continuously fi'om the feeding fimnel.

In addition, the present study determined a more selective criteria when using
fluid with higher n value (0.6 and above). Based on two preliminary extrusion run data, it
was concluded that fluid with high n, must have a consistency coefficient lower than 50
Pa sn at 25°C, otherwise the calculated average shear rate value would be out of a

reasonable range, based on Eq.(2.26).

.1.

7. = (%W (2.26)
2.5. CONCLUSIONS

This study presents an investigation of average shear rate and extruder constant in
a twin-screw extruder, following Mohamed et al. (l990)’s method. A new procedure to
measure the fluid degree of fill in a twin-screw extruder was also developed in this study.
Average shear rate was a function of two constants (extruder constant and alpha) which
were dependent on degree of fill. Extruder constant increased with degree of fill, while
alpha decreased with degree of fill.

A new model independent of flow behavior index was proposed. The model is

useful to determine average shear rate at a known degree of fill in an extruder if using the

43

same screw configuration. The model was more accurate at average shear rate <200 5'1
than at higher average shear rate. The model was used to calculate shear history in
extrusion of wheat flour (Chapter 4).

This study answered some questions raised in Mohamed et al. (1990). Although
the model developed in this study was not highly accurate at the higher screw speeds, the
novel methods to determine average shear rate are fundamentally sound and lay a basis
for follow-up studies. Results of this study show that choice of fluid and torque response

are important factors to ensure high torque response to obtain reasonable average shear

rate data.

2.6. FUTURE WORK RECOMMENDATIONS

Follow-up studies should investigate more non-Newtonian fluids with thicker
viscosity (following the fluid selectivity mentioned above) for better torque response at
higher shear rates.

Since die size affected the machine production capacity, its effect on average
shear rate should also be determined.

Lastly, Mohamed et al. (1990) investigated the effect of one type of screw flight
at 1.0 degree of fill. Changing degree of fill using only one type of screw flight and their

effect on average shear rate should be investigated.

2.7. ACKNOWLEDGMENT
Many thanks to Dow Chemical and Staley for their generous donations of

Methoce1® methylcellulose and Sweetose® corn syrup, respectively.

44

2.8. NOMENCLATURE

A... wetted area, i is an index for each screw flight, m2
A constant Eq.(2. 16)

B constant Eq.(2.16)

D}, hydraulic diameter, m

E, activation energy (J oule/ g-mole)

Ev viscous dissipation (J/s)

AE mechanical energy input (J)

AEH viscous energy dissipation in channel (J)

AE, viscous energy dissipation in flight clearance due to drag flow (J)
AEp energy to increase the pressure (J)

AEk change in kinetic energy (J)

k’ extruder constant (rev'l)

K consistency coefficient (Pa 3")

K0 reference consistency coefficient (Pa 3“)

m , mass of fluid exiting the die (kg)

m 2 mass of fluid in the screws (kg)

m 3 mass of fluid in the barrel (kg)

N screw speed (Revolutions per seconds)

n flow behavior index, dimensionless

Npo power number, dimensionless

NR6 Reynolds number, dimensionless

P pressure (Pa)

PW Power input (J/s)

Q volumetric flow rate (mB/s)

R gas units (J/g-mole*Kelvin)

T temperature (Kelvin)

V0 total void volume of extruder barrel and die (m3)
VW wetted volume (m3)

Greek symbols

a constant in Eq.(2.1)

0- shear stress (Pa)

7 shear rate (l/s)

ya average shear rate (Us)

77 non-Newtonian apparent viscosity (Pa 5)

,u Newtonian viscosity (Pa 5)

p average density of the fluid before and after it is extruded (kg/m3)

45

2.9. REFERENCES

Briggs JL, Steffe JF. 1996. Mixer viscometer constant (k') for the Brookfield small
sample adapter and flag impeller. Journal of Texture Studies 27: 671—677.

Cha JY, Suparno M, Dolan KD, Ng PKW. 2003. Modeling thermal and mechanical
effects on retention of thiamin in extruded foods. Journal of Food Science 68(8)2488-
2496.

Lai KP, Steffe JF, Ng PKW. 2000. Average shear rates in the rapid visco analyzer (RVA)
mixing system. Cereal Chemistry 77(6):714-716.

Komolprasert V, Ofoli R. 1990. Effect of shear on thermostable a-amlyase activity.
Lebensm-Wiss Technology 23:412-417.

Li Y, Lu Q, Huff HE, Hsieh F. 1996. On-line rheological properties measurements on a

co-rotating self-wiping twin-screw extruder. Food and Bioproducts Processing 74 (Part
C): 149-158.

Mackey KL, Morgan RG and Steffe JF. 1987. Effects of shear-thinning behavior on
mixer viscometry techniques. Journal of Texture Studies 15:327-335.

Metzner AB and Otto RE. 1957. Agitation of non—Newtonian fluids. America Institute of
Chemical Engineering Journal 3(1):3-9.

Mohamed IO, 0 foli RY, M organ RC. 1 990. M odeling the average 5 hear rate in a c o-
rotating twin-screw extruder. Journal of Food Process Engineering 12:227-246.

Rao AM and Cooley HJ. 1984. Determination of effective shear rates in rotational
viscometers with complex geometries. Journal of Texture Studies 15:327-335.

Steffe, JF. 1996. Rheological Methods in Food Process'Engineering, second edition
(second printing).Freeman Press, East Lansing, MI, USA.

46

CHAPTER 3:
Thermal kinetic parameters of thiamin in wheat flour at temperature >100°C

3.1. ABSTRACT

Kinetic parameters for thiamin degradation were obtained using two high-
temperature heating methods, conducted at: l) atmospheric pressure (AP) with moisture
correction; 2) controlled pressure (CP). At AP conditions, 25% (wb) moisture wheat flour
with 0.3% (wb) thiamin was heated in thin steel cells isothermally at 145, 160 and 172°C.
To obtain the moisture correction factor, a constant-moisture study was conducted at
80°C using seven moisture contents (5-26.9%).

At CP conditions, flour at 16, 22 and 25% (wb) moisture in double-seamed cans
was heated in a CP steam retort at 129.4°C. For the AP method, the corrected activation
energy for 25% moisture content was 129.5 kJ/g-mol and reaction rate at 80°C was
3.48E-4 min'l. Using the CP method, the activation energy and reaction rate were 121.0
kJ/g-mol and 9.69E-5 min'l, respectively. Results obtained from two methods were not
statistically different. These results illustrated that the correction method could be used as
an alternative for researchers without access to controlled-pressure equipment and
transient heat transfer software

The CP heating method required more complicated setup and computation than
the AP method. However, more experimental time was needed to generate data for the
AP method. While both methods had their advantages and disadvantages, the CP method
was a superior method to obtain high-temperature kinetic parameters, because constant-
moisture was achieved even during high-temperature heating, and lower standard error

was obtained.

47

3.2. INTRODUCTION

Thermal processing is commonly used in the food industry, because it is
necessary for pathogen inactivation, flavor development, and texture formation. The
intensity of heating may degrade the color and nutrients of a product, making it
undesirable. If the thermal kinetic parameters (reaction rate constant (k) and activation
energy (Ea)) of the quality factors are known, they can be used to predict the degradation
during thermal food processing (Thompson, 1982). Thus, the processing method can be
improved to minimize the loss of those quality factors.

For many food components, rate of degradation is commonly modeled using
Eq.(3.1) for first order degradation kinetics (Stumbo 1973),

—— kC 3.1
dt ( )

After integrating the left side from initial concentration Co to C, yielding

 

 

C l
1n[a]=—jo kdt (3.2)
The reaction rate often changes with temperature, following Arrhenius’ established
equation (Eq. (3.3)).
k=k~fexp _E° i— 1 (3.3)
R8 T T”,

where: k = reaction rate constant (min'l), km; = reaction rate constant at reference
temperature (T ref) (min"), E, = activation energy (J/g-mole), Rg= gas constant (J/g-mole
K), and 1/T= temperature (1/°K).

Although quality factors (such as vitamin content) are usually degraded by intense

heating, many food-processing methods involve other procedures, such as mixing and

48

shearing, which contribute to the degradation. If the vitamin’s thermal kinetic
parameters are known, the degradation due to thermal effect can be calculated and
quantified as a portion of the total degradation. The significance of all effects
contributing to the degradation can then be identified separately, and the processing
method can be optimized to obtain the minimum overall degradation.

Thermal kinetic parameters of thiamin have been investigated in a wide variety of
high moisture food products, including meat, vegetables and buffer solutions (Mulley et
al. 1975a, Guzman-Tello and Cheftel 1987, Steet and Tong 1994, Ryan-Stoneham et al.
1996). Villota and Hawkes (1986) reviewed and summarized the published kinetic
parameters for thiamin. Few researchers have determined the thiamin kinetic parameters
in low-moisture system. Guzman-Tello and Cheftel (1987) and 110 and Berghofer (1998)
utilized an extruder to determine thiamin kinetic parameters in flour and corn maize grits,
respectively. However, they neglected the changing temperature profile along the
extruder barrel and assumed isothermal heating temperature. Neglecting the varying
thermal history along the barrel could lead to an underestimation of the kinetic
parameters (Dolan 2003). This chapter compares two methods to obtain the thermal
kinetic parameters of thiamin in a low moisture system so that the parameters can be used
to quantify thermal effect and shear effect on thiamin degradation separately in an
extrusion process (Chapter 4).

Typical heating procedures to obtain these parameters are carried out at
atmospheric conditions because atmospheric heating involves simpler setup and analysis.

However, this type of heating could cause moisture loss from the heated product, if the

temperature of the heating medium is above 100°C. Cha et al. (2003) investigated

49

thiamin kinetics in flour, but high-temperature heating decreased flour moisture content
significantly.

The moisture changes could alter the rate of degradation and thus the thermal
kinetic parameters obtained might not be the true value at the desired higher moisture
content. This statement was supported by Hermann and Tunger (1966), who determined
that moisture content (MC) of flour affected thiamin degradation rate. Their study
concluded that if flour MC was less than 13% (wet basis)/ 14.9% dry basis (db), the
reaction rate was positively correlated with MC. If flour moisture content was higher than
14.9%, the reaction rate was negatively correlated with MC.

Other studies investigated the effect of water activity on the reaction rate rather
than the effect of moisture content on reaction rate. For most food products, the
relationship between MC and water activity is described in a sigrnoidal curve (the
adsorption and desorption isotherm). Since the present study did not conduct an isotherm
study, an approximate transformation from MC to water activity was based on the plot
given by Hermann and Tunger (1966) for 80°C. Studies on the water activity effect also
showed that reaction rate reached a maximum at a certain water activity (0.6-0.8, which
correlates to ~9-17.6% MC), above which it falls off (Labuza 1980a) both in reduced-
moisture systems and frozen systems. Bell and White (2000) also showed these
phenomena for thiamin reaction rate.

Since many studies have shown the significance of moisture content, it is
important to maintain constant flour MC during heating to obtain accurate thermal kinetic
parameters. To minimize moisture loss, the containers must be perfectly sealed.

However, heating perfectly-sealed containers in uncontrolled pressure conditions

50

(atmospheric) is potentially dangerous because the pressure in the container increases
with temperature. As an alternative, I hypothesized that the moisture loss problem could
be solved by correcting the high-temperature, changing-moisture kinetic parameters
based on a constant-moisture study at a lower temperature. Study at several constant-
moisture contents determines the effects of MC on the reaction rate and was conducted at
a temperature lower than 100°C to minimize moisture loss.

Another alternative procedure is to obtain the high-temperature kinetic parameters
under controlled pressure conditions. Using steam as a heating medium allows rapid heat
transfer. However, if the heated sample were a low moisture system (i.e., low thermal
conductivity) and placed in a container, a temperature gradient in the container would
exist. Since thiamin degradation is affected by temperature, it is necessary to calculate the
temperature at various location of the container so that the correct thermal kinetic
parameters could be estimated. Two general solutions had been developed and used by
many researchers to predict spatially and temporally varying temperatures in canned
foods. Numerical solutions, such as finite element, are useful for predicting temperature
in irregular-shaped dimensions or varying initial temperature condition (Wang and Sun
2003). For products with regular geometric configurations (such as a cylinder),
researchers h ave u sed a nalytical s olutions for p redicting temperature, with c omparable
results to using numerical solutions (Lenz and Lund 1977a, Garrote et al. 2001, Carroll et
al. 2003).

To date, no studies have determined the thermal effect on thiamin degradation in
low-moisture systems at high-temperature. Therefore, the overall objective of this

research was to investigate two different methods to determine kinetic parameters of

51

thiamin in flour at high-temperature. The first method was conducted at atmospheric

pressure and the second method was conducted at controlled pressure.

52

3.3. MATERIAL & METHODS
3.3.1. Sample preparations

Soft wheat flour, with moisture content (MC) of approximately 17.6% dry basis
(db) (15% wb), was obtained from the Star of the West Milling Co. (Frankenmuth, MI).
MC was determined by heating 1 g flour at 130°C for 10 minutes using a Sartorius MA-
30 moisture analyzer (Goettingen, Germany). MC in wet basis was converted to dry basis
using Eq. (3.4).

= MC(wb)
MC(db) —_1-MC(wb) (3.4)

F cod-grade thiamin hydrochloride (Spectrum Laboratory Products, Gardena, CA)
was mixed with flour at a concentration of 0.35% (db) using a V-shaped twin shell dry
blender (Patterson-Kelley, East Stroudsburg, PA). To ensure homogeneous distribution
of thiamin with a coefficient of variance <10%, the flour and thiamin were mixed for 40
minutes. Thiamin content was analyzed using the fluorometric method (Official Method
953.17, AOAC 1995), following techniques from Moore and Dolan (2003). Method of
thiamin analysis is described in Appendix l.A. Initial concentration of thiamin in flour
was analyzed at 9 different locations in the mixed flour to yield Co = 0.36 :t 0.0189 %
concentration in dry weight basis.

Flour MC was increased to the desired MC by spraying it with water. After
addition of water, the mixture was blended in food processor (Cuisinart, Model DLC-2A)
for 1 minute to ensure homogeneous distribution of moisture. Flour mixture was stored in

refrigerated temperature of ~4°C for at least 24 hr until usage.

53

3.3.2. Study la and lb: Atmospheric Pressure heating

Custom-made steel cells (Michigan State University Farrall Hall Research and
Development Shop, East Lansing, M1) were utilized to contain the flour mixture (Figure
3.1). Each cell was divided into two parts: the lid and the base. The lid was a rectangular
piece with 10.6 cm length, 1.2 cm width and 0.9 cm thickness. The base had 0.5 cm inner
thickness, 0.1 cm wall thickness and 8.6 cm height. Afier filling the base with 12 g of the
flour mixture, the lid was attached to the base with insertion of two screws on the far
right and lefi of the lid. It was ensured that the top of the flour mixture was always below
the oil surface. The lid had a small opening of 0.2 cm in the center, into which a type T
30-gauge Copper-Constantan thermocouple was inserted to measure the temperature at

the height and thickness midpoint of the flour.

8.6 cm

   

Figure 3.1. Steel cell for Atmospheric Figure 3.2. Setup for Atmospheric
Pressure heating. Pressure heating.

 

The sample in the cells was heated in a bath of silicon oil (Fisher Scientific,
Pittsburgh, PA) held at different constant temperatures in an Isotemp 10 BP heater bath
(Fisher Scientific), as shown in Figure 3.2. The heating time, the center temperature (Tc)

54

of the sample and the temperature of the oil bath data were recorded every 10 seconds
using a Digi—Sense Model 92000-00 Scanning Thermometer data logger (Cole-Parmer
Instrument Co., Barrington, IL).

The first sample was taken after the sample temperature had nearly reached a
plateau to ensure near-isothermal analysis (within 3°C of desired temperature). The cells
were taken out at 3 heating times, such that thiamin retention would be in the 20—85%
range. Heating time started as soon as steel cells were placed in the oil bath. At the end of
heating time, cells were quickly cooled in an ice bath until sample temperature reached
~5°C. All experiments were duplicated. Samples were stored at refrigerated temperature
of ~4°C until further analysis.

For thiamin analysis, the heated sample was mixed for 1 minute using the
Cuisinart processor to ensure homogeneous distribution. Two thiamin readings were
obtained from each steel cell.
3.3.2.1 Study la: Atmospheric pressure (AP) — Constant-moisture at temperature
<100°C
Objective: To determine how moisture content aflects thiamin reaction rates

Flour mixtures of 6.17, 9.67, 10.7, 17.2, 27.0 and 36.9% (db) MC were used. For
flour with <17.2% MC, the flour mixtures were dried in a convection Isotemp oven
(Fischer Scientific) at 45°C. The temperature of the oil bath was set at 80°C to minimize
flour moisture loss. At each moisture content, three heating times were selected such that
thiamin retention would be in the 20-85% range.
3.3.2.1.1. Data analysis

The natural log concentration of the thiamin was plotted against heating time (t)

to obtain the reaction rate (Eq.(3.5)) at each moisture content.

55

LnC=LnC0-kt (3.5)

At a constant temperature, the reaction rate changed with moisture content exponentially.
k = k, exp[b(Mc - MCr)] (3.6)

By linear regression of ln k versus MC, the slope of the line (b) was obtained. A positive
b value correlates to faster degradation rate at higher MC. As mentioned before, Hermann
and Tunger (1966) found two types of b. In their study, parameter b was a positive value
at MC<14.9% (db), and a negative value at MC>14.9%. In the present study, the two

slopes were denoted as b(+) for the positive slope, and b(-) for the negative slopes (Figure

3.3). The point where the two slopes intersected was called kx at MCX.

 

 

 

 

Lnk

 

 

 

 

 

MCx MC(%)

 

 

 

Figure 3.3. Example plot of the moisture content effects on reaction rate constant for
thiamin.

56

3.3.2.2. Study 1b: Atmospheric pressure (AP) — High-temperature

Objective: To determine the kinetic parameters of thiamin in flour obtained from high-
temperature heating at atmospheric pressure conditions and to correct for moisture loss
based on the constant-moisture study in study 1 a.

