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EXT RUSION COOKING TO PRODUCE NUTRITIOUS BEAN
PRODUCTS

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EXTRUSION COOKING TO PRODUCE NUTRITIOUS BEAN PRODUCTS
By

George Nyombaire

A THESIS
Submitted to
Michigan State University

In partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Food Science

2007

ABSTRACT
EXTRUSION COOKING TO PRODUCE NUTRITIONAL BEAN PRODUCTS
By

George Nyombaire

A laboratory co-rotating twin-screw extruder was used to study the effect Of
extrusion conditions on physical, chemical, and sensory characteristics Of
extruded light red kidney beans. Raw bean flour was extruded at 25% and 36%
moisture content wet basis; screw speed Of 118, 194, and 253 rpm; bean flour
feed rate of 80 and 1209/min and extrusion barrel temperatures were 105l120°C
and 115/130°C ; and die orifice was 7.00mm. Only feed rate significantly
(p=0.003) influenced average expansion ratio with 1.22 and 1.30 for 80 g/min
and 120 g/min respectively. Increasing moisture content from 25% to 36%
significantly increased average bulk density from 38.86 to 39.89 g/cm3
respectively (p=0.05). Water solubility index was significantly affected by feed
rate (p=0.0001), screw speed (p=0.0001), and moisture content (p=0.002). The
initial viscosity of extruded bean samples was much higher than that of raw bean
samples which indicates that starch was gelatinized during extrusion cooking.
Peak viscosity, hot-paste viscosity and cold paste viscosity in extruded bean
samples were much lower than those in raw bean samples. Phytohemagglutinin
activity reduction of extruded beans was over 90%. A comparison of thermal
extrusion versus traditional cooking using charcoal demonstrated a 43 % cost

reduction using extrusion.

DEDICATION

TO my mother Anna Mukashuri, my wife Phiona Bamukunde, and my brother

Francis Rusagara, for their moral support.

iii

ACKNOWLEDGEMENTS

First Of all I would like thank my thesis and academic advisor, Dr. K.D. Dolan for

his thoughtful scientific guidance, advice and friendship.

I owe a debt Of gratitude to my academic committee members: Dr. M.R. Bennink,
Dr. P.K.W. Ng, and Dr. M.A. Uebersax for their academic support throughout my

M.S. program.

I am grateful tO acknowledge all the professors who participated in broadening
my horizons through my master’s program: Drs Mark Uebersax, James Pestka,
Perry Ng, Alden Boreen, Robert Templeman, James Steffe, John Patridge, and

Winnie Chiang. Their help was highly appreciated.
I would like to thank USAlD-KIGALI, which funded my master’s program through
the Partnership to Enhance Agriculture in Rwanda through Linkages (P.E.A.R.L.)

project.

Finally, my thanks go to my lab team Mishra, Oh, Mitz, Irene, Harlem, Rabiha,

Shantanu, Kathy, Lovisa, and Norm for their support and friendship.

iv

Table of Contents

List Of Tables ............................................................................ vii
List of Figures ............................................................................ viii
CHAPTER 1: INTRODUCTION ...................................................... 1
CHAPTER 2: LITERATURE REVIEW ............................................. 6
2.1. Dry beans in the diet of man ......................................... 7
2.1.1. Nutritional importance of dry beans ........................... 7
2.1.1.1. Proteins ....................................................... 7
2.1.1.2. Carbohydrates .............................................. 8
2.1.1 ..3 Dietary fiber .................................................. 8
2.1.1 ..4 Lipids .......................................................... 10
2.1.1 .5 Vitamins ...................................................... 10
2.1.1 .6 Minerals ...................................................... 10
2.1. 1 ..7 Antioxidants In beans ..................................... 11
2.1.2. Lectins In dry beans .................................................. 12
2.1.2.1. Toxicity effects of Iectins ................................. 13
2.2. EXT RUSION COOKING ...................................................... 16
2.2.1. Extrusion terminology .............................................. 16
2.2.2. Single-Screw extruders ............................................ 17
2.2.3. Twin-Screw extruders .............................................. 17
2.2.4. Benefits Of extrusion cooking ..................................... 18
2.2.4.1. Starch gelatinization ......................................... 18
2.2.4.2. Protein denaturation ........................................ 20
2.2.5. Low-cost extrusion .................................................. 20
CHAPTER 3: MATERIALS AND METHODS ................................... 23
3.1. Raw materials ......................................................... 23
3.2. Extrusion experiments ............................................... 23
3.2.1. Fabrication of feeder ............................................ 26
3.2.2. Calibration of feeder ............................................ 26
3.2.3. Calibration of water pump ..................................... 27
3.2.4. Estimation Of the degree of fill ................................ 27
3.2.5. Residence Time Distribution .................................. 28
3.2.5.1. Preparation of dye to measure Residence
Time Distribution ......................................... 28
3.2.5.2. Residence time sample collection .................... 29
3.2.5.3. Color concentration calibration curve ................ 29
3.2.6. Specific mechanical energy ..................................... 31
3.2.7. Physical characteristics of bean extrudates ................. 31
3.2.7.1. Expansion ratio .............................................. 31
3.2.7.2. Bulky density ................................................. 32
3.2.7.3. Water Absorption Index .................................... 32

3.2.7.4. Water Solubility Index ..........................................
3.3. Starch gelatinization .................................................
3.4. Phytohemagglutinin assay .........................................
3.5. Sensory evaluation of extrudated bean porridge .............
3.6. Calculation of energy requirement for cooking

beans with firewood and charcoal ...............................
3.7. Statistical analysis ....................................................

CHAPTER 4: RESULTS AND DISCUSSION ..................................

4.1. Estimation of degree of fill ..........................................
4.2. Residence Time Distribution Analysis ...........................
4.2.1. Color-Concentration Calibration Curve .....................
4.3. Specific Mechanical Energy ........................................
4.4. Physical characteristics of bean extrudates ....................
4.4.1. Expansion ratio ...................................................
4.4.2. Bulky density ......................................................
4.4.3. Water Absorption Index ........................................
4.4.4. Water Solubility Index ..........................................
4.5. Starch gelatinization .................................................
4.6. Sensory evaluation of bean extrudates .........................
4.7. Lectins as active phytohemagglutinins
(PHA activity) ...........................................................
4.8. Calculation of energy requirement by the extruder ..........

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS .............

5.1. Conclusions ............................................................
5.2. Recommendations for Future Research ........................

Appendix 1
Appendix 2
Appendix 3
Appendix 4
Appendix 5
Appendix 6
Appendix 7

Appendix 8

Appendix 9

Water pump calibration curve ....................................
Screw speed calibration curve ...................................
Extruder feeder calibration curve ...............................
Consent form for extruded bean porridge ....................
Formula for calculating moisture content .....................
Flour moisture determination ....................................
Sensory evaluation of bean porridge

questionnaire (Kinyanlvanda) ....................................
Sensory evaluation of bean porridge

questionnaire (English) ...........................................
Extrusion variables with mean residence times ............

Appendix 10 Extrusion variables with degree of fill .........................
Appendix 11 Calculation of void volume Of twin-screw extruder JS30A
Appendix 12 Analysis of Variance (ANOVA) tables ........................

