"" ‘ V Vfi‘t“: u
.gg'r,‘ d‘m‘“

.:-4 «my.

‘Lfi‘nh -

*arm‘flmn -uo‘

=8;ch ' sk

- sa.

._ v .. ~
$1}. 6 .u- n k
1:31.651»
‘1; x a;

.‘a

.,
w

> 9,”. .9‘ 1‘}: ’2‘. i“
< $33; ‘55.

. .~ 3‘-

gf‘t’m.
£-~§é‘§~'.
‘ i

v
V

(a fififij J ‘ 3‘
A A‘ifirfi. .
1 Eiiélfg?

.. ~
5::...*...:.‘.~:r '-_ .v.
Jam; M‘ «‘33? 'r f

"u u“ J‘WVN .n :mh‘k

‘ '-‘-$4"‘. “4:3?
1.“ ,,..-‘: “~41...

as}???

. . . . ., ' L “ ‘
“ “tag”. "' - k- ' ~' ‘1. ‘ ' - may ' “""mli‘zm;

, 4-,,‘1- . , V 1. <- . “ g .} :Tugrfixfxtx; 37“.} “‘1”

l H ‘ ‘ 7a. "" ' .‘ ,... fixfigw; "‘5‘"? :1335 $3,133 {a _
‘ "~ , f” ,. , . ' ‘3‘} .“J: *5. “$5.“ .13 _ .3“

' - “‘*~n--.~1~-.1}s1~:-9:1-;-2m-

1'3“; ‘ L L...'. n-

:11-

.3.

a}

,7

.-

 

UNIVERSlTY LIBRARIES

WW\lllllllll“W“ \\ \N W

3 1293 0105

 

\l

 

 

 

 

 

 

 

 

 

 

 

This is to certify that the

thesis entitled

DEVELOPMENT OF FRUIT PASTE FROM STANLEY PLUMS
AND A STUDY OF PROCESSING AND STORAGE PARAMETERS
ON PHYSICAL, CHEMICAL AND SENSORY CHARACTERISTICS

presented by
WEN-MIN WANG

has been accepted towards fulfillment
of the requirements for

MASTER degree in FOOD SCIENCE

2 /Major professor

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

Date 1-12-94

 

 

 

LIBRARY

Mlchlgan State
Unlverslty

 

 

 

PLACE IN RETURN BOX to romovothb ohookouttrom your noord.
TO AVOID FINES roturn on or bdoro doto duo.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU to An Affirmative ActionlEqml Opportunity Institution
Una-9.1

‘ .r.”wasIimmmtlillfilllmmlmIWMi

DEVELOPMENT OF FRUIT PASTE FROM STANLEY PLUMS AND A
STUDY OF EFFECT OF PROCESSING AND STORAGE PARAMETERS
ON PHYSICAL, CHEMICAL AND SENSORY CHARACTERISTICS

By

Wen-Min Wang

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Food Science and Human Nutrition

1993

ABSTRACT

DEVELOPMENT OF FRUIT PASTE FROM STANLEY PLUMS AND A
STUDY OF EFFECT OF PROCESSING AND STORAGE PARAMETERS
ON PHYSICAL, CHEMICAL AND SENSORY CHARACTERISTICS

By

Wen-Min Wang

Stanley plums are the leading plum variety in Michigan. In order
to increase the economic significance of this commodity, there is a
need for development of new product from Stanley plums. Standard
and substandard plums were processed to pastes by heat
concentration to 25 and 30°Brix, respectively. It was not feasible to
concentrate plum paste beyond 40°Brix. Pastes made from standard
plums had higher quality and yield. Heat concentration significantly
increased total solids and apparent viscosity, but decreased water
activity, titratable acidity, Hunter color values, pectin and
anthocyanin content. Sugar addition darkened color.

24-week storage decreased titratable acidity, Hunter 'a' values,
pectin and anthocyanin content. Samples stored at 4°C had higher
color retention than at 22°C.

Sensory evaluation indicated that preference could be adequately
predicted by flavor and color under suitable Brix/ acid ratio. Storage

effect was variable based on the results of sensory analysis.

This is dedicated to Yu-Chen Wang
and Hsiu-Chu Wang-Chou

to whom I stand in debt for my education and knOwledge.

ACKNOWLEDGMENT

I wish to express my heart felt gratitude to my academic advisor,
Dr. Jerry N. Cash, for his guidance and evaluation of the manuscript.

Grateful appreciation is extended to Dr. Robert C. Herner and Dr.
Mark A. Uebersax for serving on my guidance committee, reviewing
this manuscript and making many constructive suggestions and
comments.

Special thanks is extended to Dr. James F. Steffe for his kind
help, inspiring consultation and allowing me to use equipment in his
lab. I am extremely thankful to Dr. John L. Gill for his helpful
consultation of statistical analysis.

For many helpful suggestions, critical evaluation and timely help
in preparation of this thesis, I owe a special debt of gratitude to Dr.
Muhamma Siddiq. Thanks are due to Dr. Nirmal K. Sinha for his
suggestions and technical assistance. Also, I would like to thank a
number of faculty, staff and graduate students that have helped me
during this period.

Finally, my deepest love and appreciation to my family and

friends for their love, concern and support through the highs and the

lows.

iv

TABLE OF CONTENTS

LIST OF TABLES .......................................................................... viii
LIST OF FIGURES .......................................................................... x
INTRODUCTION ........................................................................... 1
LITERATURE REVIEW ..................................................................... 2
I. Plum Description ........................................................... 2
Nutrition Composition .............................................. 2

Stanley Plum Production and Utilization .................... 4

II. Plum Paste Production .................................................... 5
Selection and Cleaning ............................................ 5

Preheating ................................................................ 6

Release of Cell Components .................................. 6

Facilitating Preliminary Operations ...................... 7

Inhibition of Undesirable Enzymatic Actions ......... 7

Preparation of Puree .................................................. 7

Heat Concentration ................................................... 8

Addition of Other Ingredients ................................... 8

Filling ..................................................................... 9

111. Storage Stability ........................................................... 10

IV. Quality Evaluation of Plum Pastes ................................. 11
Color ...................................................................... 11

Browning ........................................................... 11

Anthocyanins (ACYs) ............................................... 18

Chemical Structure ............................................ 18

ACYs in Plums ................................................... 19

Enzyme Effect .................................................... 19

Temperature Effect ............................................ 21

pH Effect ........................................................... 23

Others ............................................................... 26

Pectic Substances ..................................................... 26

Chemical Structure ............................................ 26

Pectic Enzymes .................................................. 29

Rheological Properties .............................................. 30

Flow Model ........................................................ 30

Apparent Viscosity ............................................. 30

Effect of Time on Flow Behavior .......................... 31

V

Effect of Temperature on Flow Behavior ............... 31
Using Mixing to Evaluate Rheological Properties... 32

Microbiological Content ........................................... 33
MATERIALS AND METHODS .......................................................... 35
1. Whole Plum Samples .................................................... 35
II. Plum Puree Production ................................................. 35
Pilot Plant Puree Made From Standard Plums ............. 35
Commercial Puree Made From Substandard Plums ..... 35

III. Plum Paste Production .................................................. 36
IV. Quality Evaluation of Plum Pastes ................................. 36
Processing Effect ....................................................... 36
Storage Effect ........................................................... 37

V. Physical and Chemical Analyses .................................... 37
Soluble Solids ........................................................... 37
Total Solids .............................................................. 37
Moisture Content ..................................................... 38
Water Activity .......................................................... 38

pH .......................................................................... 38
Titratable Acidity ..................................................... 38

PPO Activity ............................................................. 39
Enzyme Extraction .............................................. 39

Assay of Enzyme Activity .................................... 39

Color ....................................................................... 40

Total Anthocyanins (T ACYs) .................................... 4O
Pectic Substances ...................................................... 41
Versene-pectinase Extraction of Pectin .................. 41
Colorimetric Determination of Galacturonic acid. 42
Rheological Properties ............................................... 43
Procedure for Data Collection .............................. 43

Data Calculations ............................................... 45
Microbial Content .................................................... 46
Dilution Buffer ................................................... 46

Sample Preparation ............................................ 46
Standard Plate Count ......................................... 46

Coliform Count .................................................. 47

Yeast and Mold Count ........................................ 47

Data Calculations .............................................. 47
Statistical Analysis ................................................... 47

VI. Sensory Analysis .......................................................... 48
Sensory Analysis Test Method ................................... 48
Environmental Conditions ....................................... 49
Sample Preparation and Presentation ........................ 49

Data Analysis .......................................................... 49

vi

RESULTS AND DISCUSSION ........................................................... 51

1. Processing Effect ........................................................... 51
Puree Production ..................................................... 51

Paste Production ..................................................... 53
Yield ................................................................. 53

Soluble Solids and Total Solids ........................... 55

Moisture Content and Water Activity (aw) ........... 57

pH .................................................................... 58
Titratable Acidity .............................................. S8
Polyphenoloxidase (PPO) Activity ........................ 60

Hunter 'L' Value ................................................. 60

Hunter 'a' Value ................................................ 62

Hunter 'b' Value ................................................ 63

Hue Angle ......................................................... 63

Chroma ............................................................ 63

Total Anthocyanins (T ACYs) .............................. 65

Pectin Content .................................................. 65
Rheological Properties ........................................ 68
Microbial Analysis ............................................. 75

Sensory Evaluation ............................................ 75

11. Storage Effect ............................................................... 82
Soluble Solids and Total Solids ................................ 82
Moisture Content and Water Activity (aw) ................ 82

pH ......................................................................... 82
Titratable Acidity ................................................... 87
Hunter 'L' Value ..................................................... 91
Hunter 'a' Value ..................................................... 95
Hunter 'b' Value ..................................................... 95

Hue Angle .............................................................. 98
Chroma ................................................................. 98

Total Anthocyanins (T ACYs) .................................. 98
Pectin Content ....................................................... 102
Rheological Properties ............................................. 104
Microbial Analysis .................................................. 104
Sensory Evaluation ................................................. 108
SUMMARY AND CONCLUSIONS .................................................... 112
BIBLIOGRAPHY ........................................................................... 115
APPENDICES ............................................................................... 128

vii

Table 1

Table 2

Table 3

Table 4

Table 5

Table 6

Table 7

Table 8

Table 9

LIST OF TABLES

The contents of various compounds in the edible
portion of ripe plum fruit ......................................... 3

Quality characteristics of commercial puree
made from substandard plums and pilot plant
puree made from standard plums ............................. 52

Yields of plum pastes from commercial puree and
pilot plant puree ...................................................... 54

Effect of processing conditions on soluble solids,

total solids, moisture content, and water activity

of pastes from commercial puree and from pilot

plant puree .............................................................. 56

Effect of processing conditions on pH and titratable
acidity of pastes from commercial puree and from
pilot plant puree ...................................................... 59

Effect of processing conditions on polyphenoloxidase
activity, Hunter 'L' values, and AL of pastes from
commercial puree and from pilot plant puree ............ 61

Effect of processing conditions on Hunter 'a', 'b',
hue angle, and chroma of pastes from commercial
puree and from pilot plant puree .............................. 64

Effect of processing conditions on total anthocyanins
of pastes from commercial puree and from pilot
plant puree .............................................................. 66

Effect of processing conditions on pectin content
of pastes from commercial puree and from pilot
plant puree .............................................................. 67

viii

Table 10

Table 1 1

Table 1 2

Table 1 3

Table 14

Table 1 5

Table 1 6

Table 1 7

Table 1 8

Table 1 9

Effect of processing conditions on rheological
properties of pastes from commercial puree and
from pilot plant puree .............................................. 73

Effect of processing conditions on microbial
content of pastes from commercial puree and
from pilot plant puree .............................................. 76

Mean values of sensory attributes for pastes
made from pilot plant puree ..................................... 77

P values of analysis of variance for sensory
attributes of pastes made from pilot plant puree on
sensory evaluation .................................................. 78

Correlation coefficients of overall acceptance

with color, acidity, sweetness, consistency, and

flavor of pastes made from pilot plant puree on

sensory evaluation .................................................. 81

Correlation coefficients of titratable acidity,
total pectin, and pH of plum pastes made from
commercial puree and pilot plant puree .................... 90

Correlation coefficients of Hunter 'L' values with
other Hunter CDM values of plum pastes made
from commercial puree and pilot plant puree ............ 93

Correlation coefficients between Hunter CDM

values and total anthocyanins of plum pastes

made from commercial puree and pilot plant

puree ........................................................................ 94

P values of analysis of variance for difference
in sensory attributes of pastes made from pilot
plant puree between different storage conditions ....... 109

Values of t-test of mean scores of difference

in sensory attributes of plum pastes made

from pilot plant puree between different storage
conditions ............................................................... 110

ix

Figure 1
Figure 2
Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 1 1

Figure 1 2

LIST OF FIGURES

Reactions catalyzed by polyphenoloxidase (PPO) ....... 13
Maillard reactions ................................................... 15
The flavylium nucleus of anthocyanins .................... 20

Mechanism of anthocyanin degradation by
polyphenoloxidase (PPO) .......................................... 22

The four structures of anthocyanins which exist
in equilibria in aqueous solutions ............................. 24

The equilibrium distribution of AH+, A, B, and C
for Malvidin 3,5-diglucoside at different pH values
at 25°C ..................................................................... 25

Fragment of a pectin molecule and points of
attack by pectic enzymes ........................................... 28

Model system and flag impeller used in the
determination of rheological properties with
a mixer ..................................................................... 44

Rheogram of plum paste at constant shear rate
(20 rpm) and constant temperature (30°C) ................. 69

Shear stress as a function of shear rate of pastes
from commercial puree and from pilot plant puree... 71

Apparent viscosities of plum pastes at
different shear rates .................................................. 72

Effect of storage time and temperature on soluble
solids of plum pastes from commercial puree and
from pilot plant puree .............................................. 83

Figure 1 3

Figure 14

Figure 1 5

Figure 1 6

Figure 1 7

Figure 1 8

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Effect of storage time and temperature on total
solids of plum pastes from commercial puree
and from pilot plant puree ........................................ 84

Effect of storage time and temperature on moisture
content of plum pastes from commercial puree and
from pilot plant puree ............................................... 85

Effect of storage time and temperature on water
activity of plum pastes from commercial puree
and from pilot plant puree ........................................ 86

Effect of storage time and temperature on pH
values of plum pastes from commercial puree
and from pilot plant puree ........................................ 88

Effect of storage time and temperature on
titratable acidity of plum pastes from commercial
puree and from pilot plant puree ............................... 89

Effect of storage time and temperature on
Hunter 'L' of plum pastes from commercial
puree and from pilot plant puree ............................... 92

Effect of storage time and temperature on
Hunter 'a' of plum pastes from commercial
puree and from pilot plant puree ............................... 96

Effect of storage time and temperature on
Hunter 'b' of plum pastes from commercial
puree and from pilot plant puree ............................... 97

Effect of storage time and temperature on
hue angle of plum pastes from commercial
puree and from pilot plant puree ............................... 99

Effect of storage time and temperature on
chroma of plum pastes from commercial
puree and from pilot plant puree ............................. 100

Effect of storage time and temperature on total
anthocyanins of plum pastes from commercial
puree and from pilot plant puree ............................. 101

Figure 24

Figure 25

Figure 26

Figure 27

Effect of storage time and temperature on total
pectin of plum pastes from commercial puree
and from pilot plant puree ...................................... 103

Effect of storage time and temperature on
apparent viscosity (Tia) of plum pastes from
commercial puree and from pilot plant puree ........... 105

Effect of storage time and temperature on
consistency index (K) of plum pastes from
commercial puree and from pilot plant puree ........... 106

Effect of storage time and temperature on
flow behavior index (n) of plum pastes from
commercial puree and from pilot plant puree ........... 107

APPENDICES

Appendixl Standard curve of galacturonic acid ....................... 128

Appendix II Questionnaire for sensory evaluation ...................... 129

Appendix 111 Standard plate count of plum pastes from
commercial puree and from pilot plant puree
during storage period ............................................ 130

Appendix IV Coliform count of plum pastes from commercial
puree and from pilot plant puree during storage
period .................................................................. 131

Appendix IV Yeast and mold count of plum pastes from
commercial puree and from pilot plant puree
during storage period ............................................ 132

INTRODUCTION

Plums can be an important crop in Michigan, but in order to
increase the economic significance of this commodity there is a need
for development of new products from plums. Stanley plums are the
most abundant plum variety in Michigan and its importance to the
industry is derived from the fact that : 1) timing of harvest falls
between two major fruit crops, cherries and apples, thus optimizing
available labor and equipment; 2) cultivar of Stanley plums is
especially suited to Michigan climate (Elliott, 1983). The
development of a strong market for Michigan plums is particularly
relevant for the state's fruit growers because it is one of their most
important minor crops.

A Great deal of work has already been done in our group to
develop plum juice from Stanley, as well as from several other
cultivars of plums which may be grown in Michigan in the future. In
addition to juice, the apparent success of several recently developed
new products in the US. which use fruit pastes indicates that plum
paste might find very good acceptance in the marketplace. Such a
product could utilize fairly large quantities of fruit and give a "value
added" product which would increase use of plums. Therefore, the
objectives of this study were to 1) develop a processing procedure to
produce pastes from Stanley plums and determine the effect of
processing conditions on the chemical, physical and sensory
characteristics of plum pastes, and 2) evaluate the effect of storage
conditions on the chemical, physical and sensory characteristics of

plum pastes.

LITERATURE REVIEW

1. Plum Description _

Plums belong to Rosaceae family and Prunus genus and are native
of the temperate parts of the Northern Hemisphere. This fruit consists
of several species, such as Prunus domestica, P. cerasifera, P.
damascena, and P. salicina (Timberlake and Bridle, 1982) . Stanley
plum (P. domestica L.) is an Italian plum and characterized by oval
shape, large size, mostly free stone, firm and greenish-yellowish flesh,
and dark purple skin. The variety is harvested from August until
early October in Michigan ( Anon., 1988).

Nutrient Composition

The general nutrient composition of plum fruit is presented in
Table 1. Plum, relatively high in dietary fiber and low in calories, is a
healthy food for human beings. Due to the reported association of
low fiber diets with diverticulitis, cancer of the bowel, cardiovascular
diseases, diabetes, and other diseases of the gastrointestinal tract
(Behall and Reiser, 1986), there has been an increased interest in high
fiber foods during the past few years, especially in developed Western
countries. Consumption of pectin has also been shown to have
healthful benefits (Cara et al., 1992; Nishimune et al., 1991; and
Schneeman, 1989).

Recommendations to include more fiber in the average US. diet
could be achieved by adding commercial dietary fiber in meals,

however, this is not economically efficient. Another alternative is

Table 1 Content of various compounds in the edible portion of ripe

 

 

plum fruit
Constituent Content (96 fresh wt) Reference
Moisture 78.70 Our, 1986
Protein 0.80 Gur, 1986
Fat 0.20 Gur, 1986
Carbohydrates 21.40 Gur, 1986
Starch Trace Wrolstad & Shallenberger,1981
Sugars 7.40-7.79 Money & Christian , 1950
Glucose 1.70-5.20 Wrolstad & Shallenberger,1981
Fructose 0.70-3.50 Wrolstad & Shallenberger,1981
Sucrose 0.96 Wrolstad & Shallenberger,1981
Sorbitol 0.60-2.00 Wrolstad & Shallenberger,1981
Dietary fiber 1.06-1.56 Vidal-Valverde et al., 1982
Cellulose 0.36—0.45 Vidal-Valverde et al., 1982
Hemicellulose 0.08-0.25 Vidal-Valverde et al., 1982
Lignin 0.07-0.47 Vidal-Valverde et al., 1982
Pectin 0.38-0.58 Vidal-Valverde et al., 1982
Vitamin C 4.001 Watt & Merill, 1963

 

1 mg/lOOg fresh weight

4

consuming native high-fiber foods or food products. Kay and Truswell
(1977) also suggested that foods naturally having high pectin content
are the best source for pectin. They observed that pectin appears to
be better tolerated when it is included in the diet as a food product
rather than as a powder mixed with water, juice or other foods. Plums
are an excellent source of both dietary fiber and pectin. Plums also
contain high amounts of vitamin C and sorbitol. The high fiber and
pectin content of plums, if concentrated to a paste, might yield a
product which could be used as a substitute for shortening in the
bakery industry to develop low fat products. These characteristics
may make plum paste, a concentrated form of plums, a high

potential processed product.

Stanley Plum Production and Utilization

Stanley plum is the leading plum variety grown in Michigan,
which was ranked in the top 4 plum and prune producers in the
nation from 1986 to 1990. About 50% of the 10,000 tons of plums
produced annually is consumed fresh, while the remaining goes for
processing (Espie, 1992; 1991). The major processed plum products
available in the market are prune juice and prunes. Other processed
forms , such as plum juice, plum sauce, plum juice concentrate, prune
bits, etc., are also being developed. However, plum processed products
have not been developed and marketed on a scale similar to other
fruits like apples, pears, apricots, etc. (Siddiq, 1993). The purpose of
this work was to develop a plum paste which can utilize a large
quantity of fruit, and study the factors which affect the processing

quality and storage stability.

II. Plum Paste Production

Paste is the product resulting from the concentration by

evaporation of water from pulp, after the removal of skin and seeds
(Goose et al., 1964). Several kinds of fruit paste have been developed
and marketed. Among them, tomato paste is the most popular and
has been studied intensively. Generally, plum paste production is
conducted using the following procedure:
1) Select good quality fruit and wash; 2) inactivate undesirable
enzyme reactions and soften fruits by preheating to a certain
temperature and then holding for a short time at the temperature; 3)
remove seeds and finish the pulp by passing through a mechanical
finisher with an appropriate screen; 4) concentrate the puree by heat
or a combination of heat and vacuum; 5) add other ingredients, if
necessary, and heat for a short time; 6) fill into containers (Shol'ts et
al., 1990; Exama and Lacroix, 1989a,b; Liu and Luh, 1979; Sherkat and
Luh, 1977,1976).

According to the United States standards for grades of tomato
paste (Anon., 1977), Fine paste is the clean, sound and whole product
with high consistency, smooth texture, distinct flavor, typical red
color, and no defects. This standard can be used as a guideline to

make high quality plum paste.

Selection and Cleaning

Plums are harvested mechanically at maturity. It is possible to
have debris, leaves, and defective fruit with whole and sound fruit.
Sorting is needed for proper assurance of freedom of imperfections.
The fruit surface may also have contaminants, such as soil, chemicals,

microorganisms, and insects. Washing, in addition to separating soil

6

and foreign materials, also reduces the load of spoilage
microorganisms naturally present in foods. Washing also improves

the quality and appearance (Lopez, 1987).