Flour mixtures of 33.3% (db) MC were heated at 145, 160, and 172°C in the oil
bath. At each temperature, three heating times were selected such that thiamin retention
would be in the 20-85% range.
3.3.2.2.1. Data analysis

The natural log concentration of the thiamin was plotted against heating time (t)
to obtain the reaction rate (k) (Eq.(3.5)) at each temperature. Regression statistics were
done using Excel®.
3.3.2.3. Correction method for high-temperature reaction rate constant

Assuming that thiamin activation energy did not change with temperature (as
indicated by data from Hermann and Tunger 1966), the constant-moisture study
parameters b(+) and b(-) obtained at 80°C were used to correct the moisture loss at higher
temperature. When a sample MC dropped from MChigh to MC]ow during a high-
temperature heating, the k at MC]0w was corrected to k at MChigh using the proposed
correction method. The correction method was divided into two calculation steps, which
incorporated the constant b(+) and b(-). First, k at MC.0W was corrected to kx using b(+). In

the first step, MCx = MCr (Refer to Eq.(3.6) for the basic equation).

kMC = kx exp [b(

low

(MC,w - MC, )] (3.7)

+)
Secondly, kx was converted to k at MChigh using b(-). In this step, MChigh = MC..

k, = kMCM exp |:b(_)(MCx - MChigh )] (3.8)
Combining both equations,

57

_ kMCIOW exp[—b(+)(MClow -MCx )]

kMC _ L . (3.9)
“‘8“ exp[b(_)(MCx -Mchi 211)]

 

Once the corrected k was determined at each temperature, the activation energy
(Ea) was calculated from the slope of a regression line of In k vs average sample
temperatures [l/(Ta.g+273.15)]. The average sample temperature was the average of the
measured center temperature of the sample and the calculated temperature of the sample

at steel wall (°C).

T

avg—

_ (Tbemer +Twall J (310)
2

Tm,” was calculated by assuming that there was no temperature gradient across the steel
wall. Then, the heat flux from the oil bath to the cell wall was equal to the flux from the
wall to the center of the sample in the steel cells, assuming a straight-line approximation
of temperature gradient over the cell half-thickness of 4.5 mm.

kAs (Twall — 7banter)
Ax / 2

 

q = M3 (Toll bath — Twall) = (3-11)

The heat transfer coefficient of the oil bath (h) was estimated by Lai et a1. (2003) using
the lumped heat-capacity analysis. They determined h as a function of temperature of the
heating medium (°C),

h =1.791*(1;,,,,,,)-22.28 (3.12)

The thermal conductivity of the sample (k) was calculated at the average of the
initial and final sample temperature (T in°C), based on equation provided by Choi and

Okos (1986), taking into account carbohydrate and water content only.

58

k = (0.20141+l.3874*10‘3 *T—4.3312*10" *T’)x,,,,,,,,me
+(0.57109+1.7625*10'3*T—6.7036*10'°*T2)x

water

(3.13)

3.3.3. Study 2: Controlled Pressure heating
Objective: To determine the thermal kinetic parameters of thiamin in flour at high-
temperature heating, at controlled pressure conditions

The heating medium was a continuous steam simulation retort FMC no. 2881
(FMC Corp. Food Processing Systems Division, Madera, CA), provided with a panel for
temperature and pressure setup from ABB Automation 1900 (ABB Automation Inc.,
Warminster, PA). The retort was equipped with six locking male connector
thermocouples and one mercury-in-glass thermometer. Cylindical cans (type 201x 211;
5.15 cm inner diameter, and 6.79 cm height) were obtained from Freund Container Co.,
Chicago, IL. The use of smaller cans was essential to provide a reasonably rapid heating
and cooling transfer. A needle type thermocouple Model 1 7/16" with female fitting
attached with a C-9 Locking Receptacle and a C-16 heat-resistant gasket (Ecklund-
Harrison Technologies, Fort Myers, FL)) was inserted in each can such that the geometric

center temperature was recorded (Figure 3.4).

 

Figure 3.4. Thermocouple was inserted
into the center of can (left) so that
geometric center temperature was
recorded (right).

 

The cans were packed-filled with approximately 100 g of flour mixture and

double-seamed to ensure a hermetic seal. After seaming, the can’s thermocouple
59

receptacles were connected to the retort’s plug-end thermocouples. Cans were then
placed vertically on the bottom of the retort.

All thermocouples were calibrated prior to conducting experiments. During
heating, the center temperature of the flour was measured and recorded every 40 seconds
using a CALPlexTM data logger (TechniCal. Inc., New Orleans, LA). Flour mixtures of
19.1, 28.2 and 33.3% MC (db) were heated at retort temperature of 129.4°C. This
temperature was near the maximum allowable temperature for this type of retort. The
temperature of the retort reached 129.4°C in 2 minutes. Heating time for each flour
mixture was chosen appropriately so that thiamin retention ranged from 20-80%. At the
end of the designated heating time, cans were cooled with water at 25°C while using
overriding air pressure in the retort to prevent can deformation. All experiments were
done in triplicate. Samples were stored at ~4°C until further analysis.

For thiamin analysis, the heated sample was mixed for 1 minute using the
Cuisinart processor to ensure homogeneous distribution. Two thiamin readings were

obtained from each can.

60

3.3.3.1 Data analysis
3.3.3.1.]. Temperature calculation

The analytical solution to predict temperatures for a finite cylinder during
transient conduction heat transfer, provided by Carslaw and Jaeger (1959) was used to
determine the center and off-center temperatures in the can. This solution is valid when
there is no spatial variation in initial sample temperature and environmental temperature
is suddenly changed to a constant value. In addition, the sample k, p and specific heat
capacity (cp) values are constant. The solution for a finite cylinder was a product of the
infinite cylinder and the infinite slab solutions. The predicted center temperature was
compared with the measured center temperature to detennine the accuracy of the
solution. The root mean square error (RMSE) of the prediction was calculated as

RMSE = Predicted value—Measured value (3.14)

number of data points

 

Temperature was calculated at 25 different points in the can at the r and 2 points.
To d eterrnine the temperature at location r for an infinite cylinder (1 uring h eating, the

analytical solution was,

.0, eraser—ta

T T” M?) ”4’0“”

 

(3.15)

61

To determine the temperature at location 2 for infinite slab during heating, the analytical

solution was,

 

 

2(fljcos(hm * £Jsec(lm)exp ~13, (Gr—2t)
TOO-T.o _i k I . I . (316)
_ was)”;
k k
where thermal diffusivity (a) was
a = k (3.17)
CI) *p

Thermal conductivity (k) was determined based on Eq.(3.13). Density (,0) was calculated
by dividing the mass of the flour in the can by the volume of the can.
Kaletunc (unpublished data) developed an equation to relate temperature and

moisture content with specific heat capacity (cp) for flour.

cp =1.132+0.0058*(Tin°C)+0.037*(%MC) (3.18)

The cp for this study was evaluated at the average between the highest and lowest
temperature. Moisture content in Eq.(3. 18) was presented in dry basis.

The heat transfer coefficient of the steam (h) was set at 5500 W/mz, giving a Biot

number (%)0r[£k1:) >40, which means that the external resistance is negligible

compared to the intemal-conduction resistance. Thus, the temperature of the flour at the
can wall is virtually the same as the steam temperature.
The temperature at the specific (r, 2) location in the finite cylinder was determined

as a product of cylinder (Eq.(3.15)) and slab (Eq.(3.16)) solutions.

62

Finite cylinder = infinite cylinder x infinite slab

T(r,z)—Tw _ T,—T, x z-Tw (3.19)
T-T r-T, r—T,

I w

Since no analytical solution was suitable for a spatially-varying initial temperature
condition, the same analytical solutions (Eq. (3.19)) was used to predict the approximate
temperatures during cooling period. A justification for using Eq.(3.19) was that the
sample was heated for a sufficiently long time that, at the end of heating time, the
temperature gradient within the can was not large (~5°C from center of the can to the
edge). Mass-average temperature was calculated at the end of the heating period, and it
was set as the initial cooling temperature. Mass-average temperature (Eq.(3.20)) and
mass-average thiamin retention (Eq.(3.21)) were calculated by integration over the can
volume. For this purpose, Gauss-Legendre quadrature, a powerful numerical integration
method, was used to estimate the integral. In this method, the locations of r and z in the
can are given at unequally spaced intervals (Figure 3.5) and they are weighted such that a
high accuracy is obtained (Stasa 1985). The calculation for the r and 2 points and the

weights of each point are found in Appendix 3D. The r points were dimensionless,

r* . . . . . .
r = R: where r* rs the axral radrus and R* rs the radrus of the can. The 2 pornts were

. 2* .
also normalized so that z =l—*. Therefore, the integral for mass-average temperature

ma

 

2;,de
15 l.‘ V (3.20)

can

was,

where Vm was the normalized volume of the half-can = nRzl = 7r (1)2(1) (dimensionless).

63

 

 

 

 

0.953

 

I 0.769

0.500

(r, z = (O, O) 0.231

‘0047 0.231 0.5 0.769 0.953
R

Figure 3.5. Five-point Gauss-Legendre quadrature for off temperature calculation for
half-can.

0.047

 

 

 

 

 

 

 

 

3.3.3.1.2. Kinetic parameters estimation
The predicted mass-average thiamin retention in the can was evaluated by using
the Gauss-Legendre numerical integration. Based on first-order thiamin degradation

kinetics, at any time t,

C _ l l C de _ j] I1 exp[—k,,B(r,z)]27rrdrdz
C " C V _ o o nR’I
0 predicted 0 0 0 can

= 2 j; [0' exp[—k,,6(r,z)] rdrdz (3.21)

 

where ,6 (r, 2) at time t was

1 E, 1 l
,B(r, z) — JO exp [_E[ ram 2) - T...) ]] dt (3.22)

The time-temperature history, fl (r,z) was calculated using the trapezoidal rule by

 

integrating over each r and 2 location in the can at each heating time (t). Time intervals

varied from 40 seconds to 200 seconds.

64

The activation energy (Ea) and k, of flour with MC=19.05, 28.20 and 33.33%
were estimated by non-linear regression using Solver in Excel® while minimizing the

sum of squares of the residuals between the measured and the predicted mass-average

_ _ 2
n C C
SSQ=Z [[3] L [‘6’] ] (3.23)
i=1 a predicted ,i 0 measured .i

Written in Visual Basic application in Excel®, the Bootstrap data-based

thiamin retention.

simulation program was used to generate 1,000 new values of E, and k, (Efron and
Tibshirani 1993) as follows. The bootstrap assigns measures of accuracyto statistical
estimates. Given there were n paired values of measured and predicted thiamin retention
(in our study, n=18),

[1°] 1°) [1°] 1°) (91 1°) 1
C0 predicted C0 measured 1 C0 predicted C0 measured 2 C0 predicted C0 measured

71

The Bootstrap program randomly chose the paired retention values from the
original data points to generate a new set of n paired values. Some pairs might be chosen
more than once. Using the new set of n paired values, new values of Ed and k, were
estimated by non-linear regression using Solver. This process was repeated 1,000 times to
obtain the real probability distribution of Ea and k,, instead of just assuming a normal
probability distribution. A probability distribution is a function that expresses the relative
frequency at which measurement values can occur. The probability distribution was
plotted using MATLAB software. The distribution was also reported for its 90% joint

confidence region. The 90% or was used because of the 95% confidence limit of the two

65

parameters (i.e., (0.95)2 = 0.90). The elliptical confidence region was plotted using

MATLAB.

T-test for results from study 1a, study 1b and 2 were conducted to determine
whether the values were statistically different from each other. Since the number of

observations was not similar between each study, a pooled t-test was conducted, where

ya —.ub

t - test = 2 2
Jsetu.) + semi.)

(3.24)

pa: value (activation energy, reaction rate constant or moisture content parameter) from
study a and S601“) = standard error of ya,

,ub = values (activation energy, reaction rate constant or moisture content parameter) fiom
study b and se(,u,,) = standard error of [.11.

To be significantly different, the t-test values had to be more than the tcritical at 95%
confidence (0.05, degrees of freedom). Degree of freedom is the total number of data in
both studies minus 2.

The complete experimental design is summarized in Table 3.1.

66

Table 3.1. Summary of the experiments conducted to obtain thermal kinetic parameters of

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

thiamin
Heating Sample
medium Moisture
set temp content, % Heating
Study # Description (°C) (wb)/(db) Heating time (min) medium
1a Constant Moisture 80 5.8 / 6.15 300, 960, 1440 Oil bath
1a Constant Moisture 80 8.8 / 9.67 162, 360, 600 Oil bath
1a Constant Moisture 80 9.7/ 10.7 180, 480, 725 Oil bath
1a Constant Moisture 80 14.7/ 17.2 60, 120, 240 Oil bath
1a Constant Moisture 80 21.3 / 27.0 61, 180,270 Oil bath
1a Constant Moisture 80 26.9 / 36.9 60, 210, 300 Oil bath
1b H‘gh Tempiratme’ 145 25.0 / 33.3 25,60, 70 on bath
Atmospheric Pressure
1b H‘gh Tempi’rature’ 160 25.0 / 33.3 20, 40, 60 on bath
Atmospheric Pressure
1b H‘gh Tempiratm’ 172 25.0 / 33.3 10, 15, 20 on bath
Atmospheric Pressure
High Temperature, Steam
2 Controlled Pressure 129.4 16.0/ 19.1 20, 40, 60 retort
High Temperature, Steam
2 Controlled Pressure ”9'4 22'0 / 28'2 40’ 60’ 80 retort
High Temperature, Steam
2 Controlled Pressure 1294 25'0 / 333 40’ 60’ 80 retort

 

 

 

 

 

 

 

67

 

3.4. RESULTS AND DISCUSSIONS

Study 1a and lb. Atmospheric heating

Figure 3.6 shows plots of flour center temperature versus heating time.

 

Oil bath temperature

 

 

a172°C

b o
160 ____ 160 C

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

140 —
A 120
E, 100 —
3 ° ° ° ‘
t- : -1 ‘
60 ’15" ’ O. -— i» :
40 15 x — ‘ :\ K
20 ‘ \ ; I
O \ a‘N \
0 10 20 30 40 5° 60 70
Heating time (mill)

 

 

Figure 3.6. Plots of flour center temperature versus time for study 1a and lb.

8 Samples were taken out at 10, 15 and 20 minutes of heating time
b Samples were taken out at 20, 40 and 60 minutes of heating time
c Samples were taken out at 25, 60 and 80 minutes of heating time

68

 

3.4.1. Study 1a. Atmospheric Pressure heating- Constant-moisture

The average oil bath temperature was 808°C. Moisture content of flour mixture
stayed relatively constant with a maximum c.v at 10.4% during heating (Appendix 3.A.).
Thiamin concentration value was reproducible within each experiment with maximum
c.v at 10.9%. Concentration of thiamin was plotted against heating time on a semi-log
plot for MC $17.2 (Figure 3.7) and MC 2 17.2 (Figure 3.8). Moisture contents reported in
the plots were the mean values of 16 moisture content readings (4 initial flour MCs and 4
MCs at each heating time). In Figure 3.7, the reaction rate (slope) increased with

moisture content, but the opposite was true in Figure 3.8.

 

 

 

 

 

 

 

 

 

 

 

-0.8
0
_1 0 0
3
C = 9.67%
0
LL MC =6.15%
U L *L
54.2 ,. A ‘8"
MC = 10.7%
-1.4 ‘ -
-1.6 1 7
0 500 1000 1500
Heating time (min)

 

 

 

Figure 3.7. Semi-log plot of thiamin concentration versus heating time for 6.15, 9.67,

10.7% moisture content (db) flour heated isothermally at 80°C in an oil bath. The thinner
trend lines represent the 2nd replication.

69

 

 

 

 

 

 

 

 

 

 

 

_ _____T
-0.5
-1.0 h i L~——
' U
:1 -l.5 .
1—1
-2.0 .
ManN
25 . . ° L .
0 100 200 300 400 500
Heating time (min)

 

 

 

Figure 3.8. Semi-log plot of thiarrrin concentration versus heating time for 17.2, 27.0,
36.9% moisture content (db) flour heated isothermally at 80°C in an oil bath. The thinner
trend lines represent the 2nd replication.

The effect of sample moisture contents on k is summarized in Figure 3.9.

Parameter b(+) and b(-) were 0.439 and —0.128 respectively.

 

 

 

 

 

 

 

 

 

 

 

 

 

_ ' *7

0.0

y -- -0.128 x - 3.16 Mo'smre
R2 = O 85 content
-50 . - ~ 06.15%
é: a 09.67%
E
'4 . A10.7%
-10.0 A
/ o 17.2%
y = 0.439 x - 12.86
R2 = 0 95 027.0%
1 5 0 36.9%
0.0 10.0 20.0 30.0 40.0
MC(%) in dry basis

 

 

Figure 3.9. Effect of flour mixture moisture content (db) on reaction rate constant at 80°C

heating. k is in min'l.

70

According to Hermann and Tunger (1966), thiamin was more thermostable in a
dry medium than in moist product until MC reached 14.9% (db). In the present study, the
same trend was observed but different values of k,, b(+) and b(-) were obtained. Figure

3.10 compares the graphs obtained from Hermann and Tunger with results from the

 

 

 

 

 

 

 

 

 

 

 

present study.
-3
fr‘ \
[HT ‘
-6 - AHT at110°C
.\& 9 .. Q _______

j: I ' '9 oHrat90°c
'4 I

_9 _ I Present study at

80°C
I
-12 1 .
0.0 50.0 100.0 150.0
MC % (db)

 

 

 

Figure 3.10. Plot of Ln k versus MC % (db) of Hermann and Tunger (1966) (HT) at 90
and 110°C and the present study. k is in (min'l).

Figure 3.10 shows that the slopes obtained from the present study were steeper
compared to Hermann and Tunger’s (especially at MC>14.9%). A possible reason of this
occurrence was that their published study did not specify the container used for heating
the flour or whether moisture content was kept constant throughout. If MC decreased
during heating time, the true reaction rate value would be lower than the reported value
because reaction rate was slower at higher MC (A in Figure 3.11). Thus, in the Ln C vs

time plot, the true k value would be smaller than the reported value. Especially at high

71

MC where unbound water could evaporate rapidly, the reported k could be much higher
than the true k. Consequently, the true b(-) value (B in Figure 3.11) could be a steeper
slope. However, at the lower MC, moisture was bound tightly to flour particles, thus
even if the container was not tightly sealed, the moisture loss during heating was

minimum, Thus, the slope from their study was similar to the present study at the lower

 

 

 

 

 

 

 

 

    

 

 

 

 

 

MC.
A B
A 30% MC 4
\ True value
Ln C if MC L k \\ data
" maintained n ‘\\ . Bigger
at 30%MC True valtié‘fx } difference
— HT data if MC Lower k, of k at
decreased with steeper slope high MC

 

 

Figure 3.11. Possible reason for the difference between the result in Hermann and Tunger
(HT) (1966) and the present study.