REFERENCES .......................................................................

vi

32
33
34
36

38
38

39
39
40
4O
46
47
47
49
51
52

59

61
63

69
71
72

74
75
76
77
78
78

79

81
83

85
87

89

List of Tables

Table Page
2.1.1. Major nutrients in beans and other grains ................... 7
2.1.2. Best sources Of food antioxidants: Top 20 fruits, vegetables

and nuts (as measured by total antioxidant capacity

per serving size) ................................................... 12
3.2.1 . Experimental design .............................................. 24
3.2.2 Extruder specification ............................................ 25
4.1. Expansion ratio and bulk density under different

extrusion conditions .............................................. 50
4.2. Effect of extrusion variables on water absorption

and solubility indices ........................................... 53
4.3. Phytohemagglutinin retention in light red kidney extruded

at different conditions ........................................... 62
4.4. Energy and cost consumption for the extruder ........... 64
A1. Sensory evaluation questionnaire for extruded bean porridge

(Kinyarwanda) .................................................. 79

A2. Sensory evaluation questionnaire for extruded

bean porridge (English) ........................................ 81
A3. Extrusion variables with mean residence time ....................... 83
A4. Extrusion variables with percent fill ..................................... 84

vii

List of Figures

Figure Page
Effect of screw speed on the degree of fill ............................. 39
4.1. Color reading versus concentration Of pink dye for color
concentration calibration curve ........................................... 40
4.3 Effect of screw speed on Residence Time Distribution ............ 42

4.4. A representation of the effect of feed rate on Residence
Time Distribution ............................................................ 44

4.5. A representation of the effect of moisture content on
Residence Time Distribution ............................................ 45

4.6. Effect of barrel temperature on residence time distribution at
moisture content = 36% ................................................. 46

4.6. Effect of screw speed on specific mechanical energy at
constant flour feed rate = 809/min at two moisture contents... 47

4.7. A representative set of curves showing the effect of screw
Speed on starch gelatinization of raw and extruded beans ..... 56

4.8. A representative set of curves showing effect of feed rate
on gelatinization in raw and extruded beans ........................ 57

4.9. A representative set of curves showing effect of moisture
content on starch gelatinization in raw and extruded beans.... 58

4.10. Sensory evaluation of Sosoma and extruded bean porridges... 60

4.11. Percent Of operating expenses to produce 1 kg of extruded bean flour
in United States and Rwanda .......................................... 65

4.12. Effect Of screw speed on SME at different moisture contents
and feed rates at barrel temperature 130l115°C .................. 66

4.13. Effect of screw speed on SME at different moisture contents
and feed rates at barrel temperature 120/105°C .................. 67

A1. Standard curve for water pump used in all extrusion runs ...... 74

viii

A.2. Standard curve for screw speeds used in all extrusion runs ....... 75

A3. Standard curve for extruder feeder used in all extrusion runs..... 76

ix

CHAPTER 1: INTRODUCTION
Dry beans (Phaseolus vulgaris L.) can be an extremely beneficial component of
all diets because they are high in complex carbohydrates, protein and dietary
fiber, and low in fat, calories and sodium, and are cholesterol free. In the
developed world where cholesterol is a major health problem, dry beans are
considered as the major source Of dietary fiber (USDA, 2006). Beans are one of
the best sources of dietary fiber, containing both soluble and insoluble fiber.
Insoluble fiber, generally thought as “roughage” that moves quickly through the
digestive system, is very important because it helps promote digestion and can
reduce the risk of colon cancer (Willet, 1995). Soluble fiber helps lower blood
cholesterol levels, one of the main risk factors for the development of
cardiovascular disease in developed countries such as the United States of

America.

In developing world, dry beans are an important source of protein and calories for
middle and low income families (Bliss, 1990) because animal protein is very
expensive. In a country like Rwanda, animal protein is very limited and very
expensive, and common beans provide up to 60% Of protein needs and 25% of
calories in the diet (MINIPLAN, 1988). The most common method of cooking
beans in much of Africa and Rwanda is an open wood fire built on the ground
(Poulsen, 1980). An open wood fire is not fuel efficient because the rate of
burning cannot be controlled and much of the heat is dissipated into the

surrounding atmosphere. Large quantities of wood and charcoal used to cook the

beans 3-4 hrs leads to deforestation and erosion, as well as air pollution from the
burning of wood. Dry beans require a long time of cooking to render the grains
palatable, and to inactivate antinutritional factors such as phytohemagglutinins
(Iectins), protease inhibitors and amylase inhibitors. These antinutrients must be
inactivated, and the starch must be gelatinized before consumption. Lack of fuel
wood for cooking dry beans is a major problem facing over-populated developing
countries. Besides, continued deforestation may alter local and global climate. In

addition, smoke from the cooking fire is a major health hazard.

In most tropical countries, considerable deterioration Of dry beans can occur
during high temperature and humidity storage. The main Observed deterioration
includes an increase in cooking time, deterioration of texture and flavor, and loss
of nutritive value. Also, lack Of ideal bean storage conditions leads to increased

losses of the crop due to weevils.

Low-cost extruders are seen as one of the best alternatives for dry bean cooking,
especially in countries with low income, because the typical existing extrusion
equipment is expensive. Extrusion is a high-temperature-short-time (HTST)
cooking technique used to produce a variety Of products from different food
ingredients. Food extruders are generally available with segmented screws and a
barrel section. Segmented screws facilitate total control over the configuration of
the machine to get a combination of various process parameters. This control

makes possible many functional changes and inactivation of undesirable factors

technology. As a result, very little research has been published, but is sorely

needed.

In Rwanda, more than 90% Of the population use firewood or charcoal for
cooking all types of foods. Also, increased land pressure (approximately
8,000,000 people on 26,338 sq. km) has resulted in a scarcity of wood for fuel,
and current fuelwood demands far exceed the supply. Rwanda is the number
one country in consumption of dry beans (Phaseolus vulgaris L.) in the world
(ISAR, 2001 ). The consumption per capita is over 60 kg, one of the highest in the
world (Africa average is 11.7 kg) (ISAR, 2001) and they are the only food require
much firewood to cook. Using a low-cost extruder for cooking beans would
reduce the amount of fuelwood and increase the amount of nutrients supplied by
beans in the Rwandan diet. The extruder would have a positive impact on the
environment and enhance nutritional well-being of dry bean consumers.
Therefore, it is very important to calculate the energy requirement for cooking dry

beans with firewood or charcoal and compare it with that used by the extruder.

Therefore, the objectives of the present research were to:
1) Assess the effect of low-cost extruder conditions on the physical
characteristics Of extruded light red kidney beans;
2) Determine the fate of antinutritional components, specifically Iectins in the
extruded bean products;

3) Determine consumer acceptability Of extruded bean porridge;

4) Compare energy requirements for bean extrusion versus wood or

charcoal.

CHAPTER 2: LITERATURE REVIEW
2.1. Beans in the diet of man
Beans are one of the world’s most important food sources, especially in
developing countries, in terms of food energy as well as nutrients (August and
Klein, 1989). Common beans are a good source of proteins and are an excellent
source of carbohydrates (Sathe et al., 1985). The large amount of water-soluble
fiber is particularly effective in lowering cholesterol in the blood, whereas the
water-insoluble fiber provides bulk, pushing food through the digestive system at
a faster rate. Common beans are low in sodium. They are a good source of
vitamins (thiamine, riboflavin, niacin, vitamin 36, and folic acid) and certain
minerals (Ca, Fe, Cu, Zn, P, K, and Mg). Also dry beans contain about one
percent of polyunsaturated fatty acids (Iinoleic and linolenic). (Augustin and Klein,

1989; Mahadevappa and Raina, 1978; Sathe et al., 1985)

The contribution Of common beans to the diets of people is appreciable. In
addition, common beans are less expensive than animal food products and have
considerably longer shelf-life than many animal, fruit, and vegetable products
when stored under appropriate conditions. However, dry beans have several
undesirable characteristics such as long cooking times, ‘beany’ flavor, and the
presence Of enzyme inhibitors and hemagglutinins that must be removed for safe

dry bean consumption. (Gupta 1987; Sathe et al., 1985).

Table 2.1.1. Major nutrients in beans and other grains

 

 

 

 

 

 

 

 

 

 

Dry Beans Wheat Oats Corn Scflrum Millet
Energy (kcal) 333 339 389 361 339 378
Protein (9) 23.58 13.7 16.89 6.93 11.3 11.02
Carbohydrates 60.01 72.57 66.27 76.85 74.66 72.85
(9)
Dietary fiber (9) 24.9 12.2 10.6 7.3 6.3 8.5
Fat (g) 0.83 1.87 6.9 3.86 3.3 4.22
Iron (rgg) 8.2 3.88 4.72 2.38 4.4 3.01
Potassium (mg) 1406 405 429 315 350 195
FOlate (pg) 394 44 56 25 0 85

 

 

 

 

 

 

 

Source: USDA, 2006

The data provided in Table 2.1.1 are per 100 g dry basis. Compared with wheat,
oats, corn, sorghum and millet, beans are a good source of dietary fiber, and B
vitamins (folic acid). Dry beans also are higher in protein and minerals such as
iron and potassium. Beans provide very little fat (linolenic and Iinoleic).