Preheating

Preheating is an operation in which raw fruit is heated, usually
with continuous stirring. If the fruit is firm like plums, crushing may
take place during heating process. Once the product reaches the
temperature which is proper for the particular fruit being used, the
macerate should be held for a short time. Preheating is done for the
following reasons: a) to release cell components, b) to facilitate
preliminary operations, c) to inhibit undesirable enzymatic actions

(Lopez, 1987). These processes will be discussed below.

Release of Cell Components

Anthocyanins (ACYs) are the main color source in red-to-blue
fruits and their food products, especially plums. Plum ACYs are
located mainly in the skin (Weinert and Escher, 1989). They
accumulate in the vacuoles of the epidermal and subepidermal tissue
(Gross, 1987). Heat treatment breaks down cell integrity resulting in
the release of ACY pigments and hence improving the color of paste.

Carbohydrate polymers are also important components
contributing to the paste quality because they serve as thickening
agents. According to Morris (1973), polysaccharides are highly
hydrophilic giant molecules that can radically affect the physical
properties of up to 100 times their own weight of water. They are,
therefore, used widely in the food industry as thickeners and texture

modifiers. Carbohydrate polymers, such as cellulose, hemicellulose,

7

pectin, and lignin, are components of plant cell walls and are
liberated from cell walls when heat treatment destroys plant tissues.
The positive relationship between pectin content in tomato paste and
consistency have been proven by several authors (Liu and Luh, 1979;

Sherkat and Luh, 1977; Luh and Daoud, 1971; Luh et al., 1954).

Facilitating Preliminm Operations

In order to have smooth and good colored plum paste, it is
necessary to cook the plums to soften the tissue, extract pigments,
extract pectins and facilitate the removal of pits. The cooked plums
can be easily passed through certain types of finishers or through

screens to remove pits.

Inhibition of Undesirable Enzmatic Actions

The major enzymes which affect plum paste qualities are
polyphenoloxidase (PPO), which oxidizes phenolics and therefore
causes browning and degradation of ACYs, and pectic enzymes
(polygalacturonase, PG, and pectic esterase, PE) which break down
pectic substances and decrease paste consistency. The most effective
way to inactive these enzymes is high temperature treatment
(Langdon, 1987). In plums, this amounts to heating the whole fruit to
95°C and holding at this temperature for 10 minutes. This allows for
subsequent screening or finishing without browning. Once the puree is

obtained the product is further heated to concentrate it.

Preparation of Puree
After preheating, the skins and seeds are removed and the pulp is

passed through a finisher to break down fibers and cells so that the

8

refined pulp, or puree, is homogeneous, smooth and free from skins
and seeds ( Goose et al., 1964). The particle size within the puree can
be controlled by screen size. Usually, fine product without granules is

suggested for high quality paste (Anon., 1977).

Heat Concentration

Paste is usually processed via heat evaporation. Although it has
the disadvantage of possibly developing off-flavor, it is the most
common method of concentration (Troller and Christian, 1978).
Longer the heating time, higher the solid content and consistency.
However, increasing heating time is usually associated with
undesirable properties, such as browning, and degradation of ACY,
pectin, organic acid, flavor and vitamin content ( Wani et al., 1990;
Exama and Lacroix, 1989a ). In order to produce high quality paste
with minimal negative characteristics, heating processing under
partial vacuum is often utilized to shorten heating time and lower
heating temperature. In the current study, plum paste was processed
by heating at atmospheric pressure because vacuum processing
equipment was unavailable. This type of process gave a paste with
good consistency, color and flavor. Siddiq (1993) indicated that plum
juice ACYs were relatively stable to thermal processing with losses of

only 16% observed when the juice was heated for 70 minutes at 65°C.

Addition of Other Ingredients

Variation of paste can be accomplished by adding other
ingredients. Based on the determination of the effect of sugar
addition on the quality and usability of tomato paste at the time of

manufacture, Bash et a1. (1984) reported that sugar addition

9

increases color darkening and soluble solids, and has dilution effect on
total acidity. They also concluded that it may be more efficient to
add the required sugar at the time of paste production rather than
waiting until final product formulation as there is no effect on quality
when sugar is added during initial stage of paste production. Exama
and Lacroix (1989a), while studying the development of high protein
fruit pastes based on whey protein isolate, mango puree, and sugar,
stated that sugar content had little effect on the texture. Both of the
studies indicated that heating after the addition of ingredients is
necessary due to the possibility of microbiological contamination that
may be present in them, but heating time should not be too long as it
may induce negative changes in the composition and texture.
Wrolstad et a1. (1990) investigating the effect of sugar on the
quality of frozen strawberries reported that sucrose addition had a
significant protective effect on ACY pigment and also retarded
browning and polymeric color formation. In this study, the addition
of sugar was deemed necessary for improvement of flavor but it also

seemed to have some positive affects on consistency and color.

Filling

To prevent microbial contamination, well-mixed acidic products
(like plum paste) can be preserved in two ways: 1) hot filling into pre-
washed containers immediately followed by sealing and then inverting
containers to sterilize the lids (i.e. pasteurization processing), or 2)
filling into clean containers followed by heat processing. However, the
heat processing may cause further composition degradation.
Pasteurizing acidic products is usually the better choice if it is done

properly. Shol'ts et al. (1990) suggested that filling temperature be

10

not lower than 90°C for grape paste. Plum pastes showed no microbial
growth problems when pasteurized at 85°C and stored at ambient

room temperature.

111. Storage Stability

Factors affecting the shelf-life of a certain product include:
intrinsic properties of foods, such as composition, moisture content,
pH, etc., as well as extrinsic factors, such as time, temperature, light,
etc. Texture, color, and microbial contamination are most frequently
used as storage stability indicators (Canellas, et al., 1993; Pouget et al.,
1990; ; Wrolstad, et al., 1990; Weinert et al., 1989).

Low temperature storage extends food quality retention by
retarding chemical reactions of food composition and microbial
growth. This is because the rate of chemical reaction is dependent on
temperature. With a rise in temperature, there is an increase in
reaction rate. This concept is associated with the temperature
coefficient (Q10) which is defined as follows:

Q10 = (Velocity at a given temperature + 10°C)/Velocity at T

The Q10 for most systems is 1.5 to 2.5, so that for each 10°C rise
in temperature within the suitable range, there is a twofold increase in
the rate of reaction. For every 10°C decrease in temperature, the
reverse is true (Jay, 1992).

Comparing color, browning and water activity of raisins stored at
different temperatures, Canellas, et a1. (1993) indicated that the
refrigerated samples were of higher quality in composition as
compared with nonrefrigerated samples. Pouget et a1. (1990),

investigating the stability of ACYs under various storage conditions,

11

showed that the percentage of remaining color at 4°C was much higher
than at 22°C. After 6 months storage, blackberry and red raspberry
wines stored at 2°C had considerably higher total ACY concentration
than that stored at 20°C (Rommel et al., 1992, 1990). Palamidis and
Markakis (1975) investigated the degradation of a colorant extracted
from grapes in a carbonated beverage. They reported that the half-life
of the colorant ranged from 80 days at 38°C to 1,536 days at 3.5°C in
the dark.

Kanujoso and Luh (1967) investigated the effect of storage
temperature on peach texture and found that peach tissues softened
more rapidly at 98°F than at 80°F and 68°F and softening during
storage may be attributed to the transformation of protopectin to
water-soluble pectin. In this study, plum paste was stored at both
ambient room temperature (~ 22°C) and at refrigerated temperature
(~4°C).

IV. Quality Evaluation of Plum Paste

Color

Color of foods is often the first quality attribute judged by
consumers and is, therefore, extremely important in overall product
acceptance. Factors affecting the color of plum paste include

browning and the degree of ACY retention.

Browning
Browning reactions of foods may lead to undesirable color, flavor,

and nutrient losses, which result in poor acceptability of food

12

products. In general, browning reactions in fruits and vegetables can
be divided into 1) enzymatic browning which is the result of PPO
activity on phenolic compounds, and 2) Maillard reaction, Non-
enzymatic browning, which results from the heat-induced reaction
between sugar and amino acids (O'Brien, 1989 ; Sapers et al., 1989).

Enzymatic browning has been a problem throughout the history
of fruit and vegetable processing. The sequence mechanism of
enzymatic reactions follows: 1) hydroxylation of monophenols to o-
diphenols; 2) the further oxidation of o-diphenols to o-quinones
(Whitaker, 1972). These reactions are shown in figure 1. The 0-
quinones formed, (a) polymerize to form brown melanins and then
brown high molecular weight polymers, known as enzymatic browning,
(b) react with amino acids or proteins to form macromolecular
complex, and (c) oxidize compounds of lower oxidation-reduction
potential, such as ACYs. Reaction (c) is especially undesirable as the
quinones formed by PPO, in addition to oxidizing compounds of lower
oxidation-reduction potential, are themselves also reduced to
dihydroxyphenols providing "fresh" substrates to the enzyme (Vamos-
Vigyazo, 1981). PPO and its substrates are separated in different
compartments in plant cells. Once the plant cells are bruised or
ruptured, which occurs in the process of thawing, cutting, heating,
transportation etc., they come in contact and undergo the oxidation
reactions (Bolin and Huxsoll, 1989).

High temperature inactivation is the most effective method for
preventing these enzymatic processes (Langdon, 1987). Vamos-
Vigyazo (1981) reported that PPO did not belong to the extremely
heat-stable enzymes, and short exposure to a temperature of 70 to

90°C was sufficient for the destruction of its catalytic function in most

13

OH OH
OH
O + 02 + BH2———9 O + B + H20
CH5 CH3
13.013301 4-Methylcatcchol

A. Hydroxylation of monoghenols to O-diphenols

on 0
OH O O
2 O + 02 > 2 + 2H2

8. Oxidation of O-diphenols to O-benzoquinones

 

Figure 1 Reactions catalyzed by polyphenolosidase (PPO)

14

cases. Grape PPO activity declined very rapidly with increases in
temperature above 30°C (Cash et al., 1976). At pH 6.5 mushroom PPO
was active at 45°C but not at 70°C (McCord and Kilara, 1983). Sweet
potato PPO was markedly inactivated at 100°C for 3 minutes or 94°C
for 5 minutes (Ma et al. 1992). Pigment loss in red frozen sour
cherries could be minimized by blanching for 45 to 60 seconds prior to
freezing (Siegel et al., 1971). DaDamio and Thompson (1992) stated
that blanching mushrooms using microwave method eliminated PPO
activity.

Arnold (1992) reported that pasteurization was the best way to
inactivate PPO and preserve ACYs in plum juice. Palmasano (1972)
indicated that the rate of enzymatic browning of Stanley plum
processed products was not retarded at 82.2°C for 2 minutes.
Investigating the properties of Stanley plum PPO, Siddiq (1993)
indicated that heating at 65° and 75°C for 30 and 5 minutes,
respectively, rendered PPO completely inactive.

Maillard reaction or non-enzymatic browning, is a heat-induced

 

reaction and occurs between sugars and amino acids, peptides, or
proteins effecting changes in color, flavor, functional properties, and
nutritional value of the food (O'Brien, 1989). It may happen during
processing and storage of foods. The Maillard reaction consists of an
interconnected network of processes and has not been completely
understood. Hodge (1953) integrated the available information into a
simplified scheme (Figure 2). According to O'Brien (1989), it is still
the most appropriate description of the Maillard reaction. It is also
supported and described in more detail by recent research (Yaylayan
and Lachambre, 1990; Helak et al., 1989; Schussler and Ledl, 1989;
Velisek et al., 1989; Handwerk and Coleman, 1988). According to the

 

15

ALDOSE + AMI NO

SUGAR COMPOUND ":~ N-SUBSTITUTED

GLYCOSYLANINE “vi-{,0

 

 

 

 

AMADORI REARRANGEMENT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l . I
I-AMINO- - EOA -2-K S
‘ 1 1 D Y ETC 2
a -ZHaO ,
-3H30 II
REDUCTONESI + a-AMINO ACID
n I 7‘
{J 1 smecxsn
- AMINO -2H *2}! DEGRADATION
1) COMPD. " FISSION
paooucrs 3
HM? OR DEHYDRO- ICARBONYLS
FURFURAL REDU C‘I‘ON ES DICARBONYLS l 9
ALDEHYDE
+ AMINO COMPD. + AMINO CONPD. '* AMINO COMPD. + AMINO CCMPD.
v v v _
gees/.1 ‘41:: ’2"a’.~).’:£‘§$fiy;;z stake #rfiiiis-«t:;r-»“$3327“;:fi-foféfié?:5:*;:-.~5‘:3:‘:”sire-35'2":a:reste’tftfiififéi’t‘a'tit‘fst’iéiifii-‘fi'f'
f M E L A N I N S

O D
. BROWN NITROGENOUS POLYMERS AND COPOLYMERS ;.
£33“ :1--f.teeisi583.13:égétiisfifi’szfé‘fzé’iii$524" 3:-rezg:7;‘;g;;;;: £34:-z:t<':i>~:$3:;':?.$£3;:fi,§§:-fittiitifiéfi‘z7"?t‘rftf...’;<’ 55?.i‘gt/ngi-ia-3 Mars-.514;
‘ ACID CONDITIONS
’ BASIC CONDITIONS
’ HIGH TEMPERATURES

Figure 2 Maillard reactions

16

scheme, the first step is the condensation of the amino and carbonyl
compounds. The subsequent rearrangement of N-substituted
glycosylamine to form deoxyketose or deoxyaldose compounds,
depends on whether the reacting sugar is an aldose or ketose. Under
acidic conditions, the reaction results in loss of water with the
subsequent deamination of Amadori compounds. Under basic
conditions, the Amadori compounds may lose water and then
hydrogen to form dehydro-reductones. A variety of fission products
including reductones, other dicarbonyls and aldehydes may be
produced under high temperature condition or following the
oxidation reaction under basic conditions. Subsequent Strecker
degradation involving dicarbonyls produced in the Maillard reaction
may occur with the production of carbon dioxide and a variety of
volatiles. The final stages are complex and involve the conversion of
low weight precursors, such as furfurals, fission products, and
reductones into the high molecular weight melanoidin pigments.
Amines may be involved in such reactions. The production of
melanoidins is believed to involve aldol condensations and aldehyde-
amino polymerization.

Major factors affecting the rate of Maillard browning include: 1)
nature of reactants, 2) water activity of foods, 3) pH value of the
product , and 4) temperature (O'Brien, 1989).

Low molecular weight compounds tend to be more reactive than
high molecular weight compounds as a result of greater stearic
hindrance in the latter (O'Brien, 1989). Glucose is the main reactant
in the Maillard reaction (Jiang and Ooraikul, 1989). Leszkowiat et al.
(1990), investigating the contribution of sucrose to nonenzymatic

browning, postulated that sucrose, a non-reducing sugar, enters the

17

browning reaction by thermal hydrolysis to yield glucose and fructose.
Handwerk and Coleman (1988) mentioned that rhamnose and
galacturonic acid, becoming constituents of citrus juices when
enzymic degradation of pectin occurs during juice processing, may
undergo browning degradation to produce 2-furaldehyde and reductic
acid.

Water in food systems has an important influence on the
Maillard reaction. It exerts its influence by controlling the liquid
viscosity, concentration, or dilution of reactants (Pomeranz, 1991).
Cuzzoni et al. (1989) showed that the browning rate of the ribose-
lysine model system was increased with a decrease in the water
activity in the range of 0.98 to 0.60. Eichner and Karel (1972) also
observed the same results and postulated that it is likely the law of
mass action leads to a decreased rate of reaction at high moisture
levels.

Nursten (1980) reviewed the Maillard reaction and stated that
both the initial pH of the product and the buffering capacity of the
system influence the rate and direction of the reaction. The rate of
browning is low at acidic pH values and increases with increasing pH
to a maximum at a pH of about 10 (Ashoor and Zent, 1984).
Friedman and Molnar-Perl (1990) confirmed the observation by
measuring the browning extent of amino acid-glucose systems under
the pH range of 4 to 10.

It is generally agreed that Maillard reaction is heat induced.
Friedman and Molnar-Perl (1990) reported that browning increases
progressively as a function of heating temperature and time. Cuzzoni
et al. (1989) demonstrated that the extent of browning is significantly
higher for model systems treated at 160°C than at 100°C. The

18

browning also increases as a function of storage temperature and time.
Investigating the storage stability of dehydrated carrot at 50°C, Baloch
et al. (1973) stated that browning showed a marked increase with
storage time. Although the extent of browning increases with storage
time and temperature, the heating temperature and time during
processing has much larger influence on the formation of browning
pigments (Cuzzoni et al., 1989).

Inhibition of nonenzymatic browning has been investigated in
different ways. Sulfite, cysteine, urea, NH4C1, sulfur amino acid, and
glucose oxidase have been studied to retard nonenzymatic browning
in foods as well as model systems(Friedman and Molnar-Perl, 1990;
Pham, 1990; Jiang and Ooraikul, 1989; Baloch et al., 1973).
Maintaining the product at low temperature has been and still is the
only means to retard color deterioration of processed citrus fruit
juices, concentrates, and dehydrated products in long term storage
(Handwerk and Coleman, 1988).

Anthocyanins (ACYs)

ACYs are among the most important groups of plant pigments
(Brouillard, 1982). They are widely present in fruits and flowers and
are responsible for their attractive colors. ACYs are the main color
source in red-to-blue fruits and their food products, including plums.
Therefore, the stability of ACYs is an important factor related to

product appearance and hence its acceptance.

Chemical Structure
The ACYs are a part of the general flavonoid group of compounds

which are characterized by the flavylium nucleus. The basic nucleus

19

and the numbering of its carbon atoms are shown in figure 3. An ACY
pigment is composed of an anthocyanidin (flavonoid nucleus)
esterified to sugars or acylated sugars. These sugars consist of 4 main
monosides (glucose, galactose, rhamnose, and arabinose) and 4 main
biosides (rutinose, sambubiose, lathyrose, and sophorose); others are
comparatively rare. The triosides which occur can be linear or
branched chain(Timberlake, 1980). The main acylating groups are
the coumaric, caffeic, ferulic, p-hydroxy benzoic, synapic, malonic,
acetic, succinic, oxalic, and malic acids , in the form of acylated sugars
( Francis, 1989, Timberlake, 1980).

ACYs in Plums

Plums contain 3 ACYs : cyanidin and peonidin 3-glycoside and 3-
rutinoside (Timberlake, 1980). Ahn (1973) identified cyanidin 3-
glucoside and 3-xyloglucoside from "Santa Rosa" plums and stated
that cyanidin 3-glucoside was the most abundant pigment of the
plums. Ishikura (1975) found cyanidin 3-rhamnoglucoside in the
Japanese red-purple plums. On the basis of his investigation of 52
species, he concluded that in general, the plants belonging to a certain
genus contained the same ACYs. It seems probable that similar
pigments will be present in Stanley plums with Cyanidin and

peonidin derivatives being the main ACYs.

Enzme Effect

ACYs can be degraded by a number of enzymes found in plant
tissue. These enzymes may be classified as glycosidases (Huang, 1956,
1955), peroxidase (Grommeck, and Markakis, 1964), and
polyphenoloxidase (PPO) (Sakamura et al., 1965; Peng and Markakis,

20

 

Figure 3 The flavylium nucleus of anthocyanins

21

1963). Most of these authors have demonstrated the involvement of
polyphenoloxidase in ACY decolorization.

Peng and Markakis (1963) observed that ACYs were poor substrates
for PPO and proposed a scheme of sequential reactions (Figure 4).
According to the mechanism, PPO oxidizes pyrocatechol to o-
benzoquinone which can reduce to pyrocatechol at the expense of
ACYs. Pifferi and Cultrera (1974) supported the mechanism by
showing that chlorogenic acid and catechin accelerated the
destruction of ACYs by sweet cherry PPO. Wesche-Ebeling and
Montgomery (1990) examined the mechanism using mixture systems,
and also observed that the loss of ACYs caused by PPO and D-catechin
was 2 times greater than that by PPO alone.

Temperature Effect
The effect of temperature on the stability of ACYs has been well

studied because of their obvious importance to the quality of foods.
The general consensus is that ACY's are readily destroyed by heat
during the processing and storage of foods. Meschter (1954) reported
that the half-life was only 1 hour for the ACY pigments in strawberries
preserved at 100°C. Siddiq (1993) reported that the ACY loss of 16%
was observed when plum juice was heated for 70 minutes at 65°C.
After 6 month storage, blackberry wine and red raspberry wine stored
at 2°C had considerably higher total ACY concentration than that
stored at 20°C (Rommel et al., 1992, 1990). Adams (1973) described a
logarithmic destruction of ACY's with time of heating at 100°C and
the measurement of half-life of ACY breakdown.

The mechanism of ACY degradation by heat is not completely

understood. Brouillard and Delaporte (1977) found that , on heating,

22

,4. Degraded

OH
02 anthocyanin
V 0H

Enzymic Nonenzymic

O . .
A AAnt—hocyan‘n
“20' 0

Figure 4 Mechanism of anthocyanin degradation by
polyphenoloxidase (PPO)

23

the equilibrium was driven toward the chalcone form (C) with a
resulting loss in color, suggesting that this was the path of thermal
degradation. Adams (1973) studied the ACY degradation and
suggested that sugar hydrolysis could be part of degradation scheme.

pH Effect

ACYs are water soluble and pH dependent. They appear to be red
in acidic media, almost colorless at intermediate hydrogen ion
concentration, and blue or purple in alkaline media. Brouillard
(1982) and his co-workers (Brouillard and Delaporte, 1977; Brouillard
and Dubois, 1977) demonstrated an equilibrium system based on
kinetic, thermo-dynamic and spectroscopic techniques. Figure 5
shows the 4 ACY species and interconversion between them which
subsequently results in a color change. Structural modifications of
ACY's in water with pH are due to the high reactivity of the
anthocyanidin moiety. Sugar, acylated sugars, and methoxyl groups
have a marked effect on the reactions but, in general, do not react
themselves (Brouillard, 1982). Protonation of the blue quinoidal base
(A) of malvidin 3-glucoside gives the red flavylium cation (AH+),
which can hydrate to a colorless carbinol pseudo-base (B) which itself
can exist in tautomeric equilibrium with its chalcone form (C), also
colorless, formed by opening the heterocyclic ring (Brouillard and
Delaporte, 1977).