3.4.2. Study 1b. Atmospheric Pressure heating- High-temperature heating

Average oil bath temperature was calculated to be 144.8, 159.2 and 170.6°C. The
average sample temperature was calculated at each heating temperature using Eq. (3.10).
The Ta.g were 141.9, 156.8 and 166.4°C. Thiamin concentration value was reproducible
within each experiment with c.v ranging from 0.67-13.4%. Thiamin concentration versus
heating time was plotted in Figure 3.12. Reaction rate constants (k) were the negative

slopes obtained from the graph.

72

 

 

_1 5 § Ng=1419°c

Tavg = 156.8°C
-2.5 I \ “7

-3 .5 1 1 1
0 20 40 60 80
Heating time (min)

  

LnC

r“, = 166.4°C

 

 

 

 

 

 

 

Figure 3.12. Semi-log plot of thiamin concentration versus heating time for flour mixture
heated isothermally at 144.8, 159.2 and 170.6°C average oil bath temperature. Talvg is the
average sample temperature. The thinner trend lines represent the 2"d replication.

Figure 3.12 shows that higher temperature caused higher degradation rates of thiamin.
The retention of thiamin in the flour mixture at oil bath temperatures of 144.8, 159.2 and
170.6°C indicated a first—order reaction, as shown by the linear fit on a semi-log plot
(Figure 3.12).

3.4.2.1. Corrected high-temperature reaction rate constant

During high-temperature heating, the flour mixture MC dropped from 33.3% to

~6.0% (Figure 3.13).

73

 

40.0

 

 

 

  
 

 

 

 

 

 

 

 

 

 

 

 

35.0

2 . —LLLLLLL .
'3 30.0 we 1 —O— Tavg = 141.9 C
°\: 25 0 \1\ __ ' ' O ' ' Tavg = 156.8°C
E . \i, “in" \_ + Tavg = 166.4OC
o \\ .
3. 15.0 —--—‘*1\ ix,
‘2 \
'8 10.0 L ___---__-
E l\ “ \ /.

5.0 LLLLLLLL - .- ...... 8. _ _ _ _ _ _ :4 _.__L%L

0.0 1 1 I

0 20 40 60 80

Time (minutes)

 

 

 

Figure 3.13 Plot of flour moisture content versus heating time during high temperature
heating in study 1b.

 

Reaction rate constants were corrected to 33.3% MC using the constant b(+) and
b(-)based on Eq.(3.9) to account for the moisture loss. The corrected and uncorrected k

were plotted against reciprocal of Tavg to obtain the respective activation energy.

74

 

2.0

 

Corrected to 33.3%MC : y = -15,587x + 36.19

    
     

 

 

R2 = 0.99
11.11 1
r...g = 166.4°C T
L l 156.8°C

 

1: -2.0

i
"I \l.\ 141 .9°C
-411 1

Uncorrected : y = -15,030x + 31.68\.

 

 

 

 

 

 

R2 = 0.98
-6.0 . . .
0.00225 0.00230 0.00235 0.00240 0.00245
l/T 1..g (1/K)

 

 

Figure 3.14. Arrhenius plot for the corrected and uncorrected reaction rate constants. k is
in min'l. Tavg is the average sample temperature.

The reaction rate constant increased after it was corrected from the MCIow to the
MChigh ,as expected. The reaction rate calculated at 80°C (kgooc) increased from 1.85x10'5

min'1 to 3.48x104 min'l. However, the increase in k values only yields a 3.7% increase of

activation energy from 124.9 to 129.6 kJ/g-mole.

3.4.3. Study 2: Controlled Pressure heating

Predicted center temperature versus measured center temperature of the flour in
the heated cans was plotted for 33.3% MC. The plots for the other two MCs can found in
Appendix 3E. The RSME for predicted versus measured temperature for flour 19.1%,

28.2% and 33.3 % flour MC were 12.3, 10.1 and 806°C, respectively.

75

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

140 LL--. ......
I
120 1‘
RMSE=8.06 " ”"
9C: 100
E 80
[.1
E) 60 -1.-. oHeatingdata L
U
'23;
3: 40 W- ’ i i i 1|Coolingdata H
O
O
20 - ‘
O 1 1 1 1 1 1
0 20 40 60 80 100 120 140
Measured Tum, (°C)

 

Figure 3.15. Plot of measured versus predicted center temperature for 33.3% (db) MC
flour in 201x211 cans heated at 129.4°C retort temperature.

The plot above shows that there was good agreement between the predicted

temperature and the measured temperature, suggesting a good accuracy of the analytical

solutions.

Temperatures at each r and z location determined by Gauss-Legendre quadrature
were calculated. The mass-average thiamin retentions in the cans were calculated based
on Eq.(3.21). Activation energy and reference reaction rate at 80°C were changed by
iteration to obtain minimum sum of squares (Eq.(3.23)) of thiamin retention. The
reference temperature chosen was 80°C as it was the average of the initial and final
sample temperature. Figure 3.16 shows good agreement between measured retention and

predicted retention for 33.3% MC. Appendix 3.F shows those of 19.1% and 28.2% MC.

76

 

 

 

 

0.8
RMSE = 0.0360
O

 

 

.9
a
l
1

 

Predicted retention
O
J;
|

 

 

 

 

.9
N
1
1
1
1
l

 

 

 

0.0 1 1 1

0.0 0.2 0.4 0.6 0.8
Measured retention

 

 

 

Figure 3.16. Plot of measured thiamin retention vs predicted thiamin retention for
33.3%MC (db) flour in 201x211 cans heated at 129.4°C retort temperature.

For 19.1% MC, Solver was unable to converge to a reasonable value of Ea and k,
regardless of any initial values and reference temperature. The coefficient of variance for
this MC’s measured retention was the highest (14%). Thus, a higher RMSE was
expected.

Table 3.2 shows that estimated E, from 28.2% and 33.3% MC was not
significantly different. It was deduced from Hermann and Tunger (1966)’s data that MC
had no significant effect on activation energy. Therefore, for data of 19.05% MC, the
value of E, was fixed at the average of the two E, values of 28.2 and 33.3% MC, and

Solver iterated on k, only. Table 3.2 listed the E, and k, values for all MCs.

77

Table 3.2. Activation energy, reference rate constant and pre—exponential constant

 

 

 

 

 

generated from study 2
MC % (db) kgooc (111111") 114111111") 15., (kl/g-mole) RMSE ”R2
19.1 2.91E-04 1.2013+14 a119.31 0.126 0.75
28.2 1.45E—04 3.66E+13 117.59 0.0239 0.97
33.3 9.69E-05 7.67E+13 121.03 0.0360 0.92

 

 

 

 

 

 

 

3: average of 117.59 and 121.03 kJ/g-mole
b = R2 obtained from the plot of measured thiamin retention vs predicted thiamin retention

The bootstrap program estimated 1,000 values of E, and k30°c based on random
generation of the 18 retention data for flour with 28.2% and 33.3% MC.

In the case of 19.05% MC, bootstrap predicted 1,000 values of kgooc only. A 95%
confidence interval was defined as the 25th and 975th sample of the 1000 values, sorted in
ascending order. The confidence interval was (2.49x10'4, 3.79x104)min'1.

Results from the bootstrap program for 28.2% and 33.3% MC are shown in Table
3.3.

Table 3.3. Statistic analysis from bootstrap results of 1,000 E, and k, values.

 

 

 

Mean kgooc i Std deviation Mean Ea i Std deviation Correlation
MC % (db) (min'l) (kJ/g-mole) coefficient, p
28.2 1.46E-4 i 3.22E—6 117.5 i 0.27 -O.62
33.3 9.67E-5 i 6.62E-6 121.1 i 1.48 -0.94

 

 

 

 

 

 

For both data, the correlation coefficient fell below the critical value of 0.99,
which meant that there was not high correlation between the Ea and k, values. An
example of the bivariate three-dimensional normal probability distribution of the two
parameters is shown in Figure 3.17 for flour with 33.3% MC. The volume under the

curve is equal to one.

78

 

Confidence region
95%

 

i-‘-‘--,-— 90%

800\LLUMLU.-U-

  
     
   

600\L,LHLLLLLU. .

400\UL,,HL,L,L

 

 

P (probability)

 

 

 

 

 

12 E5

10 E5 126
lmin 124
kr [1 l 8 E-S 122
120
6E-5 116 “8

E [kl/(g m01)l

 

 

 

Figure 3.17. 3-D bivariate normal probability distribution [90 & 95% confidence region]

for estimated activation energy (kJ/g-mol) and reaction rate constant kgo (min") for
MC=33.3% flour obtained from bootstrap data.

The two contour lines represent the confidence regions, and the highest frequency

of the appearance is at the peak. Confidence region was plotted instead of confidence

interval because each pair of E, and k, value was correlated to one another; thus the

region would show the appearance frequency of each pair. A 95% confidence region

means that 95% of the bootstrap data lay within this region. The contour lines of the

confidence regions are plotted in a two-dimensional plot in Figure 3.18.

79

The 95 and 90% contour joint confidence region for MC = 33.3% flour are shown
in Figure 3.18. Figure 3.18 also shows that the parameters in Table 3.2 (k, = 9.69E-05
111111", E. = 121.0 kJ/g-mole) and Table 3.3 (k, = 9.67E-05, E, = 121.1 kJ/g-mole) fell

within the joint confidence region. Appendix 3.G. shows the confidence region for MC =

 

 

 

 

 

28.2% flour.
kr [l/min]
I 1 1 I
12.0 136 ._
(N96 Confidence level
11056— ------ ' m - i I

 

10.0 E-S

 

 

9.0 E—S

 

8.0 E-S

 

 

7.0 E-5

 

 

 

 

 

 

6.0 E— ‘L 1 1 1
fl6 118 120 122 124 126

E [kJ/(g mol)]

Figure 3.18. 90% and 95% joint confidence region for estimated B, activation energy
)

(kJ/g-mol) and reaction rate constant kgo (min' for MC=33.3% flour obtained from

bootstrap data.

 

 

 

80

3.4.4. Comparison of the kinetic parameters obtained by the two methods

Two methods were proposed in this study to obtain the hi gh-temperature kinetic
parameters. In the first method (study lb), since moisture content decreased during
heating, reaction rate constant was corrected using the parameters obtained in the
constant-moisture study (study 1a). In the second method (study 2), moisture content was
maintained constant at high temperature, and a smaller standard error (more accuracy)
was obtained.
3.4.4.1. Activation energy

Table 3 .4 shows that the activation energy obtained from study 1b and 2 w ere
comparable. A student t-test on the two values shows that t= 0310, thus they were not
significantly different at 95% confidence level (using t (005,22) = 1.717 as the test of
significance). Despite the changing moisture content during heating, the activation energy
in Study lszncorrected was similar to that of study 2. Furthermore, the two studies were
conducted at different temperatures. Hence, it could be concluded that activation energy
of thiamin was independent of moisture content and temperature. The values obtained in
this study were also within the range of activation energy in most food products (Table
3.7).

Table 3.4. Comparison of activation energies for MC= 33.3% flour

 

 

 

 

 

 

H t' d' Activation Regression N b f1
Study # t °° 111g“? “‘3‘ energy Statistics d u: Cf;
° a mu
empera e ( ) (kJ/ 8'm019) Std error of E0 p
Study lb‘ U”°°”°°t°d 144.8, 159.6, 170.6 124.9 a1.07 6
Study lb: Corrected a
Atmospheric pressure heating‘ 144.8, 159.6, 170.6 129.6 7.27 6
Study 2 b
Controlled pressure heating 129'4 121'0 1-48 18

 

 

 

 

 

 

aBased on linear regression analysis
bStandard deviation based on 1,000 bootstrap data

81

3.4.4.2. Reaction rate congant

Table 3.5 shows that the corrected reaction rate in study lb was higher than the
reaction rate in study 2. However, a student t-test on the two values shows that t = 1.311,
meaning that they were not significantly different at 95% confidence level (using
t(0.05,22) = 1.717 as the test of significance).

Table 3.5. Comparison of reaction rate constant for MC= 33.33% flour

 

 

 

 

 

Regression N b fdata
Study # Temperature (°C) ($3) Statistics um gin;
Std error of kr p
, 144.8
Uiiugeg’éd 159.6 1.85*10’5 “1.297110”5 6
170.6 '
144.8
Study 1b: .4
159.6 3.48*10 3191411104 6
Corrected 17 0. 6
Study 2 129.4 9.69"‘10'5 b6.67*10'° 18

 

 

 

 

 

 

 

8Based on linear regression analysis
bStandard deviation based on 1,000 bootstrap data

Effect of moisture content on reaction rate

It was concluded from this study, that for MCSl7.23%, reaction rate increased
with MC and for MC217.23%, reaction rate decreased with MC. The latter statement was
justified by results from study 1a and study 2 (Table 3.6) where a similar trend was
observed. A student t-test on the two b(-) values shows that F1871, thus the b(-) value
obtained from study 1 a and study 2 w ere not significantly different (using t(0.05,7) =
1.895 as the test of significance). This shows that temperature did not affect b(-) which

validate the assertion that thiamin activation energy did not change with temperature.

82

Table 3.6. Moisture content parameter b(-) based on two studies

 

 

 

 

 

Rggression Statistics
Study # b(.) value R2 Std error Number of data points
Study 1a
conducted at 80°C -O.128 0.85 0.0273 6
Study 2
Conducted at .
129.4°C -0.0769 0.99 0.00088 3

 

 

 

 

 

 

Thiamin reaction rate reached a maximum at 17.27% MC for several reasons.
Firstly, thiamin reacts readily in Maillard reaction, and Maillard reaction proceeds
optimally at MC ranging from 11.1% to 25% MC (Hermann and Tunger 1966).
Therefore, it was expected that the maximum thiamin loss (i.e maximum reaction rate)
would occur at the specified range of MC. Secondly, at the low MC, water molecules
bind tightly to ionic groups, such as carboxyl and amino groups. There is no aqueous
phase available for dissolution and diffirsion for taking part in the Maillard reaction; thus
thiamin loss is minimum. Reaction rate passed a maximum and then started to decrease at
higher MC. At this time, water is unbound and exists as free water found in capillary
pores, and the reactant becomes too ‘diluted’.

In this study, two methods were utilized to obtain the rate of thiamin degradation
in wheat flour (min'l).

From Atmospheric Pressure methods, a wider range of moisture content was studied:

at flour MC < 17.2% (dry basis) or 14.7 %(wet basis),

 

k(T,MC) = 3.48*10“ exp[’129596[ 1 1

R T(°K) — 353

8

)+O.439(MC-33.3):|

83

at flour MC >17.2%,

1.1,116)-3.11L11—4...[m[1 1

———)—0.128(MC-33.3)
R, r 353

From Controlled Pressure methods,

At flour MC > 19.1% (dry basis) or 16% (wet basis)

k(T,MC)=9.69110'5exp[————"121030[1 1

————)—0.0769(MC-33.3)
R, r 353

84

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85

3.5. CONCLUSIONS

The atmospheric pressure heating study involved a much simpler setup and
mathematical analysis m ethod to o btain kinetic parameters. B ut at higher temperature,
flour mixture moisture content is difficult to hold constant. Based on this study, it was
concluded that a changing-moisture hi gh-temperature parameter could be corrected based
on a lower temperature constant-moisture study. A limitation of this method is that more
experiments are needed to generate data. However, this method could be used by
researchers without access to controlled-pressure equipment or to an interactive program
code of the analytical conduction heat solution.

Another method was proposed where experiments were conducted at controlled-
pressure heating. Although it involved a more complex calculation and experimental set-
up, the reaction rate constant obtained was more accurate, as moisture content was kept
constant throughout the heating period, and lower standard error was obtained.

Results of this study showed that the activation energy of thiamin was
independent of sample moisture content and temperature. On the other hand, thiamin
reaction rate was affected significantly by sample moisture content. Thus, a product
developer should be aware of the maximum degradation range when formulating a
product with moisture content near the range, if thiamin retention is a concern.

The thiamin kinetic parameters obtained from this study could be used to quantify
the thermal effects on thiamin degradation separately from other significant effects of a

food process (Chapter 4).

86

3.6. FUTURE WORK RECOMMENDATIONS
Thiamin kinetic parameters should be investigated in the lower moisture range
(<15%) using the controlled-pressure heating.

Using a smaller can size is recommended as it will reduce sample come-up time.

3.7. ACKNOWLEDGMENT

Many thanks to Star of the West Milling Co. for their generous donations of flour,
Robert Templeman and Huang Xue Wen of Department of Animal Science and Statistics
respectively, for their help in statistical analysis. Lastly, we thank John Mark Dolan for

translating the Hermann and Tunger (1966) paper.

87

3.8. NOMENCLATURE

r*

T
Tavg
Tcenter
T:
Tma

T wall
T oilbath
T r

T ref
T2

Too

1

Ax

1/temperature in °Kelvin

surface area, m2

moisture content parameter (positive slope)
moisture content parameter (negative slope)

dry basis thiamin concentration in flour, concentration
mean average thiamin retention, concentration
initial dry basis thiamin concentration in flour, concentration
specific heat capacity, J/(kg °C)

activation energy, J/(g-mol)

heat transfer coefficient, W/(m2 °C)

thermal heat conductivity, W/(m °C)

reaction rate constant, min'l

reference reaction rate constant, min’l

maximum reaction rate constant, min’l

half length of can, 0.03395 m

normalized half length of can (dimensionless) = l
moisture content of flour, db

reference moisture content, db

moisture content at maximum reaction rate, db
conducted heat, J/s

Ideal-Gas Constant, 8.3144 J/(g mol °K)

radius of can, 0.0258 m

normalized radius of can (dimensionless) = 1
' ' - - . . r *
radlal locatlon relative to radlus R (d1mensronless) r = R:

radial location, m

temperature, °C

average sample temperature for study 1a and lb, °C
measured sample temperature for study la and lb, °C
initial sample temperature, °C

mass-average temperature for study 2, °C
wall temperature for study 1a and 1b, °C

oil bath temperature for study 1a and 1b, °C
temperature at r location for study 2, °C

reference temperature, °K

temperature at 2 location for study 2, °C
environment temperature for study 3, °C

heating time, min

wall thickness, m

88

xwmr water content, in wet basis, fraction
xcarbo carbohydrate content, fi'action
hydrate
Vcam V2 volume of the can (dimensionless)
. . . . . z *
z ax1al location relative to length l (dimensmnless) z = l—*
2* axial location, m
Greek symbol
a thermal diffusivity, mz/s
,6 time temperature history, 3
2,, eigen value, dimensionless
. h]
for slab, 11,. satlsfies 2,, tan 2,.=(I)
. . hR

for cylinder, 2,. satisfies 2.". J, (Am) - —k- JO (2,.)