2.1.1 . Nutritional importance of beans

2.1.1.1. Proteins

The most important role of legumes in the diet is as an inexpensive protein
source. This role is crucial in the developing countries as beans are frequently
the major source Of high quality protein in the diet. Methionine is always the first
limiting amino acid in legumes (Carpenter, 1981), but they are endowed with
relatively high lysine levels. This lack Of methionine explains beans’ historical
association with cereal grain. Because legumes are looked upon as a good
source of protein in vegetable-based diets, much effort has been spent in
investigating the protein quality Of legumes. The protein efficiency ratio (PER) of
raw and cooked legumes is approximately 0 and 1.2, respectively (Rockland and

Radke, 1981 ).

 

2.1.1.2. Carbohydrates

Beans are rich in complex carbohydrates (Table 2.1.1), one of the nutrients that
provides energy to the muscles and brain. Carbohydrate content in dry beans
ranges from 50 to 60 % (Sathe et al., 1985). Dry beans have the best type of
carbohydrates because they are considered to be low glycemic index making

beans a suitable food for diabetics.

Monosaccharides and some oligosaccharides are present in dry beans but these
make a minor contribution to the total carbohydrate. Soluble sugars are present
in the range of 5.5 to 8% (Reddy et al., 1984). Those present in greatest
concentration are sucrose and stachyose with raffinose and verbascose also
present. Raffinose containing oligosaccharides constitute from 31-76% of the
total sugar fraction in dry beans (Naivukul and D’Appolonia, 1978; Akpapunam
and Markakis, 1979).

2.1.1.3. Dietary fiber

Dietary fiber constitutes 25% of the dry beans by weight twice as high as that in
wheat and corn (Table 2.1.1)

The indigestible residue Of dry beans is an important component and makes up
from 8 to 9% to the total carbohydrate fraction (Reddy et al., 1984). The most
prevalent fiber components in Phaseolus vulgaris varieties are cellulose,

hemicellulose and lignins, but pectins are also present. Dry beans contain

approximately 13% water-insoluble fiber and 11% water-soluble components

(Asp and JohanssOn, 1981).

The importance Of dietary fiber in human nutrition has received a great deal of
attention in recent years from scientists and consumers (Hughes, 1991; Hughes
and Swanson, 1986; Olson et al., 1087; Schweizer, 1989). Numerous health
benefits (Table 2.1.1) have been associated with consuming adequate amounts
Of dietary fiber, including lower blood cholesterol, reduced risk of heart disease
(Schneeman, 1986), increased fecal bulk, decreased intestinal transit time,
reduced risk of colon cancer, and improved glucose tolerance, which is

especially beneficial for diabetics (Toma and Curtis, 1986).

Dietary fiber is categorized as soluble and insoluble. Soluble fibers form gels,
increasing the viscosity of intestinal contents, which may affect glycemic index.
Soluble fibers are generally highly ferrnentable and affect the animal indirectly by
production of gas, short chain fatty acids (SCFA), and lactic acid as a result of
ferrnentative digestion in the small intestine (Roberfroid, 1993). Insoluble fibers,
that cannot be digested in the human digestive tract (Trowell et al., 1976)

contribute to fecal bulk and ease of laxation.

2.1.1.4. Lipids

Common beans contain only 1 to 3% lipids depending on the species (Patte et
al., 1982; Sathe et al., 1985). Total lipid content may vary depending on the
variety, origin, location, climate, environment conditions, and the type of soil in
which they are grown (Worthington et al., 1972). The majority Of the fatty acids in
dry beans are unsaturated (Patte et al., 1982; Sathe et al., 1985; Watt and Merril,
1963). Oleic (7 to 10%), linoleic (21 to 28%) and linolenic (37 to 54%) are the
major unsaturated fatty acids, which range from 64 to 87% Of total lipids. The
polyunsaturated fatty acids, such as linoleic and linolenic, cannot be synthesized
by animals and humans, and these two acids are required for normal growth, cell
structure, functions Of all tissues, and prostaglandin synthesis (Lehninger, 1975;
Sathe et al., 1985). Linoleic and linolenic help to lower blood cholesterol

(Mahadevappa and Raina, 1978).

2.1.1.5. Vitamins

In addition to supplying carbohydrates and proteins, dry beans are significant
source of vitamins especially folic acid (0.171 to 0.579 mg per 1009), thiamine
(0.86 to 1.14 mg per 1009), riboflavin (0.136 to 0.266 mg per 1009), niacin (1.16
to 2.68 mg per 1009), Vitamin B6 (0.336 to 0.636 mg/100g).

2.1.1.6. Minerals
Dry beans are also rich in minerals, such as iron, potassium, and folate (Table

2.1.1). Hosfield and Uebersax (1980) measured ash content in 34 varieties of dry

10

beans and the average of the samples was 3.94%. The mineral content Of beans
should be considered in conjunction with its bioavailability (Sathe et al., 1985).
Phytic acid and proteins can complex with dietary essential minerals, such as
calcium, zinc, Iron, and magnesium, and render them biologically unavailable for
absorption (Fritz, 1976; Martinez, 1977; Sathe et al., 1985). Physicochemical
modifications of bean proteins to produce desired functional properties may alter
the binding of minerals to food components, thereby influencing the mineral

availability (Sathe et al., 1985).

2.1.1.7. Antioxidants in beans

Eating beans could help people reduce their risk of developing a chronic disease
(Wu et al, 2004). Chronic diseases are conditions that typically take many years
(10 to 30 years) to develop and include certain types of cancers, type 2 diabetes
mellitus, heart disease, and other diseases Of the blood system. These diseases
are the most common causes of death In the United States and significantly

lower the quality of life for millions (Geil and Anderson 1994).

Beans are loaded with antioxidants (Table 2.1.1.7). Antioxidants are chemicals
that destroy free radicals and are highly common in many varieties of beans (Wu
et al., 2004). In 2004, the USDA nutritionists analyzed total antioxidant levels
using the oxygen radical absorbance capacity (ORAC) in assay in over 100

different foods, including fruits and vegetables. Among the foods analyzed, dry

11

beans (small red, red kidney, pinto, and black beans) were surprisingly found to

have high levels of antioxidants (Table 2.1.2).

Table 2.1.2. Best sources of food antioxidants: Top 20 fruits, vegetables
and nuts (as measured by total antioxidant capacity per

serving size)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rank Food item Serving size Total antioxidant capacity
per serving size (pmol of
TE')
1 *Small Red Bean (dried) Half cup 13727
2 Wild blueberry 1 cup 13427
3 *Red kidney bean (dried) Half cup 13259
4 *Pinto bean Half cup 11864
5 Blueberry (cultivated) 1 cup 9019
6 Cranberry 1 cup (whole) 8983
7 Artichoke (cooked) 1 cup (hearts) 7904
8 Blackberry 1 cup 7701
9 Prune Half cup 7291
10 Rasgerry 1 cup 6058
11 Strawberry 1 cup 5938
12 Red Delicious Apple One 5900
13 Granny Smith Apple One 5381
14 Pecan 1 ounce 5095
15 Sweet cherry 1 cup 4873
16 Black plum One 4844
17 Russet potato (cooked) One 4649
18 *Black bean (dried) Half cup 4181
19 Plum One 41 18
20 Gala Apple One 3903

 

 

 

 

Source: Wu et al., 2004

*Dry beans

 

aTrolox Equivalent

1.1.3. Lectins in beans
Landsteiner and Raubitschkek (1908) reported the ability of been seed extracts
to agglutinate red blood cell from various animal sources. The name “lectin” was

given to proteins responsible for this activity (Boyd and Shopleigh, 1954). Lectins

12

are glycoproteins with the unique property of being able to bind disaccharides in
a highly specific fashion. In addition to erythrocyte agglutination, the Iectins can
interact with other types of cells (Sgarbieri and Whitaker, 1982). Various names
have been given to Iectins. Lectins in dry beans are known as
phytohemagglutinins. Lectins in dry beans make up 6 to 12% of the total protein,
suggesting that they may play an important role in the physiology of the plant.
Some of the suggested functions for the Iectins are (1) acting as antibodies to
counteract soil bacteria, (2) protecting against fungal attack, (3) participating in
transportation or storage Of sugars, and (4) playing a key role in the development

and differentiation of embryonic cells (Purtzai, 1991 ).