Brouillard (1982) illustrated the color change of ACY's in acidic
media with the distribution of structures with change in pH (Figure 6).
In very acidic solution (pH < 0.5), the red AH+ is the only species.
With increasing pH, the AH+ hydrates to the colorless B, resulting in

color decrease. At the equilibrium pH, there is some formation of the

24

 

R
OH
HO 6

/ ‘ R

OGL ———>~ \ '/ 06L

__
H
~ +

A: OUINOIDAL BASE AH :FLAVYLIUM CATION

(BLUE) (RED)

 

C = CHALCONE B :CARBINOL PSEUDO-BASE
(COLORLESS) (COLORLESS)

Figure 5 The four structures of anthocyanins which exist in
equilibria in aqueous solutions

25

 

 

 

 

1001 AH+ 8
is
“E50
”6.93
\00- A
o . . - ,Cji
1 2 3- 4 5
pH

Figure 6 The equilibrium distribution of AH+, A, B, and C for
Malvidin 3,5-diglucoside at different pH values at 25°C

26

colorless C and of the blue A. The proportions of B, C and A continue
increasing with increasing pH at the expense of the red AH+°

In terms of visual color, the amount of the AH+ form is the most
important. Francis (1989) reported that among the four forms of
ACYs, the AH+ form is the most stable. Therefore, ACYs in acidic
condition should be most stable.

Lukton and co-workers (1956) reported that the breakdown of
ACYs in the presence of oxygen was dependent on pH and inversely
proportional to the amount of AH+ form. Adams (1973) found
similar results when cyanidin-3-glucoside and cyanidin-3-rutinoside
were heated in the pH range of 2 to 4. Meschter (1953) stated that
the rate of ACY breakdown was dependent on pH and that lowering
the pH resulted in greater degree of stabilization. Daravingas and
Cain (1968) similarly observed that lowering the pH significantly slows
down the breakdown of the major ACYs in raspberry.

.Oth_ers

In addition to above factors, loss of ACYs could also result from
reaction with light, oxygen, metal-ACY complex formation, and
copigmentation with other compounds. Ascorbic acid has also been

known to accelerate destruction of ACYs (Francis, 1989).

Pectic Substances
Chemical Structure

Pectic substances are polyuronides composed mostly of
anhydrogalacturonic acids. They are present in the growing tissues of
many higher plants where they serve as the cementing agent of cells

and regulate the water content by bonding to calcium, mainly in the

27

middle lamella, and to cellulose in the primary cell membrane
(Pomeranz, 1991).

Pectin is composed primarily of essentially linear polymers of D-
galactopyranosyluronic acid units joined in a-D(1,4) glycosidic
linkages. The polymer chains are esterified to various degree with
methanol (Richardson and Hyslop, 1985) (Figure 7). This regular
structure is interrupted with rhamon units and with side chains
containing other neutral sugars. The polymer chains may also be
partially acetylated (Kertesz, 1951). In addition to being
heterogeneous in structure, it is also heterogeneous with respect to
molecular weight. From molecule to molecule, both the number and
percentage of individual monomeric unit type will vary. The degree
of polymerization and esterification can vary with the modification
during ripening, processing, and storage. The alterations are highly
responsible for texture change of foods (Fishman et al., 1989; Van
Deventer-Schriemer and Pilnik, 1976).

According to the structures and properties, pectin can be divided
into 1) pectic acids which are polygalacturonic acids without or with
only a negligible content of methyl ester groups. Salts of pectic acids
are called pectates, 2) pectinic acids which are galacturonic acids
containing more than a negligible proportion of methyl ester groups.
Salts of pectinic acids are called pectinates, and 3) protopectins which
are water-insoluble parent pectic substances and yield the above two
water-soluble compounds upon restricted hydrolysis. (BeMiller, 1986;
Rouse and Atkins, 1955; Kertesz, 1951).

Pectin solutions exhibit the non-Newtonian, pseudoplastic
A behavior characteristic of most polysaccharides. The rheological

behavior of a pectin solution is related to the molecular weight, degree

toocH3

28

pectin csterase
(0004 l/
3 tolom3 coon COUCH3 (00013

' 0 o _
0H 0H 0H

/

 

Figure 7

Pecfinmterasc

Q®®®®©

OH- OH

Polygalacmmnasc _ OH I OH I OH

Fragment of a pectin molecule and points of attack
by pectic enzymes

29

of esterification, pH, and presence of counter ions. Kaneko et al.
(1989), investigating various parameters related to texture of
processed plum, concluded that increase in acid content, resulting in
low pH, gives rise to chelate binding of divalent cations combined with
pectic substances. The release of these divalent cations, changing the
pectic substances to some degree, consequently causes a decrease in

firmness.

Pectic Enzmes

Enzymes showing specific actions on pectic substances in higher
plant tissues are mainly pectinesterase (PE) and polygalacturonase
(PG). PE cleaves methanol from esterified carboxyl groups yielding
low-methoxyl pectin and polygalacturonic acids. PG depolymerizes
de-esterified polygalacturonic acids by hydrolyzing at the a'l,4
position (Pressey, 1986; Richardson and Hyslop, 1985), as shown in
Figure 7.

The inactivation of pectic enzymes during processing and storage
can be achieved by heat treatment. High temperature inactivation of
pectic enzymes has been intensively studied and applied in the fruit
and vegetable processing industry. Luh and Daoud (1971) reported
that pectic enzymes in tomatoes may be inactivated by giving the
macerated fruits a hot break temperature higher than 93.3°C. They
also concluded that the effect of break temperature on consistency
was much greater than that of the holding time. Sherkat and Luh
(1977, 1976) studied the effect of break temperature on quality of
tomato paste and reported that heat inactivation of pectic enzymes,

at 100°C during maceration, stopped undesirable biochemical changes,

30

and hence yielded a product with higher pectin retention and

consistency.

Rheological Properties

The measurement of fundamental rheological properties of foods
is critical in optimizing product development efforts, processing
methodology and testing final product quality. Many fluid foods,
such as applesauce, orange juice concentrate, tomato paste, and

honey, exhibit non-Newtonian behavior (Steffe, 1992).

Flow Model

Several flow models have been employed to describe the flow
behavior of non-Newtonian foods. The Herschel-Bulkley model has
been applied extensively to relate shear rate and shear stress of these
foods (Steffe, 1992; Guariguata et al., 1979; Toledo et al., 1977;
Odigboh and Mohsenin, 1975) :

o - my! + q, (l)

where o is shear stress, K is the consistency index, y is shear rate, n is
the flow behavior index, and q, is yield stress. This model is a general
model. Newtonian (n=1, 05:0), power law (shearing-thinning when
0<n<1, or shearing-thickening when 1<n<oo, and oa=0), and Bingham

plastic (n=1, ob>0) behavior may be considered as special cases (Steffe
and Morgan, 1986).

Apparent Viscosig

Apparent viscosity, another parameter to evaluate the
rheological behavior of fluids, is defined as shear stress divided by

shear rate:

31

na = 0/i (2)
where 'la is apparent viscosity.

For Herschel-Bulkley fluids, apparent viscosity is

via = 0/i = [Kmn + 0b1fl= KO)“1 + 00 / i (3)
Therefore, the apparent viscosity for power law food fluids is
na = KG)“1 (4)

Effect of Time on Flow Behavior

Some non-Newtonian fluids exhibit time-dependent flow behavior.
In these cases, thixotropic materials exhibit decreasing shear stress
over time at a fixed rate of shear, i.e. time—dependent thinning
behavior. And rheopectic materials exhibit increasing shear stress over
time at a fixed rate of shear, i.e. time-dependent thickening behavior
(Rao and Anantheswaran, 1982). The response of substance to stress is
instantaneous and the time-dependent behavior is due to changes in
the structure of the material itself. In most cases, the time span over
which this behavior encountered is relatively short. The measurement
of flow behavior, to be conservative, can be done on the basis of
magnitudes after the time-dependent span (Steffe, 1992; Rao and
Anantheswaran, 1982).

Effect of Temgrature on Flow Behavior
The effect of temperature on the viscosity of non-Newtonian fluids
can be expressed in terms of an Arrhenius type equation:
na = A exp (Ea/RT) (5)
where 'la is apparent viscosity, A is a constant determined from
experimental data, Ea is the energy of activation, R is universal gas

constant, and T is absolute temperature. Rheological properties are

32

highly temperature dependent and, based on equation (5), the
increase in temperature decreases apparent viscosity of food fluids
(Steffe, 1992).

Using Mixing to Evaluate Rheological Properties
Mixers for rheological studies have been used by investigators for

different food products, such as apricot puree (Castell-Perez, et al.,
1987; Ford and Setffe, 1986), applesauce (Rao, 1975), and tomato
sauce (Rao, 1975). The general principle of measurement used in
mixer viscometry is based on the determination of the torque on the
shaft of the impeller as a function of its rotational speed. Thus, a
suitable value of the apparent viscosity for a non-Newtonian fluid can
be obtained from the viscometric measurement if a representative
value of shear rate in the given vessel can be predicted. Castell-Perez
(1990) evaluated three system models for the approximation of the
average shear stress in the mixing system and established a new model
using the flag impeller. The procedure is simplified and has been
tested to be suitable for power law fluids. Based on the model, the
shear rate is given by

i= 4m (6)
where, y = shear rate, 1/ s

N = impeller rotational speed, rev/s
And the shear stress is approximated by

a = ZM/(adzb) (7)

where, o = shear stress, Pa

M= torque, Nm

d= diameter of flag impeller, m

b= flag impeller blade height, In

33

For the power law behavior within the rpm ranges :
o = KO)“ (8)
The power law parameters were determined from a linear regression

analysis of shear stress versus shear rate as :

ln(o) = ln(K) + n ln(?) (9)
The apparent viscosity is

n. = ch? = K(i)°/i = Km“ (10)
Since o=K(7)”, Eq.(9) becomes

n. = K(t)“/i = Km“ (11)

This procedure was used to evaluate the rheological properties of

plum paste.

Microbiological Content

The contamination of microorganisms in foods has been
considered critical for the reason of food safety, shelf life and food
quality. The HACCP (Hazard Analysis Critical Control Point) system
has been applied in industry for many foods to control organisms in
ingredients at the point of production and preparation of foods (Jay,
1992).

The plants and animals that serve as food sources have all
evolved mechanisms of defense against the invasion and proliferation
of microorganisms. Fruits generally consist of high level of water,
some carbohydrate, and trace amount of protein, fat and ash. On the
basis of nutrient content, fruits would appear to be capable of
supporting the growth of bacteria, yeasts, and molds. However, their
pH is below the level that generally favors bacterial growth. Therefore,
the major microorganisms that exist in fruit products are yeasts and
molds (Jay, 1992).

34

The extent of microorganism contamination in processed food can
be controlled in many ways: 1) by reducing the microbial load on raw
materials, personnel as well as processing facility, 2) by reducing the
microbial load by thermal process, 3) by controlling the growth of
microorganisms by intrinsic and extrinsic parameters of foods, such as
pH, water activity, temperature, and preservatives, 4) by preventing
further contamination during processing and storage. Basic and
traditional measurements used to monitor microbial content should
be done for bacteria, yeasts, and molds for newly developed food

products.

 

MATERIAIS AND METHODS

1. Whole Plum Samples

Stanley plums grown in northern Michigan, harvested at maturity
in September, 1992 were used for this study. The plum samples were
frozen to -20°C immediately after harvest and kept at this

temperature until further processing was required.

11. Plum Puree Production

Pilot plant Puree Made From Standard Plums

Stanley plums were removed from -20°C storage and allowed to
thaw overnight at 4°C. The plums were washed with tap water and
debris was removed. The plums were heated to 95°C and macerated
for 10 minutes in double jacketed stainless steel kettles. The macerate
was then cooled slightly down and the pits removed by passing
through a particular screen. The pitted macerate was passed through
a finisher (Dodge, Mishawaka, IN) equipped with 0.060 .in. screen.

The plum puree was stored at -20°C until further processing was

required.
Commercial Puree Made From Substandard Plums

Stanley plums grown in southern Michigan, harvested at maturity

in September, 1992 were processed by Cherry Central Inc. (Traverse

35

36

City, M1) to puree using a somewhat similar procedure as described

above and then stored at -20°C until further processing was required.

111. Plum Paste Production

The procedure for making plum paste was carried out according
to the method of Shol'ts et al. (1990). The two puree samples (i.e.
commercially produced and produced in our pilot plant) were
removed from -20°C storage and allowed to thaw overnight at 4°C.
Upon thawing the samples were concentrated by heat in double
jacketed, stainless steel kettles. A portion of each sample was
removed when the soluble solids reached 25°Brix. The remainder of
each sample was further concentrated to 30°Brix. One batch was filled
hot into jars. The other batch had sucrose added to give a 15°Brix
increase. The paste with added sugar was mixed well, heated, and hot
filled into 12-oz glass jars (Ball Corporation, Muncie, IN). The jars were
sealed immediately, inverted for 3-4 minutes, cooled to room

temperature in air, and then stored at 4:2°C and 22:2°C in dark.

IV. Quality Evaluation of Plum Paste

Processing Effect

The puree and paste samples were used to determine the effect of
heat treatment and sugar addition on yield, PPO activity, soluble
solids, total solids, moisture content, water activity, pH, titratable
acidity, color, total anthocyanins (T ACYs), pectin content, rheological

properties, and microbial counts. Sensory evaluation for color,

{F

37

sweetness, acidity, consistency, flavor, and overall acceptance were

done on pastes from standard plums.

Storage Effect

The plum paste samples stored at 422°C and 22:2°C in the dark
were evaluated every 4 weeks for up to 24 weeks for soluble solids,
total solids, moisture content, water activity, pH, titratable acidity,
color, T ACYs, pectin content , rheological properties, and microbial
counts. Sensory evaluation for color, sweetness, acidity, consistency,

flavor, and overall acceptance were done on pastes from standard

plums.

V. Physical and chemical Analyses

Soluble Solids

Percent soluble solids of samples was measured using an Abbe-3L
(Bausch & Lomb Optical Co., Rochester, NY) refractometer (sensitivity
0.1%). The results were expressed as °Brix at 20°C. The refractometer

was calibrated using distilled water.

Total Solids

Six grams of samples were weighed into aluminum weighing dishes
which had been dried in a vacuum oven (Hotpack, Phila., PA) for 1
hour at 100°C under a pressure of 27 in Hg. Drying of samples was
done in the vacuum oven for 8 hours at 100°C under a pressure of 27

in. Hg. The dried samples were allowed to cool in a desiccator for 30

 

38

minutes and then weighed. The percent total solids were calculated

using following formula:

96 total solids = (dried sample weight/ fresh sample weight)x 100

Moisture Content
The moisture content of samples was calculated from percent
total solids using following formula:

96 moisture content = 100 - 96 total solids

Water Activity
Approximately 2 grams of sample were measured using a water
activity system (CX-l, Decagon Devices, Inc., Pullman, WA) at storage

temperatures (422°C and 222°C).

pH
Five grams of sample were diluted with 45ml distilled water and

then measured with a pH meter (Model 601A, Corning Glass Works,
Medfield, MA.).

Titratable Acidity

Five grams of sample were mixed with 95ml distilled water and
titrated to pH 8.1 with a 0.1N NaOH solution using a pH meter.
Results are expressed as percent malic acid by weight using the
following formula:

96 malic acid = ml NaOH x 0.1N NaOH x 0.067 mEq x 100/5g sample

39

PPO Activity
Engage extraction

The method of Cash et al. (1976) modified by Siddiq (1993) was
used. All extraction materials were maintained at low temperature (2-
5°C) to reduce enzymatic activity during extraction. Twenty grams of
sample was blended in Waring blender with 100 m1 of 0.1M Tris
hydroxymethyl aminomethane (Trizma) buffer (pH9.5) for 2 minutes.
The slurry was filtered through 8 layers of cheese cloth and the filtrate
was precipitated by slowly adding 200 ml of -20°C acetone with gentle
stirring. When precipitation was complete, the precipitate was
collected by straining through 45 micron mesh nylon cloth. The
precipitate was suspended in 50 ml of 0.1M sodium acetate (pH 7.0).
Pectic substances were precipitated by the addition of 8.0 ml of 0.05M
calcium chloride. The solution was centrifuged in refrigerated
centrifuge at 4400 x g for 10 minutes and the supernatant was used as

crude enzyme extract.

Assay of enzyme activip;

Enzyme activity for PPO was assayed according to method of Cash
et al. (1976). The standard reaction mixture consisted of 3.4 ml of
0.1M sodium acetate buffer (pH 6.0); 0.4 ml of 0.3M catechol; and 0.2
ml of freshly prepared enzyme extract. A spectrophotometer (Milton
Roy Spectronic-70, Rochester, NY) was used to monitor change in
absorbance at 420 nm for 3 minutes for assay of PPO activity. The

increase in absorbance was recorded every minute.

40

One unit of enzyme activity was calculated from the slope of the
curve which determined AA420nm/min due to the oxidation of

catechol (i.e. one unit = change in absorbance of 0.001/ min).

Color

Color of samples was measured by Hunter Color Difference Meter
(D25 DP-9000 system, Hunter Associates Laboratory, Reston, VA).
Approximately 200 grams of sample were placed in a standard optical
cell for the measurement after standardization with a pink tile
(L=73.49; a=17.34; b=10.28). This system is based on the Hunter 'L', 'a'
and 'b' coordinates. The L represents lightness, going from white
(L=100) to black (L=0), and the a and b indicate hue, measuring +a

(redness), -a (greenness), +b (yellowness) and -b (blueness).

Total Anthocyanins (T ACYs)

Extraction of T ACYs was carried out using a method of Cash et
al. (1976) with minor modification based on the method of Lees and
Francis (1971). Ten grams of sample were mixed with 20 ml of 0.1N
HCl buffer. The mixture was blended in a Waring blender for 1 minute
with 100 ml of acidified ethanol solution (9596 ethanol:1.5N HCl =
85:15, v/v). The extraction solution was made up to 200 ml and was
kept in the dark for 2 hours. The mixture was centrifuged under
refrigeration at 9000 x g for 10 minutes and then the absorbance was
measured using a spectrophotometer (Milton Roy Spectronic-70,
Rochester, NY) at 535nm. Acidified ethanol was used as a blank.

The T ACYs was calculated using following formula:

T ACY, mg/100g = [(absorbance x dilution factor)/ E] x (100g/ 10g)

41

The factor B is 98.2 for the acid-ethanol solvent (Francis, 1982; Fuleki
and Francis, 1968a,b).

Pectic Substances
Versene-metinase Extraction of Pectin

Total pectin The procedure for extraction of pectic substance
was the method of McCready and McComb (1952). Ten grams of
sample were blended in a Warning blender for 1 minute with 150 m1
9596 ethanol. The mixture was filtered through Whatman #1 paper
under suction and the pulp was washed with 400 ml 7596 ethanol.
The filtrate was discarded and the alcohol-insoluble residue was
transferred to a 250 ml beaker. Cations were sequestered and the
pectin de-esterified with 100 ml of a 0.596 Versene solution at pH 1 1.5
(adjusted with 1N NaOH) for 30 minutes. The mixture was acidified to
pH 4 with glacial acetic acid, 0.1 ml of pectinase (EC 3.2.1.15, from
Aspergillus niger) was added, stirred for 1 hour, diluted to 500 ml with
distilled water and filtered through Whatman #1 paper. The first few
drops of filtrate were discarded before collecting 2 ml for analysis.

Protopectin The procedure was modified from the method of
Kanujoso and Luh (1967). The alcohol-insoluble residue was prepared
as described above. Two hundred ml distilled water were added to the
residue and stirred for 1 hour. The solution was filtered through
Whatman #1 paper under suction and the residue was washed with
400 ml distilled water. The filtrate was discarded and the water-
insoluble residue was transferred to a 250 ml beaker. Cations were
sequestered and the pectin de-esterified with 100 ml of a 0.5% Versene
solution at pH 11.5 (adjusted with 1N NaOH) for 30 minutes. The

mixture was acidified to pH 4 with glacial acetic acid, 0.1 ml of

42

pectinase (EC 3.2.1.15, from Aspergillus niger) was added, stirred for 1
hour, diluted to 500 ml with distilled water and filtered through
Whatman #1 paper. The first few drops of filtrate were discarded

before collecting 2 ml for analysis.

Colorimetric Determination of Galacturonic Acid

The colorimetric measurement of galacturonic acid was done
using the method of Kintner and Van Buren (1982). The pectin
extract was diluted in order to obtain absorbance reading within the
range of the standard ( 10-80 ug galacturonic acid). One ml sample
containing pectin was pipetted into a 15x180 mm pyrex test tube and
placed in ice-water bath for 5 minutes. Subsequently 6 ml of
HZSO4/tetraborate solution (0.0125M solution of sodium tetraborate
prepared in concentrated sulfuric acid) was added to each tube in the
ice-water bath and the tube was shaken carefully using Vortex mixer.
The mixture was heated in a 100°C water bath for 5 minutes and then
immediately placed in an ice-water bath to cool. Duplicate samples
were developed by adding 0.1 ml 0.1596 m-hydroxydiphenyl solution
(in 0.5% sodium hydroxide) , mixing and allowing to stand for at least
20 minutes at room temperature to allow bubbles to dissipate
(absorption values were stable for up to 1 hour). A blank was
prepared by replacing m-hydroxydiphenyl with 0.1 ml 0.596 NaOH,
keeping all other additions and treatments similar. The blank
absorbance was later subtracted from the total absorbance to obtain
the absorbance due to m-hydroxydiphenyl. Absorbance
measurements were taken at 520nm using a Milton Roy Spectronic-70
spectrophotometer. A reagent blank containing 1 ml distilled water, 6

ml sulfuric acid/tetraborate solution and 0.1 ml 0.5% NaOH was used

43

to zero all instruments. The concentration of pectin was calculated

from the standard curve of galacturonic acid (Appendix 1).

Rheological Properties
Procedure for Data Collection

The experimental procedure was based on the method of Castell-
Perez (1990). A Brookfield HBTD viscometer (Brookfield Engineering
Laboratories, Inc., Stoughton, MA) connected with a data acquisition
system (Dianachart PC-Acquisition Model PCA-14, Dianachart Inc.,
Rockaway, NJ) was used to measure the rheological properties of plum
pastes. The sample temperature was controlled at 30:):0.Z°C by
Brookfield water circulator.

Samples were loaded into a cylindrical cup, with flat bottom,
made of stainless steel with fluid jackets for temperature control.
Inside diameter was 2.54 cm (d/D=0.59) and cup height was 4.0 cm.
Fluid level was kept at 1.2D and impeller depth (distance from the
bottom of the impeller to the bottom of the cup) set at 0.5d which
allowed completed immersion of the flag impeller (Figure 8) under a
significant volume of fluid. The effect of other geometric parameters
was found to be negligible (Castell-Perez, 1990).