Jo bessel function of type zero, dimensionless

89

3.9. REFERENCES

AOAC International. 1995. Official Methods of Analysis, 16“1 edition. AOAC
International, Arlington, VA.

Bell LN and White KL. 2000. Thiamin stability in solids as affected by the glass
transition. Journal of Food Science 65(3): 498-500.

Carroll T, Chen P and Fletcher A. 2003. A method to characterise heat transfer during
high-pressure processing. Journal of Food Engineering 60(2): 131-135.

Carslaw HS and Jaeger J C. 1959. Conduction of heat in solids, second edition. Great
Britain at the University Press, Oxford.

Cha JY, Suparno M, Dolan KD, NG PKW. 2003. Modeling thermal and mechanical
effects of retention of thiamin in extruded foods. Journal of Food Science 68(8): 2488-
2496.

Choi Y and Okos MR. 1986. Effects of temperature and composition on the thermal
properties of foods. Food Engineering and Process Applications Vol. 1. Transport
Phenomena, LeMaguer M and J elen P, Eds, Elsevier, New York.

Dolan K D. 2 003. E stimation o f kinetic p arameters for n onoisothermal food p rocesses.
Journal of Food Science 68(3): 728—741.

Dwivedi BK and Arnold RG. 1973. Chemistry of thiamine degradation in food products
and model systems: A review. Joumal of Agricultural Food Chemistry 21 :54.

Efron B and Tibshirani RJ. 1993. An introduction to the bootstrap. Chapman and Hall.
New York.

Feliciotti E and Esselen. 1957. Thermal destruction rates of thiamine in pureed meats and
vegetables. Food Technology 11(2):77.

Garrote RL, Silva ER and Bertone RA. 2001. Kinetic parameters for thermal inactivation
of cut green beans lipoxygenase calculated using unsteady-state methods. International
Journal of Food Science and Technology 36: 377 - 385.

Guzman-Tello R and C heftel J C . 1 987. Thiamine loss during extrusion c ooking as an
indicator of the intensity of thermal processing. International Journal of Food Science and
Technology 22:549-562.

Hermann F and Tunger L. 1996. Thermal loss of thiamin in relation to moisture content
of foods, with special reference to flour products. Nahrung 10(8): 705-712 (in German).

90

110 S and Berghofer E. 1998. Kinetics of thermomecham'cal loss of thiamin during
extrusion cooking. Journal of Food Science 63(2): 312-316.

Labuza TP. 1980a. The effect of water activity on reaction kinetics of food deterioration.
Food Technology 4: 36-41, 59.

Lai KPK, Dolan KD and Ng PKW. 2003. Modeling thermal and mechanical degradation
of anthocyanins in extrusion processing (Thesis). Michigan State University, East
Lansing, MI.

Lenz MK and Lund DB. 1977a. The lethality-Fourier number method: experimental
verification of a model for calculating temperature profiles and lethality in conduction-
heating canned foods. Journal of Food Science 42(4): 989-996, 1001.

Lenz MK and Lund DB. 1977b. The lethality-Fourier number method: experimental
verification of a model for calculating average quality factor retention in conduction-
heating canned foods. Journal of Food Science 42(4): 997.

Mulley EA, Stumbo CR and Hunting WM. 1975a. Kinetics of thiamin degradation by
heat. A new method for studying reaction rates in model systems and food products at
hi gh-temperatures. Journal of Food Science 40:985.

Moore J C and Dolan KD. 2003. Optimization of oxidation steps used in fluorometric
determination of thiamin in soft wheat flour. Cereal Chemistry 80(2): 23 8-240.

Steet J A and Tong CH. 1994. Thiamin degradation kinetics in pureed restructured beef.
Journal of Food Processing and Preservation 18: 253-262.

Ramaswamy H, Ghazala S, van de Voort F. 1990. Degradation kinetics of thiamine in
aqueous systems at high-temperatures. Canadian Institute Food Science and Technology
23(2/3): 125-130.

Ryan-Stoneham TA, Tong CH and Clark PM. 1996. A research note: Effect of moisture
content and initial thiamin concentration on thiamin degradation kinetics. Journal of Food
Processing and Preservation 21: 257- 266.

Stasa FL. 1985. Applied finite element analysis for engineers. The Dryden Press,
Sanders College publishing, New York. pp: 542-545.

Thompson DR. 1982. The challenge in predicting nutrient changes during food
processing. Food Technology 36(2): 97-115.

Villota R and Hawkes JG. 1986. Kinetics of nutrients and organoleptic changes in foods
during processing. In: Okos MR, editor. Physical and chemical properties of foods.
Chicago: ASAE Publisher. pp 266-366.

91

Wang L and Sun DW. 2003. Recent developments in numerical modeling of heating and
cooling processes in the food industry - a review. Trends in Food Science and
Technology 14(10): 408-423.

Yajnik MM, Dolan KD, Ng PKW. 2003. Thermal and mechanical effects on retention of

food-grade B-carotene during extrusion processing (Thesis). Michigan State University,
East Lansing, MI.

92

Chapter 4. Modeling thermal and mechanical effect of extrusion processing of
wheat flour on thiamin retention in extruded products

4.1. ABSTRACT

Some researchers have reported the total thiamin degradation in extruded wheat
and corn flour, but the mechanical effects could not be uncoupled from thermal effects.
Using the proposed model, thermal effect and mechanical effect were quantified
separately.

Soft wheat flour at 25% moisture content (wb), mixed with 0.3% thiamin (wb)
was extruded at screw speed of 100-300 rpm with barrel temperature profile from feed
port to die of 50/85/115/130/155°C at constant degree of fill [0.65 (i 0.08)],
50/80/ 1 10/ 140/ 165°C at 0.58 (i 0.04) degree of fill, and at varying fill. Effect of moisture
content was also investigated by varying the dough moisture content from 23 to 32%
(wb). Thiamin content of all extruded samples was analyzed using a fluorometric analysis
method. The thermal effect of extrusion on thiamin was calculated using the kinetic
parameters 0 btained in C hapter 3 , accounting for the v arying time-temperature history
along the extruder barrel. The mechanical effect was calculated by mathematically
removing the thermal retention from the total thiamin retention.

Total thiamin degradation was affected by barrel temperature and moisture
content. Higher temperature resulted in lower retention while, higher moisture contents
increased thiamin retention. Thiamin loss decreased with screw speed at constant degree
of fill. At 155°C die temperature, mechanical effects caused 47.3% to 64.5% of total
thiamin loss. At 165°C die temperature, mechanical effects caused 42.2% to 53.3% of

total thiamin loss, indicating that as temperatures increase, thermal effects predominate

93

over mechanical effects with respect to thiamin loss. A different trend was observed at
when degree of fill was varied as screw speed increased; thiamin loss increased with
screw speed. H owever, at 1 65°C die temperature, m echanical e ffects c aused 2 8.9% to
48.3% of total thiamin loss; thus also indicating that thermal effect predominates over
mechanical effects. A final thiamin retention model was developed as a function of

thermal and mechanical effects of extrusion.

94

4.2. INTRODUCTION

The intensity of extrusion cooking has many positive and negative impacts on
extruded products. One of the negative impacts is the degradation of vitamins. In a
commercial extrusion process, thiamin is among the many vitamins, which is usually
fortified in the raw material pre-mix, to meet the minimum standard regulated by United
States Food and Drug Administrations. A model to predict thiamin retention in an
extrusion process would be helpful so that the process could be optimized to achieve
minimum thiamin degradation.

Many studies have observed the trend of thiamin retention in extruded food
products. Some of the similar trends were that increasing extrusion temperature reduced
thiamin retention, while increasing moisture content increased thiamin retention (Beetner
et al. 1974, Maga and Sizer 1978, Cheftel 1986, Guzman-Tello and Cheftel 1987, [lo and
Berghofer 1998). Among these studies, several modeled thiamin retention. Beetner et al.
.(1974, 1976) modeled thiamin retention in extruded corn grits and triticale, respectively
as a function of barrel temperature, screw speeds and moisture content. Guzman-Tello
and Chefiel (1987) and 110 and Berghofer (1998) modeled thiamin reaction rate and
activation energy (thiamin kinetic parameters) as a function of temperature, dough
moisture content, and screw speed. However, for their model development, they assumed
near-isothermal temperatures in the extruder, which was not the case, because barrel
temperatures varied from feed port to die. Their near-isothermal assumptions in
developing the kinetic parameters caused ~30% underestimation of activation energy and
80% underestimation of reaction rate constant (Dolan 2003). These models were

developed as functions of equipment-dependant variables (e. g: barrel temperature, screw

95

speed). These types of models are limited in their applicability to predict thiamin
retention in different sized extruders. Although two extruders are running at the same
screw speed, a larger extruder may have a different residence time compared to the
smaller extruder, yielding a different thiamin retention. Extruder size also affects other
equipment-independent variables such as overall degree of fill, shear history or specific
mechanical energy input (SME). Therefore, a model that is developed as a function of
equipment-independent variables would be more valuable for scale-up purposes.

An equipment-independent model was proposed by Cha et al. (2003) for thiamin
retention in extruded wheat flour. They proposed a model where total thiamin retention
(R7) was a product of the thermal effect (Rfl) and mechanical effect (R5) of extrusion. As
mentioned earlier, temperature affected thiamin retention. A shorter heating time should
result in higher thiamin retention. However, extrusion at higher screw speed (shorter
residence time) decreased thiamin retention (Guzman-Tello and Cheftel 1987, Schmid et
al. 2002). These facts suggest that mechanical or shear effect also plays a role in thiamin
degradation. Cha et al. (2003) isolated thermal effects by heating flour mixed with
thiamin isothermally in an oil bath to estimate kinetic parameters. Using the kinetic
parameters, R1; was calculated, taking account of the changing product temperature
profile along the extruder barrel and the product residence time. The mechanical effect
(RS) was calculated by mathematically removing thermal effect fi'om the total thiamin
retention. The quantified Rs was then modeled as a function of SME and shear history.

Results of their study showed that RS decreased with increasing SME and shear
history. However, as the shear effect terms increased, product temperature also increased

because of their equipment limitations on cooling the extruder. Since extrusion was only

96

conducted at one barrel temperature profile, they were not able to determine whether
there was interaction between mechanical effects and temperature. In addition, their
extrusion study was only conducted at one constant degree of fill and at one dough
moisture content, thus the applicability of the developed model for different degrees of
fill and moisture contents was unknown.

Therefore, the objectives of this present study were 1) to investigate the effect of
temperature, degree of fill and moisture content on thiamin retention and 2) to develop a
model to predict thiamin retention as a function of thermal effects and mechanical effects
of extrusion. The average shear rate model from Chapter 2 was used to calculate shear
history to describe mechanical effects and the thermal kinetic parameters from Chapter 3

was used to calculate thermal effects of extrusion on thiamin retention.

97

4.3. MATERIALS AND METHODS
4.3.1. EXTRUSION
4.3.1.1. Equipment specification

The extruder used for this study was a co-rotating and interrneshing twin-screw
extruder (APV, Grand Rapids, MI MP19TC-25). The length: diameter ratio of the
extruder was 25:1, the barrel diameter was 19 mm, and the die diameter was 3 mm.
Screw configuration was set up for high shear effect (Table 4.1). A control panel was
connected to the extruder to monitor the percent torque required to turn the screws, the
screw speed (rpm), die pressure (psi), product temperature (°C), and barrel temperature
(°C). Product temperature was measured using five thermocouples, flush-mounted on the
bottom of the barrel and die plate, adjacent to the electrical heating rods and water-
cooling jackets. The distances of thermocouples from the feed port were 12.55, 27.16,
34.14, 41.92, and 47.48 cm. Pressure at the die was measured using a pressure transducer
(Dynisco, Model #EPR3-3M-6, Hickory, NC), located at 7 mm before the die entrance.
Desired barrel temperature was achieved and maintained using electrical heating rods to
add heat, and a water-cooling jacket to remove heat when necessary. The rate of flour
entering the feed port was controlled using a K—Tron K2M twin-screw volumetric feeder
(K-Tron Corp., Pitrnan, NJ). Water added to attain desired moisture content of dough was
pumped into the extruder by an E2 Metripump positive displacement metering pump
(Bran & Luebbe, Northhampton, UK). The water injection port was located at 5.5 cm

from the feed opening.

98

Table 4.1 Screw configuration for high shear extrusion

Length (cm) Screw Type

Feed port 15.2 SD“ Twin Lead Screw (TL)

3.32 7x30° Forward Kneading Paddles (FKP)
7.60 4DTwin Lead Screws

1.90 4x60° Forward Kneading Paddles

1.90 4x30° Reverse Kneading Paddles

3.80 2D Twin Lead Screws

2.85 6x60° Forward Kneading Paddles

1.90 4x3 0° Reverse Kneading Paddles

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

V 1.90 1D Single Lead Screw (SL)
3.32 7x90° Kneading Paddles
Die 3.80 2D Single Lead Screws
*D = 19 mm

4.3.1.2. Pre- extrusion preparation

 

Soft wheat flour, with moisture content of approximately 15% wet basis (wb)
/1 7.6% dry basis (db) was obtained from the Star of the West Milling Co. (Frankenmuth,
MI). Moisture content was determined by heating 1 g flour at 130°C for 10 minutes using
a Sartorius MA-30 moisture analyzer (Goettingen, Germany). Food-grade thiamin
hydrochloride (Spectrum Laboratory Products, Gardena, CA) was mixed with flour at a
concentration of 0.35% (db) using a V-shaped twin shell dry blender (Patterson-Kelley,
East Stroudsburg, PA). To ensure homogeneous distribution of thiamin with a coefficient
of variance <10%, the flour and thiamin were mixed for 40 minutes. Thiamin content was
analyzed using the fluorometric method (Official Method 953.17, AOAC 1995). Method
of thiamin analysis is described in Appendix 1.A. An initial concentration of thiamin in
flour was analyzed at 9 different locations in the mixed flour to yield C0 = 0.36 i 0.0189
% concentration (dry basis).

The flour feeder and water pump feeder were calibrated prior to extrusion runs to

determine the a mount 0 f w ater n ceded to a chieve d esired m oisture c ontent. Flour w as

99

dyed blue at 40% concentration (w/w), using water-based blue (#1070-0500,
drafistorecom, Cordova, TN, USA) for mean residence time measurement.
4.3.1.3. Extrusion processing

Approximately 60 g of extrudate samples for thiamin analysis were collected after
the process reached constant readings of die pressure, die temperature, and torque
(steady-state condition). At the time of extrudate collection for thiamin analysis, die
pressure (psi), barrel and product temperature (°C) and percent torque (load torque) were
measured. Base (non-load) torque was measured before each extrusion run. In addition to
temperature at five zones, product temperature at the die was measured b y inserting a
handheld T-Type needle thermocouple (Cole-Parmer, Vemon-Hills, IL) into the die hole
during the extrusion run. Following data collection, 0.5 g of blue-dyed flour was dropped
into the feed port for mean residence time measurement. Time taken for dye to appear in
the extrudate was recorded, followed by extrudate collection at the die outlet, at 5- second
intervals until dye disappeared from extrudate. Table 4.2 shows the extrusion conditions
tested. All samples were dried overnight at 22°C, 40% RH until they reached constant
moisture content of 13.63% (db). Samples were first ground in a Krups coffee grinder
(Peoria, IL, USA) and then in a Udy Cyclone Mill (Udy Corp., Fort Collins, CO) with a
0.5 mm screen. Powdered extrudates were stored at 4°C until analysis for thiamin and
moisture content.

After an extrusion run at 200 rpm, dough mass was measured by first dead-
stopping the extruder, then taking the dough in the die plate, wrapping it tightly using a

plastic wrap, and weighing it. The volume of the dough was measured by water

100

displacement. The density of the dough was measured as the mass divided by the volume,

based on two readings.

Table 4.2. Extrusion conditions (all experiments were duplicated on different days)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Extrusion Barrel Terrperature Screw Flour Feed rate Dough Morsture
condition (Zone 1/2/3/4/Dre) Speed (rpm) (g/min) content
(°C) wb/db(%)
1a 50/85/115/130/155 100 28.0 25.0 / 33.3
lb 50/85/115/130/155 150 32.0 25.0 / 33.3
10 50/85/115/130/155 200 33.5 25.0 / 33.3
1d 50/85/115/130/155 250 36.0 25.0 / 33.3
1e 50/85/115/130/155 300 39.0 25.0 / 33.3
2a 50/80/ 1 10/ 140/ 165 100 28.0 25.0 / 33.3
lb 50/80/110/140/165 150 32.0 25.0 / 33.3 .
2c 50/80/ 1 10/ 140/ 165 200 33.5 25.0 / 33.3
2d 50/80/110/140/165 250 36.0 25.0 / 33.3
2e 50/80/110/140/165 300 39.0 25.0 / 33.3
2f 50/80/1 10/ 140/ 165 200 33.5 23.0 / 29.8
2g 50/80/ 1 10/ 140/ 165 200 33.5 28.0 / 38.8
2h 50/80/ 1 10/ 140/ 165 200 33.5 32.0 / 47.1
3a 50/80/ 1 10/ 140/ 165 100 35.9 25.0 / 33.3
3b 50/80/ 1 10/ 140/ 165 150 35.9 25.0 / 33.3
3c 50/80/1 10/ 140/165 200 35.9 25.0 / 33.3
3d 50/80/ 1 10/ 140/ 165 250 35.9 25.0 / 33.3
3e 50/80/ 1 10/ 140/ 165 300 35.9 25.0 / 33.3

 

In extrusion conditions 1 and 2, approximate constant fill was maintained by
increasing the feed rate as screw speed was increased. Effect of temperature on thiamin
retention was studied by using two different temperature profiles (conditions 1 and 2).
Dough moisture content was varied in conditions 2f, 2g and 2h at a constant screw speed
and temperature. Degree of fill was varied at condition 3 by maintaining constant feed
rate as screw speed was increased. Data from condition 3 was used to determine whether

the model developed from a constant degree of fill (conditions 1 and 2) extrusion

101

 

condition could accurately predict data in a varying degree of fill extrusion condition
(condition 3).
4.3.2. ANALYSIS
4.3.2.1. Residence Time

Residence time (RT) is the time spent by each flour particle in the extruder. Due
to the axial mixing in the extruder, each flour particle exits at different times. Residence
time can be measured using the dye-tracer technique (Peng et al. 1994). A 0.5 g of blue-
dyed flour was fed into the feed port. Time taken for the dye to appear in the extrudate
was recorded, followed by colored-extrudate collection at the die outlet, at 5- second
intervals until dye disappeared from extrudate. These colored-extrudates were air-dried at
room temperature (37°C) for at least 2 days and then ground using Krups coffee grinder
for 5 seconds. A 1.5 g o f ground colored-extrudate was analyzed for intensity of blue
color (b *) using a HunterLab D25 colorimeter (Hunter Associates Laboratories, Inc.,
Reston, VA, USA). An extrudate strand with no dye added was used as a color control.
Real color value was reported as blue color minus control sample color. Before usage, the
colorimeter was calibrated using a black tile and white tile (Standard No. C2-30954).