1.1.3.1 . Toxicity effects of Iectins

Lectin’s mode of action in the plant is probably related to their toxic activity in the
diet. The main physiological characteristic of Iectins is their specific affinity for
certain sugar molecules. Most animal cell membranes contain these molecules,
and the Iectins can be characterized by their ability to bind to and agglutinate red
blood cells (hence the name haemagglutinins). However, their toxic activity
derives from their ability to attach on the same sugar moieties on intestinal cell
membranes. The nature of this toxicity can range from long-term impaired
nutrient uptake to serious acute food poisoning symptoms. Symptoms include
nausea, vomiting, and stomach pain. Most lectin sources do not cause a

problem, and they are easily denatured by the heating processes occurring in

13

normal cooking. However, they are specific exceptions, the most well known and

significant of which is red kidney beans.

Raw kidney beans are significantly toxic and must be cooked adequately before
consumption. Given the wide availability of dried, raw kidney beans in the UK
marketplace, and adverse TV publicity in the summer of 1981, the then
department of Health and Social Security issued instructions to the food industry
on the giving of general advice to purchasers Of raw beans for their preparation.

The form of wording suggested for labeling of beans for sale was:

“After soaking ovemight and throwing away the water, these beans should be
boiled bn'skly for at least 10 minutes and then cooked until soft otherwise they
may cause stomach upsets. Never cook in a small casserole unless the beans

have first been soaked and boiled this way. Do not eat raw beans” (Hutton, 2002)

Phytohemagglutinin, the toxic agent, is found in many species Of beans, but it is
in highest concentration in red kidney beans (Phaseolus vulgaris L). The unit of
toxin measure is the haemagglutinating unit (hau). Raw kidney beans contain
from 200,000 to 700,000 hau, while fully cooked beans contain from 200 to 400
hau. White kidney beans, another variety Of Phaseolus vulgaris L., contain about
one-third the amount of toxin as the red variety; broad beans (Vicia faba) contain

about 5 to 10 % the amount the red kidney beans contain.

14

Toxicity of Iectins in red kidney beans has been reported in the United Kingdom.
Seven outbreaks occurred in the UK. between 1976 (Noah et al., 1980). Two
more incidents were reported by Public Health Laboratory Services (PHLS),
Colindale, UK. in the summer of 1988. Reports of this syndrome in the United

States are anecdotal and have not been formally published.

The disease course is rapid. All symptoms usually resolve within several hours of
onset. Vomiting is usually described as profuse, and the severity of symptoms is
directly related to the dose of toxin (number of raw beans ingested).
Hospitalization has occasionally resulted, and intravenous fluids may have to be
administered. Although of short duration, the symptoms are extremely

debilitating.

All persons, regardless of age or gender, appear to be equally susceptible; the
severity is related to the close ingested. In the seven outbreaks mentioned above,

the attack rate was 100 %.

One of the most important nutritional problems of dry beans is low protein
digestibility. Apparent protein digestibility values Of different colored beans are
low (48%-62%) compared with animal protein digestibility for meat (82%-86%).
Possible factors that influence protein digestibility Of lightly cooked beans include
Iectins and protease inhibitors. The toxicity of Iectins is due to the Iectins

combining with epithelial cells of the small intestines, interfering with intestinal

15

enzyme activity, and damaging intestinal epithelial surfaces (Kim et al., 1976;

Rouanet and Resancon, 1979; King et al., 19803 and b) . Boiling for minimum of

10-12 minutes is necessary to adequately detoxify Iectins (Bender and Reaidi,

1982).

2.2. EXT RUSION COOKING

2.2.1. Extrusion terminology

The names of extruder parts depend on each extruder manufacturer. In most

cases the terminology is confusing and hard to understand. The following are

most of the terms commonly used in the extrusion process (Riaz, 2000):

Feedstock. the material or mixture to be processed in an extruder
Pre-conditioner. an assembly that adjusts moisture content and
temperatures of the ingredients and may partially or completely cook them
before entering the extruder

Screw. the member that conveys the product through the extruder

Shear. a working, mixing action that homogenizes and heats the conveyed
product

Bamel: a pipe-like retainer in which the extruder screw(s) turn(s)

UD (Length-tO-diameter) ratio: distance from the internal rear edge to the
discharge end Of the barrel, divided by the diameter of the bore

Die plate: Final assembly for shaping the product as it leaves the extruder
(Die holes may be drilled directly into the plate for shaping the product and

may be made Of hard-wearing material).

16

2.2.2. Single-Screw extruders

Single-Screw extruders may be regarded as friction pumps, since they rely
entirely on friction between the material being processed and the barrel wall to
convey materials (Purvis 1987, Starer 1996). Thus they rely on drag flow for
conveyance. The mass of the material being processed must stick to the barrel
wall in order to be forwarded, and the higher the friction forces, the more efficient

the conveyance is.

Single-Screw extruders consist of three sections: feed, transition, and metering.
The extrusion screw sequentially conveys and heats food ingredients and works
them into a continuous plasticized mass while rotating in a tightly fitting barrel.
The screw can be designed either a single piece or as a splined shaft that
accepts screw sections of varying configurations to increase versatility and

reduce the cost of replacing worn sections (Harper, 1989).

2.2.3. Twin-Screw extruders

Twin-Screw Extruders consist of two screws of equal length placed inside the
same barrel for its entire length (Martelli 1983). Twin-Screw extruders are
classified according to the position Of the screws in relation to one another and to
the direction Of screw rotation (lFT, 1989; Riaz, 2000). Therefore, twin-screw
extruders can be (1) counterrotating and corotating twin-screw extruders. These
categories Of twin-screw extruders can be further subdivided into intermeshing

and non-intermeshing. In intermeshing twin-screw extruders, the flights of one

17

screw engage or penetrate the channels of the screw while in non-intermeshing

twin-screw extruders each screw turns without interference from the other.

2.2.4. Benefits of extrusion cooking

Extrusion is a processing technology used to produce foodstuffs such as
breakfast cereals, snack foods, baby foods, pet foods, modified starches, etc. By
controlling variables such as temperature, moisture, and screw speed in the
extruder, food ingredients undergo physical and chemical changes such as
starch gelatinization and protein denaturation. These molecular transformations
convert food material into a visco-elastic dough under the presence of heat,

moisture, shear, and pressure.

2.2.4.1. Starch gelatinization

Starch granules undergo gelatinization and melting by the action of heat and
moisture on hydrogen bonding among tightly packed polysaccharide chains in
the granule structure. Under conditions of excess water, hydrogen bonding in the
less ordered amorphous regions of the granule is disrupted first, allowing water
to associate with free hydroxyl groups. This is marked by polymer chain
mobilization and can be called glass transition, Tg. Swelling is the result, and
further opening Of the granule structure to the action Of water occurs. Melting Of
the crystalline fraction results in complete disappearance of birefringence, which

is irreversible.

l8

As starch is heated to gelatinization temperature, the heat energy begins to
dissociate the more weakly bonded regions within the starch granules, water
moves into the granule and it begins to swell. The swelling continues as the
temperature is raised. Shorter of the linear molecules actually diffuse out of the
swollen granule and into the surrounding liquid. However, the longer linear
chains wander through the granule among the bushy amylopectin molecules and
act to keep the molecule together and prevent complete solubilization. As the
granules take up water and swell, they occupy more space and friction is created
between granules. The starch paste becomes thicker, the consistency reflecting
the resistance to stirring of the mass of swollen particles. The greater the granule
swelling the higher will be the viscosity. However, swollen granules are fragile
and are deformed and fragmented by swelling with the consequent thinning of

the mixture (Schultz et al., 1969)

The final collapse of the granule is marked by release of remaining hydrated,
gelatinized contents into the cooking medium. Viscosity of the medium increases
rapidly until a majority of the granules are completely collapsed, which results in

a set back in viscosity.

The gelatinization process allows greater susceptibility of starch tO enzymatic

hydrolysis and, subsequently, higher starch digestibility.

19

2.2.4.2. Protein denaturation and digestibility

The nutritive value of a protein depends on the ease with which it can be
digested. Many factors including the presence of protease inhibitors can reduce
the amount of protein for intestinal absorption. The heat generated during
extrusion cooking improves the digestibility Of proteins by inactivating enzyme
inhibitors and denaturing the protein, which may expose new sites for enzyme

aflack.