Once loaded into the cylindrical cup, the temperature of the
sample was controlled with a water bath connected to the cup jacket.
When the temperature reached 30°C, the flag impeller was immersed
into the solution and readings (96 torque) at a selected rotational
speed were recorded after steady state was reached (constant
readings). For any given run, the rotational speed varied (a stepwise

increase) from 20 to 100 rpm.

44

 

 

I L -- "-032
. Li 1 J...”

I I I 1.5

--l P—O-S

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Model system Flag impeller

Figure 8 Model system and flag impeller used in the
determination of rheological properties with a mixer

45

Data Calculations
The shear rate in the mixing system was calculated as:
7 = 4:1N (12)
where, i = shear rate, 1/s
N = impeller rotational speed, rev/s
And the shear stress is approximated by
or = 2M/(ud2b) (13)
where, o = shear stress, Pa
M = torque, Nm
d = diameter of flag impeller, m
b = flag impeller blade height, m
It was assumed that the rheological properties of plum paste follow
the power law behavior within the rpm ranges :
a = KW)“ (14)
where, K = consistency index, Pa 8n
n = flow behavior index, dimensionless
The power law parameters were determined from a linear regression

analysis of shear stress versus shear rate as :

ln(o) = ln(K) + n mm (15)
The apparent viscosity is
n. --— o/t' = K(i)“/v' = Km“ (16)

where, = apparent viscosity, Pa s
Since o= KG)“, Eq.(15) becomes
n. = K(i)“/i = Km“ (17)

46

Microbial Content
Samples were tested for total (standard) plate count (SPC),

coliform counts, and yeast and mold counts using the methods of
Pestka (1993).

Dilution buffer

A stock phosphate buffer was prepared by combining 34 g
KHzPO4/liter distilled water and adjusting to pH 7.2 with sodium
hydroxide. The dilution water was prepared by combining 1.25 ml
stock phosphate buffer/ liter distilled water, dispensed out in 90 ml

aliquots, and autoclaved for 15 minutes.

Sample preparation

Ten grams of sample were aseptically weighed and put into a
sterile stomacher bag, with 90 ml of sterile buffer, and homogenized
for 1 minute using stomacher lab blender (Model 400, T ekmar Co.,

Cincinnatti, OH).

Standard plate count
SPC agar was prepared according to package directions, by heating

to boil to dissolve completely, separated into 250 ml increments,
sterilized in the autoclave for 15 minutes at 15 pounds pressure and
121°C, and cooled to 45°C. One ml of sample was pipetted into a petri
dish and about 15 m1 of hot, liquid agar was poured in the plate,
incubated at 32°C for 48 hours in inverted position, and the colonies

were counted using a Quebec colony counter.

47

Coliform count

Violet red bile (VRB) agar was prepared according to package
directions, by heating to boil to dissolve completely, and cooled to
45°C. One ml of sample was pipetted into a petri dish and about 15
ml of hot, liquid agar was poured in the plate, incubated at 32°C for
24 hours in inverted position, and the colonies were counted using a

Quebec colony counter.

Yeast and mold counts

Sabouraud dextrose agar (for culturing yeasts, molds, and aciduric
microorganisms) was prepared according to package directions, by
heating to boil to dissolve completely, separated into 250 ml
increments, sterilized in the autoclave for 15 minutes at 15 pounds
pressure and 121°C, and cooled to 45°C . One ml of sample was
pipetted into a petri dish and about 15 ml of hot, liquid agar was
poured in the plate, incubated at 22-25°C in the dark for 5-7 days in
inverted position, and the colonies were counted using a Quebec

colony counter.

Data calculations

After counting the colonies, the results were expressed by

following formula:
Dilution factor = initial dilution x amount plated

Total count, CFU per gram = colonies counted / dilution factor

Statistical analysis
In this study, the experiment was designed as a three factor

(source x concentration x sugar) (for processing condition effects) and

48

a five factor (source x concentration x sugar x time x temperature) (for
storage condition effects) randomized model with balanced data. All
determinations were made in duplicate, except for Hunter color
values, which were determined in triplicate. Mean, standard
deviation, standard errors, ANOVA tables, and correlations were done
using the Super ANOVA software (Abacus Concepts, Inc., Berkeley, CA),
Lotus software, and SAS software. Interactions between statistically
significant factors may not be biologically significant. Therefore, those
interactions important both statistically and biologically were
focused. LSD test for multiple comparisons was applied to determine

significantly different treatment effects.

VI. Sensory Analysis

Sensory Analysis Test Method

The sensory test of paste from whole plums was carried out to
determine the effect of processing conditions and storage conditions at
the beginning and end of storage using the descriptive test with
unstructured scaling (Poste et al., 1991). Samples were tested by a
panel of 60 people for color, acidity, sweetness, consistency, flavor, and
overall acceptance. Panelists were asked to evaluate the first 5
descriptors by intensity only and the last one by personal preference.
A 15-cm horizontal line with an anchor at mid-point was used. Each
line was labeled with a descriptor expression at each end. A separate
line was used for each sensory attribute to be evaluated. Panelists
were asked to record each evaluation by marking the horizontal line

at the point that best reflected their perception of the magnitude of

49

that property. Each panel consisted of 60 panelists from the faculty,
staff, and students in the Food Science and Human Nutrition
Department. Panelists ranged in age from 18-55 years old and

included both males and females (see Appendix 2 for sample ballot).

Environmental Conditions

All sensory tests were held in the sensory evaluation laboratory of
the Department of Food Science and Human Nutrition at Michigan
State University. This laboratory is equipped with fifteen isolated
testing booths that have temperature regulated positive airflow, and
constant illumination. Panelists evaluated the paste samples under

white fluorescent lighting.

Sample Preparation and Presentation

Approximately 15 grams of sample was put into 2-oz cups
labeled with a three-digit random numbers for identification. The
samples were allowed to come to room temperature prior to the
sensory evaluations. All sample presentation orders were randomized
and balanced. Subjects were instructed to drink ambient temperature
distilled water, as well as eat unsalted crackers ad libitum prior to and
between sample evaluations. Panelists were also allowed to swallow or
expectorate the paste samples. The tests were held consecutively on

one day lasting from mid-morning to mid-afternoon.

Data Analysis
The points on horizontal lines were measured in cm and
translated into numerical values for statistical analysis. Three-way

ANOVA was used to test the significance of main effects and

50

interactions of processing conditions using Super ANOVA (Abacus
Concepts, Inc., Berkeley, CA). The correlation coefficient of overall
acceptance and other attributes were calculated .

To determine the effect of storage time, the difference of each
value for each attribute and two-way ANOVA were used to test the
significance of effect of concentrations and sugar addition on time
effect. If it was not significant, the t-test was conducted to see if time
affected storage ability significantly.

To determine the effect of storage temperature, the difference of
each value for each attribute and two-way ANOVA were used to test
the significance of effect of concentrations and sugar addition on
temperature effect. If it was not significant, the t-test was conducted

to see if temperature affected storage ability significantly.

RESULTS AND DISCUSSION

1. Processing Effect

Puree Production

The yield of puree from standard plums (i.e. pilot plant product)
was 71.2596 by weight. The quality characteristics of the commercial
and pilot plant purees are listed in Table 2. The processing
conditions for both batches of purees were basically the same. Pilot
plant puree had significantly (P<0.01) higher soluble solids, total
solids, titratable acidity, Hunter 'a' value, chroma, T ACYs, total
pectin, Protopectin, apparent viscosity (na), consistency index (K), and
flow behavior index (n) than the commercial pure. The commercial
puree was higher in water activity, moisture content, pH , Hunter 'L'
value, Hunter 'b' value, and hue angle. However only moisture
content and hue angle were significantly different at 596 level. From
subsequent background investigation it was determined that the
commercial puree was made from substandard plums, therefore, the
lower quality was were predictable. No PPO activity was detected in
either puree. This indicated that the preheating temperature (95°C)
with 10 minutes holding time was sufficient to inactivate PPO in
Stanley plums. Siddiq (1993) also reported that heating at 75°C for 5
minutes rendered Stanley plum PPO completely inactive. Microbial
count showed that commercial puree was free from microorganism

contamination but pilot plant puree was contaminated by yeasts and

molds.

51

52

Table 2 Quality characteristics of commercial puree made from
substandard plums and pilot plant puree made from
standard plums

 

 

Characteristics Commercial puree Pilot plant puree
Soluble solids (°Brix) 9.900a1 16.425b
Total solids (96) 10.320a 18.075b
Moisture content (96) 89.68b 81.92a
Water activity 0.999a 0.998a
pH 3.50a 3.45a
Titratable acidity

(96 malic acid, wet basis) 0.784a 1.357b
Hunter color

L 24.397b 21.915a

a 27.720b 39.230a

b 12.650a 12.610a

Hue angle 0.42 8b 0.31 1a

Chroma 30.473a 41.207b
PPO activity

(A420nm/minx10'1) nd2 nd
Total anthocyanins

(mg/ 100g, wet basis) 8.846a 18.455b
Total pectin

(g/100g, wet basis) 0.330a 0.722b
Protopectin (g/100g, wet basis) 0.048a 0.722b
Apparent viscosity ( Pa s) 0.921a 4.048b
Consistency index (K) 7.090a 20.872b
Flow behavior index (n) 0.138a 0.306b
Standard plate count (CFU/ g) 0 0
Coliform count (CFU/ g) 0 0
Yeast and mold count (CFU/ g) 0 200

 

1 Values with the same latters in horizontal rows are not significantly

different at 5% level of significance

2 not detected

53

Paste Production

Our preliminary experiment showed that it was not feasible to
concentrate plum pastes beyond 40°Brix. However, Wani et al. (1990)
stated that the pulp from 3 plum varieties in his studies could not be
concentrated beyond 26°Brix. The difference may come from the
different varieties and characteristics of fruits. Pastes higher than
30°Brix were very thick and almost did not flow, but lower than
25°Brix were too thin. It was found that plum paste with 25-30°Brix
had most attractive color and best consistency. Therefore, pastes with
the soluble solids of 25 and 30°Brix became the standards for all
subsequent work. Relatively longer processing times were needed for
pastes with higher soluble solids. Also, due to the high acidity of
paste, it was necessary to add sweetener to ameliorate the flavor.
Pastes sweetened with sugar addition to increase 5, 10, 15 and 20°Brix
were evaluated. According to the results from preliminary sensory
test, sweetened pastes with sugar addition to increase 15°Brix were best
accepted. Therefore, unsweetened and sweetened pastes with 15°Brix

increase were used for subsequent study.

Yield

Table 3 shows the yields of pastes from commercial puree and

 

pilot plant puree. The yields of pastes from commercial puree were
38.73% for 25°Brix paste and 31.60% for 30°Brix paste. The yields of
paste from pilot plant puree were 59.62% for 25°Brix and 50.2396 for
30°Brix, calculated based on puree weight. The lower yields of paste
from commercial puree were due to their lower soluble solids, which
meant that more water had to be evaporated to reach the same degree

of soluble solids. The yields of paste from pilot plant puree were

54

 

 

Table 3 Yields of plum pastes from commercial puree and pilot
plant puree
Yield Yield Sugar
Treatment from fruit from puree addition
(%Wt) (%Wt) (%Wt)
From commercial puree
25°Brix - 38.73 -
30°Brix - 31.60 -
25°Brix, sugar added to 40°Brix - - 17.75
30°Brix, sugar added to 45°Brix - - 19.43
From pilot plant puree
25°Brix 42.47 59.62 -
30°Brix 35.78 50.23 -
25°Brix, sugar added to 40°Brix - - 20.08
30°Brix, sugar added to 45°Brix - - 21.53

 

55

42.47% for 25°Brix and 35.78% for 30°Brix, calculated based on fruit
weight. The sugar amounts needed to increase 15°Brix soluble solids

were a little higher for paste from commercial puree. The average was
19.70% of weight.

Soluble Solids and Total Solids .

During manufacture it is important to know the degree of
concentration of puree or paste for the quality control (Goose, 1964).
The commercial puree contained lower soluble solids (9.90°Brix) as
compared to the pilot plant puree (16.42°Brix). Therefore, the heating
time required to produce the paste with the same degree of soluble
solids was longer for the production of pastes from commercial puree.
Also, the 30°Brix pastes needed longer heating time than 25°Brix
pastes. Time required for heat concentration process, at 100°C, to 25
and 30°Brix was approximately 50 and 70 minutes for commercial
puree and 30 and 45 minutes for pilot plant puree, respectively. Heat
concentration increased soluble solids of the pastes made from
commercial puree by 14.55 and 20.50 units for 25 and 30°Brix paste,
respectively, and by 8.08 and 13.27 units for 25 and 30°Brix paste
from pilot plant puree, respectively. The longer heating time resulted
in higher soluble solids, total solids and less moisture content, as has
been reported previously ( Shol'ts et al., 1990; Exama and Lacroix,
1989a).

The pattern of soluble solids and total solids change, due to
processing is shown in Table 4. Degree of soluble solids and percent
total solids were increased by heat evaporation which removed water

from puree and sugar addition which resulted in an increase of the

56

88858me .00 _o>o_ 00m 00 80.80.06
30:358me you 0.8 026.” 80:08.5: 5 Game 8:00. 0328 08.00 5 0.882 080.0 65 fits 82.0> A

 

 

 

 

 

a10.0.0 8040.0 nmnmd 930.0 0000.0 £006 33800 0803
mvmdm www.mm £3.00 £5.60 umaéw owméw 83:8 0.5502
000.06 umndv amodm amndN $0.3 30.3 06:8 :38.
03.34 ommdm amodm nemém «NYE «~83 06:00 Ens—om
«000.0 800.0 9050.0 0000.0 0000.0 6000.0 .0308 be;
00m.mm womdm £33 3 3K uwodw 03.3 $00 8888 0.50082
uOméV uOde nmwgm nowfim 0&de mmmdfi $00 00:00 :38.
03.34 uovdm novdm nmvem 000.0 H0000 can; 8:8 Ens—om
00.50 30.8888 80¢

a 8.8.0

8 9 858300.830
xtmbm xtmb N xtmbm . xtmh N xtmbm xtmb N 5808000.?

.cllot.._.nlpmullmll.8 5m cosmbaouconv 000m «Iowa.

 

008d 0803 Home 80.: US... mound 80.8888 89a 830d 00 .3380

883 pew .8888 0.80808 .0028 ~98 .0230 03200. no 8032088 9:008er .00 Seem v 030...

57

soluble solids. The total solids increased significantly (p<0.05) with

increase of soluble solids.

Moisture Content and Water Activig (aw)

Moisture content and aw loss were inversely (p<0.05) related to the
increase of soluble solids due to heat evaporation and sugar addition
(Table 4). After heat evaporation, plum pastes still had relatively
high aw: 0.986 and 0.978 for 25°Brix pastes made from commercial
puree and from pilot plant puree, and 0.970 and 0.973 for 30°Brix
pastes from commercial puree and from pilot plant puree. The result
was parallel to that of Troller and Christian (1978). They pinpointed
that the concentration of foods did not always produce measurable
reduction in aw and the principle advantage in concentrating this
material was to increase nutrient contents and achieve economic
reductions in volume and weight. They reported aw of 0.99 for
tomato paste, 0.92 for orange juice, 0.99 for evaporated milk and 0.98
for canned vegetable soup.

The addition of sugar to food products has been applied to
enhance taste and prevent microbial growth by reducing water
activity (Jay, 1992). The aw of foods containing up to 60% sucrose
fall into the range of 1.0 to 0.90 (Troller and Christian, 1978). Plum
pastes with sucrose added contained approximately 2096 sucrose and
had aw of 0.955, 0.949 for 40°Brix pastes from commercial puree and
from pilot plant puree, and 0.949 and 0.931 for 45°Brix pastes from
commercial puree and from pilot plant puree, respectively. The aw
decreased by an average of 0.33 due to sugar addition.

Water activity is an important factor with respect to chemical

and physiological reactions as well as microbial stability during

S8

storage. Preventing or retarding the microbial spoilage of food
products can be achieved by pH, moisture content and temperature.
Approximate minimum aw values for growth of most spoilage bacteria
is 0.90, and for most spoilage yeast and mold is 0.80 (Troller and
Christian, 1978). Although under the range of aw (0.986-0.931), only
some spoilage bacteria can not grow. The low pH of plum pastes
(3.45-3.50) is considerably below the minima for most food spoilage
and all food poisoning bacteria (Jay, 1992). Therefore, yeast and
mold spoilage would be more important for plum pastes, and this can

be controlled by heat destruction and low temperature storage.

12E

The pH values of purees and pastes are shown in Table 5. pH
values remained unchanged during heat concentration and sucrose
addition, at 3.50 for commercial puree and pastes made from it and
3.45 for pilot plant puree and pastes made from it. Minor changes in
pH during concentration process has been reported in literature (Wani
et al., 1990; Exama and Lacroxi, 1989a). The effect of sugar addition
on pH values agree with the that of Bash et al. (1984) who indicated
that pH of tomato pastes was affected very little by the addition of

sugar.

Titratable Acidigg

The titratable acidity (TA) expressed as percent of malic acid is
shown in Table 5. According to the data on wet basis, evaporation
process had significant concentrating effect (p<0.01) on the percent of
TA for all pastes, but sugar addition showed significant dilution effect

(p<0.01) on them. This is confirmed by Bash et a1. (1984). While

59

00000—08000 00: 0.00

0088:8000 00 _0>0_ 000 00 000000050

030.0 00000020: 8 0000.0 00:00 03200 0800 E 000000: 0800 0:0 5:5 0020> ~

200 0:08 00 00 000030000 H

 

 

 

 

 

 

 

00.0 00.0 0000 .00 .00 003

00000 00000 n00~.0 003.0 0000.0 0000.0 0:000 0.09

00mm; 0504 00mm.~ 0m0w.H 00mm.: 000mg 3000 0030
03200 03000.03.
000.0 000.0 000.0 000.0 000.0 000.0 :0

00.8 000: 00: 8000

00.0 00.0 @000 .00 .00 003

0:000 00mw.m 0000.0 008.0 0000 .0 0000.0 0000 0.50

£00.: 0:00.: 0:03.. 0000.: 0000.0 0000.0 00000 0030
0000200 030000000.
000.0. 0000 000.0” 0000 0000 0000.0” :0

800010. 08000
00 00 00000000000020
00.0me 0000.0 N 00.5.00. 0000.0 N xtmbm 0000.0 N 000800.000.
000600 000% 0000000000000 000: 0|00fl

 

00.50 0000 00:0 80.: 000 00.80
30008800 80.: 000000 .00 03200 030000: 000 I0 00 00050000 050000000 00 0000:: m 0300.

6O

comparing the data on dry basis, heat process decreased the content
of TA. Commercial puree has higher TA (on dry basis) than pilot
plant puree. The degradation of TA was a function of heating time
and pastes made from commercial puree lost much more TA as

compared to pastes made from pilot plant puree.

Pol henoloxidase PPO Activi

Table 6 shows that no PPO activity of purees and pastes was
detected, which indicated that the possibility of enzymatic browning
in these products was negligible. However, Wesche-Ebeling and
Montgomery (1990) indicated that even when enzyme activity is
inhibited, the quinones and intermediate oxidation products formed
before the enzyme was inactivated could be sufficient to initiate
polymerization reactions and degradation of ACYs. The enzymatic
reaction could occur during thawing of the frozen fruit, as well as
during preheating before the inactivation temperature reached.
Enzymes derived from mold contamination (Pilando et al., 1985)
should also be considered in addition to native fruit enzymes.
Minimizing mold contamination, enzyme inactivation, rapid thawing

and preheating procedures are recommended to reduce browning

reaction.

Hunter 'L' Value

The common methods used to measure the extent of browning
are spectral absorbance measurements at 420nm and Hunter 'L'
readings. The changes in 'L' values have been proven to have very
high correlation with the extent of browning for fruit and vegetable

products, such as potato (Jiang and Ooraikul, 1989) and plum juice

61

002000 .8030 000000-— - 002200 .8050 00004 u 44 0
000000000000 0000 0.00.0004 - 0000000000000 0000 00004 n .2 0
000000800 00 _0>0~ 000 00 0000000000
0000008000 000 0.8 030.— Hficonton 5 0000.0 00:00 05200 0800 E 000002 0800 000 0:3 0020> 0

00000000 000 0
H.0Héme\80000< a :0: 0

 

 

 

 

 

000.N- 00 0.N- 000 .0- 000.0- .3
0000 H 000.0H 00m .0 H 00N.0 H 0N0. H N 0N0. H N .0. 00055
0: 00 0: 0: 0: 0: 00500 0%
000.0- 00000- 00H.0- 0 0N0.0- .3
000.0 H 000.0 H 00N.0 H 000.0 H 000.0N 0000.0N .0. 000033
0: H0: 0: 00 Us 00: 1003000 000
00.30 0000008 800 80.00
00.0.00 00.0.00

00 00 00000000000000
0000.00 00.0000 N 0000.00 00.000 N 00.00.00 xtmh N 000800000.

0000000 00.0040 09-00403 .0I0Hmm

 

00.50 0000 00:0 80.0 000 00.30 30008800 80.0
000000 00 04 000 ...H.. 00:32 0003000 00008200000300 :0 000000000 050000000 00 000tm 0 00000.

62

(Chang, 1993). The advantages of using Hunter 'L' values as browning
index is the simpler procedure as well as elimination of the
interference problem caused by non—browning pigment (Baloch et al.,
1973; ‘

Hunter 'L' values indicate the lightness and darkness. White color
has the value of 100 and black color, 0 (Anon, 1987). A decrease in 'L'
values is indicative of browning (Monsalve-Gonzalez et al., 1993;
Sapers et al., 1990). The extent of darkening effect resulting from
processing conditions is more clear when expressed as AL. Commercial
puree was lighter in color than pilot plant puree. Pastes from
commercial puree also had lighter color compared to pastes from
pilot plant puree (Table 6). Hunter 'L' values were significantly
(p<0.01) decreased by heat concentration for all pastes. Processing
browning increases as a function of heating time (Friedman and
Molnar-Perl, 1990; Velisek etal., 1989) were also observed in this
study. The addition of sugar significantly (p<0.01) darkened pastes,
which is supported by Bash (1984). According to Leszkowiat et al.
(1990), sucrose contributes to the non-enzymatic browning by thermal
hydrolysis to yield glucose and fructose, which are the main reactants
in the Maillard reaction (Jiang and Ooraikul, 1989). The darkening
could be caused by pigment polymerization, such as anthocyanin-
phenolic condensation, Maillard reaction, ascorbic acid degradation,

and caramelization during processing.