Mean residence time (T) was calculated using Levenspiel (1999) method,
t— : ZtiE(t,.)At,. (4.1)
where t is the exit time and E(t) is the normalized color units

E(t) __.__’ZZ__ (4.2)

Zb“, At,

E(t) was plotted against exit time (t) to obtain the residence time distribution curve.

102

4.3.2.2. Color-concentration calibration curve

Due to the effect of saturation, color value does not increase linearly with
concentration at higher concentration. Therefore, a calibration curve of dye
concentrations versus b* value was made to ensure that b* value from the colored-
extrudates were within the linear range. Five batches of blue-dyed flour with different
concentrations (0.4, 1, 2, 6% (w/w)) were prepared and then extruded at 200 rpm, 33.3%
MC (db), 32.7 g/min flour feed at 160°C. The concentrated extrudate samples were
collected after steady-state condition was reached. They were analyzed using the same
method mentioned in section ‘Residence Time’. Color values from these concentrated
extrudate samples (b ’) were then plotted against the dyed-flour concentrations. If b“ from
the colored-extrudates was within the linear range of the plot, conversion of b* values to
dyed-flour concentrations was unnecessary and b* color units was used for the
calculation in Eq.(4.2).
4.3.2.3. Degree of fill

The degree of fill during extrusion run varied in each barrel section due to the
varying screw configuration. As flour particles moved towards the die, the screws were
configured such that the degree of fill would increase to a maximum of 1.0. The degree of
fill at section 1' (fl) could be estimated by visual observation during dead-stopping of
extruder where screw speed and flour feed rate were stopped instantly at the end of an
extrusion run and the extruder was opened rapidly.

If an approximate f i v alue w as known, the time spent b y e ach flour p article in
section 1' c ould b e c alculated. B y approximation, the residence time o f the p article in

section 1' at exit time t was

103

 

 

.. v,
At,- e f'Q [a (4.3)

The void volume of the extruder in each section i was calculated using the equation
below (V i):

V,- = Barrel volume in section ,- - screw volume in section,- (4 4)
= (Length of barrel in section,- * barrel surface area) -screw volume in section,- '

The length of barrel and screw volume in each section and barrel surface area are
specified in Chapter 2.
The overall extruder degree of fill could be calculated without the labor-intensive

method of dead-stopping the extruder at each run. Using the mean residence time (T) and

extruder void volume (V),

Degree of fill =31- (4.5)
Vp

4.3.2.4. Thiamin

Method of thiamin analysis is described in Appendix 1.A. For each experimental

condition, thiamin analysis of the extrudate was performed in duplicate.

104

4.3.3. MODELING

The model developed by Cha et al. (2003) was based on the assumption that an
extruder is a continuous chemical reactor (Levenspiel 1999), by which the nutrient
particle travels at different speed to the exit stream due to the axial mixing in the
extruder, following the residence times distribution of E(t). The mean concentration of a
nutrient at the exit stream can be calculated as the sum of the nutrient concentration

exiting from time = 0 to t= oo multiplied by E (t),

C" °° C
0 exit 0 0 nutrient

In an extruder, two main variables affected nutrient degradation, thermal and mechanical

effects. The thermal component is included in Eq. (4.6), as [E] can be modeled
nutrient

0
as a function of temperature. Since mechanical effects are also responsible for nutrient
degradation, C ha et a I. (2003) incorporated m echanical e ffects into Levenspiel’s b asic

model as an empirical function (f(S)). Thus, the model for thiamin retention in an

extrusion process is

5 °° C
. _. = — E(t)dt f (S) (47)
[C0 1&in {J0 (C0 )thiamin }

RT = Rfi X Rs
Where RT = total thiamin retention in the extruded flour, R p: thiamin retention due to

thermal effect of extrusion, R3 = thiamin retention due to mechanical effect of extrusion.

105

4.3.3.1. Thermal effect of extrusion on thiamin retention= Rg
To calculate the thermal effect of extrusion on thiamin retention, first we defined

that thiamin retention followed a first-order kinetic reaction,

[g] = exp(—kt) (4.8)
MMmm

0

where the reaction rate constant (k) can be modeled as a function of temperature and

moisture content (Guzman-Tello and Cheftel 1987, 110 and Berghofer 1990).

 

k = k, exp[—§“ [%——Tl:]+b(MC—MC,)] (4.9)

The thermal kinetic parameters k, and E, and the moisture content parameter, b
were estimated by isolating the thermal effect on thiamin by heating thiamin in flour in a
shearless environment (Chapter 3, study 2). The extruder barrel was set at progressively
higher temperature from feed inlet to die; thus the product temperature became a tirne-
dependent variable (T = T (t)). Temperature as a function of time T (t) is determined using
the measured temperature at five locations of extruder barrel. Moisture content of dough
is usually maintained constant throughout extrusion process and it is therefore not time-
dependent.

Since the residence time that the thiarnin particle spent in each barrel section was
known (Eq.(4.3)), and the temperature at each barrel section was also known

(T (t)=T (x)), then we could calculate the time-temperature history (,6) of each thiamin

particle traveling along the barrel with an exit time t.

,B(t) =J exp|:—Ifa [FEB-%H dt 2: Z exp[—§a [T(lx.) —71"_]:H:fi%(%)] (4.10)

 

 

 

106

 

Thus, Eq. (4.8) became

C

[F] = exp {—k, exp[b(MC - MC, )1} .3 (4-11)

0

Eq. (4.11) represented the thiamin retention for only one exit time. By adding up each
thiamin particle with various exit times (from the initial until the end of the residence

time distribution curve), the final equation for R p was

R fl = J: {exp <-k, (exp [b(MC — MC,)]) £fl(t)dt>}E(t)dt (4.12)

4.3.3.2. Mechanical effect of extrusion on thiamin retention =Rg
The mechanical or shearing effects (S) of an extruder can be represented using
specific mechanical energy, shear rate or shear history (Komolprasert and Ofoli 1990).
Specific mechanical energy (SME) is defined as the net mechanical energy input

per unit mass (Levine, 1989).

SME(J/kg) = Ev = M2 (4.13)

' m

 

5

where PW = 2.64 * (%Load - %Base Torque) * N (given by extruder manufacturer).

On the other hand, shear history may be a more accurate indicator of a process
history than SME, because shear history accounts for the duration of shearing (Cha et al.
2003). Shear history ((1)) can be approximated as the product of the average shear rate of

the extruder and the mean residence time of product in the extruder.
(D = 70 T (4.14)
The average-shear-rate model ( 70) for the extruder used in this study was developed in

Chapter 2 and it was a function of extruder constant (k'), degree of fill, screw speed (N)

and constant alpha (a).

107

 

7". =k'N" (4.15)
where k' = 3039* Degree of fillL508 and or = - 1.308 * Degree of fill + 2.144

In summary, RT = total measured thiamin retention in extrudate,

oo

 

t
—Ea 1 1
Rfl =exp(—k, exp[b(MC—MC,)]) exp Joexpl: R (TU—EH dt E(t)dt,
RS = RT /Rfl =f(SME)or f((D) (4.16)

4.3.3.3. Model validation

Once the model for R); and R3 was developed, the accuracy of the models was
determined. Data from a varying degree of fill extrusion conditions (condition 3 and
Schmid 2002) was utilized. Schmid (2002) conducted their extrusion studies at barrel
temperature profile of 40/60/90/ 130/ 150°C at 200, 250 and 300 rpm at 22% wb / 28.2%
db dough moisture content. Rs values were calculated using their shear terms (screw
speed, shear history and specific mechanical energy) profile and Rp values were also
calculated using their mean residence time and product temperature data. The product of
RS and R); was termed as predicted Rx Predicted R;- was plotted versus experimental (or
measured) R T. The root mean square error (RMSE) of the prediction was calculated as

RMSE = Pr edrcted value -— Measured value (417)

number of data po int 3

 

108

 

4.3.4. THIAMIN LOSS
The significance of mechanical effect and thermal effect on thiamin retention
could be calculated by first transforming the retention equation to loss equation. Total

thiamin loss was
XT=1—RT=1—RflRS (4.18)
If there were no mechanical effect during extrusion, RS would be = 1, thus the total loss
would be solely due to thermal effects (X r) = X p: l-Rp.
The thiamin loss due to mechanical effects was defined as the difference,
XS =XT—Xfl (419)
Then, the significance of mechanical effect was calculated as the percentage of the effect

on total loss.

109

4.4. RESULTS AND DISCUSSIONS
4.4.1. Mean residence time

Minimum b* color units of the dyed extrudates read from Hunter colorimeter was
—5.0 color units, which is within the linear range of the concentration calibration curves
(Appendix 4.A). Thus, color b* values were used in the calculation of E(t). An example
plot of residence time distribution curve is shown in Figure 4.1. The mean residence
times for extrusion conditions 1 and 2 extruded at barrel temperature

50/85/115/130/155°C and 50/80/110/140/165°C are summarized in Table 4.3.

 

 

 

  
      

 

 

 

    

 

 

” 1
0.024
300 rpm, MRT = 94.7 s l
. 200 rpm, MRT = 125 s l
S l
”-1 l
5’
.5 0.016 —
5
I-
2
8
”U
0 1
a 0.008 -—~_e --r
E
Z
0.000 1 - , u . -
0 50 100 150 200 250 300 1
Exit time (s) j

 

Figure 4.1. Residence time distribution curves of flour extruded at 50/80/ 1 10/ 140/ 165°C
barrel temperature at 100, 200 and 300 rpm. MRT = mean residence time.

As seen from Figure 4.1, the residence time of flour particles decreased as screw
speed was increased. In contrast, residence time was only slightly decreased as barrel
temperature was increased, which was the reverse trend found by Altomare and Ghossi

(1986)’s (Table 4.3). However, both in the present study and theirs, the effect was

110

nominal. Increasing dough moisture content slightly decreased the residence time (Table

4.4)

Table 4.3. Data for extrusion at barrel temperature 50/85/115/130/155°C and
50/80/ 1 10/ 140/ 165°C for 33.3% MC (db) dough (based on two extrusion days)

 

 

 

 

 

 

 

 

 

 

, Product .
E66233: 332:: temperature at Meagézszgence 2233/33?) Degree of fill
(rpm) die (°C)
la 100 154.1 (i 0.46) 175.6 (r 7.49) 34.5 0.71 (r 0.04)
lb 150 156.7 (i 1.15) 152.2 (i 15.7) 39.0 0.70 (r 0.09)
lo 200 157.0 (:1: 1.15) 144.1 (i 0.82) 40.6 0.69 (i 0.00)
1d 250 156.3 (1 1.50) 119.3 (i 0.12) 43.3 0.61 (i 0.00)
16 300 154.5 (1 1.73) 96.2 (r 4.39) 47.0 0.53 (r 0.03)
2a 100 162.3 (: 0.29) 160.5 (i 10.2) 34.5 0.65 (i 0.05)
2b 150 163.1 (r 0.52) 135.1 (i 0.14) 39.0 0.62 (:1: 0.00)
29 200 164.2 (: 1.85) 124.3 (: 1.52) 40.6 0.59 (i 0.01)
2d 250 163.4 (i 1.33) 113.9 (i 5.80) 43.3 0.58 (r 0.04)
26 300 163.4 (:1: 0.75) 95.1 (i 0.36) 47.0 0.52 (r. 0.00)
3a 100 161.8 (i 0.69) 158.9 (:1: 11.0) 42.9 0.80 (r 0.07)
3b 150 161.5 (: 0.58) 135.4 (i 10.9) 42.9 0.68 (i 0.07)
39 200 159.9 (i 0.52) 120.5 (i 2.28) 42.9 0.61 (r 0.01)
3d 250 161.5 (1: 1.10) 109.7 (:1: 6.98) 42.9 0.55 (i 0.04)
39 300 163.4 (:1: 0.75) 101.6 (:t 2.18) 42.9 0.48 (r 0.06)

 

 

Table 4.4. Data for extrusion at barrel temperature 50/80/ 110/ 140/ 165°C at 200 rpm for

various moisture contents (based on two extrusion days)

 

 

 

 

 

 

 

 

~ Extrusion Moisture Product Mean Dou h feed
condition content % temperature residence time rate %g/min) Degree of fill
(wb)/(db) at die (°C) (s) ‘
2f 23 /29.8 165.9 (i 0.14) 121.5 (1 0.77) 39.7 0.58 (i 0.00)
2c 25 / 33.3 164.2 (i 1.85) 124.3 (i 1.52) 40.6 0.59 (i: 0.01)
2g 28 / 38.8 161.7 (i 0.42) 117.2 (:1: 2.53) 42.2 0.56 (i 0.01)
2h 32 / 47.1 162.6 (i 0.64) 112.7 (i 0.29) 44.5 0.54 (i 0.00)

 

111

 

4.4.2. Degree of fill

Figure 4.2 shows that the flour changed to a viscoelastic melt at the cooking zone.
The degree of fill was increased to 1.0 at this point, due to compressing nature of the
single-lead screws and the kneading paddles. Most single-lead and paddles had the
highest degree of fill (Table 4.5). Due to the difficulty in weighing shafls afier dead-

stopping, degree of fill at each location was approximately visually.

.7“. 1 r ’ I. ii! -' i I * ‘ :4: pg,

’ Kneading zone Feeding zone

‘ 7 ~ a
arm '-

6—%<5 ?<4>*<—w 3 %< 2 ><— 1—>

   

r i 1_'§ Cruz. ‘. 1" j V
Figure 4.2. Pictorial view of an opened extruder barrel, showing the extruder degree of
fill at specific barrel sections opened afier dead- stopping at 200 rpm.

Table 4.5. Visual observation of sectional degree of fill after dead-stop at 200 rpm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Section Screw configuration Approximate degree of fill
1 8D TL 0.4
2 7x30° FKP 0.8
3 4D TL 0.]
4 4x60° FKP 1.0

4x30° RKP 1.0

5 2D TL 0.2
6x60° FKP 1.0

4x30° RKP 1.0

6 1D SL 1.0
7x90° KP 1.0

2D SL 1.0

Die plate 1.0

 

 

 

 

TL = Twin-lead screws, FKP = Forward kneading paddles, RKP = Reverse kneading
paddles, SL = single-lead screws. D = 19 mm.

112

The overall degree of fill of all extrusion run was calculated using Eq.(4.5), with
known values of the dough flow rate, mean residence time, void volume and dough
density. The overall degree of fill is shown in Table 4.3 for extrusion condition 1 and 2.
At these conditions, constant overall degree of fill was expected, as feed rate was
increased simultaneously as screw speed was increased. Exactly constant degree of fill
was only achieved at the lower screw speed (100, 150 and 200 rpm) for condition 1.
However, for condition 2, a smaller variation of degree of fill was attained. For condition
3, flour feed rate was maintained constant as screw speed was increased. As a result,

degree of fill dropped from 0.80 to 0.48 as screw speed increased from 100 to 300 rpm

4.4.3. Effect of screw speed on thiamin retention (Measured, Thermal and
Mechanical retention)

At each extrusion conditions 1 and 2, we attempted to maintain constant degree of
fill and die temperature. The cooling system was able to remove excess heat at the higher
screw speed, so the standard deviation of the die temperatures was low (Table 4.3). For
conditions 1 and 2, the average die temperatures were 155.7 (i1.66)°C and 163.2
(i1.85)°C, respectively. Over the screw speed range, average degree of fill was
maintained at 0.65 (i 0.08) for condition 1 and at 0.58 (i 0.04) for condition 2. The

standard deviations were nominal such that die temperature and degree of fill would be

referred as constant die temperature and degree of fill in the further discussions.

113

4.4.3.1. Condition 1, barrel termeragrre = 50/85/115/130/155°C, constant degree of fill

For condition 1, the observed overall trend was measured thiamin retention (RT)
increased with screw speed (Figure 4.3). Nevertheless, screw speed of 100-250 rpm
seemed to have little influence on thiamin retention. The measured thiamin retention
increasing from 0.81-0.88.

Since temperature was maintained constant, the only factor contributing to
t_l_re_rrpal effect on retention (R3) was the residence time. The residence time that thiamin
particles were exposed to thermal heat was shorter at higher screw speed. Thus, an
increasing thermal retention trend was observed as screw speed was varied from 100-300
rpm (Figure 4.3).

On the other hand, no apparent trend was observed for mechanical retention (R5)

at those screw speed range as retention values stayed approximately at 0.90.

 

 

 

 

 

 

 

 

 

 

 

 

1.10
‘" I Thermal I
g g 1.00 I - retention
= R4
g Q i I A Mechanical
"" O 90 §-— I E retention
.2 t Rs
Lg ; O f f 0 Measured
{-1 0.80 — " retention
T
0.70 r 1 7
O 100 200 300 400
Screw speed (Rpm)

 

Figure 4.3. Thermal and mechanical effects on thiamin retention versus screw speed for

samples extruded at barrel temperature 50/85/115/130/155°C (condition 1). Data shown
are the averages from two replications, on different days.

114

4.4.3.2.Condition Zap-e, barrel temperature = 50/80/ 1 10/ 140/ 165°C, constant degree of fill

For condition 2a-3, the same trend was also observed where RT increased with
screw speed. Figure 4.4 shows that, at screw speed of 150-250 rpm, R7 was also not
affected. R7 was lower than that of condition 1, because temperature profile was higher at
condition 2. RT values ranged from 0.67-0.77. Rp also increased with higher screw speed,

due to the shorter residence time. No evident trend was observed for R5 at that screw

 

 

 

 

 

 

 

 

 

 

 

 

speed range.
1.10
g 1'00 L flThermal
'2 retention
8 0.90 “ 3 ‘ R
e r i i i ”
.E i a AMechanical
S 0.80 é retention
0- .
‘3 l i 5 RS
0.70 T 4. 0 Measured
i retention
. RT
0.60 r r .
0 100 200 300 400
Screw Speed (rpm)

 

 

 

Figure 4.4. Thermal and mechanical effects on thiamin retention versus screw speed for

samples extruded at 50/80/ 1 10/ 140/ 165°C (condition 2a-e). Data shown are the averages
from two replications, on different days.