Alteration from the naturally ordered conformation of a protein molecule to a
randomly structured molecule is called denaturation (Orten and Neuhaus, 1970).
Most proteins are sensitive to changes in pH, ion concentration and temperature.
The highly native protein is easily disrupted as weak cross-linkages are broken.
The polypeptide chains may unfold and the helix becomes disordered.
Denaturation does not include breaking of the peptide linkage in a hydrolysis
process. Hydrolysis Of proteins, except when carried out by enzymes, requires

extreme conditions of heat and acidity and alkalinity.

2.2.5. Low-cost extrusion cooking

Low-cost extrusion cooking has been studied with encouraging success (Harper
and Jansen, 1981) and could offer the long-term solution the malnutrition
problem among children in developing countries, for example. Africa. Childhood
malnutrition is a serious health problem in several countries of the world. In a

country such as Tanzania, in East Africa, 200,000 children die annually under the

20

age Of five as a result of inadequate protein, energy. and/micronutrients (Mosha
and Bennink, 2004). However, most of studies (Harper and Jansen, 1981) were
on soybean and did not include foods local to the developing countries such as

root/stem tubers and dry beans.

Low-cost extrusion cooking has been suggested as a suitable alternative for
mass production Of pre-cooked, nutritious cereal and legume foods are shelf-
stable (Harper and Jensen, 1985). Extrusion cooking technology is still limited in
developing countries. Developing countries can benefit from low-cost extruders in
the following ways. (Moquet et al, 2003).

1. Women in the countryside can save time they use gathering firewood to
cook beans;

2. Low-cost extruders can be used to process local foods such as corn,
cassava, potato, beans into nutritious snacks. The snacks can be ground
into powder that can be used to prepare nutritious porridge that can
prevent malnutrition, especially among children;

3. Low-cost extruders are suitable for countries Of low income as they are

cost-effective and require less technology skills.

In most developing countries, extrusion cooking is not very popular in food
processing enterprises because its full potential has not been well recognized
(Dedeh and Saalia, 1997). One Of the major reasons why adoption Of extrusion

cooking for processing of ready-tO-eat foods and infant flours is very limited in

21

poor countries is that the present extruders are designed for large scale
production, thus requiring very high investment and technical knowledge (Moquet
et al., 2003). Even the so-called low-cost extruders, that were designed for the
production of complementary foods around 19803 by the University of Colorado
(Harper, 1985; Harper and Jansen, 1985; Said, 2000), are too costly and their
production capacity is too high (approximately 55,000 US. dollars for an extruder
with production capacity of 1 ton an hour). These extruders are thus not
affordable for developing countries. Therefore, the development of a small and
simple low-cost extruder (about 22,000 dollars with production capacity of about

100 kg an hour) would be Of great potential interest for countries with low income.

22

CHAPTER 3: MATERIALS AND METHODS
3.1. Raw material
Whole dry light red kidney beans (Phaseolus vulgaris L.), harvested in 2005 and
having ~13% moisture content (appendix 6), were purchased from Bayside Best
Beans, LLC (Sebewiang, Mich., USA.) The beans were hand-sorted to remove
splits, wrinkled seeds, and any debris and stored at 4°C until needed for

extmsion processing.

3.2. Extrusion experiments (Objective 1)

Before extrusion dry light red kidney beans were ground with a hammer mill
(Model D comminuting Machine, The W.J. Fitzpatrick Company, Chicago USA)
to pass through mesh NO. 50 US standard. Extrusion runs of raw ground red
kidney beans were carried out in duplicate using a low-cost (less than $20,000)
laboratory co-rotating twin-screw extruder model JS30A manufactured in China
by Qitong Chemical Industry Equipment CO, Ltd. The screws are 30 mm in
diameter and the barrel has a L/D of 14. A full factorial design was used. Raw
light red kidney bean flour was extruded at 25% and 36% moisture content wet
basis; screw speed was 118, 194 or 253 rpm; feed rate of bean flour was 80 or
1209/min and extrusion barrel temperatures were 105 and 120°C (temperature
profile 1) and 115 and 130°C for temperature profile 2 (Table 3.2.1) where 120°C
and 130°C are nearest the die end of the extruder. The die was a plate with one
7-mm diameter circular hole. Moisture content was determined using the formula

in appendix 5.

23

Table 3.2.1. Experimental design

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample Screw
Number Barrel Temperature Moisture Speed Flour Feedrate
(°C) Content (%)* (rpm) (9/min)
1 120/105 25 1 18 80
2 120/105 25 184 80
3 120l105 25 253 80
4 120/105 25 118 120
5 120/105 25 184 120
6 120/105 25 253 120
7 120/105 36 1 18 80
8 120/105 36 184 80
9 120/105 36 253 80
10 120/105 36 118 120
11 120/105 36 184 120
12 120/105 36 253 120
13 130/115 25 118 80
14 130/115 25 184 80
15 130/115 25 253 80
16 130/115 25 118 120
17 130/115 25 184 120
18 130/115 25 253 120
19 130/115 36 118 80
20 130/1 15 36 184 80
21 130/1 15 36 253 80
22 130/115 36 118 120
23 130/115 36 184 120
24 130/1 15 36 253 120

 

 

 

 

 

*Moisture content was calculated using the formula in appendix 5

24

 

Table 3.2.2. Extruder specification

 

Kneading and cooking

. Mixing lobes Reverse
TWIN-lead paddles
sectlon

JS30A extruder is a twin-screw extruder. The 425 mm length solid twin screws
with fixed configuration are divided into four segments. The first segment is a
twin-lead section in the feeding zone. It is followed by mixing lobes and 30°
reverse paddles. The next segment towards the die end that is used for kneading

and mixing has uniform configuration of 90° mixing lobes.

25

3.2.1. Fabrication of feeder

The feeder used throughout the study was designed in the shop Of the
Department of Biosystems Engineering, Michigan State University. Motor and
auger were purchased from Grainger (Lansing MI) while other parts like hopper
and general assembling of the parts were done in the shop of the Department of

Agricultural and Biosystems Engineering of Michigan State University.

3.2.2. Calibration of feeder

The single-screw extruder feeder described in 3.2.1 above was calibrated by
setting a range of feed rates and weighing feed material every 30 seconds. Each
collection was done 5 times. The feeder had a coefficient Of variation (CV) Of
about 3%. Afterwards a calibration equation was made for extrusion

experiments.

3.2.3. Calibration of water pump

Calibration of water pump was done in a similar way as the extruder feeder
(3.2.2). Water was collected at different pump rates every 30 seconds and
weighed. Each collection was done five times. A calibration equation was

Obtained for extrusion.

3.2.4. Estimation of degree of fill
Degree of fill is affected by changing screw speed and feed rate. Extruding at
different conditions such as screw speed and feed rate may affect the degree of

fill and shear and amount Of mixing on the material being processed. Lower

26

degree Of fill allows more mixing. This may influence the quality characteristics of
extruded products. To estimate the degree of fill of the extruder used for all runs,
we measured the volume of the twin screws. Briefly the screws were submerged
in 2000 volumetric cylinder and the volume of water displaced was taken as the
volume of screws which was 0.000384 m3. The volume of the screws was then
used in the computation of void volume of the extmder. Percent fill was

calculated as follows:

%fiII=—”’—’x100

vd
Where
n“: = mass flow rate of dough (m flour + n“: water) (kg/s)
i = residence time, s
v = void volume of the extruder (m3) was 2.02 x 10" m3

d = dough density (kg/m3) was 1100 mm3

For the dough density measurement, the method used by Schmid et al., 2005
was used. Briefly, a sample of dough was taken near the entrance of the extruder
die, wrapped in a pre-weighed plastic wrap and then weighed. After recording the
weight, the dough was place in a 100 mL graduated cylinder filled with 30 mL
distilled water. Dough volume was recorded as the volume of water displaced by
the dough. The density Of the dough was calculated as the weight Of the dough

(kg) divided by the dough volume (m3).

27

3.2.5. Residence Time Distribution

Average retention time is very important during extrusion cooking. Residence
time distribution is a measure of the length of time the material spends in an
extruder barrel. Residence time distribution in an extruder is a useful means of
determining optimal processing conditions for mixing, cooking, and shearing
reactions during the process. From knowledge Of RTD function one can estimate
the degree of mixing, the residence time of mass flow, and the average total
strain exerted on the mass during its transition and thus provide a clearer picture
of how an extruder behaves as chemical reactor (Fichtali and Van de Voort,
1989). Residence time distribution, like degree of fill, is also affected by feed rate

and screw speed.