Hunter 'a' Value
Hunter 'a' values show red when positive and green when

negative. Plum purees and pastes had positive Hunter 'a' values

63

which significantly decreased (P<0.0S) by heat concentration and

sugar addition (Table 7). This result is supported by Bash (1984).

Hunter 'b' Value

Hunter 'b' values shows yellow when positive and blue when
negative. Both positive values of Hunter 'a' and 'b' indicated that
color of plum puree and pastes were red-yellow. The values were
significantly decreased (P<0.0S) by processing, as shown in Table 7.
Bash (1984) observed that tomato paste color went to less red and
less yellow when the sucrose level increased and explained that the

change may have been caused by heat processing after sucrose

addition.

Hue Angle

Hue angle, defined as tan-1 (b/a) while it was in the yellow-red
quadrant (Little, 1975), is the attribute of color perception by which
an object is judged to be red, yellow, green, blue, and so forth (Anon.,
1987). Smaller the hue angle, more red than yellow the object is.
Heat concentration showed increasing effect (P<0.0S) on hue angle of
pastes from commercial puree, but decreasing effect (P<0.0S) on pastes
from pilot plant puree (Table 7). Hue angles of pastes from pilot
plant puree were significantly decreased (P<0.0S) due to sugar

addition.

Chroma
Chroma (saturation index) determines how far is the color from
the gray toward the pure hue (Anon, 1987) and is calculated as

(a2+b2)1/2. It is negatively correlated to percentage of polymeric color

64

 

 

0000050000 00 H0>0H 000 00 5000.03

0000003000 00: 0.00 030.0 85000.80 5 000.0 00000 03200 0800 5 0.00002 0800 000 0005 005H0> 0
00100 + 000 00 00005200 003 080.30 N

03:88 00 00005000 H

 

 

 

 

0NN.ON 0000N n00.0N nH00.0N 0H N. H0 0H NH0 080.50
000N.O 0N0N.O 000N.O 0H0N.o 0H Hmd nHHmd 20:0 05$
000.0 0m 0.0 000.0 000.0 0H0.N H 0H0.N H .0. 00053
000.0 H 0H0.NN 000.0N 000.0N umN.0m 00N.0m .0. 00005:
0N 0 .ON 00 0 .NN 0H 0.NN 0N H .0N 000.00 000.00 N0500£U
0000.0 0Nmm.o 00N0.O 30 H 0.0 00N0.o 00 N00 H2000 0::
00 de 000. H H 00N0 H 00m.N H 000.N H 0000 H .0. 00003..
0H 0.0 H 000.0 H 0000 H 000.H N 0N0.0N 00N0.0N .0. 00005:
00.50 30.008800 8000
500.00 03.00.00
00 00 00300000000000
00.00.00 5.00.0 N 0030.00 03.0000 N xtmbm 0300.0 N 5000500000.
00003000 00050 0200000000000 0003 00.50

 

00.50 503 00:0 80.: 000 0050 300008800 8000
000000 00 080000 000 .2000 050 .0020> .0. ..0. 0000500 00 000000000 050000000 00 0000.3 0 0300.

65

(Rommel et al., 1992). Significant decrease (P<0.0S) of chroma due to
heat concentration and sugar addition was detected. Similar pattern
of chroma and T ACY change implied that loss of T ACYs was due

more to degradation than polymerization.

Total Anthocyanins (T ACYs)

Table 8 shows effect of processing on the content of T ACYs in
samples. pilot plant puree had higher T ACYs than commercial
puree. The fact that pastes had higher T ACYs than purees indicated
that heat processing had a concentrating effect on the content of T
ACYs. However, the degradation of pigment can be seen from the T
ACYs based on dry weight. Commercial puree lost 25.34% and 42.48%
of T ACYs when making 25 and 30°Brix pastes, respectively. pilot
plant puree lost 23.90% and 44.76% while producing 25‘ and 30°Brix
pastes, respectively. Siddiq (1993) reported that plum juice lost 16%
of T ACYs after heat treatment at 65°C for 70 minutes. Meschter
(1954) reported that the half-life was only 1 hour for the pigments in
strawberries heated at 100°C.

ACYs are the major color source of plums. For pH 3.45-3.50 of
plum purees and pastes, the ACYs were in the form of AH+ and
represent red color (Brouillard and Delaporte, 1977). The dilution

effect of sucrose addition on T ACY contents was significant (p<0.01).

Pectin Content

Table 9 shows the changes in pectin content during processing.
Pilot plant puree contained significantly higher level (p<0.01) of total
pectin than commercial puree. Heat process resulted in a significant

degradation (P<0.0S) of total pectin. Loss of pectin in commercial

66

050050000 00: 00

0000000006 00 _0>0_ 80 00 5000.05
0300 00500.80 5 0000.0 00:00 20200 0800 E 000300 0800 000 0:3 0020> N

08:08 0 ES 0

 

00.00 H0.0N

 

 

0.0000 009 800

 

 

 

 

000.00 000.00 000.00 0HN.00 oHH.NOH oHH.NOH $0000 .69
00 H.0H 00 m .0 H 000.0 H 0N H00 000.0 H 000.0 H 0.000 0030
0500000050 H0000.
00.50 yam—Ia 0005 8000
00.00 00 .mN 3000 be 3.00
000.0N 000.00 00N.00 000.00 oN000 oN000 $7.00 009
0Nm.HH 0H0.NH 000.0 H 000.0 H 000.0 ~000.0 00000 0020
H 0500000050 0000.0.
0050 000808800 8000
an.“ 030
9 00 0000000000000
0% a xlmflqw a god 5.0.3. 000508...
3 0000000000000. 000: and.

 

00.50 505 0000 80.0 000
00.50 30.008800 80.0 000000 00 0050000050 0009 no 00000500 0580005 .00 000.00 0 0300.

00000000 000 m

 

 

 

 

0000008me
00 H0>0H 80 00 8000.03 300000303 000 000 0000.0 0000» 03200 0800 E 000002 0800 000 003 00205 N
08:0 0 0:5 0

00 0: 0: 00 $5 $5 223 be
0: 0: 0: 0: :00 :00 00.2 00>: 588895

900 030 00.2 .00 .00 83

0000.0 0000.0 £80 00000 0080 0080 803 .09
£30 £80 0:5 000.0 023 «~80 023 32: :0qu Bob

00 0: 0: 0: $0.0 80.0 2.08 .08
0: 0: 0: 00: 03.0 03.0 002 830000000980

mm? mm? 293 .00 00 33
0 «Bad 88.0 semi 083 080m 080m 003 be
pogo £800 £30 #30 «.800 0330 0038 33:00qu 53
0% 5H9.

00 00 0000000000000
39% a a a 5030.. 04.04.00 0858.0.

 

COUMUUN .HNMDM GOmumhquUCOU H603 mmqu

 

00.50 0003 0000 80.0
000 0050 0000008800 800 000000 .00 0000000 00000 00 000000000 080000000 00 000.00 0 0300.

68

puree was much higher (40.3296 loss for 25°Brix paste and 45.73% loss
for 30°Brix paste), when compared to a 4.50% loss for 25°Brix paste
and 9.40% loss for 30‘Brix paste from pilot plant puree. Luh et al.
(1954) stated that marked losses in pectic substances occurred when
tomato pastes were processed. However, negligible decrease in pectin
content during plum pulp and juice concentrating process was
reported by Wani et al. (1990). Sawayame and Kawabata (1989)
studied the effect of pH and heat on the physicochemical properties of
pectic substances and stated that heating induced acid-hydrolysis of
pectin in the pH range of 2 to S which results in lower molecular size
distribution of pectin. Gubenkova et al. (1988) also stated that
heating caused deformation of pectin polymers. Our study showed
that the commercial puree consisted of significantly (P<0.01) lower
protopectin than the pilot plant puree. No protopectin was detected
in either paste. It is possible that heat process caused
depolymerization to segments and then decomposition. Since
commercial puree contained less high molecular pectic substances
and had to be heated for a longer period of time during processing,
the pectic substances depolymerized as well as decomposed, resulting
in marked losses in total pectin contents. Pilot plant puree contained
more high molecular pectic substances, the heat process caused
depolymerization but less decomposition, resulting in small losses in

total pectin content.

Rheological Promrties

The response of decreasing shear stress to time at constant shear
rate indicated that plum paste exhibited time-dependent thixotropic

behavior (Figure 9). The time scale was about 5 minutes and plum

69

 

Shear stress (Pa)

 

 

 

 

Time (min)

Figure 9 Rheogram of plum paste at constant shear rate (20 rpm)
and constant temperature (30°C)

7O

pastes and purees showed time-independent behavior after the time
period. Rao and Anantheswaran (1982) showed that the time span
related to this time-dependent behavior is relatively short, and
because of various mechanical operations in a processing line, the
behavior will not persist for long. Therefore, they suggested that the
magnitudes of rheological parameters measured after the time span
could be used to describe fluid phenomena and for equipment design.
The study was based on time-independent properties and data was
collected after time-independent period reached. Shear stresses
required to induce a given rate of shear on pastes are shown in Figure
10. At shear rates in the order of 20 to 100 rpm in increasing heat
concentration generally resulted in increased resistance to flow, but
sugar addition resulted in a slightly lower resistance flow. Apparent
viscosity is defined as shear stress divided by shear rate (Steffe, 1992).
Pastes requiring higher shear stress to have a given shear rate are
thicker and have higher apparent viscosity. The apparent viscosity
can be used to express the thickness (or consistency) of pastes. The
apparent viscosities at different rpms showed similar tendency (Figure
11), therefore, the apparent viscosity at 50 rpm was used to illustrate
the viscosity of samples.

Table 10 shows the effect of heat concentration and sugar
addition on the rheological properties of pastes. The magnitude of
the apparent viscosity (na), consistency index (K) increased
significantly (P<0.0l) with an increase in heat concentration.
Increasing heat concentration resulted in significantly (P<0.0l)
decreased flow behavior index (n). Sugar addition showed little effect
on rheological behavior of either paste. This corresponded to the

results reported previously that higher apparent viscosity is positively

‘- -'

71

 

50

4o-

shear stress (Pa)

 

 

 

shear rate (1 / sec)

 

110

Figure 10 Shear stress as a function of shear rate of pastes
from commercial puree and pilot plant puree

Plum pastes from commercial puree

I
O
X
+

25°Brix
30’Brix
25°Brix, sugar added to 40°Brix
30’Brix, sugar added to 45°Brix

Plum pastes from pilot plant puree

A

O
A
O

ZS‘Brix
30°Brix
25°Brix, sugar added to 40°Brix
30’Brix, sugar added to 45°Brix

'72

 

\

 

50
4o-
>~
.t’
3 30-
o
.22
>-
‘a‘
o 20'-
i-
E
10-
0

 

d

20

I ' I

' 1 1 I
40 60 80 100

shear rate (rpm)

1'

 

120

Figure 1 1 Apparent viscosity of plum pastes at different

shear rates

Plum pastes from commercial puree

I
O
X
.1.

25°Brix
30°Brix
25°Brix, sugar added to 40°Brix
30°Brix, sugar added to 45°Brix

Plum pastes from pilot plant puree

F

OD.

25°Brix
30°Brix
ZS‘Brix, sugar added to 40°Brix
30°Brix, sugar added to 45°Brix

 

73

 

0000003000

00 30>0H 000 00 5000000 300000800 000 000 050.0 00000 03200 0800 E 000002 0800 030 303 005H0> 0

0003200085 0
=0 00 0m 0:: ~
0 00 00 08: H

 

 

 

 

 

 

3H00.0 3000.0 3000.0 3000.0 0000.0 0000.0 20 x008 0030303 30E
300.00 33.00 300.00 300.00 000.00 000.00 0: x008 00000000000
30.2 000.0 000.2 000.0 003. 000+ 05 .0080? 888%.
300 H0 300 H0 000 H .0 3000 H .0 00 0 H .0 00 0 H .0 0: 0x005 0030003 30E
3 5.00 H 38.0 0 00 0 .00 H 3N0.m0 000.0 000.0 0: N505 ~A0000000000
80.2 000.2 000.8 003 0 080.0 0.88.0 0.5 000803 05.00%
0050 3000008 800 8000

00.00.00 00.00.00
00 00 00000000000030
0000.00 V0.00.0 N 00.00.00 0000.0 N 00.00.00 x0.00.0 0 300800000.

0000000 000100. 000000000000 000: M0430.

 

0050 200—0 00:0 80.0 000

00.50 30.008800 80.0 000000 .00 000000000 8300—003.— co 000000000 050000000 .00 000.00 OH 030...

74

correlated to higher solid content (Steffe and Morgan, 1986) but sugar
does not greatly influence texture (Canellas et al., 1993; Exama and
Lacroix, 1989a; Nusrten, 1986). Values obtained for the flow behavior
index (n) of the plum pastes ranged from 0.1 to 0.5, confirming the
pseudoplastic nature of the samples. Similar pseudoplastic behavior
(0<n<1) was found in fruit puree and juice concentrate (total solids
ranged from 5.8 to 58.4%) (Rao et al., 1986; Steffe and Morgan, 1986).
The general consesus that the consistency index is higher for the more
pseudoplastic fluids (Rao et al., 1986) was confirmed in this study.
Commercial puree had lower soluble solids and apparent viscosity
(0.92 Pa 5) as compared to Pilot plant puree (4.05 Pa 5). Similar
results were reported by Rao et al. (1986) who found the rheological
properties of apple sauce is dependent on the soluble solids. However,
the pastes made from commercial puree with a lower pectin content
(dry basis) had significantly (P<0.01) higher apparent viscosity than
those made from pilot plant puree. In this study, no significant
relationship was found between apparent viscosity and pectin
content. Pectin has been demonstrated to be an important
contributor to the consistency of tomato pastes (Liu and Luh, 1979;
Sherkat and Luh, 1977,1976). However Luh et al. (1954) studied the
consistency of tomato pastes and puree from different varieties and
found that besides pectin other high non-pectin carbohydrate
constituents may also be effective in determining consistency. Luh et
al. (1984) confirmed the above research by finding that the thicker
consistency of tomato pastes contained higher molecular weight pectic
fractions and other carbohydrates, such as fiber, cellulose, lignin and
cutins in tomato which are all important in imparting consistency.

Marsh et al. (1980) also indicated that total solids of tomato

75

concentrate are involved to a much higher extent in determining
consistency than are the percentage of water-soluble compounds,
such as water-soluble pectin which is the major type of pectin in plum
paste.
Microbial Analysis

Table 11 shows the content of bacteria, yeast, and mold in purees
and pastes under different processing conditions. Standard plate
count as well as yeast and mold count are mainly used to monitor the
microbial contamination from raw materials and equipment.
Coliform count is mainly used to control the microbial contamination
from water (Pestka, 1993). There were no microorganisms detected in
commercial puree or the pastes made from it. Although pilot plant
puree was contaminated with yeasts and molds, pastes made from it
were free from microbial contamination. These results were expected
because the heat process necessary for concentration of the puree to
paste was sufficient to destroy yeasts and molds (Jay, 1992). The
results indicated that the sanitation during processing was under

control.

Sensog Evaluation

Four types of pastes made from pilot plant puree were used to
evaluate color, acidity, sweetness, consistency, flavor, and overall
acceptance in the sensory evaluation. Mean values of the sensory
scores are shown in Table 12, and P values of analysis of variance are
shown in Table 13. The interaction of heat concentration and sugar
addition were not significant.

leo_r The effect of heat processing and sugar addition on

lightness of pastes was perceived by panelists (P<0.01). 30°Brix paste

L

0500 00 ES 0

 

 

0 0 0 0 000 000 0:300 068 0:0 0000»
0 0 0 0 0 0 00:00 8000:00
0 0 0 0 0 0 20:00 0003 00000000
0 0 0 0 0 0 H0008 038 000 0000»
0 0 0 0 0 0 H0550 800.0000
0 0 0 0 0 0 H0008 0003 00000000

76

 

 

500. 00 500.00

 

00 00 00000000000030
V000.00 0000.0 0 V000.00 50000 500.00 500.00 000800000.
l0000000..lw.|00 :0 IIIH000000H000.H0.|||.I00 00000 00000

 

00000 0003 00:0 8000
000 00000 0000008800 8000 000000 .00 0000000 000300008 00 000000000 0000000000 .00 80.00 H H 2300.

77

Table 12 Mean values of sensory attributes for plum pastes made
from pilot plant puree

 

 

 

Heat concentration Sugar addition
Treatment/ 2 5°Brix 30°Brix 2 5°Brix 30°Brix
to to
Sensory attributes 40°Brix 45°Brix
Color 8. 1 6 10.53 10.60 1 2.02
Acidity 9.60 10.35 5.38 5.23
Sweetness 4.34 4.34 8.76 8.74
Consistency 7.9 8 1 0.34 8.85 1 0.63
Flavor 8.35 9.1 1 9.26 9.10

Overall acceptance 5.98 5.58 10.24 9.80

 

78

Table 13 P values of analysis of variance for sensory attributes of
plum pastes made from pilot plant puree on sensory
evaluation

 

Sensory Attributes

 

Color Acidity Sweetness Consistency Flavor Overall

 

 

Source acceptance
A1 0.0001 0.407 1 0.9784 0.0001 0.4564 0.2097
B2 0.0001 0.0001 0.0001 0.0497 0.2679 0.0001

AxB 0.0887 0.2147 0.9849 0.3332 0.2553 0.9652

 

A Heat concentration
B Sugar addition

79

was darker than 25°Brix paste. Sugar addition also darkened the
pastes, with higher difference of score (2.44) on 25°Brix paste than
30°Brix paste (1.49).

Acidity Acidity was significantly affected by the addition of
sugar (P<0.01), but not by heat concentration. Taste panel scores
indicating the decrease in intensity of acidity due to sugar addition
was 4.22 for 25‘Brix paste and 5.12 for 30°Brix paste.

Sweetness Similar results were shown by panelists for acidity
and sweetness. Sugar addition decreased acidity rating and increased
sweet perception of pastes, by score of 4.42 and 4.42 for 25 and 30°Brix
pastes, respectively. This may due to the increased Brix/acid ratio of
plum pastes by sugar addition. The addition of sugar increased
Brix/acid ratio from 13.08 to 24.40 and from 13.31 to 24.47 for 25 and
30°Brix pastes, respectively.

Consistency Heat concentration showed a significant effect
(P<0.01) on consistency as compared to that of sugar addition
(P=0.0497). Consistency score was higher for 30°Brix paste (10.34)
than for 25°Brix paste (7.98). Sugar addition gave only a slight
increase in consistency ratings of plum pastes.

Flip; Both heat concentration and sugar addition showed
little influence on flavor of plum pastes. The average score of 8.96 for
all plum pastes indicated that panelists considered plum pastes to be
characterized by a relatively strong plum flavor.

Overall acceptance Only sugar addition showed significant
influence on overall acceptance (P<0.01). The sweetened 25°Brix paste
had the highest score (10.24) of overall acceptance, while unsweetened
25°Brix paste had a score of 5.98 only. Sugar addition also elevated

the score of overall acceptance from 5.58 for unsweetened 30°Brix

80

paste to 9.80 when sweetener added. The increase in mean score by
an average of 4.24 due to sugar addition indicated that people
accepted sweetened plum pastes better than the unsweetened
counterpart. These results agree with Chang (1993) who reported that
the higher the sweetness the higher acceptability of plum juices.

Panelists commented that unsweetened plum pastes were too sour
to accept. The correlation coefficient between overall acceptance and
other sensory attributes (Table 14) confirmed this concept. For
unsweetened pastes, the overall acceptance was significantly (P<0.01),
negatively correlated to acidity and positively correlated to sweetness.
But for sweetened plum pastes, people graded the overall acceptance
based on not only sourness and sweetness but also on flavor, color,
and thickness, in order of significance. Flavor intensity was correlated
to overall acceptance of sweetened 25°Brix paste by r=0.439 (P<0.01)
and sweetened 30°Brix paste by r=0.682 (P<0.01). Color had
significant correlation (P<0.01) with overall acceptance for both
sweetened plum pastes. Thickness was significantly correlated
(P<0.05) to overall acceptance of sweetened 25°Brix paste.

The results indicated that plum pastes could be characterized by
acidity, sweetness, thickness sensations, but the preference could be
adequately predicted by flavor and color under suitable brix/acid

ratio.

81

Table 14 Correlation coefficients of overall acceptance with color,
acidity, sweetness, consistency, and flavor of pastes made
from pilot plant puree on sensory evaluation

 

Heat concentration

Treatment/ 25°Brix

Sensory attributes

3231i;

Sugar addition
m 393%
to to
40°Brix 45°Brix

 

Color —0.058
Acidity —O.347**
Sweetness 0.508**
Consistency 0. 1 06
Flavor 0.090

-0.056
—O.482**
0.435“
-0.078
0.105

O.326** 0.335“
-O.393** -0.091
O.447** 0.349“
0.293* 0.245
0.439Mr 0.682“

 

* Significance at 5% level
** Significance at 1% level

82

11. Storage Effect

Soluble Solids and Total Solids

The measurement of solid content is fundamental for examining
the quality of fruit pastes during storage (Goose, 1964). No substantial
changes were detected in soluble solids or total solids of plum pastes
during storage (Figure 12 and 13). Changes in composition during
storage which result in variation of soluble solids and total solids
have been reported by Kanujoso and Luh (1967) and O'Brien (1989).
However, no significant differences in soluble solids and total solids of

plum pastes were found in this study.

Moisture Content and Water Activi aw

Moisture content and aw of plum pastes were not significantly
influenced by storage temperature and time, as shown in Figure 14
and 15. Like solid content, the changes in moisture content and aw
may be related to composition variation. Canellas et al. (1993)
postulated that water released in Maillard browning reactions under
acidic conditions and the crystallization of sugar is highly responsible
for an increase in water activity of food products during storage.
However, water is needed in degrading reactions of pectin, ACYs, and
other components (Markakis, 1982; Kertesz, 1951). Changes in aw of
fruit paste packaged in polypropylene film and stored at different RH

environment was also reported (Exama and Lacroix, 1989b).