115

4.4.3.3. Condition 3. barrel temperature = 50/80/ 1 10/ 140/ 165°C. vaw' g degree of fill
Degree of fill dropped from 0.80 to 0.48 as screw speed increased from 100 to

300 rpm. The trend observed in Figure 4.5 where thiamin retention decreased with screw

speed was also observed in many published literature (Beetner et al. 1974, Guzman-Tello

and Cheftel (1987), Schmid (2002)).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1.10 '
1.00
g I Thermal
g ‘1’ retention
,3 0.90 I i R73
E é E A Mechanical
5 0.80 i ? retention
:3 Rs
{-1
0 70 ; i ; i 1- . Measured
' ‘L "L i retention
RT
0.60 i 1 1
O 100 200 300 400
Screw Speed (rpm)

 

Figure 4.5. Thermal and mechanical effects on thiamin retention versus screw speed for
samples extruded at 50/80/1 10/ 140/ 165°C (condition 3). Data shown are the averages
from two replications, on different days.

Data from conditions 2 and 3 were combined to compare the measured thiamin
retention. Figure 4.6 shows that at screw speed of 150 and 200 rpm, measured thiamin
retention at condition 2 overlapped with that at condition 3. However, at screw speed of
250 and 300 rpm, condition 2 had a higher degree of fill than condition 3, thus higher
thiamin retention was observed. At screw speed of 100 rpm, condition 3 had a higher

degree of fill, thus higher thiamin retention was observed at this condition. A possible

reason why higher degree of fill caused higher retention were that higher degree of fill

116

allowed less mixing in the extruder, therefore less thermal effect (shorter residence time)
for the thiamin particle.

Therefore, the trend of lower thiamin retention at higher screw speed which are
observed in condition 3 and in other published literature was due to the decreasing degree
of fill. Since many researchers extruded products at a varying degree of fill condition,
data from this condition type [condition 3 and Schmid (2003)] were used to determine the

accuracy of the model which were developed fi'om data at constant degree of fill.

 

 

 

 

 

 

 

 

 

 

0.80
:1
.3 i
:1
8 -r
e . .
.E. é * I Condrtron 2
E 1. ]' 0 Condition 3
g 0.70 .. :l; 9
a
T
8 .1
0
2

0.60 r r r

0 100 200 300 400
Screw speed (rpm)

 

 

 

Figure 4.6. Plot of measured thiamin retention for condition 2 at constant degree of fill
and condition 2 at varying degree of fill. Data shown are the averages from two
replications, on different days.

117

4.4.4. Effect of moisture content on thiamin retention

To study the effect of moisture content on thiamin retention, moisture content was
varied at 4 levels, at screw speed of 200 rpm and at condition 2’s barrel temperature
profile (condition 20, 2f-h).

RT increased markedly with moisture content. This finding was in agreement with
Guzman-Tello and Cheftel (1987). The reaction rate constant was lower at higher
moisture content (Chapter 3) and mean residence time slightly decreased at higher
moisture content, yielding a higher R p with increasing moisture content. Figure 4.7 shows

that R5 was not a strong function of moisture content.

 

 

 

 

 

 

 

 

 

 

 

 

1.00
i I Thermal
T retention
5 0.90 If i Rfl
t:
8
g 0 80 l i A Mechanical
.5 ' i l retention
l Rs
A
I" 0'70 " L 0 Measured
{ retention
0.60 T . . . , RT
20 25 30 35 4O 45 50
Moisture content in dry basis (%)

 

 

 

Figure 4.7. Thermal and mechanical effects on thiamin retention versus moisture content
for samples extruded at 200 rpm and 50/80/ 1 10/ 140/ 165°C barrel temperature. Data
shown are the averages from two replications, on different days.

118

4.4.5. Modeling thiamin mechanical retention, Kg at constant fill condition

Figure 4.3, 4.4 and 4.7 represented Rs as a function of screw speed at constant fill
condition. The calculated R3 was also fitted as a function of shear history and specific
mechanical energy. Shear history and SME values for each extrusion condition can be
found in Appendix 4. Since no apparent trend was also observed for the other shear terms
at the two conditions, a linear regression analysis was performed to determine statistically
whether R3 was influenced as the shear term increased, for each condition (Table 4.6).

Table 4.6 shows that Rs did not change significantly (zero slope) at the specified
range of screw speed, shear history and SME. Since none of the shear terms significantly
affected R5, the Rs data of the two temperature profile were paired for t-test in Excel® to
determine whether there was significant difference between the R5 of condition 1 and
condition Za-e at 95% confidence level. The two-tailed student t-test analysis of the mean
Rs indicated that R; at condition 2a—e was significantly higher (P < 0.001) than R5 at
condition 1. It could be concluded from this t-test that, there was interaction between Rs
and temperature. Due to equipment limitations, the extruder barrel temperature could not
be set higher than 165°C; therefore, we were unable to conduct more temperature studies.
Extrusion at lower temperatures could be done, but thiamin retention and calculated RS

would be too close to 1.0, which could result in inaccurate modeling.

Table 4.6. The significance of the shear term on the thiamin mechanical retention, Rs

 

 

 

 

! Shear term Shear range Condition 1 Condition 2a-e
Screw speed (Rpm 100-400 p = 0.795 p = 0.129
Shear history _ =
(dimensionless) 4000-12000 p — 0.381 p 0.119
SME (Id/kg) 100-600 p = 0.208 p = 0.116

 

 

 

 

 

119

p<0.05 means that the slope of the regression line was not equal to 0 at 95% confidence level

 

Despite the difference between the R5 of the two temperatures profile, they
behaved in a similar trend (dropping from retention of 1.0 to a certain minimum) (Figure
4.3 and 4 .4). T herefore, w e n eglected the interaction b etween R s and temperature and
combined the two temperatures data for model development.

RS data points in Figure 4.7 did not show an apparent trend with moisture content.
The effect of moisture content on R3 was then determined using linear regression
analysis. The calculated p values was 0.40, indicating that moisture content did not
influence RS. This result showed that there was no interaction between Rs and moisture
content.
4.4.5.1. Combining dafitam model development

Another extrusion study which was conducted at a constant degree of fill and the
present study’s temperature range was Cha et al. (2003). Their extrusion run was
conducted at die temperature varying from 155°C to 167°C, dough moisture at 20% (wb)
/25% (db) and at approximately 0.44 degree of fill. Since we neglected the temperature
effect on RS and there was no interaction between Rs and moisture content, data from Cha
et al. (2003)’s extrusion run was combined with the present study. Thus, for full model
development of Rs, all data from constant degree-of-fill extrusion were included, which
consisted of conditions 1, 2 and Cha et al. (2003). The combined R3 was fitted as a
function of screw speed, shear history and specific mechanical energy (SME). Among the
three shear terms, Rs versus specific mechanical energy (SME) had the better fit with R2
= 0.64 (Figure 4.10). The R2 values indicated that there was considerable variability with

the widely different extrusion conditions.

120

4.4.5.2. Model development. R5 = f( screw speed)

Figure 4.8 shows that Rs data of Cha et al. (2003) decreased significantly as screw
speed was increased from 100 to 150 rpm and then stayed relatively constant at 0.85 from
screw speed 150 to 300 rpm. The justification for this was, during their extrusion run,
cooling water was insufficient to remove the increasing heat as screw speed was
increased. As a result, product temperature increased significantly (DT increased from
155.5 at 100 rpm and to an average of 163.2°C as screw speed was increased from 150-
300 rpm). Since the present study determined that there was an interaction between R5
and temperature, a significant decrease in Rs from 100 to 150 rpm was expected.

Model: Rs = 0.864+0.136[exp(—0.0166*SS)].

 

 

 

 

 

 

 

 

 

 

“ ' ""‘r—fi

1.10 A DT =163.2°C, MC = 33.33% 0 DT =155.7°C, MC = 33.3%

A DT = 163.2°C, MC = 29.9% I Cha et al. (2003)
g A DT = 163.2°C, MC = 38.8% _Predicted mechanical retention
O
'2 1-00 A DT= 163.2°C, MC=47.1%
0
E
.E
S
E 0.90
.10“. R2=0.60
5
g 0.30 -. __W M. L T
3 u
0.70 ' 7 T r
O 100 200 300 400
Screw speed (rpm)

 

 

 

Figure 4.8. Plot of thiamin mechanical retention versus screw speed for all data. DT =
Die Temperature in °C, and MC = dough moisture content in db. DT in Cha et al. (2003)
ranged from 155.5-167°C and MC = 25% (db).

121

4.4.5.3. Model development. R5 = f( shear histog)

Although the R2 of Rs versus shear history (Figure 4.9) plot was similar to that of

Rs versus screw speed (Figure 4.8) at 0.60, inclusion of mean residence time, degree of

fill and screw speed in shear history represented the extrusion shearing history better.

Comparing data based on screw speed alone was not sufficient because degrees of fill and
mean residence time of the two data could be different. An apparent example was, when
data from Cha et al. (2003) at 100 rpm (Figure 4.8) was translated to shear history, the
data separated from the present study’s as their degree of fill and mean residence time
was lower. Then, it was apparent that at shear history < 4,000 (Figure 4.9), R5 dropped

from 1.0 to 0.9 and decreased slowly to a minimum within shear history range of 4,000-

13,000 to an approximate Rs value of 0.87.

Model: RS = 0.869 + 0. 1 3 1 [exp (—0.000571 * (13)].

 

1.10

1.00

0.80

Mechanical thiamin retention, RS

0.70

 

0.90 -

 

 

 

 

 

 

 

 

A DT = 165°C, MC = 33.3% o DT = 155°C, MC = 33.3%
A DT = 165°C, MC = 29.9% I Cha et al. (2003)
A DT = 165°C, MC = 38.8% —Predicted mechanical retention
A DT =165°C, MC = 47.1%
' 8
I ' 9A A 8
Q A
0 Ar A
I
‘ ‘ ‘ A1 I ‘ 2
a A " R =0.60
A
I A A
0 2000 4000 6000 8000 10000 12000 14000 16000

Shear history (dimensionless)

 

Figure 4.9. Plot of thiamin mechanical retention versus shear history for all data. DT =
Die Temperature in °C, and MC = dough moisture content in db. DT in Cha et al. (2003)
ranged from 155.5-167°C and MC = 25% (db).

122

 

4.4.5.4. Model development, Rg = f(SME)

SME represents the net mechanical energy input per unit mass, which was
calculated using parameters such as extruder torque and pressure reading. The model of
Rs as a function of SME has the best fit among the three shear terms (R2 =0.64). It is
shown in Figure 4.10 that for Cha et al. (2003) data, there was an overall decrease of R3.
The reason was explained earlier where there was temperature difference for Cha et al.
(2003) data as SME was increased. The figure also shows that R5 was higher for DT =
155°C. SME should account for the temperature effects (barrel temperature affects dough
viscosity, thus affecting torque reading), but since there was interaction between shear
effect and temperature, the same trend was observed in Figure 4.10.

Model = R, = 0.834 + 0.166[exp (—0.00485 * SME)].

 

 

 

 

 

 

 

 

 

 

 

A DT = 165°C, MC = 33.3% o DT = 155°C, MC = 33.3%
1-10 A DT = 165°C, MC = 29.9% I Cha et al. (2003)
A DT = 165°C, MC = 38.8% —Predicted mechanical retention
" = o = o
1.00 A DT 165 C, MC 47.1/o
fl
.2
E
8
3 o 90
.E'. '
E
.9.
[E
0.80 —
0.70 I 1 1 . a
0 100 200 300 400 500 600
Specific mechanical energy (kJ/kg)

 

 

 

Figure 4.10. Plot of thiamin mechanical retention versus specific mechanical energy for
all data. DT = Die Temperature in °C, and MC = dough moisture content in db. DT in
Cha et al. (2003) ranged from 155.5-167°C and MC = 25% (db).

123

4.4.5.5. Model validation

To determine the accuracy of the three Rs models, data from a varying degree of
fill extrusion conditions (condition 3 and Schmid (2002)) were utilized. Rs values were
calculated using their shear term profiles and R3 values were also calculated using their
mean residence times and product temperature data. The product of Rs and R); equaled
predicted RT, Then, R1 was plotted against measured (experimental) RT (Figure 4.9). The

line was a 45 degree line intersected at (0,0).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1.10
1.00
k ' " 0 Condition
°< 0.90 3
E / RMSE =
.2 0.0036
3 030 . a; O Schmid Ct
E . al. (2002)
:0
0.70 ° ° , 9,
0.60 l fir 1 7
0.60 0.70 0.80 0.90 1.00 1.10
Observed R r

 

 

 

Figure 4.11. Plot of predicted measured retention versus experimental retention for data
from condition 3 and Schmid et al. (2002) using R, = 0.869 + 0. 1 3 1 [exp (41.000571 * <D)]

model.

Figure 4.11 shows the predicted RT versus the experimental RT, using the shear
history model to predict RS. There was a good agreement between the predicted and the
experimental RT, especially for condition 3. Some of the data from Schmid (2002) were
under-predicted and some were over-predicted. The under-predicted data was due to the

following reasoning: Their mean residence time values were much shorter, which

124

increased their calculated Rfl values and thus most of their calculated R3 was higher than
the present study’s. Therefore, when using our Rs model to predict RT, the predicted
values became lower than the observed R7. Predicting K;- using the SME and screw speed
models yielded a RMSE of 0.00394 and 0.00396, respectively. Low RMSE means that
the model can still be used to predict mechanical effect of extrusion on thiamin retention
for extrusion temperature from 150- 165°C, using known value of screw speed, shear
history and specific mechanical energy.

Since there was interaction between temperature and mechanical effects, its
relationship should be investigated by doing extrusion at multiple temperature profiles. In
doing so, the RTprediction could be used for extrusion at various temperatures.

Therefore, the final model for thiamin retention in terms of shear history was

 

RT = {exp[—l .62 x10"6 [—0.0773(MC - MC, )]] ED exp ,8 x E(t) dt}

+ {0.869 + 0. l 3 1 [exp (—0.000571x (I))]}

 

(4.20)
and in terms of SME in (kJ/lgg) was
RT = {exp[—1 .62 x10.6 [—0.0773(MC — MC,)]] J: exp ,6 x E(t)dt}
+ {0.834 + 0.166[exp(—0.00485 * SME)]}
(4.21)

 

where ,B(T,t) =J emf-12% 942 ( Tit) ——Tl_]] dt

and T is in °K, t is time in seconds, MC, is percent moisture content in dry basis (33.3%).

125

4.4.6. Thiamin loss (thermal and mechanical)

. Table 4.7 shows that overall, percentage loss caused by thermal effects decreased
as screw speed increased. At condition 1, thermal loss dropped fi'om 9.8% to 4.0% as
screw speed was increased. This was due to the shorter residence time at higher screw
speed. Thermal loss was higher at condition 2 (higher temperature). Thermal loss was
also higher at lower moisture content, as shown in Chapter 3. Percentage loss caused by
mechanical effects did not show an apparent trend. However mechanical loss was higher
at condition 2, suggesting there was interaction between mechanical effect and
temperature. Mechanical loss was not affected by moisture content, suggesting there was
no interaction between mechanical effect and temperature.

Mechanical effects also predominated over thermal effects as moisture content
increased (Table 4.7-2f, 2g, 2b). This was because at higher moisture content, thiamin
reaction rate decreased (Chapter 3), causing less thiamin to be degraded thermally; hence,
more of the loss was caused by mechanical effects.

At higher screw speeds, mechanical effects slightly predominated over thermal
effects for thiamin loss. At condition 1, mechanical effects caused 47.3% to 64.5% of the
total thiamin loss. At higher temperature (conditions 2 and 3), mechanical effects caused
42.2% to 53.3% and 28.9% to 48.3%, respectively of the total thiamin loss. Thus, thermal

effects slightly prevailed over mechanical effects for thiamin loss at higher temperature.

126

 

 

 

 

 

 

 

 

 

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127

4.4.7. Obtaining the moisture content parameter (b) in extrusion

The moisture content parameter, b, described how reaction rate was affected by
moisture content. Two moisture content parameters for thiamin were obtained in a
shearless environment using different methods in Chapter 3. The first method was

conducted at atmospheric heating condition, at 80°C and the second method was at

controlled-pressure heating condition, at 129.4°C. A student t-test showed that the
parameters obtained from the two studies were not significantly different at 95%
confidence level. The moisture content parameter could also be obtained using the
extrusion data. For this purpose, another RS model as a function of shear history was
developed using all data at constant fill at the reference moisture content of 33.3% (db)
(condition la-e, 2a-e). Using the model, R3 was calculated at its respective shear history.
R3 was modeled as a function of shear history, since predicting R 7 using shear history had

the best R2. R5 = 0.886 + 0.114[exp(—0.0899*<D)]).

R p was calculated using the established thiamin kinetic parameters, accounting for
the time-temperature history along the extruder barrel. Predicted RT was then computed
using the calculated value of R5 and RS. Parameter b was estimated by non-linear
regression using Solver in Excel®, while minimizing the sum of squares of the residuals
between the measured RT and predicted R 7.

Using bootstrap program, 1,000 1) values were generated. Table 4.8 shows the
moisture content parameters obtained from study 1, study 2 in Chapter 3 and extrusion. A
student t-test on the b values between study 2 (chapter 3) and extrusion shows that t =
0.071, thus the two values were not significantly different [using t(0.05, 17) = 1.740 as

test of significance]. Bootstrap and t-test method can be found in Chapter 3. Since the

128

result obtained in a shearless environment was similar to the result obtained in an intense
shear environment (extrusion), it could be deduced that there was no interaction between
shear and moisture content, which confirmed our previous findings.

Table 4.8. Moisture content parameter b based on three studies

 

 

 

 

 

 

 

 

 

 

Number of data
b value aR2 Std error points
Chapter 3, Study 1a, Atmospheric
pressure heating -O.128 0.85 ‘10.0273 6
Chapter 3, Study 2, Controlled
pressure heating -0.07 69 0.99 a0.00088 3
Chapter 4, Extrusion study -0.0647 0.99 b00294 16

 

aValues obtained from linear regression of Ln reaction rate constant versus MC (db)
bStandard deviation based on 1,000 bootstrap data.
4.5. CONCLUSION

Thiamin retention in extruded flour w as investigated at different 3 crew sp eeds,
moisture contents, temperatures and degrees of fill. Increasing screw speed at a constant
degree of fill increased thiamin retention slightly, however, had no effect on mechanical
retention. Increasing moisture content resulted in higher thiamin retention but moisture
content did not influence mechanical retention. A higher barrel temperature also yielded
in lower total thiamin retention and mechanical retention. The latter result indicated that
there was interaction between temperature and mechanical retention. Increasing screw
speed at varying degree of fill extrusion condition decreased thiamin retention.
Comparing data fiom extrusion at constant fill and varying fill condition at constant
temperature, higher retention was obtained at higher degree of fill.