3.2.5.1. Preparation of dyed flour to measure Residence Time Distribution

Twenty grams Of extruded bean flour was mixed with 8 mL of water-based red
dye #1080-0500 (Craft Store, Cordova, TN) by weight. The dye was poured on
the flour and mixed until the dye was completely absorbed. The mixture was the
let to dry at room temperature until sufficient moisture had evaporated for the
sample to be milled. The dye-flour mixture was coarsely ground using a mortar

and a pestle.

3.2.5.2. Residence time sample collection

Mean residence times were determined using a tracer (red dye) described in

3.2.4.1. At each extrusion run, approximately 4.0 g of the residence time dye was

28

added instantaneously to the barrel hopper. Time in seconds was recorded from
when the dye was added until color was seen coming out through the die.
Samples were then collected every five seconds from the time color appeared in
the extrudate until the there was no more color visible in the bean extrudate. A
strand was collected prior to color injection to represent the color value at time
zero. The samples were placed in aluminium pans in sequence and allowed to
dry at room temperature for 24 hr until they were dried. A coffee grinder
(Sunbeam Corporation, Maitland, FL) was used to grind each strand. Each
sample in the amount of approximately 2.0 g was then placed into a round disc
with a 3.5 cm diameter and 0.5 cm height. A hunterLab 025 L color meter
(Hunter Associates Laboratory, Reston, VA) measured the a* value (redness) Of
the ground samples. Results were reported as color minus control color. A white
tile (Standard NO. 02-30954) was used to standardize the colorimeter. Redness
values were recorded and were used to represent the intensity color (t) of red

color at exit time t.

3.2.5.3. Color concentration calibration curve

The idea of color-concentration curve for residence time distribution was
developed by Peng et al., (1994) and was applied for all residence time samples
in this study. Unlike the linear “standard curve” typically used for High
Performance Liquid Chromatography (HPLC), the calibration curve for
concentration versus color is non-linear. At high concentrations, there is a color
saturation effect, where large increases of concentration cause only minimal

changes in color readings. Seven batches Of flour were prepared by mixing 5, 10,

29

25, 75, 100, 150, and 200 mL dye with 3009 bean flour. A spray bottle was used
to spray the dye onto the flour in aluminium pan. Sprayed flour was allowed to sit
overnight so that the flour could fully absorb the dye. The flour mixtures were
then placed in the dryer at approximately 80°C. After drying to a state that could
be extruded, the samples were extruded at 809/min feed rate; 25% moisture
content and 118 rpm screw speed. Each of seven batch was extruded
separately and after a steady state was attained, samples for color reading were
collected. Samples were placed in aluminium pans and allowed to dry for 4 hours
in the oven at 80°C. A coffee grinder was used to grind samples and color
readings were taken in triplicate. Color was measured using a Hunter Color
Difference Meter (025 DP 9000 System Hunter Color Associates Lab., Reston,
VA). Color readings (a*) were plotted against dye concentration to obtain a
calibration curve. This relationship was then applied to all residence time data to
estimate mean residence time. This calibration curve is used to convert all
extrudates color values to color concentration, c. Normalized concentration E(t)

was calculated according to Levenspiel (1999):

cf
‘ z,- ciAti

 

E(t) = c")
Ojoc(t)dt
0

The normalized concentration, E(t), was used to calculate mean residence time,

t

30

E: tE(t)dt=—'————

3.2.6. Specific mechanical energy

Efficiency is always a major concern for engineers. Food extrusion is an energy
efficient process because a substantial amount Of the mechanical energy from
the extruder motor is dissipated during the viscous flow within the extruder barrel.
Specific mechanical energy (SME) is a measure Of the viscous energy
dissipation per unit mass of dough (Mason and Hosneney, 1986). This energy
originates from the direct current motor supply which provides the required
torque to turn screws at a given screw speed. A portion of total power supplied to
the shaft is used to push dough along the barrel against back pressure generated
at the die (Mohamed et al., 1990). The remaining power is transferred into the
dough via fluid friction. Therefore, specific mechanical energy is calculated as the
total power supplied to the shaft (kW), divided by the mass flow rate.

3.2.7. Physical characteristics of bean extrudates (Objective 1)

3.2.7.1. Expansion ratio

After drying extrudates at room temperature for 24 hours, the average diameter
of 5 randomly selected extrudates were measured for each treatment using a
vemier caliper. Per sample, five strands were randomly selected and three
measurements were taken along the product. The ratio of the mean diameter of

the extrudates to the die diameter of 7 mm was calculated as the expansion ratio.

31

3.2.7.2. Bulk density

The bean extrudate pieces that were approximately 0.5 cm long of extrudate
were placed in a 100 mL graduated measuring cylinder. The graduated cylinder
with extruded bean pieces was tapped gently on a flat surface before weighing.
The bulk density was calculated as weight per unit volume, as:

Bulk density = g of sample per 100mL
100mL

Duplicate determinations were made for each sample.

3.2.7.3. Water Absorption Index

The determination of Water Absorption Index was determined according to the
method reported by Mason and Hoseney (1986), Gomez and Aguilera (1983)
and Anderson et al., (1969). Briefly, 20 g Of extruded bean extrudate was mixed
in 20 mL of distilled water at 30°C and centrifuged at 1000 x g for 15 min. The
supernatant was dried in an oven at 130°C for 2 hours. Taking two
measurements per sample, Water Absorption was calculated as the increase in
weight Of the sediment (gel) formed after decanting the supernatant.

WAI = (weight Of sediment + centrifuge tube) — (weight Of centrifuge tube)
Sample dry weight

3.2.7.4. Water Solubility Index
The supernatant from the water absorption determination was decanted in a pre-

weighed moisture dished and evaporated to constant weight in the oven. Water

32

Solubility Index was calculated as a percentage of soluble material using the

following equation:

% WSI = (weight of dish + dried sgpematant) - (weight of dish) x 100

Sample dry weight
3.3. Starch gelatinization
Sample preparation for Rapid Visco Analyzer
After extrusion, the extrudates were dried in a tray drier at 60°C for overnight to
Obtain dry samples having moisture content of approximately 5 %. Extrudates
were then ground in a coffee grinder so that they could pass through a 80-mesh
United States Standard sieve and used for the determination of pasting

characteristics.

Viscosity measurements

The pasting profile was determined using a RVA (Newport Scientific, Narabeen,
Australia) according to the manufacturer’s instructions using the following profile:
a 2 min hold at 25°C followed by a target temperature Of 95°C at 7 min., holding
at 95°C to 10 min and cooling back to 25°C at 15 min and holding to complete
profile at 20 min. A 3-9 sample (14% moisture dry basis) was mixed with 25 mL
of distilled water and transferred to the aluminium sample holder can (Walker et

al., 1988; Deffenbaugh & Walker, 1990).

The parameters that were Obtained from RVA included:

33

a) Initial viscosity (IV), i.e. the viscosity Obtained at 25°C at the beginning of
RVA study.

b) Peak Viscosity (PV), i.e. the highest viscosity shown by the paste in the
peak formed by joining the inflection points of the base line viscosity
curves during the heating phase.

C) Hot-paste viscosity (HPV), i.e. the viscosity of the paste at the end of the
heating phase at 95°C

d) Cold-paste viscosity (CPV), i.e. the viscosity of the paste at the end Of the

cooling phase, namely at 25°C.

The area under the peak occurring during the heating phase Of the pasting curve
exhibited by the extrudated samples, relative to that Of raw beans (as 100%),
represented the ungelatinized or uncooked part, which after subtraction from 100

yielded the extent Of gelatinization (Newport Scientific, Narabeen, Australia).

3.4. Phytohemagglutinin assay (Objective 2)

Boniglia et al., (2003) identified Iectins (phytohemagglutinins) in kidney beans as
a major antinutrient factor. Phytohemagglutinins are proteins present in a variety
of legume seeds including dry beans (Phaseolus vulgaris L.) Lectins are believed
to have antinutritional properties by interfering with growth and utilization of
dietary nutrients (Puztai, 1977). Active phytohemagglutinins are also believed to

cause food poisoning.