2L1
Storage time showed significant influence on pH of plum pastes

(P<0.05), while no significant effect by storage temperature was

83

55.? 3 825 553 55.8 p
55.9. 9 .83W 553. 35.2 >
.. 55.05 +

xtm.m~ o
PNN am @803. 53me SSE

55.2. 8 BB... 553 £5.05 .
xtmbv 9 poop“ Swan .xtm.m~ 4
xtmbm l
xtmbm o

9v 3 p39,... 53me ESE

mound Ema uoza So: was 3:5

 

 

 

 

 

365888 80¢ 58me SEQ Mo 8:0..." Ens—om co EBEoQEB new was mwmeoum Ho Hootm NH oSwE
Anxoogv oEfi Ans—ooze 05:.
«N 8 S 2 w v o v~ 8 S 2 5 v o
- - p p - p n n p u — n p - ON
- o .lollolololllAYIIo 1 TulolllollulTolllo.lo
. mN
. Ill-I'llllll I I I on m
. . n
- 5 m
- 1 mm a
l Ill-HIV} 1 if [T lb! 1 T llll 1. fimv
wound yam—Q uozo EOE . $55 398688 Scum
- - _ u a - u . q l- a - - u Om

 

 

84

55.9. 9 885 558 55.8 >
55.9. 9 9.69... 55:... 55.2 >
xtmbm +

xtm.m~ o
U.NN 2w p.395 .53me ESE

xtmhv 9 poo—om Ewan .xtmbm o
xtmbv ou pop—um Ewan 5..th d
xtmbm I
5..th o

0% 2... 3.83. 53me ESE

mound Ema uoza Eot new mound

 

 

 

 

 

EUEEES Eoc won—mam ESE go mom—om :39 co menumeoQEou new oEs owweoum ho batm— mH PSwE
Amxooiv oEF Ava—32¢ oEF
.5 8 . S N, 5 v o v~ 8 E .2 a v o
n n p p p p n b F p p P p b ON
mound “cw—Q uoza E8". . mound _m_o._oEEou Eofi
TTlofinfo 1 u 1 mm
. . - om
_ _ Am . l .. Alli-[IT'- %
m.
.. - mm s
. 5 .0.
£1 1 I mv
1 Ti;
— u q a u u -

 

 

 

Om

85

55.2 8 8555 55% 55.55 >
55.9. 9 8555 55:5 55.2 >
55.55 +

5.5th O
U.NN 55 @885 585.3 ESE

xtmhv O5 825 555.55 .xtmbm o
55.9. 8 55555 5555 55.2 q
xtmbm I
5..th O

0.5. 55 8.855 58me ESE

OOESQ SEE uoza Eot p55 OOESQ EUEEEOO

 

Eot 5855a ESE EO ESCOO 835508 co ouSSEmQEB paw oEfl $5.555 EO Sootm E ESwE
335 25 385 «E:
«N 2 55 N. 5 e o 55 2 5. ~— 5 v o
p P _ p p p — n p p p - p r
. cm
5 5
.‘flflu‘flulllllll. I’lllfiulllll
- f.
1 FfiGUIITIIIIH ETTOIIAT'H .. ow
. 5
1 fl mm
. . . T +llllllllulllnlflllll .
1 lll+|l-Inn“‘”‘u“1ll|n. . 1. ON.
Olllolllnollo l:
1 TITI¢1|IHH®HQHHHfiIIIO C O I 2.

OOESQ SEE uoza EOE

 

 

 

 

8.55. EUEEEOO EOE

 

 

— q a u a q -

11131003 BJI’IJSIOW

86

55.9. 9 8555 558 55.05 >

55.5.. 8 555.2. 558 55.05 c
55.9. 9 9.9.5 55:... 55.2 p

55.9. 8 5559.... 558 55.2 5
5.5.05 + 55.05 I
55.2 o 55.2 O

PNN .5 .5885 55.555. ESE o... .5 .9805 55.55.. ESE

OOESQ 2.53 .0an Eot .055 OOESQ
BUSEEOO Eot 53me ESE 50 53.35 .353 CO OESEEQEOS .055 on... omwuoum mo Sootm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

m. 2:55
Aflooiv SEE. Amy—003V SEC.
.5 8 5. 5. 5 v. 5 ..~ 2 5. N. 5 v o
P . p p p . . . p . . p . . 5 mm.
1 k ..1 l T u. 511.111., . .
1 1 {h- h. |+I up! ill.” 1 Va.
1 I JIDIR llhwl hull ill 1 1mm. M
OIIIOIIIIO o a
1 .. ololllolllllolloll __ O .- 5.... J
. . n
1.9
l I T .01 1h: 1.1 1911' 1" 11m: T Na. M”
. 11.1 4 1+. 4W ml 4 . in... L... 5T 5. «A.
. NE .T 1 . .. - 5..
1 II + lI/I1‘ll/I1I“. Ullllfl .h Ulllllnplllla
l . l I am
OIIO‘IIOIIOITIOIIIIO
. . o O . .
1F. OOESO SEE Sosa EOE . . .

 

 

OOESO EubEEOo EOE . . . .

87

observed. Variations in pH of plum pastes during storage are shown
in Figure 16. pH was stable in all samples during the first weeks of
storage, then increased for most plum pastes at the end of storage,
except the sweetened 25’Brix plum paste made from pilot plant puree.
An increase in pH of 0.05 was observed for pastes made from both
commercial puree (3.50 to 3.55) and from pilot plant puree (3.45 to
3.50). However, the effect of type of puree, heat concentration, and

sugar addition on pH of plum pastes were not significant.

Titratable Acidig; (TA)

Significant decrease (P<0.05) as a function of storage time in TA
was Observed, as shown in Figure 17. However, no significant
difference was found between samples stored at different
temperatures. No processing parameters (i.e. type of puree,
concentration, and sugar addition) showed effect on the stability of
TA.

Correlation coefficients between pH and titratable acidity as well
as total pectin are listed in table 15. The decrease in titratable acidity
and total pectin (mainly water-soluble) of plum pastes was
significantly related to the increases in pH. Similar relation was
Observed by Kanujoso and Luh (1967) who found the increase in
acidity was accompanied by a decrease in pH and an increase in
water-soluble pectin. Rommel et al. (1992 and 1990) also concluded
that titratable acidity and pectin content showed similar trends and a

pattern of change Opposite to pH in fruit juice and wine.

88

55.9. 8 .55.... 5555 55.55 p 55.5.. o. .5555 5555155.05 c

55.9. o. 892. 5555 55.2 > 55.9. 9 55555 55:5 55.2 a
x...m.0m + xtmbm I
55.2 o . 5.5.2 o

PNN .5 .5395 55.5.3 ESE U... .5 .5895 55.5.3 ESE

$.55. Sam—Q .0an EO:

 

 

 

p.25 OOESQ EUEEEOO E01... 535mm ESE 50 In SO OESSMEOQEB US. 2.... owmuoum EO Sootm o. ESwE
382.. 58.. .583. 2....

..~ 2 5. ~. 5 .. c 5 2 5. N. 5 v .o

r . . . . . . p . . . . . Wm
1 1 1 NI.
1 1 1 3.5
1 + I I I I I 1 .
1 1 1 5...».
1 1 1 5....”
1 1 I I I . 5.5 m.
1 1 1 ~55
1 1 .
1 1 1 vmd
1 1 v
1 1 1 mm.m
11 8.5.. 5:53 .23 50E 11 OOESO EUEEEOO EOE .1 55.5

_ u u u a u _ q _ -

 

 

 

 

- u u

89

55.5.. o. .5555 5.555 55.55 p 55.5.. o. .592. 55:5 55.3 o

55.0.. O. 55.5.55 .553. 5.5.2 > 5.5.0.. O. .5525 55:5 .xtm.m~ q
xtmbm 1.. xtmbm I

55.2 0 5.5.2 o

0.2 .5 55.0.5 55.555. ESE o... .5 815.5 55.55.. ESE

55.55. 2.53 .23 E0... 9.5 55.5.. _5.O..OEEOO
Eo... 55.55.. ES... .0 .0685 555.55.. CO m..S.5..wQEm. 95 5E: $550.5 .O .855 C meE

 

 

 

 

 

 

 

 

3.552.. 55:. 3.5.1.2.. 58F
..N ON 5. N. w v o v~ o~ m. N. w v o
. p . . . p _ p . . . . . . V. P
1 .T 1.11 U .1 5..
1 1 1 5..
A 1 .
1 1 1 N.
4 1
1 1 1 5..
1 1 Q.
1 1 ~
1 ul/m/ 1 .5
J {I l N N
555%. .553 .025. EOE 55.5.. .5.u..oEEOo EOE
q a u u u u u —

 

Kuppe alqmenu

. . . . . . M.N

9O

.5>5. 8. .5 50:50....cw.m «1
.5>5. 8m .5 50:50.1..cw.m 1
8.05.. .5.01.. N

10.0.05 5...5.5...... .

 

1.5.0 11mm... 113.0 inwd 110.1... 1150.0 .31de 11mm... ..1.11<..1
1.3.0- 3.? 15...? 113.01 112.01 113.0. 11.5.9 11.5.0- 5.1.1:.
*QVdn Nm.O| RN61. «*m©.On «aluhd- 13.0501 «*mhfivn «*whAvu H<FaIQ
.811...“ I551... 5.1.55 3.11911 355151.20
0. 05.005 18?... 0. 053.5 .5mnm

xtmbm .3.th xtmbm x..m.m~ 5.5.0” .3.th xtmbm 5.th

 

55...... .85... .2... 80... 55.3.. .5.0.58800 80....

 

55.3.. .85... .2... 80.... .85 55...... 30.58800 80...
5.058 1.5.55. 83... .0 mm .85 8.05.. .5.0. 1.3.0.05 535.58.. .0 51.85.05.500 82.5.5800 m. 5.05...

91

Hunter 'L' Value

Figure 18 shows changes in Hunter 'L' (lightness index) values of
plum pastes during storage. For pastes from commercial puree stored
at 22°C, increase in Hunter 'L' values ranged from 0.99 to 1.68.
Changes in Hunter 'L' values ranged from 0.09 to -0.09 at the end of
storage was deteced in samples from commercial puree stored at 4°C.
However, the Hunter 'L' values of samples from pilot plant puree kept
decreasing during the 24 weeks of storage, with higher rate of change
for samples stored at 4°C. Canellas et al. (1993) observed no browning
during the first 3 months of storage in fruit and vegetable products.
They indicated that after 3 months of storage, the browning began.
This is similar to the results from pastes made from commercial
puree. Increasing browning as a function of storage time, especially
over a long time, was observed in raisin (Canellas et al., 1993), citrus
fruit products (Handwerk and Coleman, 1988) and carrot (Baloch et
al., 1973), which was confirmed in this study, too.

Hunter 'L' values increased with degradation of T ACYs and
decreased with browning or polymerization reactions (Rommel, 1992).
For plum pastes made from commercial puree, high negative
correlation of Hunter 'L' with T ACYs (Table 17) and Hunter 'a' values
(Table 16) indicated that lightness in color was related to degradation
of T ACYs. Negative correlation of Hunter 'L' values and chroma
(Table 16) indicated polymerization reactions occurred during storage,
however, the extent of browning was less than degradation of T ACYs
resulting in lightening of plum pastes. For plum pastes made from
pilot plant puree, higher positive correlation of Hunter 'L' values
(Table 16) with chroma than T ACYs (Table 17) and Hunter 'a' values

(Table 16) implied that polymerization reactions overpowered

92

5.5.5.. o. 55555 .553. .x...m.0m > 5.5.5.. 9 555.55 1.5538505 0

5.5.0.. o. 55555 .553. 5.5.5. 5 5.5.0.. o. .5555 .553 5.5.5. 4
1 x..m.0m ... x..m.0m I

x..m.m~ o x..m.m~ o
U.NN .5 05.0... 55.55.. 8:... o... .5 05.0.. 55.55.. 8:...

55.3.. .853 .23 80... .585 55.0..
.5.0.58800 80.. 55.55.. 833 .0 .1.. .583. :0 5.5.5.5385. .85 58.. 5w5.0.5 .0 .05.... m. 5.35....

 

. 382.. 5.51. 38>... E...
55 55 5. 5. 5 v 0 55 55 5. 5. 5 v 0
p n p - p p - p h p p p p p
55.3.. .253 .23 80 .11. . 55.5.. .5.0.58800 80... m

I:
1. ]l+ .-

. ,1 . 1..
1 1 3

[mp

 

 

,1, 131111111;

 

 

 

 

93

.5>5. 8. .5 5.852.858 .3.
.5>5. 8m .5 50850....8w.m «

 

 

5.4.00 .0 3.00.0 5.10 5.0 .155 v.0 5550.0: Vm.0- 5.1m m.0.. .3. H 5.0. NEOHSU
5500.0: «:10 m.0n «.th 0.0: «.5090- 5*Hw.0 .3. H 5.0 55Vw.0 5*m0.0 2mg USE
.3. H 0.0.. .3. H m.0n 5.4mm .0: *«N0.0n 5*mw.0 55.5w .0 5500.0 5.4.00.0 b. hum—GD:
*5Mw.0 «5.00.0 5.5.05.0 5.50.0.0 $505.0- *5H0.0u «.5M5.0u 5500.0. .5... .quDI
xtmhv 5.5.0.. x..m.mv .8.me 52.585.05.580
0. 05005 8w... 0. 05005 .5585
5.9% x..m.w~ xtmhm x..m.wm x..m.dm xtmhm xtmbm .8.th

 

55.83 .853 .23 80.3

 

55.83 8.0.5880. 80.3

 

55.83 .853 .23 085 55.83 8.5.5880. 80.. 5058 55.553

883 .0 w58.5> EDD .38.... .550 5.2. m58.5> a. .388... .0 5.85.0550. 82.5.5800 o. 535...

.5>5. 8. .5 55855...8w.m t.
.5>5. 8m .5 558550.8m.m 5

 

94

.3de
333.0.
iwmd.
3.03.0
1.00. .-

580.80
5.w85 58m
.0. .888...
.5. .383.

8. .523:

 

0. 05005 .5w85 0. 05005 .5m8m

 

 

 

55.83 .853 .23 80.3 55.83 .5.5.58805 80.3

52.25.55.580

 

55.83 .853 .23 80.. 085 55.83 .5.5.58805 80.. 5058 55.553
88.3 .0 58.85.508.85 .5.0. 085 m58.5> ECU .888: 8553.50 5.85.5558 82.25.00 5. 5.05...

95

degradation of T ACYs. We could assume that the browning effect
observed was mainly nonenzymatic since no PPO activity was detected
in any of the samples at the beginning of storage. The number of
potential condensation reactions which could contribute to pigment
polymerization and then browning are numerous: ACY
copigmentation, ACY-phenolic condensation, Maillard reaction and
ascorbic acid degradation all are possible (O'Brien, 1989; Makakis,
1982).

Wrolstad et al. (1990) indicated that sugar has protective effect
on color retention during storage. The positive influence of sucrose
could be steric, with sucrose serving as a diluent, interfering with
condensation reactions. However, no significant protective effect of

sugar was found in this study.

Hunter 'a' Value

Figure 19 shows the effect of storage conditions on Hunter 'a'
values, which represent redness. As storage time increased, the Hunter
'a' values of plum pastes decreased, which means a reduction in
redness. The rate of change significantly increased (P<0.05) with
storage temperature, which is similar to change pattern of T ACYs.
These results indicated that as expected low temperature storage was
better for color retention of plum pastes. However, sugar addition did
not show obvious protective effect on the Hunter 'a' values of plum

pastes.

Hunter 'b' Value

The effects of storage time and temperature on Hunter 'b'

(yellowness index) values of plum pastes are shown in Figure 20. The

96.

5.5.? 9 800.... .553 .xtmbm p
xtmbv 8 855.... .558 288.2 >
88.8 +

5.9mm 0
U.NN .5 05.0.. 55.553 88.3

5.5.? 8 8555 .558 2.5.8 o
58.9. 8 8555 .853 58.2 a
xtmbm _.

8.5.3 o
0... .5 05.0.. 55.553 88:.

55.83 .883 8.380.. 085 55.83

 

 

 

 

 

_5_0.58800 80... 55.553 88—3 .30 .5. .5.88I 80 5.8.5.5385. 085 583. 5m5.o.m 00 .05.:m 0H 5.89...
383. as: 38;. 8.:

v~ ON 0.. N. w v o v~ cu 0. ~_. 0 v o

. p . . . . A . . . . . p _ . O—
1 1 1 ~—
1 O o v/ I. l V—
- . . ./ 1. mm. H
L /0 I 0’ n
1 v 1.1/ I L I m— u

. ’7 ./ . . m
l O O 1‘ 1 O I ON JO
1 C O O) . 1 C v e.-
1 o // 1 o .. NN
1 . b 1 v
1 1 .. v~
A . 1 1
1 1 1 mm
. 55.83 .823 .0:3 80.3 . 55.83 30.58800 80.3 .
0
q q - u u a -

 

 

u u u q u q _

QN

97

xtmhv 8 82.5 .55... .8505 p
.2.me 0. 05005 .5585 5....th b
xtmbm +

.8.th 0

0.2 .5 05.0.5 55.553 88E

.8.me 0. 05005 .59... .xtmbm o
.8.me 0. 05005 .5w85 5.9mm 0
xtmbm I
8.9mm o

0.8 .5 05.0.5 55.553 823

55.83 .853 .023 80.. 085 55.83

_5_0.58800 80... 55.553 823 .0 b. .5.88I 80 5.8.5.5385. 085 58.. 5w5.0.5 .0 .05tm ON 5.89.

 

 

3830 ms... 333. 2::
em o.~ 5.. 5.. w v v... .05 5. N. 5 v o
. — . p n n p _ p
. 5.5.83 .853 .023 80.3 55.83 30.58800 80.3 5
. - .
w m

 

 

 

1:

 

 

,q, JanunH

: z - b \O r. MP

 

1m—

 

 

98

Hunter 'b' values of all plum pastes kept increasing during storage
time. The retarding effect of storage temperature was significant
(P<0.05) on plum pastes from commercial puree, however, not on
plum pastes from pilot plant puree. Neither source of pastes,
concentration of pastes, or sugar addition had obvious interaction

with storage time and temperature.

Hue Angle

Influence of storage time as well as temperature on hue angle of
plum pastes are shown in Figure 21. As the storage time increased, the
hue angle of plum pastes increased, with a significantly higher
increasing rate of samples stored at 22°C (P<0.05). Type of purees,
concentration of pastes, or sugar addition had no obvious interaction

with storage time and temperature.

Chroma

All paste samples showed a similar decreasing pattern, which was
significantly influenced (P<0.0S) by source of pastes, storage
temperature and time (Figure 22) , with higher decreasing rate for
samples from pilot plant puree. Rommel et al. (1992) reported that
chroma decreased with increasing percentage of polymeric color and
browning, which was confirmed by high positive relation between
Hunter 'L' values and chroma (Table 16) of pastes made from pilot

plant puree.

Total Anthocyanins (T ACYs)
Figure 23 shows the changes in T ACYs of plum pastes due to

storage conditions. The results indicated that room temperature

99

5.3.9. 0. 05005 .595 .x..m.0m 0
8.5.9. o. 82.5 .55... 5.5.2 4
x..m.0m I
x..m.m~ 0

0... .5 05.0.5 55.553 88.3

x..m.mw 0. 05005 .5w85 .x..m.0m b
x..m.ov 0. 05005 .5m85 .x...m.m~ D
x..m.0m +

x..m.m~ o

0.NN .5 05.0.5 55.553 88.3

55.83 .85.3 .0..3 80.. 085 55.83

 

 

8.0.5880. 80.. 55.553 88.3 .0 5.w85 58.. 8o 5.8.5.5385. 085 58.. 5m5.0.5 .0 35.5. .N 5.85....
38;. up... 382.. 2....
v.5 o.~ 5.. ~.. w v o 5.5 8 5. ~. 5 e o

n p h p p p p b h .
5...

. 55.83 .85.3 .0..3 80.... 55.83 .5.0.58800 80.". .
. 1 - 55.
.. - 5...

.3
1n
018% an};

 

 

 

 

 

100

5.5.5.. o. 55555 .55.... 5.8.5.05 >
585.05 8 55505 .5555 5.85.55 >
V5.5.05 +

x..m.m~ 0
0km .5 05.0.5 55.553 88.3

5.5.55 8 5555.... .55... 55.5.05 0
x..m.ov 0. 05005 .5w85 .x..m.m~ 0
xtmbm I
. x..m.m~ o

0... .5 05.0.5 55.553 88.3

55.83 .85.3 .0..3 80.. 085 55.83

 

.5.0.58800 80.. 55.553 88.3 .0 580.80 80 5.8.5.5385. 085 58.. 5w5.o.5 .0 .05..m. mm 5.8m.3
3.83. as... 382.. 55F
55 05 5. N. 5 v v~ 55 5. ~. 5 v 0
p p b - p p n n n _ b — — VP
P 5" II A w
l/ 1 I mp
1. «ll/l //14J l .1. mp
1 I 1 r
1 1 1 05
1 1 1 55
L O/Q\\O/P/.ll. 4 v
1 1 1 vm
1.. C l r wN
1 .
1 1 . 1 55
55.83 .85.3 .0..3 80.3 1 55.83 .5.0.58800 80.3 .

 

 

 

 

 

 

 

- a u u - u

among)

101

5.5.5.5 o. 55555 .553. 55.5.55 >
5.5.55 8 552.5 .55:5 55.5.55 >
8.5.8 +

8.5.55 0

0km .5 05.0.5 55.553 88.3

55.83 .85.3 .0..3 80.. 085 55.83 .5.0.58800
80.. 55.553 88.3 .0 58.85.308.85 .5.0. 80 5.8.5.5385. 085 58.. 5w5.o.5 .0 .05..m

3552.. 55F
55 55 5 . N . 5 v

5.9m.» 0. 05005 .5585 .x..m.0m 0
5.5.0.. 0. 05005 .5585 58.5.2. 0
x..m.0m I
x..m.m~ o

0... .5 05.0.5 55.553 88.3

38;. 2....
55 55 5 . ~ . 5 5

n - b b n .

mm 5.35..

 

.3 80.3

 

55.83 .85.3 .0.
_ —

    

 

.15
.5.
.5.
.1:
.5.
.5.
.o~

 

 

-

(sgan mm 3001 /3u.1) suguexaoqiue r2101,

102

storage had a tremendous influence (P<0.01) on T ACYs. During the
first lZ-week storage period, all plum pastes stored at 22°C showed
much higher decreasing rate of T ACYs (P<0.01). Then the rate slowed
down to the rate similar to that of plum pastes stored at 4°C. Similar
results for higher retention of T ACYs in samples stored at refrigerated
temperature than those stored at nonrefrigerated temperature were
also observed in blackberry juice and wine (Rommel et al., 1992), in
raspberry juice and wine (Rommel et al., 1990), and in grape pigments
(Palamidis and Markakis, 1975). Protective effect of sugar on ACY
pigment of strawberries during storage as reported by Wrolstad et al.
(1990) was not significant in this study.