Constant degree-of-fill extrusion models for mechanical retention as a function of

screw speed, shear history and specific mechanical energy were deve10ped, using two

129

 

temperatures (1 ata from the p resent study and d ata from C ha et a I. (2003). T he three
models were then assessed for accuracy for a varying degree of fill extrusion condition.
The model with shear history was the best predictor, yielding reasonably accurate
experimental thiamin retention (R2: 0.76). This suggests that the model could be used to
predict thiamin retention at temperatures ranging from 1 50-165°C. S ince s hear history
and specific mechanical energy are equipment-independent variables, modeling Rs as a
function of these two shear terms is more applicable for scale-up purposes. Rp could be
calculated using the known thiamin reaction rate, activation energy, product temperature
profile and mean residence time from extrusion run. Then, experimental time for thiamin
analysis could be reduced, as total thiamin retention could be calculated. Since the model
was equipment-independent, this model could be used to predict thiamin retention in any
extruder. The optimum extrusion condition could also be determined so that maximum

thiamin retention was achieved.

4.6. FUTURE WORK RECOMMENDATIONS

Since the present study determined that there was interaction between temperature
and mechanical retention, 2 or 3 more temperature profiles should be conducted to
determine how mechanical retention behaved with temperature.

Extrusion should be conducted at lower dough moisture content than 23.0% (wb)/
29.8% (db) to obtain lower thiamin retention, reasonably in the range of 0.2-0.4 so that

mechanical retention could be modeled optimally.

130

4.7. NOMENCLATURE

b moisture content parameter

b * blue color intensity, Hunter color units

C dry basis, thiamin concentration in flour, %

Co dry basis, initial thiamin concentration in flour, %
DT die temperature, °C

E(t) normalized residence time distribution curve, 1/s
Ea activation energy, J/gmol (chapter 3)

Ev viscous dissipation of mechanical energy, W
fl visual degree of fill in barrel section, fraction

1' index for barrel sections or time, dimensionless

k reaction rate constant, l/s

k, reaction rate constant at reference temperature, 1/s (chapter 3)
k' extruder constant , 1/rev (chapter 2)

MC moisture content (db), wt/wt

MC, reference moisture content (db), wt/wt

rh dough mass flow rate = mass flow rate of flour + mass flow rate of injected water,

kg/s

N screw speed, rps

AP die pressure, Pa

PW total mechanical energy input to the extruder fi'om the motor, W
Q volumetric flow rate, m3/s

R ideal gas constant, 8.3144 J/gmol-K

RT measured thiamin retention, fraction

RI; thermal effect on thiamin retention, fiaction

RS mechanical effect on thiamin retention, fraction

T temperature, °K

T , reference temperature, °K

7 mean residence time, s

t exit time, s

At,- residence time in barrel section 1', s

V void volume =l .18E—4 m3

V, void volume in each barrel section 1', m3

X I measured thiamin loss, fraction

Xb thiamin thermal loss, fraction

XS mechanical thiamin loss, fraction

Greek symbols

,6 time-temperature history, s

p dough density = 1200 kg/m3

4) shear history, dimensionless

70 average shear rate, Us

131

4.8. REFERENCES

AOAC International. 1995. Official Methods of Analysis, 16th edition. AOAC
International, Arlington, VA.

Altomare RE and Ghossi P. 1986. An analysis of residence time distribution patterns in a
twin-screw cooking extruder. Biotechnology Progress 2(3). 157-163.

Beetner G, Tsao T, Frey A and Harper J. 1974. Degradation of thiamine and riboflavin
during extrusion processing. Journal of Food Science 39(1): 207-209.

Beetner G, Tsao T, Frey A, Lorenz K. 1976. Stability of thiamine and riboflavin during
extrusion processing of triticale.Joumal of Milk and Food Technology 39 (4): 244-245.

Cha JY, Suparno M, Dolan KD, NG PKW. 2003. Modeling thermal and mechanical
effects of retention of thiamin in extruded foods. Journal of Food Science 68(8): 2488-
2496.

Cheftel J C. 1986. Nutritional effects of extrusion-cooking. Food Chemistry 20(4): 263-
283.

Dolan K D. 2 003. E stimation o f k inetic p arameters for n onoisothermal food p rocesses.
Journal of Food Science 68(3): 728-741.

Guzman-Tello R and C heftel JC. 1 987. Thiamine loss during extrusion c ooking as an

indicator of the intensity of thermal processing. International Journal of Food Science and
Technology 22:549-562.

110 S and Berghofer E. 1998. Kinetics of thermomechanical loss of thiamin during
extrusion cooking. Journal of Food Science 63(2): 312-316.

Levenspiel O. 1999. Chemical reaction engineering. 3rd edition. John Wiley and Sons.

Maga JA and Sizer CE. 1978. Ascorbic acid and thiamin retention during extrusion of
potato flakes. Lebensmittel Wissenschaft und Technologie 11(4): 192-194.

Peng J, Huff HE and Hsieh F. 1994. An RTD determination method for extrusion
cooking. Journal of Food Processing and Preservation 18: 263-277.

Schmid, Abigail H. 2002. The effect of extruding wheat at lower temperatures on
thiamin loss and physical attributes when using carbon dioxide gas as a puffing agent
(Thesis). Michigan State Univeristy, East Lansing, MI.

132

Chapter 5: Conclusions and novelty of model development

In C hapter 2 , m atching viscosity assumptions b ased o n mixer v iscometry were
applied to estimate the average shear rate in an extruder. The average shear rate was
modeled as a function of degree of fill and screw speed. The extruder constant increased
as degree of fill was increased. In general, at constant screw speed, average shear rate
increased at higher extruder degree of fill. In this study, a novel method was developed to
measure extruder degree of fill and extruder constant was modeled as a function of
degree of fill.

In Chapter 3, thiamin kinetic parameters were obtained using two methods:
atmospheric-pressure heating condition and controlled-pressure heating condition.
Moisture content parameter were determined to correct the changing-moisture high-
temperature kinetic parameters. After the correction, the kinetic parameters were
comparable to the results fiom controlled-pressure heating; thus, the correction methods
could be applied for researchers without access to controlled-pressure equipment. In this
study, a novel method was developed to correct the kinetic parameters where loss of
moisture was unavoidable for heating at atmospheric-pressure condition.

In Chapter 4, thermal effects and mechanical effects of extrusion on thiamin
retention were quantified separately. Results indicated that there was interaction between
thermal and mechanical in thiamin degradation. Thermal effects on thiamin retention
were calculated, accounting for the time—temperature history in each barrel section. The
mechanical effects were calculated by mathematically removing the thermal retention
from the total thiamin retention. The best thiamin retention prediction was when using

shear history to model the mechanical effects. The moisture content parameter was also

133

obtained from an extrusion study, and was similar to results from Chapter 3, indicating
that there is no interaction between mechanical effect and moisture content. In this
chapter, results from chapters 2 and 3 were utilized to obtain a model for predicting
thiamin retention in extruded products as a function of degree of fill, mean residence

time, product temperature, moisture content, screw speed.

134

APPENDIX

135

Appendix 1

Thiamin analysis and standard curve

136

 

Appendix 1.A. Thiamin analysis

Thiamin c ontent w as analyzed u sing the f luorometric m ethod (Official Method

953.17, AOAC 1995). Procedure was adapted from Schmid (2002) and Moore and Dolan

(2003). Thiamin fluorescence was measured using spectrofluorometer SF-330 Varian

(Palo Alto, CA) at excitation wavelength of 373 nm and emission wavelength of 410 nm.

A xenon lamp was used as the light source for UV light.

Reagents and Materials

A.

B
C.
D

Sodium hydroxide solutions - 15%

. Hydrochloric solution — 0.1 N

HPLC grade Isobutyl alcohol (2-methyl-lpropanol)

. Quinine sulfate stock solution - Dissolve 10 mg quinine sulfate in 0.1N H2804 to

make 1L. Store in light-resistant containers.

Quinine sulfate standard solution -— Dilute lvolume quinine sulfate stock solution
with 39 volumes 0.1N H2804. Store in light-resistant container.

Thiamin Hydrochloride standard solutions
Primary stock standard solution (1000 pg/ml = 1g/1000 ml)

1. Weigh _1_g USP Thiamin Hydrochloride Reference Standard (Spectrum
Laboratory Products, Gardena, CA) which has been dried to constant weight over
CaSO4 in desiccators.

2. Dilute to 1000 ml with 20% ethanol which has been adjusted to pH 3.5- 4.3 with
0.1N HCl.
3. Store at approximately 10°C in glass stoppered, light resistant bottle.

Secondary Stock Standard Solution (100 pg/ml)
1. Dilute 100 ml aliquot of primary stock standard solution to 1000 ml with 20%

ethanol which has been adjusted to pH 3.5-4.3 with HCl.
2. Store at ca 10°C in glass-stoppered, light resistant bottle.

137

Working standard solution (15.6 ,ug/ml)

1. Dilute 15.6 ml thiamin-HCI stock solution and 5.0 gram of salt (NaCl) to 100 ml
with ca 0.1 N HCl. (1 ml = 0.2 pg thiamin-HCI).
2. Prepare solution on day used.

 

G. Oxidizing Stock Solution (0.2796%)

1. Dissolve 0.2796 g of Potassium F errocynide in 15% NaOH solution to make 1%
ml

2. Ere-pare solution on day used.
H. Oxidizing Working Solution (0.01398%)

1. Take 10 ml of aliquot of the oxidizing stock solution and dilute it to 200 ml with
15% NaOH.

2. Prepare solution on day used.

Extraction procedures

Thiamin extraction

Weigh z 10 g of salt, and record mass.

Weigh z 1 g of flour sample and record mass.

Place the salt and the flour sample in a 250 ml centrifuge tube.

In a 200 ml volumetric flask, add 200 ml of 0.1 N HCl.

Add HCl into the centrifuge tube.

Hand-shake tube for 15 seconds.

Put in shaking water bath (Precision Scientific, Chicago, IL) for l/2 hour

Cool tubes to room temperature with ice cubes for 45 minutes.

Centrifuge tubes at 5000 rpm (4,066 x g) for 15 minutes using a RC-SB centrifuge
(Sorval Instruments, Newton, CT).

pwsgwawwr

Thiamin oxidation

For oxidized tubes
1. Add 2.5 ml aliquots of thiamin extract of the centrifuged flour mixture solution.
2. Add 10 ml of oxidizing working solution.
3. Add 13 m1 of anhydrous isobutyl alcohol (Sigma).
4. Hand-shake tube for 15 seconds.

For blank tubes (unoxidized)
1. Add 2.5 ml of the centrifuged flour mixture solution.
2. Add 10 m1 of NaOH.
3. Add 13 ml of isobutyl alcohol.

138

 

4. Hand-shake tube for 15 seconds.

5. Shake all oxidized and blank tubes together in a mechanical shaker (Mexi-Mix
III, Termolyne, Dubuque, IA) for 2 minutes and centrifuge for 3 minutes at
10,000 rpm (11,950 x g).

6. Pipet 3.3 mL of isobutanol thiochrome extract (upper layer) to plastic cuvette for
thiochrome measurement.

Fluorometer setup for thiochrome measurement

1. Set excitation slit at 5 nm, emission slit at 10 nm, sensitivity at x1/10 for oxidized
samples and at x10 for blanks.

2. Calibrate fluorometer with 0.25 mg/L of quinine sulfate solution at excitation
wavelength of 343 nm and emission wavelength of 459 nm.

3. For isobutanol thiochrome extract, dial excitation wavelength at 373 nm and
emission wavelength at 410 nm.

139

Appendix LB. Standard Curve and Thiamin Calculation
Standard curve
When new reagents of sodium hydroxide and hydrochloric solution were prepared, a new
standard curve was created. Standard curve is done at four concentrations in duplicate.

The setup for each tube is shown in Table LB. 1.

Table LB. 1. Amounts of reagents used to determine standard curve

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Working . . . Final Thiamin
T1;be standard 5311i??? 51) 81013231113833) Concentration
solution (ml) (pg/ml)
1 Oxidized 3.00 12.00 3.60
2 Oxidized 2.25 9.00 2.70
3 Oxidized 1.55 6.20 1.86
4 Oxidized 0.75 3.00 0.90
5 Un-Oxidized 3.00 12.00 ' 3 .60
6 Un-Oxidized 2.25 9.00 2.70
7 Un-Oxidized 1.55 6.20 1.86
8 Un-Oxidized 0.75 3.00 0.90
W

For oxidized samples
To 40 m1 tubes, add the amount indicated above:
0 Working solution
0 Oxidizing agent
0 Immediately, add 13 ml isobutanol, and hand-shake for 15 secs

Un-oxidized tubes
To 40 m1 tubes, add the amount indicated above:
0 Working solution
0 15% NaOH
0 Immediately, add 13 m1 isobutanol, and hand-shake for 15 secs

Shake all oxidized and blank tubes together in a mechanical shaker (Mexi-Mix III,
Termolyne, Dubuque, IA) for 2 minutes and centrifuge for 3 minutes at 10,000 rpm
(11,950 x g).

Pipet 3.3 ml of isobutanol thiochrome extract (upper‘layer) to plastic cuvette for
thiochrome measurement.

140

 

_-_..____ -_ x _..._._.1

500

 

 

 

 

 

 

 

 

 

-‘P 400 A
E. y=99.15x+54.01
g R2 > 0.99
E 300 ~
3 200 / y: 104.96x + 38.63
5 / R2 > 0.99
0
g 100
2
In

0 . . 1

o 1 2 3 4

Thiamin concentration (pg/ml)

 

 

 

Figure 1.B.l. Standard curve for fluorescence reading vs thiamin concentration
constructed in duplicate on two different days.

To construct a standard curve, plot final thiamin concentration versus fluorometric
reading (oxidized-blank). Determine the slope and the intercept.

Fluorometric reading (oxidized-blank)
= thiamin concentration (pg/m1) * slope + intercept

Thiochrome Fluorescence Calculation

% thiamin calculation (w/w) =

 

.5
Thiamin concentration * (S—M— + F—M- + ml HCL ) * -—1— * ml isobmanol * 10 g * 1 * 100%
SD FD mlmp,c Hg masssamplc
SM = salt mass (g) =
SD = salt density (g/ml) = 2.170 g/ml
PM = flour mass (g)
FD = flour density (g/ml) = 0.475 g/ml
mlsamplc= volume of thiamin extract solution added into the 50 ml centrifuge tube (ml)
mlisobumol = volume of isobutanol solution added to sample (m1)
masssamp.e = mass of sample (g)

% thiamin in dry basis = % thiamin (w/w) / (1- MC (w/w))

141

Appendix 2

Extrusion data collection for Chapter 2

142

Appendix 2.A Data collection during extrusion run

Table 2.A.1. Data collection during extrusion run for corn syrup, n = 1.00

 

Avg anSity (g/ml) = 1375 n = 1.006*10-l6 exp (11980/1‘)Yn.l

 

 

 

 

 

 

1.0 Degree
of fill
Non—load Load Die
Screw Temp Viscosity Torque Torque Pressure Mass flow

Speed (rpm) (°C) Q’as) (%) Q/g) (psi) rate (g/min)
50 23.6 35.01 11.6 15.6 30 92.2
100 24.6 30.57 13.0 20.0 40 177.8
200 23.3 36.72 14.1 26.8 100 312.2
300 24.2 32.27 14.9 29.6 100 354.0
400 24.4 31.41 15.3 31.0 90 457.0
50 24.4 31.41 10.8 14.6 40 128.4
100 23.1 37.74 11.9 18.4 60 177.6
200 22.6 40.14 13.2 26.6 90 324.0
300 23.5 35.74 14.1 30.0 110 355.2
400 24.4 31.41 15.0 31.0 90 457.0

Average

density (g/ml) = 1.367 n = 1568*10'” exp (1 1117/1") 7""

0.7-0.9 Degree of fill

Non-load Load Die Mass flow
Screw Temp Viscosity Torque Torque Pressure rate

Speed (rpm) (°C) (Pa~S) (%) (%) (psiL (g/min)
50 22.8 39.05 11.30 14.6 10 40.4
100 23.3 36.47- 12.25 18.2 20 86.6
200 23.2 37.23 13.30 20.9 50 108.2
300 23.0 38.00 14.50 25.6 30 126.8
400 24.2 32.49 14.80 27.7 40 170.8
50 22.1 35.98 11.75 14.95 10 46.2
100 22.9 32.50 12.80 16.6 20 78.0
200 22.9 32.70 13.75 20.95 30 85.0
300 23.8 29.18 14.65 21.8 30 139.6
400 23.7 29.37 15.20 26.5 40 150.6

 

143

 

Table 2.A.1. (continued). Data collection during extrusion run for corn syrup, n = 1.00

 

 

 

 

Avg density (g/ml) = 1.367 n = 1.568*10"5 exp (11117/1‘) y“
0.4-0.6 Degree of fill

Mass

Non-load Load Die flow

Screw Viscosity Torque Torque Pressure rate
Speed (rpm) Temp CC) (Pa.s) (%) (%) (psi) (g/min
50 22.2 42.70 11.30 13.8 0 22.0

100 22.5 40.97 12.25 17.2 10 26.2

200 23.0 38.00 13.30 19.0 0 18.6

300 23.3 36.47 14.50 21.4 0 19.0

400 22.7 39.59 14.80 21.5 0 16.8

50 22.8 32.91 11.75 13.6 10 23.6

100 22.2 35.53 12.80 16.8 10 26.6

200 22.8 32.91 13.75 17.4 10 31.6

300 23.8 29.00 14.65 21.7 20 26.6

400 24.6 26.39 15.20 23.2 10 29.2

 

144

 

Table 2.A.2. Data collection during extrusion run for A40m, n = 0.24

 

1.0 Dgree of fill

Average density (g/ml) =

0.825

 

Temp Non-load

Load

Die Pressure Mass flow rate

 

 

Screw Speed (rpm) (°C) Torque (%) Torque (%) (psi) (g/min)

50 9.4 10.95 11.65 10 55.0

100 9.3 11.95 12.65 10 54.0
200 9.6 13.25 13.95 10 49.6

300 9.2 13.95 14.75 10 56.8
400 9.8 14.70 15.30 10 51.0
0.7-0.9 Dgree of fill
Temp Non-load Load Die Pressure Mass flow rate