34

For all treatments including raw dry beans (control), samples were extracted
according to the method of Boniglia and others (2003). Briefly, 1-g samples Of
finely ground extruded beans (0.5 mm mesh size) were extracted in 20 mL of
PBS (phosphate buffer solution, 10 mM, pH 7.2 containing 150 mM NaCl) by
stirring overnight using a magnetic stirrer at room temperature. After
centrifugation (10,000 X g, 35 min, 10 °C), the supernatant was collected and the
pellets were re-extracted twice in 10 mL PBS, stirred as above for 2 h at room
temperature and centrifuged as above. The clear supernatant was collected and

stored at 4 °C until further analysis.

The detection of active phytohemagglutinin activity (PHA) in bean samples was
performed by ELISA, according to the method of Boniglia and others (2003).
Microtiter plates, coated overnight at 4 °C with 0.1 mL Of porcine thyroglobulin (8
ng/pL in 50 mM carbonate-bicarbonate buffer, pH 9.8), were washed twice with
PBT (phosphate buffer 10 mM, pH 7.2 containing 0.05% Tween 20) and once
with PBS (phosphate buffer 10 mM pH 7.2 containing 150 mM NaCl). Remaining
plastic reactive sites were blocked by incubation (1 h, 37 °C) with PBS
supplemented with 0.5% bovine serum albumin (BSA). The wells were then
washed as described above and loaded in triplicate with 0.1 mL sample extracts
diluted 1:50 in PBS. After 1 h at 37 °C, the wells were washed, loaded with 0.1
mL rabbit anti-PHA lgG diluted 1:5000 in PBS containing 0.25 BSA (P888) and
incubated for 1 h at 37 °C. After washing, 0.1 mL alkaline phosphatase-

conjugate monoclonal anti-rabbit lgG diluted in PBS (1:10000) was added to

35

each well and incubated for one more h at 37 °C. The wells were washed twice
with PBT and once with PBS followed by 0.1 mL of P-nitrophenyl phosphate for
color development. After 1 h at 37 °C, the reaction was stopped by the addition
of 50 pL of 3M NaOH and the absorbance read at 405 nm (Benchmark

Microplate Reader; BiORad, Hercules, Calif, USA).

3.5. Sensory evaluation of extruded bean porridge (Objective 3)

Sensory evaluation of extruded bean porridge was carried out at the National
University hospital located in the southern of province of Rwanda. 75 panelists
comprised mostly of adult low-income women who evaluated bean porridge and
compared it with a local porridge known as sosoma. Sosoma is a blend Of corn,
sorghum, wheat, and soy and is fed to undernourished populations. Only
panelists that could sign the consent statement were selected. The MSU
Biomedical, Health Sciences lntuitional Review Board, approved the study
protocol (appendix 4). The panelists were asked to read and sign a consent
statement and were compensated with a free bottle of soda at the end of sensory
exercise for their participation in the study. All evaluations were conducted at
room temperature (24 1: 1 °C) on the same day in the hospital kitchen Of the

Faculty of Medicine of the National University Of Rwanda.

Extruded bean porridge was prepared the same morning the sensory evaluation

was carried out. Extruded bean porridge was prepared approximately in the ratio

of 1:1:8(w/w) for extruded bean powder, sugar, and water respectively. On the

36

same morning of sensory evaluation, approximately 40-9 samples of extruded
bean porridge were placed in 85-9 clear plastic cups that were labeled with three-
digit random codes (723 and 829 for sosoma and extruded bean porridge
respectively) and kept at room temperature before serving to the panelists. The
hospital nurses were trained to assist the panelists on how to fill out the sensory
questionnaire. Samples were presented in random order and panelists were
asked to rate their liking for color, texture, sweetness, flavor and overall
acceptability on a 1-9 hedonic scale (9=like extremely, 8=like very much, 7=like
moderately, 6=dislike slightly, 5=neither like nor dislike, 4=dislike slightly,
3=dislike moderately, 2=dislike very much, 1=dislike extremely) (Meilgaard and
others 1999). Questionnaires were prepared and provided to the panelists using
SIMS Sensory Evaluation Software, version 6.0 (Sensory Computer Systems,
Morristown, N.Y., U.S.A.). Panelists’ responses were entered manually in a
computer for analysis using. A score of 5 or below was considered a limit of

acceptability for all sensory attributes tested.

3.6. Calculation of energy and cost consumption by extruder (Objective 4)
The energy and cost consumption by the extruder was calculated using the
following parameters:

1. Total feed rate (kg/hr)

2. Power meter reading (kW)

3. Cost Of1 kWhr

37

Specific Mechanical Energy (SME) (kJ/kg) was calculated by dividing averaged
power reading by total feed rate. Specific Mechanical Energy (kWh/ton) was
calculated by multiplying SME (kJ/kg) by 3.6. The cost of SME (kWh/ton) was
calculated by multiplying the SME (kWh/ton) by the cost Of 1 kWh. Energy and
cost consumption by extruder was calculated for both United States and Rwanda

(Table 4.4).

3.7. Statistical analysis
All data were analyzed either by Analysis of Variance (ANOVA) using JMP IN
software, version 5.1 (SAS Institute, Inc., Cary, NC, USA.) or Microsoft excel

(plots).

38

CHAPTER 4: RESULTS AND DISCUSSION

4.1. Estimation of degree of fill

Figure 4.1 shows the effect of screw speed on the degree of fill at 25% and 36%
moisture. Increasing screw speed while keeping mass flow rate constant
significantly (p=0.0234) decreased the degree Of fill at 36% moisture content. At
25% percent moisture, increasing screw speed did not significantly (p= 0.0900)
decrease the degree of fill. Because moisture content has a nominal effect on the
mean residence time (Altimore and Ghossi, 1986), increasing moisture content at

constant flour feed rate increased total mass flow rate which increased the

degree of fill (figure 4.1).

 

 

 

 

 

 

 

0.80
0.75 ~+ MC=36%
p=0.001
0.70 ~
E 055° MC=25%
o 0.50 . p=0.13
0
g 0'55 ‘ MC=36%
a 0.50— 9:002
0.45 ‘ M-C=250/°
0.40 - p-0.09
0.35 . . . .
50 100 150 200 250
Screw speed (rpm)

 

Figure 4.1 Effect of screw speed on the degree of fill

Higher fill levels result in a shorter and tighter residence time distribution (RTD)

and less shear, and lower fill levels are associated with wider RTD and more

39

 

shear (Supamo, 2004). Fill level approximations help explain why different
processes benefit from comparative fill level percentages. For lower barrel

temperature, the lines are reversed because mean residence times are reversed.

4.2. Residence Time Distribution Analysis

4.2.1. Color Concentration Calibration Curve

Figure 4.2 below shows a relationship between color reading and dye
concentration. The curve was approximately linear up to a*=15 at cconcentration

of approximately 20 mL dye/3009 flour. At higher concentration, the curve was

 

 

 

 

I Color a* (Hunter units) I

nonlinear.
250 e - f -- z 32 -29 ,1 I
f I I
. I I
i '5 200: 4 3 ’ I I
I ,g y=0.0045x -0.1553x +1.8023x2-7.2758x+13.185 I ;
i 2: I I
I £15m R 0.97 ; s
n I I
I E . I I
I 'o 100 I I
I “5 I I I
I -' I y=1.031x+0.0956 I
I E 50I R2=0.99 I ‘
ol- ————k T'F .__._______..T ,‘ ———————~—-—I I
° I
I
I

 

 

Figure 4.2. CalibratiOnwcu—rve for color concentration versus Hunter colOr
values (a*) for extruded light red kidney bean flour

40

Figure 4.2 above shows the data points dye concentration versus Hunter color
values for samples extruded at 36% moisture content; flour feed rate of 120
g/min; screw speed of 253 rpm; and barrel temperature of 120 (zone 1 near die
end)/105 (zone 2 near feed zone). Two trend lines were used to fit data points at
lower and higher concentrations. One trend line did not pass through data points
at higher concentrations. The calibration curve was used for all extrusion runs to
convert all Hunter a* color to color concentration for determination of mean

residence time.