Table 17 shows the correlation coefficients between T ACYs and
Hunter CDM values. High positive correlations of both Hunter 'a'
values and hue angle with T ACYs confirmed that ACY pigments are
the major color source of plums (Timberlake and Bridle, 1982) and
appear as red in acidic medium (like plum paste) (Brouillard, 1982).
ACY pigments may be degraded to colorless components or may
undergo polymerization (Markakis, 1982). Negative correlation of
Hunter 'L' and Hunter 'b' values and T ACYs implied degradation of
ACY pigments to colorless components. High positive correlation of T
ACYs with chroma indicated that loss of T ACYs also contributed to

polymerization.

Pectin Content

Figure 24 shows the changes in total pectin during storage. The
changes in total pectin were significantly influenced (P<0.05) by
storage time and type of purees, but not by temperature, sugar or

concentration. Plum pastes from pilot plant puree showed higher

 

 

103

 

5...? 9 8.0.0.... 5.8 .x..m.om > 5...? o. 82.... .59.. 5.0.8 o

5.99. o. 00.00.. 3.8 5.0.2 > 5.0.3 o. 800... .88 .5.0.... a
55.8 + 55.8 ._

x..m.m~ o 5.8mm o

Pmm .0 00.05 8.23 82. U... .0 00.0.. 003.00 82.

00.30 .520 .020 80.. .080 00.50
30.08800 80.. 3.000 820 .o 5.000 8.0. :0 0.5.0.0080. 9.0 08.. 0920.... .o .00.... 0N 0.00.".

 

 

1 L4 1 A l n 1

00.2. .803 3:0 80.".

0.0.003. 08:. A3003. 08F
v.~ ow 0. N. w v o v~ ow @— . N. w v o

n p p p p _ n n . n n p n M.
. ... g - ... m
1 1 w .. m:
1 vi m d
.. .. . 3
. . I 0. m.
1 1 a U
T N. )
.. . m

I m.

.

- m
m
19
O.
m.
m...

 

00.30 30.08800 80....

q q u. q u u u q - - N.F

 

 

 

104

degradation rate during the first 12-week storage than those from
commercial puree (P<0.05). After that, only slight changes in total
pectin content of plum pastes were observed. Pectin degradation
accompanied with texture loss during storage has been observed in a
number of fruit products (Reid et al., 1986; Kanujoso and Luh, 1967).
However, parallel decreasing pattern of total pectin and consistency

was not observed in this study.

Rheological Properties

Storage conditions had significant effect (P<0.05) on apparent
viscosity (na), consistency index (K), and flow behavior index (n) of
pastes made from commercial puree (Figure 25, 26 and 27), however,
the tendency of change was not constant. No significant influence of
storage on rheological properties of plum pastes made from pilot
plant puree was detected. Samples from pilot plant puree were better
homogenized than those from commercial puree. Both particle size
and air bubbles had interference with rheological parameters. Alviar
and Reid (1990) reported that for high consistency samples loading is
quite difficult without incorporation of air bubbles, which affect the
flow behavior of fluids. However, during actual processing of pastes,
the presence of air bubbles can be expected, so the K and n values that
were obtained through this test may be more practical than if they

had been obtained for samples which were degassified.

Microbial Analysis
Appendices III to V list the results of standard plate count,

coliform count and yeast and mold count of plum pastes. During 24

weeks of storage, only 3 samples had yeast and mold contamination.

105

5...? o. 0%... 3.... .5...o. > 5...? o. 0000... a...” 5...... o

5....00 o. 000.00 .003. 05.0.3 > 5.0.0.. 0. 000.00 .003. 5.8mm 4
xtmbm + , xtmbm I

5.9mm o x..m.mN O

UoNN a“ @0095 wmuqu 83—h UL. um Uthum mwuwmfl ESE

00.30 80.0 .0:0 80.. .080 00.30 30.08800
80.. .0300 83.0 .0 2.5 3.80.? 3.0.0000 :0 0.3.0.0080. .000 08.. 000.0... .0 .00..m 3 0.30..

332.. 2.... Es... 2.:
vw 0N m P N— w v o VN ON 2 N F w v o

p p n b p n n p -

 

- n p p p m
00.30 30.08800 80.0

.L
t.
1
CO

.
de ()9 12 (3h) [figsoasgA nuamddv

 

00.30 80.0 .020 80.0

n u - - _ -

 

 

 

 

 

106

5.0.0.... 0. 00000 .003. .x..0.0.m > 5.0.0.. 0. 000.00 .003. 00.0.00 0

x00.00 o. 00000 .003. 00.0.0 0 > 5.0.0... o. 00000 .003. 00.0.0 0 4
x00.00 + x00.00 I

x00.00 0 00.0.00 0

0.00 .0 00.0.. .0..00 83.0 o... .0 00.0.. .0..00 83.0

00.30 80.0 .0..0 80.. 0:0 00.30 .0.0.08800
80.. .0..00 83.0 .o 0: x00:. 500....000 :0 0.3.0.0080. 080 08.. 000.9. .0 .00..0 00 0.30.0

38;. as: 38.5. as:
.0 o. S N. . . v o v~ 8 8 ~— . v o

h p n n p p n p n -

 

 

. . . m N
flail ._ UOESQ _NmU.~UEEOU EOhnm ..

1 .. 00—

L I v
1 ImNF

.. . 10v—

 

00.30 2.0.0 .020 80....

 

 

- q - u u - - - u u - q u u

()l) XBPU! Kaualsgsuog

107

5...? o. 00.0.0 0.... 5...... >
5...? o. 0000.... 0.3 5..... >
x00.00 +

5...... o

0.00 .0 00.0.. .0..00 83.0

8.0.00 0. 00000 .003. 5.0.00 0
V0.0.00 0. 00000.003. 00.0.0 0 4
x€0.00 I
V0.0.00 o

0.0 .0 00.0.. .0..00 83.0

00.30 80.0 .020 80.. 080 00.30 .0.0.08800

80.. .0..00 83.0 .0 .5 .808. .o.>0~.0n 30: 80 0.3.0.0080. 080 08.. 000.8. .0 .00..0

33.... as:
00 ON 0 F N _. w v

— p p — _ —

.N 0......

 

00.30 80.0 .020 80.0

 

 

 

 

 

$855...

0..

C. H
o
M

I... m
w
m.

.00. o
J
m.

0.. W
x

.0. m

00.30 .0.0.08800 80.0
.

 

 

. . _ _ _ NV.

108

This contamination may have happened during preparing samples for
measurement. Since most of the plum pastes contained no live
microorganisms from 0 to 24 weeks of storage, it can be assumed that
they indicated that microorganisms were destroyed during processing

procedure and products were not contaminated during storage.

Sensory Evaluation

Sensory tests were conducted at 0 and 24 weeks of storage. Before
determining effect of storage time and temperature on sensory quality
of plum pastes made from pilot plant puree, the interference of
processing parameters in the effect of storage conditions were
measured using 2—way analysis of variance. Table 18 shows the p
values of ANOVA measuring the difference between storage times and
temperatures for sensory attributes and these results indicate that the
interference of concentration and sugar addition were not significant
at 5% level.

The effect of storage time and temperature on sensory
characteristics are shown in Table 19. Storage for 24 weeks at 4°C
significantly decreased (P<0.05) color of unsweetened and sweetened
30°Brix pastes, acidity of pastes except 25°Brix paste, sweetness of
pastes, and overall acceptance of all pastes except 25°Brix paste.
Except for 25°Brix paste, thickness also increased significantly (P<0.01)
for all pastes.

However, the results in part II of Table 19 show that most sensory
characteristics were not significantly affected by 24 weeks of storage at
22°C, except for increased color and acidity of 30°Brix paste and

decreased thickness of sweetened 30°Brix paste.

109

Table 18 P values of analysis of variance for difference in sensory
attributes of pastes made from pilot plant puree between
different storage conditions

 

 

 

 

Sensory Attributes
Source Color Acidity Sweetness Consistency Flavor Overall
W
I
A 0.377 0.73 1 0.446 0.522 0.955 0.288
B 0.069 0. 100 0.868 0.898 0.766 0.934
AxB 0.076 0.056 0.427 0.553 0.441 0.063
11
A 0.600 0.620 0.494 0.356 0.786 0.548
B 0.283 0.092 0.9 1 0 0.690 0.983 0.479
AxB 0.592 0.593 0.787 0.660 0.335 0.994
111
A 0.720 0.897 0.97 1 0.789 0.741 0.658
B 0.455 0.101 0.965 0.794 0.752 0.514
AxB 0.242 0.180 0.628 0.317 0.832 0.061

 

1 Difference between the beginning and the end of storage at 4°C
11 Difference between the beginning and the end of storage at 22°C
111 Difference at the end of storage between 4°C and 22°C storage
A Heat concentration

B Sugar addition

110

Table 19 Values of t-test of mean scores of difference in sensory
attributes of plum pastes made from pilot plant puree
on sensory evaluation between storage conditions

 

Heat concentration Sugar addition

 

Treatment/ 25°Brix 30°Brix 2 5°Brix 30°Brix
to to
Sensory attributes 40°Brix 45°Brix
1
Color 0.244 -5.088** 0.339 -2.131*
Acidity 1 .340 -3.1 95** 4.1 20** -7.357**
Sweetness -3.976** -3.91 1** -2.716** -5.83 1**
Consistency -1 .242 3.71 7** 2.690** 2.783**
Flavor -0.394 -1.828 -1.346 -0.31 1
Overall acceptance -6.3 7 1 ** —0.509 -2.473* -4.075**
11
Color 1.222 3.347** 0.142 0.122
Acidity 1 .923 3.986“ 0.385 0.459
Sweetness -1 .447 -0.61 3 -1 .759 0.1 50
Consistency 0.400 -0.569 0.480 -2.248*
Flavor -0.773 1.703 1 .202 0.1 88
Overall acceptance 0.722 -0.466 —0.679 -1.902
111
Color -1 .283 -1 .779 -0.435 -2.064*
Acidity -3.062** -0.634 -3.667** -6.61 8**
Sweetness -5.240** -4.343** -4.359** —5.404**
Consistency -1 .593 -3.064** -3.078** -0.53 1
Flavor -1 . 1 76 -0.090 -0.1 1 9 -0. 1 1 9
Overall acceptance 5.65 1 ** 0.996 -3. 1 92** 6.069**

 

1. Difference between the beginning and the end of storage at 4°C
11. Difference between the beginning and the end of storage at 22°C
III. Difference at the end of storage between 4°C and 22°C storage

* Significance at 5% level
** Significance at 1% level

111

Effect of storage temperature is listed in part III of Table 19. After
24 weeks of storage, plum pastes stored at 22°C had significantly
(P<0.05) lighter color for sweetened 30°Brix paste, lower acidity for all
pastes except 30°Brix paste, lower sweetness for all pastes, and lower
thickness for pastes except 25°Brix paste, as compared to pastes stored
at 4°C. 25‘Brix and sweetened 30°Brix pastes stored at 22°C had
significantly higher overall acceptance (P<0.01) as compared to
samples stored at 4°C. Sweetened 25°Brix paste stored at 4°C had
significantly higher overall acceptance (P<0.01) .

In conclusion from the sensory evaluation, storage time decreased
quality and overall acceptance of plum pastes, but storage
temperature showed variable effect. However, those results that lower
titratable acidity, lower T ACY s, darker color, and constant rheological
properties determined by objective analysis were not confirmed by
subjective evaluation. Less sensitive results from sensory evaluation
was also observed for plum juice (Arnold, 1992) and canned tomato
paste (Eckerle et al., 1984).

«gm-l

 

SUMMARY AND CONCLUSIONS

In this study, two batches of Stanley plums (different quality)
were processed to purees using similar procedure. Commercial puree
was processed using substandard fruit by Cherry Central Inc. (Traverse
City, MI). Pilot plant puree was processed using standard quality fruit
in our pilot plant. Both purees were heat concentrated to 25°Brix and
30°Brix in our pilot plant, respectively. Sucrose was added to give a
15°Brix increase. Samples were stored at refrigerated and
nonrefrigerated temperatures in the dark for up to 24 weeks.

Physical and chemical characteristics including soluble solids,
total solids, moisture content, water activity, PPO activity, Hunter
color values, total anthocyanins, pectin content, rheological properties
and microbial content were measured. Sensory evaluation was also
conducted for plum pastes from pilot plant puree.

Comparing quality of two batches of purees, pilot plant puree was
significantly higher in soluble solids, titratable acidity, Hunter 'a'
value, chroma, total anthocyanins, total pectin, protopectin, apparent
viscosity (na), consistency index (K), and flow behavior index (n).
However, significantly higher moisture content and hue angle were
found in commercial puree. No PPO activity was detected in any of
the puree samples. Only yeasts and molds were detected in pilot
plant puree.

Heat concentration resulted in component degradation, such as
titratable acidity, total anthocyanins and pectin content, as well as

concentration of these components. On the other hand, sugar

112

 

113

addition showed dilution effect on compositions. Both of heat
concentration and sugar addition decreased lightness of color.
Rheological properties were significantly increased by heat
concentration but not by sugar addition. The extent of influence of
these characteristics was a function of heat processing. pH values were
constant during processing procedure. Sensory evaluation indicated
that plum pastes from pilot plant puree could be characterized by
acidity, sweetness, and consistency sensation, but the preference could
be adequately predicted by flavor and color under suitable Brix/ acid
ratio.

As storage time increased, concentration of titratable acidity,
total anthocyanins and total pectin decreased. Among them, only
higher degradation rate in total anthocyanins was found in samples
stored at nonrefrigerated temperature. Decrease in consistency as a
function of storage conditions was not found. Comparing color of
plum pastes stored at different temperatures showed that the
refrigerated samples were of higher quality than nonrefrigerated
samples.

Further areas of research could be done in following areas:

1. Application of vacuum equipment to heat concentration
processing to shorten time and lower heating temperature, and
hence to minimize negative characteristics caused by heat, such as
browning and degradation of anthocyanins and pectin.

2. Variation of pastes with other ingredients, such as protein, other
fruit pastes, or different amount of sugar addition.

3. Utilization of substandard fruit to make acceptable product using

blends of higher quality fruit.

114

4. Development of the application of plum pastes in other products,
such as candy fillings, reconstituted juice, ingredients in bakery,
etc.

5. Investigation of the contribution of components to consistency of
pastes.

6. Study of changes in anthocyanin composition during processing
and storage and its relationship to Hunter color values. Once the
relation is set up, the anthocyanin stability may be monitored by

Hunter color values, an easier measurement.

 

BIBLIOGRAPHY

BIBLIOGRAPHY

Adams, J.B. 1973. Thermal degradation of anthocyanins with
particular reference to the 3-glycoside of cyanidin I. In acidified
aqueous solution at 100°C. J. Sci. Food Agric. 24:747.

Ahn, S.Y. 1973. Identification of the anthocyanins in plums.
Han'guk Nonghwahakhoe Chi 16:53. [In Chem. Abstr. (1974)
80:94348w.]

Alviar, M.S.B., and Reid, D.S. 1990. Determination of rheological
behavior of tomato concentrates using back extrusion. J. Food Sci.
55:554.

Anonymous. 1988. 1988 Michigan food and fiber facts. Michigan
Department of Agriculture Press and Public Affairs Division.

Anonymous. 1987. Analyzing appearance by measurements. Hunter
Association Laboratory, Inc., Reston, VA.

Anonymous. 1977. United States standard for grades of tomato
paste. U.S.D.A. Agric. Food Safety Quality Service.

Arnold, J.F. 1992. Inactivation of polyphenol oxidase in Stanley
plum juice using an immobilized protease enzyme. Sc. D. thesis,
Michigan State Univ., East Lansing, MI.

Ashoor, S.H., and Zent, J.B. 1984. Maillard browning of common
amino acids and sugars. J. Food Sci. 49:1206.

Baloch, A.K., Buckle, K.A., and Edwards, R.A. 1973. Measurement of
non-enzymic browning of dehydrated carrot. J. Sci. Food Agric.
24:389.

Bash, W.D., Dalmasso, J.P., and Gould, W.A. 1984. The addition of
sugar to tomato paste. Food Processing and Technol. 1984: A
summary of research. Ohio Agri. Res. Develop. Center, The Ohio State
Univ., Wooster, Ohio.

115

 

116

Behall, K., and Reiser, S. 1986. Effects of pectin on human
metabolism. Ch. 19. In "Chemistry and Function of Pectins," M.L.
Fishman and J.J. Joseph (Ed.), p. 249. American Chemical Society,
Washington, DC.

BeMiller, J.N. 1986. A introduction to pectins: structure and
properties. Ch. 1. In "Chemistry and Function of Pectins." M.L.

Fishman; J.J. Jen (Ed.), p. 1. American Chemical Society,
Washington, DC.

Bolin, H.R., and Huxsoll, CC. 1989. Storage stability of minimally
processed fruit. J Food Preces. preser. 13:281.

Bolton, R.P., M.R.C.P., M.A., Heaton, K.W., F.R.C.P., M.D., and
Burrroughs, L.F. 1981. The role of dietary fiber in satiety, glucose, and
insulin: studies with fruit and fruit juice. Am. J. Clin. Nutr. 34:21 1.

Bontovits, L. 1981. The effect of processing technologies on colour
changes in tomato. Acta Aliment. 10:215.

Brouillard, R., 1982. Chemical structure of anthocyanins. Ch. 1. In
"Anthocyanins as Food Colors," P. Markakis (Ed.), p. 1. Academic
Press, Inc.,, New York, NY.

Brouillard, R., and Dubois, J.E. 1977. Mechanism of the structural

transformation of anthocyanin in acidic media. J. Am. Chem. Soc.
99:1359.

Brouillard, R., and Delaporte, B. 1977. Chemistry of anthocyanin
pigments. 2. Kinetic and thermodynamic study of proton transfer,
hydration, and tautomeric reactions of malvidin 3—glucoside. J. Am.
Chem. Soc. 99:8461.

Canellas, J., Rossello, C., Simal, S., Soler, L., and Mulet, A. 1993.
Storage conditions affect quality of raisins. J. Food Sci. 58:805.

Cara, L., Dubois, C., Borel, P., Armand, M., Senft, M., Portugal, H., Pauli,
A.M., Bernard, RM, and Lairon, D. 1992. Effects of oat bran, rice
bran, wheat fiber, and wheat germ on postprandial lipemia in healthy
adults. Am. J. Clin. Nutr. 55:81.

Cash, J.N., Sistrunk, W.A., and Stutte, C.A. 1976. Characteristics of

Concored grape polyphenoloxidase involved in juice color lass. J.
Food Sci. 41:1398.

 

117

Castell-Perez, M.E. 1990. Evaluating the rheological properties of
power-law fluids using mixer viscometry. Dissertation, Michigan State
University.

Castell-Perez, M.E., Steffe, J.F., and Morgan, R.G. 1987. Adaptation of
a Brookfield (HBTD) viscometer for mixer viscometry studies. J.
Texture Stud. 18:359.

Chang, TS. 1993. Optimization of processing parameters and study
of the physical-chemical characteristics of plum juice. Sc. D. thesis.
Michigan State Univ., East Lansing, MI.

Cuzzoni, M.T., Stoppini, G., and Gazzani, G. 1989. Effect of storage on
mutagenicity, absorbance and content of furfural in the ribose-lysine
Maillard system. Food. Chem. Toxic. 27:209.

DaDamio, P.A., and Thompson, DB. 1992. Mushroom (Agaricus

bisporus), its polyphenoloxidase, and polyphenolics affect in vitro iron
availability. J. Food Sci. 57:458.

Daravingas, C., and Cain, R.F. 1968. Thermal degradation of black

raspberry anthocyanin pigments in model systems. J. Food Sci. 33:
138.

Eckerle, J.R., Harvey, CD, and Chen, TS. 1984. Life cycle of canned
tomato paste: correlation between sensory and instrumental testing
methods. J. Food Sci. 49:1 188.

Eichner, K., and Karel, M. 1972. The influence of water content and
water activity on the sugar-amino browning reaction in model systems
under various conditions. J. Agric. Food Chem. 20:218.

Elliott, M.J. 1983. Studies on the maturity, postharvest physiology

and canning of 'Stanley' plums. Sc. D. thesis, Michigan State Univ.,
East Lansing, MI.

Espie, M. 1991. Michigan agricultural statistics 1990. Michigan
Agricultural Statistics Service, Lansing, MI.

Espie, M. 1992. Michigan agricultural statistics 1991. Michigan
Agricultural Statistics Service, Lansing, MI.

 

 

118

Exama, A., and Lacroix, C. 1989a. Development of a high protein fruit
paste. 1. Influence of some process parameters. Sci. des Aliments
9(2):285. [ In Food Sci. Technol. Abstr. (1989) 21(12):12J75.]

Exama, A., and Lacroix, C. 1989b. Development of a high protein fruit
paste. 11. Storage stability. Sci. des Aliments 9(2):285. [ In Food Sci.
Technol. Abstr. (1989) 21(12):12J76.]

Fishman, M.L., Gross, K.C., Gillespie, D.T., and Sondey, S.M. 1989.
Macromolecular components of tomato fruit pectin. Archives of
Biochemistry and Biophysics. 274:179.

Ford, E.W., and Steffe, J.F. 1986. Quantifying thixotropy in starch-
thickened, strained apricots using mixer viscometry techniques. J.
Texture Stud. 17:71.

Francis, F.J. 1989. Food colorants : anthocyanins. CRC Critical Rev.
Food Sci. Nutri. 28:273.

Francis, F.J. 1982. Analysis of anthocyanins. Ch. 7. In "Anthocyanins
as food colors," P. Markakis (Ed.) p.182. Academic Press, Inc.,, New
York, NY.

Friedman, M. and Molnar-Perl, I. 1990. Inhibition of browning by

sulfur amino acids. 1. Heated amino acid-glucose systems. J. Agric.
Food Chem. 38:1642.

Fujita, S., Tono, T., and Kawahara, H. 1991. Purification and
properties of polyphenol oxidase in head lettuce (Lactuca sativa). J.
Sci. Food Agric. 55:643.

Fuleki, T.; and Francis, F.J. 1968a. Quantitative methods for
anthocyanins. 1. Extraction and determination of total anthocyanin
in cranberries. J. Food Sci. 33:72.

Fuleki, T.; and Francis, F.J. 1968b. Quantitative methods for
anthocyanins. 2. Determination of total anthocyanin and degradation
index for cranberry juice. J. Food Sci. 33:78.