 

 

 

 

Screw Speed (rpm) (°C) Torque (%) Torque (%) (psi) (g/min)
50 13.2 11.00 11.65 0 4.6
100 12.1 11.75 12.65 0 9.6
200 12.5 13.25 13.95 0 14.6
300 12.9 14.00 14.65 0 22.2
400 13.0 14.65 15.3 0 18.2
0.4-0.6 Degree of fill
Temp Non-load Load Die Pressure Mass flow rate
Screw Speed (rpm) (°C) Torcme (%) Torque (%) (psi) (g/min)
50 13.8 11.00 11.65 0 1.2
100 14.5 11.75 12.55 0 7.8
200 14.4 13.25 13.9 0 15.8
300 14.0 14.00 14.7 0 9.6
400 14.2 14.65 15.25 0 12.6

 

145

 

Table 2.A.3. Data collection during extrusion run for A40m, n = 0.28

 

1.0 Degge of fill

Average density (g/ml) = 0.843

 

Temp Non-load

Load Die Pressure Mass flow rate

 

 

 

 

 

 

 

Screw Speed (rpm) (°C) Torque C/o) Torque (%) (psi) (Emil)
50 18.1 11.15 11.95 10 55.0
100 17.8 12.20 12.90 10 54.0
200 17.7 13.50 14.25 10 49.6
300 17.7 14.50 14.95 10 56.8
400 17.7 15.30 15.65 10 51.0

0.7-0.9 Degree of fill
Temp Non-load Load Die Pressure Mass flow rate

Screw Speed (rpm) (°C) Torque (%) Torque (%) (psi) (g/min)
50 17.8 11.15 11.95 0 4.6
100 18.55 11.95 12.75 0 12.8
200 17.8 13.35 13.85 0 14.6
300 17.8 14.25 14.75 0 22.2
400 17.9 14.85 15.40 0 18.2

0.4-0.6 Degree of fill
Temp Non-load Load Die Pressure Mass flow rate

Screw Speed (rqm) (°C) Torque (%) Torge (%) (psi) (g/min)
50 17.85 11.15 11.85 0 1.2
100 17.90 12.20 12.80 0 7.8
200 17.80 13.50 13.95 0 15.8
300 17.80 14.50 14.65 0 9.6
400 17.95 15.30 15.50 0 12.6

 

146

 

Table 2.A.4. Data collection during extrusion run for K99, n = 0.60

 

Average density (g/ml) = 1.038

 

 

 

 

 

 

 

1.0 Degree of
fill
Screw Speed Non-load Load Torque Mass flow rate
(rpm) Temp (°C) Torque (3/6) (%L Die Pressure (psi) (g/min)
50 9.35 11.05 12.3 20 79.6
100 9.50 11.85 13.65 20 128.4
200 9.60 13.25 15.25 20 173.6
300 9.50 14.15 16.15 20 233.0
400 9.70 14.75 16.75 20 199.4
0.7-0.9
Dmflee of fill
Screw Speed Non-load Load Torque Mass flow rate
(rpm) Temp (°C) Torque (%) (%) Die Pressure (psi) (g/min)
50 10.80 10.95 12.25 10 41.6
100 11.00 12.05 13.25 10 48.8
200 11.10 13.45 14.65 10 71.6
300 11.20 14.25 15.55 10 80.0
400 11.30 14.95 16.40 10 114.0
0.4-0.6
Degree of fill
Screw Speed Non-load Load Torque Mass flow rate
(rpm) Temp (°C) Torque (%) (%) Die Pressure (psi) (g/min)
50 13.3 11.05 11.95 0 15.6
100 13.35 11.85 12.85 0 19.0
200 13.35 13.25 14.15 0 28.2
300 13.35 14.15 15.25 0 35.0
400 13.50 14.75 15.90 0 37.0

 

147

 

Table 2.A.5. Data collection during extrusion run for K99, n = 0.67

 

 

 

 

 

 

Avg density (g/ml) = 0.995
1.0 Degr_ee of fill
Die
Screw Speed Temp Non-load Pressure Mass flow
(rpm) (°C) Torque (%) Load Torque (%) (psi) rate (g/min
50 23.55 11.40 12.80 30 62.40
100 23.95 12.50 13.90 30 108.20
200 24.35 13.60 15.60 30 192.60
300 24.80 14.50 16.60 30 284.40
400 24.65 15.10 17.50 40 372.00
0.7-0.9 Degree of fill
Die
Screw Speed Temp Non-load Pressure Mass flow
(rpm) (°C) Torque (%) Load Torque (%) (psi) rate (g/min)
50 21.75 11.00 12.15 10 41.40
100 22.20 12.15 12.90 0 33.20
200 22.15 13.50 14.40 0 56.60
300 22.15 14.35 15.30 0 71.40
400 22.15 15.00 16.00 0 62.80
0.4-0.6 Degree of fill
Die
Screw Speed Temp Non-load Pressure Mass flow

 

 

(rpm) (°C) Torque (%) Load Torque (%) (psi) rate (g/min)
50 19.05 11.20 12.25 10 10.80
100 20.25 12.35 13.20 10 12.20
200 20.35 13.55 14.45 10 27.60
300 20.25 14.35 15.20 10 30.80
400 20.30 15.05 15.90 10 35.20

 

148

 

Appendix 2.B. Average shear rates data

Table 2.B.1 Average shear rates data for non-Newtonian fluid

 

 

 

 

 

 

 

 

 

 

Flow behavior Screw speed Measured average shear
index, n Fill degree (Rpm) rate (US)
0.24 1.0 ’ 50 32.3
0.24 1.0 100 50.9
0.24 1.0 200 85.1
0.24 1.0 300 104.3
0.24 1.0 400 167.3
0.24 0.7 50 17.7
0.24 0.7 100 24.5
0.24 0.7 200 56.4
0.24 0.7 300 77.4
0.24 0.7 400 114.1
0.24 0.4 50 10.5
0.24 0.4 100 10.9
0.24 0.4 200 31.8
0.24 0.4 300 48.0
0.24 0.4 400 60.7
0.28 1.0 50 40.9
0.28 1.0 100 75.6
0.28 1.0 200 128.2
0.28 1.0 300 230.6
0.28 1.0 400 401.9
0.28 0.7 50 24.8
0.28 0.7 100 52.2
0.28 0.7 200 139.8
0.28 0.7 300 348.8
0.28 0.7 400 395.7
0.28 0.4 50 15.0
0.28 0.4 100 34.2
0.28 0.4 200 124.4
0.28 0.4 300 395.1
0.28 0.4 400 277.7

 

149

 

Table 2.B.] (Continued).Average shear rates data for non-Newtonian fluid

 

 

 

 

 

 

 

 

 

Flow behaviour Screw speed Observed average shear
index, n Fill degree (Rpm) rate (US)
0.60 1.0 50 22.7
0.60 1.0 100 32.7
0.60 1.0 200 68.6
0.60 1.0 300 74.8
0.60 1.0 400 83.8
0.60 0.7 50 10.6
0.60 0.7 100 25.8

0.60 0.7 200 65.1
0.60 0.7 300 105.8
0.60 0.7 400 141.6

0.60 0.4 50 6.1
0.60 0.4 100 23.5
0.60 0.4 200 64.1
0.60 0.4 300 152.5
0.60 0.4 400 231.9
0.67 1.0 50 . 24.5
0.67 1.0 100 83.1
0.67 1.0 200 113.1
0.67 1.0 300 181.8
0.67 1.0 400 212.2
0.67 0.7 50 10.4
0.67 0.7 100 54.9
0.67 0.7 200 143.2
0.67 0.7 300 275.3
0.67 0.7 400 404.3
0.67 0.4 50 3.3
0.67 0.4 100 19.9
0.67 0.4 200 77.5
0.67 0.4 300 153.6
0.67 0.4 400 271.8

 

150

 

 

Appendix 3

Data and Figures for Chapter 3

151

Appendix 3.A. Data for constant-moisture study (study la)

Table 3.A.1. Moisture content of flour mixture

 

 

 

 

 

 

 

 

Reported moisture alaverage initial alaverage final Coefficient
content, % (db) moisture content, moisture content at the of variance
%(db) end of heating %(db) %

6.15 6.41 5.71 7.70

9.67 10.7 8.50 9.47

10.7 12.6 9.7 10.4

17.2 19.8 15.4 8.82

27.0 30.4 23.5 8.70

36.9 41.6 33.0 6.89

 

 

 

 

8Based on four readings

Table 3.A.2. Thiamin concentration value of 80°C heating for MC= 6.15, 9.67 and 10.7%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MC (wb) = 5.8 MC (wb) = 8.8 MC (wb) = 9.7
MC (db) = 6.15 MC (db) = 9.67 MC (db) = 10.7
% Thiamin % Thiamin % Thiamin
Dry Weight Dry Weight Dry Weight

Time (min) Basis Time (min) Basis Time (min) Basis
0 0.403 0 0.403 0 0.403
0 0.357 0 0.357 0 0.357
0 0.349 0 0.349 0 0.349
0 0.352 0 0.352 0 0.352
0 0.376 0 0.376 0 0.376
0 0.351 0 0.351 0 0.351

0 0.350 0 0.350 0 0.350
0 0.353 0 0.353 0 0.353
300 0.324 162 0.349 180 0.290
300 0.341 162 0.356 180 0.288
300 0.31 1 162 0.344 180 0.286
300 0.302 162 0.342 180 0.283
960 0.308 360 0.324 480 0.271
960 0.309 360 0.322 480 0.268
960 0.300 360 0.324 480 0.272
960 0.318 360 0.326 480 0.273
1440 0.303 600 0.327 725 0.246
1440 0.303 600 0.325 725 0.242
1440 0.298 600 0.319 725 0.264
1440 0.294 600 0.31 1 725 0.265

 

152

 

Table 3.A.3. Thiamin concentration value of 80°C heating for MC=17.2, 27.0 and 36.9%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MC (wb) = 14.7 MC (wb) = 21.3 MC (wb) = 26.9
MC (db) = 17.2 MC (db) = 27.0 MC (db) = 36.9
% Thiamin % Thiamin % Thiamin
Dry Weight Dry Weight Dry Weight
Time (min) Basis Time (min) Basis Time (min) Basis
0 0.403 0 0.403 0 0.403
0 0.357 0 0.357 0 0.357
O 0.349 0 0.349 0 0.349
0 0.352 O 0.352 0 0.352
0 0.376 0 0.376 0 0.376
0 0.351 0 0.351 0 0.351
0 0.350 0 0.350 0 0.350
0 0.353 0 0.353 0 0.353
60 0.326 61 0.343 60 0.351
60 0.313 61 0.339 60 0.351
60 0.286 61 0.362 60 0.381
60 0.280 61 0.353 60 0.379
120 0.170 180 0.326 210 0.340
120 0.194 180 0.346 210 0.350
120 0.202 180 0.317 210 0.348
120 0.222 180 0.315 210 0.355
240 0.113 270 0.292 300 0.325
240 0.110 270 0.294 300 0.327
240 0.103 270 0.287 300 0.312
240 0.089 270 0.282 300 0.315
Table 3.A.4. Regression analysis for constant-moisture study
Moisture Average k (1/min) Regression Statistics
content %
(i SD)
(db) 2
R Std error
6.15 0.000055(:1: 3.84E—5) 0.43 1.985"‘10'S
9.67 0.000184(i 1.37E-5) 0.70 3.795"‘10'5
10.7 0.000222(i 2.22E-4) 0.80 3.502“‘10'5
17.2 0.005860(:t 3.72E-4) 0.96 3.860"‘10'4
27.0 0.000893 (:1: 2.74E-4) 0.84 1.215"‘10‘t
36.9 0.000532(:l: 3.43E-4) 0.73 1.020"‘10'4

 

 

 

 

 

153

Appendix 3.B.
Data for high-temperature heating at atmospheric pressure (study 1b)

Table 3.B.1. Thiamin concentration of 25% MC (wb)/ 33.3% MC (db) at high-
temperatures (Study 1b)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tavg = 141.9 Ta, = 156.8 Tm = 166.4
% Thiamin % Thiamin % Thiamin
Dry Weight Dry Weight Dry Weight
Time (min) Basis Time (min) Basis Time (min) Basis
0 0.403 0 0.403 0 0.403
O 0.357 0 0.357 0 0.357
0 0.349 0 0.349 0 0.349
0 0.352 0 0.352 0 0.352
0 0.376 O 0.376 0 0.376
0 0.351 0 0.351 0 0.351
0 0.350 0 0.350 0 0.350
0 0.353 0 0.353 0 0.353
25 0.275 20 0.212 10 0.261
25 0.274 20 0.209 10 0.256
25 0.266 20 0.222 10 0.279
25 0.269 20 0.221 10 0.287
60 0.174 40 0.088 15 0.162
60 0.174 40 0.085 15 0.165
60 0.186 40 0.103 15 0.204
60 0.188 40 0.101 15 0.209
70 0.163 60 0.061 20 0.104
70 0.163 60 0.060 20 0.105
70 0.165 60 0.058 20 0.121
70 0.165 60 0.063 20 0.118
Table 3.B.2 Regression analysis of high-temperature atmospheric heating data (Study 1b)
Average reaction rate Regression analysis
Tavg (°C) 9011513111 (1/ min) Reaction rate constant
(i SD) R2 Std error
Uncorrected 141.95 0.0113(zt 9.57E-4) 0.988 0.000384
Uncorrected 156.82 0.032(i 8.38E-4) 0.960 0.00206
Uncorrected 166.45 0.08% 3.13E-3) 0.960 0.00206
Corrected 141.95 0.269(i 2.22E-2)
Corrected 156.82 0.926(:t 8.77E-2
Corrected 166.45 2.222(1 1.46E-2)

 

 

 

 

 

 

154

 

 

 

 

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Appendix 3.D. Gauss-Legendre quadrature (Stasa 1985)

Gauss-Legendre started with the integral of

I=m iwif(xi)

i=1

where n is the number of Gauss-Legendre points and w,- is the weights and x.- is the

sampling point and m is

 

For study 2

b was defined as the normalized radius of the can (b=1) and a was the normalized center
of the can (a=0).
For n = 5 Gauss-Legendre, r and 2 points were calculated as
r =l(b+a)+-1—(b—a)t
2 2

l 1
= _ b _ b_ t
z 2( +a)+2( a)

 

 

 

 

 

 

 

n t r and z z* 1* i and j w
points
0 0.5 0.0170 0.0340 3 0.56888889
0.53846931 0.76923 0.0262 0.0340 4 0.47862867
5 -0.53846931 0.23077 0.00783 0.0340 2 0.47862867
0.90617985 0.95309 0.0324 0.0340 5 0.23692689
-0.90617985 0.04691 0.00159 0.0340 1 0.23692689

 

 

 

 

 

 

 

 

Gauss-Legendre integral was transformed into a double-integral for r and 2 points,
5 5

5 5
I=m,mz Z Zwiwjf(ri,zj)=-‘1;Z ZWinf("i,2j)

i=1 j=1 i=1 j=l

156

Evaluating the integral for mass-average temperature by using the Gauss-Legendre

integration, Eq. (3.19) became

1 5 5

Tmassaverage = 22 2 wt w] 2,1722

i=1 1:1

Implementing the Gauss-Lagendre integral into Eq. (3.20) for improved accuracy, the

final equation for mean average thiamin retention was

5 1 5 5
[6‘] = I: Z w, wjzr, exp[-k, [1],,z

1:1 1:1

157

Appendix 3.E. Plot of measured vs predicted center temperature for study 2

 

140

 

 

fl
N
O

RMSE = 12.3

 

 

é

 

00
O

 

 

C‘
O

 

 

.h
C

 

 

N
o
1

 

Predicted center temperature (°C)

 

 

 

0 1 1 T I 1 r
0 20 40 60 80 100 120 140
Measured center temperature (°C)

Figure 3.B. 1. Plot of measured vs predicted center temperature for 19.1% MC (db) flour
in 201x211 cans heated at 129.4°C retort temperature.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

140
H“

120 ‘
O RMSE = 10.1 ‘
2., 100
g A
8
h
*3
8
-e
8
U
2

0 20 40 60 80 1(1) 120 140
Measured center temperature (°C)

 

Figure 3.B.2. Plot of measured vs predicted center temperature for 28.2% MC (db) flour
in 201x211 cans heated at 129.4°C retort temperature.

158

Appendix 3.F. Plot of measured vs predicted thiamin retention in study 2

 

 

 

 

 

 

 

 

 

0.8
o o. o o
RMSE =0.126
0.6
fl
.2
H
=
8
2
.,_., 0.4
0 .0
.‘2?
-e
2
9..
0.2
.0.
O J I I
0.0 0.2 0.4 0.6 0.8
Measured retention

 

 

Figure 3.F .1. Plot of measured vs predicted thiamin retention for 19.1% MC flour in
201x211 cans heated at 129.4°C retort temperature.

 

 

 

 

 

 

 

 

 

 

 

0.8
RMSE = 0.0239

0.6
E
i
.5 0.4 — a
i

0.2 ,

0 l I J
0.0 0.2 0.4 0.6 0.8
Measured retention

 

 

Figure 3.F.2. Plot of measured vs predicted thiamin retention for 28.2% MC flour in
201x211 cans heated at 129.4°C retort temperature.

159

Appendix 3.G. Confidence region for 28.2% MC flour

 

kr [l/min]
1.60 E-4 i r

 

Confidence level

1.55 E-4 ‘

1.50 E-4

1.45 E-4

1.40 E-4

 

1.35 134— -------------------- , ----- ---------------------- --------------------------- ~

 

 

 

 

116.5 ll'l.0 11i7.5 118.0 118.5
E [kJ/(g mol)]

 

 

 

 

Figure 3.G. 90% joint confidence region for estimated activation energy (kJ/g—mol) and
reaction rate constant kgo (min'l) for MC=28.8% flour obtained from bootstrap data.

160

Appendix 4

Data for Chapter 4

161

Appendix 4.A. Color concentration curve

 

 

 

 

 

 

 

 

 

2
c 0 -_. .
a
:2
g '2 Q
I-
e
73'
r. -4 -.
3
g 0
a: -6
O
-8 1 1 1 T 1 1
O 1 2 3 4 5 6 7
Blue dye concentration (% wb)

 

 

 

Figure 4.A. Plot of Hunter b’ color units versus blue—dye concentration (%wb) of flour
extruded at 200 rpm at 160°C (Based on two color readings).

Minimum b* values from mean residence time ground extrudate is —4.0.

162

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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