Goose, P.G., A.R.I.C., A.I.L.(It), and Binsted, R. 1964. "Tomato Paste,
Puree, Juice and Powder," Food Trade Press Ltd., London.

Grommeck, R., and Markakis, P. 1964. The effect of peroxidase on
anthocyanin pigments. J. Food Sci. 29:53.

 

119

Gross, J. 1987. Anthocyanins. In "Pigments in Fruits," p.74.
Academic Press, Inc.,, London.

Guariguata, C., Barreiro, J.A., and Guariguata, G. 1979. Analysis of
continuous sterilization processes for Bingham Plastic fluids in
laminar flow. J. Food Sci. 44:905.

Gubenkova, A.A., Somov, V.K., and Shenson, V.A. 1988.
Physicochemical properties of pectin and pectin-based solution and
jellies. Pishchevaya Poromyshlennost', USSR 5: 13. [In Food Sci.
Technol. Abstr. (1990) 22(3): 3T18.]

Gur, A. 1986. Plum. In "CRC Handbook of Fruit Set and
Development," S.P. Monselise (Ed.), P. 401. CRC Press Inc., Boca Raton,
FL.

Handwerk, R.L., and Coleman, R.L. 1988. Approaches to the citrus
browning problem. A review. J. Agric. Food Chem. 36:231.

Helak, B., Spengler, K., Tressl, R., Rewicki, D. 1989. Formation of 7H-

cyclopenta[b]pyridin-7-ones as proline-specific Maillard products. J.
Agric. Food Chem. 37:400.

Hodge, J.E. 1953. Dehydrated foods: chemistry of browning reactions
in model systems. J. Agric. Food Chem. 1:928.

Huang, H.T. 1955. Decolorization of anthocyanins by fungal
enzymes. J. Agric. Food Chem. 3:141.

Huang, H.T. 1956. The kinetics of the decolorization of anthocyanins
by fungal enzymes. J. Am. Chem. Soc. 78:2390.

Ishikura, N. 1975. A survey of anthocyanins in fruits of some
angiosperms, 1. Bot. Mag. Tokyo 88:41.

Jay, J.M. 1992. "Modern Food Microbiology," 4th ed. Van Nostrand
Reinhold. New York. NY.

Jiang, z., and Ooraikul, B. 1989. Reduction of nonenzymatic
browning in potato chips and French fries with glucose oxidase. J.
Food Proces. Preser. 13:175.

 

 

120

Kaneko, K., Ota, K., Kawano, K., and Maeda, Y. 1989. Relationships
between varies parameters, especially organic acid content and
picking time, on the processing of plums into Ume—Zuke. J. Jap. Soci.
Nutri. Food Sci. 42:179. [In Food Sci. Tech. Abstr. (1990) 22(8): 8J36.]

Kanujoso, B.W.T., and Luh, BS. 1967. Texture, pectin, and syrup
viscosity of canned cling peaches. Food Tech. 21(3):457.

Kay, R.M., and Truswell, AS. 1977. Effect of citrus pectin on blood
lipids and fecal steroid excretion in man. Am. J. Clin. Nutr. 30:171.

Kertesz, 2.1. 1951. The pectic substances. Interscience Publishers Inc.,
New York, NY.

Kintner, P.k.; and Van Buren, JP. 1982. Carbohydrate interference
and its correction in pectin analysis using the m-hydroxydiphenyl
method. J. Food Sci. 47:756.

Langdon, T.T. 1987. Preventing of browning in fresh prepared
potatoes without the use of sulfating agents. Food Technol. 41(5):64.

Lees, D.H.; and Francis, F.J. 1971. Quantitative methods for

anthocyanins. 6. Flavonols and anthocyanins in cranberries. J. Food
Sci. 36:1056.

Leszkowiat, M.J., Barichello, V., Yada, R.Y., Coffin, R.H., Lougheed, E.C.,
and Stanley, D.W. 1990. Contribution of sucrose to nonenzymatic
browning in potato chips. J. Food Sci. 55:281.

Little, A.C. 1975. Off on a tangent. J. Food Sci. 40:410.

Liu, Y.K. and Luh, BS. 1979. Effect of harvest maturity on free amino
acids, pectins, ascorbic acid, total nitrogen and minerals in tomato
pastes. J. Food Sci. 44:425.

Lopez, A. 1987. Canning operations. Ch. 9. In "A Complete Course
in Canning and Related Processes. Book I - Basic Information on
Canning." p.182. The Canning Trade Inc., Baltimore, MD.

Luh, B.S., and Daoud, H.N. 1971. Effect of break temperature and

holding time on pectin and pectic enzymes in tomato pulp. J. Food
Sci. 36:1039.

121

Luh, B.S., Dempsey, E.H., and Leonard, S. 1954. Consistency of pastes
and puree from Pearson and San Marzano tomatoes. Food Technol.
8(12):576.

Luh, B.S., Sarhan, M.A., and Wang, Z. 1984. Pectins and fibres in
processing tomatoes. Food Technol. Aus. 36(2):70.

Lukton, A., Chichester, C.O., and MacKinney, G. 1956. The breakdown
of strawberry anthocyanin pigment. Food Technol. 10(9):427.

Ma, S., Silva, J.L., Hearnsberger, J.O., and Garner, Jr., J.O. 1992.
Prevention of enzymatic darkening in frozen sweet potatoes
[Impomoea batatas (L.) Lam.] by water blanching: relationship among

darkening, phenols, and polyphenol oxidase activity. J. Agric. Food
Chem. 40:864.

Markakis, P. 1982. Stability of anthocyanins in foods. Ch. 6. In
"Anthocyanins as food colors," P. Markakis (Ed.) p. 163. Academic
Press, Inc., New York, NY.

Marsh, G.L., Buhlert, J.E., and Leonard, SJ. 1980. Effect of

composition upon Bostwick consistency of tomato concentrate. J.
Food Sci. 45:703.

McCord, J.D., and Kilara, A. 1983. Control of enzymatic browning in
processed mushroom (Agaricus bisporus). J. Food Sci. 48:1479.

McCready, RM; and McComb, EA. 1952. Colorimetric determination
of pectic substances. Anal. Chem. 24:1630.

Meschter, E.L. 1954. Effects of carbohydrates and other factors on
strawberry products. J. Areic. Food Chem. 1:579.

Money, R.W., and Christian, W.A. 1950. Analytical data of some
common fruits. J. S. F. A. 1:8.

Monsalve-Gonzalez, A., Barbosa-Canovas, G.V., Cavalieri, R.P., McEvily,
A.J., and Iyengar, R. 1993. Control of browning during storage of
apple slices preserved by combined methods. 4-hexylresorcinol as anti-
browning agent. J. Food Sci. 58:797.

 

122

Morris, ER. 1973. Polysaccharide conformation as a basis of food
structure. In "Molecular Structure and Function of Food
Carbohydrate," G.G. Birch, and L.F. Green (Ed.) p.125. Wiley, New
York, NY.

Nishimune, T., Yakushiji, T., Sumimoto, T., Taguchi, S., Konishi, Y.,
Nakahara, S., Ichikawa, T., and Kunita, N. 1991. Glycemic response
and fiber content of some foods. Am. J. Clin. Nutr. 54:414.

Nursten, HE 1980. Recent developments in studies of Maillard
reaction. Food Chem. 6:263.

Nusrten, HE. 1986. Maillard browning reactions in dried foods. In
"Concentration and Drying of Foods," D. McCarthy (Ed.) p.53.
Elsevier App. Sci. Pu., New York, NY.

O'Brien, J., and Morrissey, RA. 1989. Nutritional and toxicological
aspects of the Maillard browning reaction in foods. CRC Criti. Rev.
Food Sci. Nutri. 28:211.

Odigboh, E.V., and Mohsenin, N.N. 1975. Effects of concentration on
the viscosity of cassava starch paste during the cooking-cooling
process. J. Texture Stud. 5:441.

Palamidis, N., and Markakis, P. 1975. Stability of grape anthocyanin
in a carbonated beverage. J. Food Sci. 40:1047.

Palmasano, R.A. 1972. Processing effects on Stanley and Bluefree
plum nectar, plum juice and canned plums. Sc. D. thesis, Michigan
State Univ., East Lansing, MI.

Peng, C.Y., and Markakis, P. 1963. Effect of phenolase on
anthocyanins. Nature 199:597.

Pestka, J.J. 1993. "Food microbiology laboratory manual," Dept. of
Food Sci. Hum. Nutri. Michigan State Univ. East Lansing. MI.

Pham, C.B. 1990. Influence of salts, amino acids and urea on the
non-enzymatic browning of the protein-sugar system. Food Chem.
37:251.

Pifferi, P.G., and Cultrera, R. 1974. Enzymatic degradation of

anthocyanins : the role of sweet cherry polyphenol oxidase. J. Food
Sci. 39: 786.

123

Pilando, L.S., Wrolstad, R.E., and Heatherbell, DA. 1985. Influence of
fruit composition, maturity and mold contamination on the color
and appearance of strawberry wine. J. Food Sci. 50:1 121.

Pomeranz, Y. 1991. "Functional properties of food components,"
Academic Press, Inc., San Diego, CA.

Poste, L.M., Mackie, D.E., Bulter, G., and Larmond, E. 1991.
"Laboratory Methods for Sensory Analysis of Food," Research Branch
Agric. Canada, Ottawa.

Pouget, M.P., Lejeune, B., Vennat, B., and Pourrat, A. 1990. Extraction,
analysis and study of the stability of Hibiscus anthocyanins.
Lebensm.-Wiss. u.-Technol. 23:103.

Pressey, R. 1986. Polygalacturonases in higher plants. Ch. 13. In
"Chemistry and Function of Pectins." M.L. Fishman; J.J. Jen (Ed.)
p.157. American Chemical Society, Washington DC. MD.

Rao, MA. 1975. Measurement of flow properties of food suspensions
with a mixer. J. Text. Stud. 6:533.

Rao, M.A., and Anantheswaran, RC. 1982. Rheology of fluids in food
processing. Food Technol. 36(2):1 16.

Rao, M.A., Bourne, MG, and Cooley, H.J. 1981. Flow properties of
tomato concentrates. J. Text. Stud. 12:521.

Rao, M.A., Cooley, H.J., Nogueira, J.N., and McLellan, M.R. 1986.
Rheology of apple sauce: effect of apple cultivar, firmness, and
processing parameters. J. Food Sci. 51:176.

Reid, D.S., Carr, J.M., Sajjaanantakul, T., and Labavitch, J.M. 1986.
Effects of freezing and frozen storage on the characteristics of pectin
extracted from cell walls. Ch. 16. In "Chemistry and Function of
Pectins," M.L. Fishman; J.J. Jen (Ed.) p.201. American Chemical
Society, Washington DC. MD.

Richardson, T. and Hyslop, DB. 1985. Enzymes. Ch. 6. In "Food
Chemistry," O.R. Fennema (Ed.) p. 424. Marcel Dekker, NY.

124

Rommel, A., Heatherbell, D.A., and Wrolstad, RB. 1990. Red raspberry
juice and wine: effect of processing and storage on anthocyanin
pigment composition, color and appearance. J. Food Sci. 55:1011.

Rommel, A., Wrolstad, R.E., and Heatherbell, DA. 1992. Blackberry
juice and wine: processing and storage effects on anthocyanin pigment
composition, color and appearance. J. Food Sci. 57:385.

Rouse, A.H., and Atkins, GD. 1955. Pectinesterase and pectin in
commercial citrus juices as determined by methods used at the citrus
experiment station. Technical Bulletin No. 570. Agric. Exp. Stations,
Univ. of Florida. Gainesville, FL.

Sakamura, S., Watanabe, S., and Obata, V.J. 1965. Anthocyanase and
anthocyanins occurring in eggplant. 3. Oxidative decolorization of the
anthocyanin by polyphenol oxidase. Agr. Biol. Chem. 29:181. '

Sapers, G.M.; Douglas, JR., F.W.; Bilyk, A.; Hsu, A.F.; Dower. H.W.;
Garzarella, L.; and Kozempel, M. 1989. Enzymatic browning in
Atlantic potatoes and related cultivars. J. Food Sci. 54:362.

Sapers, G.M., Garzarella, L., and Pilizota, V. 1990. Application of
browning inhibitors to cut apple and potato by vacuum and pressure
infiltration. J. Food Sci. 55:1049.

Sapers, G.M., Hicks, K.B., Phillips, J.G., Garzarella, L., Pondish, D.L.,
Matulaitis, R.M., McCormack, T.J., Sondey, S.M., Seib, P.A., and Ei-
Atawy, Y.S. 1989. Control of enzymatic browning in apple with
ascorbic acid derivatives, polyphenol oxidase inhibitors and
complexing agents. J. Food Sci. 54:997.

Sawayama, S., and Kawabata, A. 1989. Effect of pH, heat and salts on
the physicochemical properties of pectic substances. J. Jap. Soci.
Nutri. Food Sci. 42:461. [In Food Sci. Technol. Abstr. (1990)
22(8):8L15.]

Schneeman, B.O. 1989. Dietary fiber. Food Technol. 43(10):133.

Schussler, U., and Ledl, F. 1989. Direct determination of 2-amino-6-
(2-formyl-5-hydroxymethyl-l-pyrrolyl)-hexanoic acid in hydrolyzed
protein by reversed-phase HPLC. Z. Lebensmittelunters. U. Forsch.
189:32.

125

Sherkat, F., and Luh, BS. 1977. Effect of break temperature on quality
of paste, reconstituted juice, and sauce made from M-32 tomatoes. J.
Inst. Can. Sci. Technol. Aliment. 10:92.

Sherkat, F., and Luh, BS. 1976. Quality factors of tomato pastes
made at several break temperatures. J. Agric. Food Chem. 24:1 155.

Shol'ts, E.P., Karakozova, E.V., Sokolov, A.S., Okolelov, V.S., Smirnov,
1.1., and Dombrovskii,V.V. 1990. Paste from substandard grapes.
Pishchevaya Promyshlennost', USSR 2:20. [ In Food Sci Technol. Abstr.
(1991) 23(11):11J42.]

Siddiq, M. 1993. Characterization of polyphenol oxidase from Stanley
plums and a study of its involvement in anthocyanin loss in plum
juice. Ph. D. dissertation. Michigan State Univ., East Lansing, MI.

Siddiq, M., Sinha, N.K., and Cash, J.N. 1992. Characterization of
polyphenoloxidase from Stanley plums. J. Food Sci. 57:1 177.

Siegel, A., Markakis, P., and Bedford, C.L. 1971. Stabilization of
anthocyanins in frozen tart cherries by blanching. J. Food Sci. 36:962.

Steffe, J.F. 1992. "Rheological methods in food process engineering,"
Freeman Press, East Lansing, MI.

Steffe, J.F., and Morgan, R.G. 1986. Pipeline design and pump
selection for non-Newtonian fluid foods. Food Technol. 40(12):78.

Timberlake, CF 1980. Anthocyanins-occurrence, extraction and
chemistry. Food Chem. 5:69.

Timberlake, C.F., and Bridle, P. 1982. Distribution of anthocyanins in
food plants. Ch. 5. In "Anthocyanins as Food Colors" P. Markakis
(Ed.), p. 126. Academic Press, Inc.,, New York, NY.

Toledo, R., Cabot, J. and Brown, D. 1977. Relationship between

composition, stability, and rheological properties of raw comminuted
batters. J. Food Sci. 42:725.

Troller, J.A., and Christian, J.H.B. 1978. "Water Activity and Food,"
Academic Press, Inc., New York, NY.

Vamos-Vigyazo, L. 1981. Polyphenol oxidase and peroxidase in fruits
and vegetables. CRC Crit. Rev. Food Sci. Nutri. 15:49.

126

Van Deventer-Schriemer, W.I-I., and Pilnik, W. 1976. Fractionation of
pectins in relation to their degree of esterification. Lebensm-Wiss. u.-
Technol. 9:42.

Velisek, J., Davidek, T., Davidek, J., Trska, P., Kvasnicka, F., and
Velcova, K. 1989. New imidazoles formed in nonenzymatic browning
reactions. J. Food Sci. 54:1544.

Vidal-Valverde, C., Blanco, 1., and Rojas-Hidalgo, E. 1982. Pectic
substances in fresh, dried, desiccated, and oleaginous Spanish fruits.
J. Agric. Food Chem. 30:832.

Wani, M.A.M Saini, S.P.S., and Bains, 0.8. 1990. Physical-chemical
changes during preparation of plum juice concentrate. J. Food Sci.
Technol., India 27:29. [In Food Sci. Technol. Abstr. (1990) 22(9):
9H66.]

Watt, B.K., and Merill, A.L. 1963. Composition of foods: raw,
processed, prepared. U.S.D.A. Agric. Handbook No. 8.

Weinert, I.A.G., Solms, J., and Escher, F. 1990. Quality of canned
plums with varying degrees of ripeness 2. texture measurements and

sensory evaluation of texture and colour. Lebensm.-Wiss. u.-Technol.
23:1 1 7.

Weinert, I.A.G., Solms, J., and Escher, F. 1989. Quality of canned
plums with varying degrees of ripeness 1. chemical characterization of
colour changes. Lebensm.-Wiss. u.-Technol. 22:307.

Wesche—Ebeling, P., and Montgomery, W. 1990. Strawberry
polyphenoloxidase: its role in anthocyanin degradation. J. Food Sci.
55:731.

Whitaker, J.R. 1972. Polyphenol oxidase. Ch. 22. In "Principles of
Enzymology for Food Sciences." p. 571. Marcel Dekker, New York, NY.

Wrolstad, RE. 1976. Color and pigment analysis in fruit products.
Station bulletin 624. Agricultural experiment station, Oregon State
University, Corvallis.

Wrolstad, R.E., and Shallenberger, RS. 1981. Free sugars and sorbitol

in fruits - a complication from the literature. J. Assoc. Off. Anal.
Chem. 64:91.

1'27

Wrolstad, R.E., Skrede, G., Lea, P., and Enersen, G. 1990. Influence of

sugar on anthocyanin pigment stability in frozen strawberries. J. Food
Sci. 55:1064.

Yaylayan, V.A., and Lachambre, S. 1990. Pyrylium betaines as
reactive intermediates in Maillard reaction. J. Food Sci. 55:1124.

APPENDICES

Absorbance at 520nm

128

 

 

 

 

Appendix I Standard curve of galacturonic acid
1.2
y = 4.8182e-4 + 1.3811e-2x RAZ = 0.997

1.0 -

0.8 -

0.6 -

0.4 -

0.2 -

0.0 a. . 1 ‘ fi fi

0 20 40 60

Galacturonic acid (ug/ml)

80

129

Appendix II Questionnair for sensory evaluation

SENSORY EVALUATION OF PLUM PASTE

' Name: Date: Product: Plum Paste

Direction:

1. Listed below are 6 descriptors. Pleasescale the first 5 descriptors
for intensity only, not your liking or disliking.

2. Before tasting the samples and between each sample, rinse your
mouth with water. You may also use the crackers to remove the
flavor from your mouth at any time.

3. Taste the samples in the order listed on your questionnaire. You
may either swallow or spit out the samples.

4. Indicate your rating on this ballot by placing a Cross on the

horizontal line scale ( e.g. + ). The anchor point is located at
center of each line.

 

Sample code:
Color :

 

light dark
acidity :

 

—l.

slightly acid extremely acid

Sweetness :

—-1l—

slightly sweet ' extremely sweet

Consistency:

 

d-

 

very thin very thick
Flavor :
slight ' , strong

Overall acceptance :

unacceptable very acceptable

Comments 1

130

288“... 88o a :5 H

 

 

o o o o o o o o VN
o o o o o o o 0 ON
0 o o o o o o o 3
o o o o o o o o NH
o o o o o o o o w
o o o o o o o o v
o o o o o o o o o
leo «uoumllukm
o o o o o o o o VN
o o o o o o o 0 ON
0 o o o o o o o 3
o o o o o o o o NH
o o o o o o o o w
o o o o o o o o v
o o o o o o 0 Ho 0
M3
xtmhv xtmbv 5.5.9» 58me Amxoogv
9 82% 8mg. 9 Boom 8mg 083 $8on

xtmbm xtmhm xtmodm 5.8th xtmbm xtmhm xtmbm xtmhm

 

 

885 83a 80an 80.5 mound 30.8888 808m

 

boron 098on 9:86 8:5
88d “can 80.: 88 09:6 30.88800 89c 83mm 893 do 898 88a Pans—8m

E 56:83.

 

 

Ill-lull. -. ii

131

was“... 820 a 85 H

 

 

o o o o o o o o 0N
o o o o o o o 0 ON
0 o o o o o o o 3
o o o o o o o o NH
0 o o o o o o o w
o o o o o o o o v
o o o o o o o o o
8.. «land. 3. Pm... N
o o o o o o o o VN
o o o o O o o 0 ON
0 o o o o o o o 3
o o o o o o o o NH
o o o o o o o o w
o o o o o o o o w
o o o o o o 0 Ho 0
Imlm «uoumllouy
xtmhv 8..me xtmhv xtmbv A8835
9 00000 .895 8 08200 89.5 883 89805

xtmbm xtm.m~ xtmbm 038th xtmbm xtmhm xtmhm xtmhm

 

 

88.3““ 803 Homo 808m 8.50 8888800 80.5

 

0280 $8on mats—0
00.50 803 “0:0 80¢ 98 88.5mm 88.88800 80¢ 88me 820 2.0 8:00 88:30 >_ 598ng

 

132

820 a :5 H

 

 

o o o o o o o o 0N
o o o o o o o 0 ON
0 o o o o o o o 3
o o o o o o o o NH
o o o OH o o o o w
0 ON 0 ON 0 o o o v
o o o o o o o o o
lmllllll0 8on PNN
o o o o o o o 0 Hum
o o o o o o o 0 ON
0 o o o o o o o 3
o o o o o o o o NH
o o o o o o o o w
o o o o o o o o v
o o o o o o o Ho 0
mug
xtmbv xtmbv xtmhv xtmbv 608005
00 00000 85.5 00 00000 .895 080 098on

54% 5.0. 00:50 a 0.00% a [0189... [0.8.2

 

 

0050 0520 00:0 8000 00.50 #8088800 80.80

 

02800 098000 9:50 00.50
880 00:0 8000 08 00.50 080808800 80.0 003.00 820 00 5500 088 0.8 0000» > xm0c000<

S

MICHIGAN TnTE UNIV. LIBRARIES
[HIVWIWII [NullNIH”"H"INHIHIWWWI
312 3010517898

 

9