Importance of residence time

Each particle experiences a different residence time. This affects gelatinization,
protein denaturation, product texture, flavor, color, pathogen destruction (food
safety), expansion, viscosity, water solubility index, water absorption index,
inactivation Of antinutritional factors. Shear history is affected most by feed rate

and screw speed (Altimore and Ghoss, 1986).

Efiect of Screw Speed on the residence time

Screw speed is one Of the process parameters which has a strong effect on
Residence Time Distribution (RTD) and Mean Residence Time (MRT). Screw
speed determines the amount of time the material resides in the extruder barrel.
According to figure 4.3 below, increasing screw speed decreased mean
residence time. Screw speed is one of the variables determining the amount of

time the material resides in the extruder. When all factors, for example, feed rate,

41

moisture content are held constant, when screw speed is increased, the
residence time is reduced. This effect has been validated by Ainsworth et al.,
(1997), Yeh and Jaw (1998), Ollet and et al., (1989), Gogoi and Yam (1994).
Altimore and Ghossi, (1986) also reported shorter mean residence times when
screw speed was increased at constant throughput. Increasing screw speed also
shortens residence time distribution curve. De Ruyck (1997) also reported that

increasing screw speed decreases mean residence time.

0.35

 

0.30 «

0.25 «

0.20 .

0.15 ~

0.10 ‘

Normalized concentration, E(t)

0.05 I

 

 

 

0.00

 

 

20 30 40 50 60 70 80 90 100
Exit age (5)

I_-___

 

 

Figure 4.3 A representative of the effect of screw speed on Residence Time“
Distribution

*Exit age is the time measured from when the color tracer was dropped into the extruder
entrance (hopper) until color appeared at die exit.

A: Screw speed = 118 rpm; Feed rate = 80 glmin; Moisture = 25 %;
Mean Residence Time = 70.65 (sample 3, Table 3.2.1)

8: Screw speed = 184 rpm; Feed rate = 80 glmin; Moisture = 25 %;
Mean Residence Time = 66.35 (sample 2, Table 3.2.1)

C: Screw speed = 253 rpm; Feed rate = 80 glmin; moisture = 25 %;
Mean Residence Time = 57.05 (sample 1, Table 3.2.1)

42

I

Effect of feed rate (throughput)

Feed rate is the input rate of the material into the extruder. It is another process
variable which has a pronounced effect on residence time. Mean Residence
Time and Residence Time Distribution have been reported to decrease with
increase in feed rates (De Ruyck, 1997), Yeh et al., 1992. As figure 4.3 shows,
the influence of throughput on the residence time is dramatic. As shown by the
figure, at the lower feed rates where the extruder is less filled, there is less
tendency for the extruder to provide positive conveyance. According to the
present study the effect of throughput was more pronounced than that of screw
speed (appendix Table A.3). Ainsworth and others (1997) also reported that
increasing throughput decreased mean residence time than screw speed. When
throughput is increased there is more material going through the extruder with
time, leading to a decrease in the time the material will stay in the extruder, thus

decreasing residence time.

43

 

a l .
H1303. ~

lgo.25~
13.2} '
ié ’1 I
‘3045 '
i; 0-1l ‘
lE0-05* ,
E 0L k l
20 .'

Exlt age (5) ‘

 

Figure 4.4. A representation of the effect of feed rate on Residence Time
Distribution

A: Feed rate = 80 glmin; Screw speed = 253 rpm; Moisture = 25 %; MRT=57.05
(sample 3, Table 3.2.1)
B: Feed rate = 120 glmin; screw speed = 253 rpm; Moisture = 25%; MRT=50.45
(sample 6, Table 3.2.1)

When the feed rate is increased there will be more material going into the
extruder with time, reducing mixing leading to a decrease in the time the material

will stay in the extruder, thus decreasing the residence time.

Effect of Moisture content on residence time distribution

Moisture content of the feed material is another process variable that affects the
residence of the dough inside the extruder. Generally, for the present study
increasing moisture content slightly resulted in wider residence time distribution.
Gogoi and Yam (1994), Altomare and Ghossi (1986) reported that moisture
content has a nominal effect on the mean residence time. In their study,

increasing moisture from 10% to 28.4% only raised the residence time from 21 to

44

24.5 seconds. However the effect is not as pronounced as for feed rate and

screw speed.

3 J
l
l
l
1
|
}

ES“
'8

.0
N

 

.0
.3
U1

i

.0
—L

 

Nornglized Concenb'atro
'o
01

 

O

|
0 20 40 60 80 100 i
‘ Exlt age (seconds) ‘

 

Figure 4.5. Effect of moisture content on residence time distribution at
barrel temperature 120I105°C

A: Feed rate = 120 glmin; Screw speed = 253 rpm; Moisture = 36 %; MRT=44.25 (sample 12, Table 3.2.1)
8: Feed rate = 120 glmin; screw speed = 253 rpm; Moisture = 25%; MRT= 50.45 (sample 6, Table 3.2.1)

45

 

 

. E l
‘ g 0.25 i l
l E 0.2 i 5 1
1 Em A l l
’ § 0.1- ' I
i €0.05.
l o . -- _ l ~
20 100
; Exittime(s) l
L i

 

 

 

Figure 4.6. Effect of barrel temperature on residence time distribution at
moisture content = 36%

A: Feed rate = 80 glmin; Screw speed = 253 rpm; Moisture = 36 %; MRT=49.85 at barrel
temperature 120/105°C (sample 9, Table 3.2.1)

8: Feed rate = 80 glmin; screw speed = 253 rpm; Moisture = 36%; MRT= 53.25 at barrel
temperature 130/115°C (Table 3.2.1)

4.3. Specific Mechanical Energy

Effect of screw speed on specific mechanical energy

At a constant feed rate, increasing screw speed resulted in an increase in
specific mechanical energy (SME) input (figure 4.6). A5 a consequence, there

was a simultaneous increase in the product temperature (PT) at the extruder die.

46

R2 = 0.8195 '

 

 

Specific Mechanical Energy (kJIkg)
K3
.8
o

 

 

1 A !

l l
’ MC 36% l

i 9°” 1 Mc=25% p=0.0184 l
' l

l . ,
. l ‘

600.0 -+- - --—T—---—— , -fii __ _ _ .. AT- ,7! _ _J_ .

80 130 180 230 280 E

Screw speed (rpm) 1

L_E__ l

Figure 4.6. Effect of Screw speed on specific mechanical energy at
constant flour feed rate = 809Imin at two moisture contents
From figure 4.6 above, it is clear that the specific mechanical energy increases

 

 

with increase in screw speed and decrease in total feed rate. It can therefore be
implied that the specific mechanical energy will be lowest when the mean

residence time will be the lowest.

4.4. Physical characteristics of been extrudates

4.4.1. Expansion ratio

The expansion ratio is an important characteristic of extruded products. Highly
expanded products have softer texture. Expansion ratio is a measure of cross

sectional area of the extrudate. Expansion takes place due to sudden exit of

47

molten mass from the restricted die from very high pressure to atmosphere giving
improved texture to the extrudate. The results of expansion ratio are shown in
Table 4.1 below. For all the extmsion variables studied, only feed rate
significantly (p=0.003) increased expansion ratio. This effect may be due to fully
developed flow at the die that caused some expansion. Moisture content
(p=0.13), screw speed (p=0.10), and product temperature (p=0.4245) did not
significantly affect expansion ratio. This lack of effect was probably due to the
presence of high level of protein in light red kidney beans which reduced
expansion. The high levels of disulfide and sulfhyde groups in legumes may
affect the physical properties of extruded bean products. Iwe and Ngoddi (1998)
reported the same results. Berrios and Pan (2001) reported that the fine—ground
bean flours produced extrudates with significantly higher expansion ratio than the
extrudates from medium- and coarse-ground raw material flours. Therefore, the
course-ground flour used as a raw material may be one of the factors that
caused low expansion indices of extruded light red kidney beans. Also,
extrudates with high protein contenttend to have low expansion ratio and high
bulk density (Anderson, 1998). This may be the cause of toughening in high
protein extrudates such as beans. Expansion ratio of dry beans (100 %) is very
low. Addition of sodium carbonate to the bean flour before extrusion increases

expansion ratio (Berrios and Pan, 2001).

48

4.4.2. Bulk density

Bulk density, expressed as g/cm3, is also a measurement of expansion ratio of
the extrudate. Edwards et al. (1994) indicated that bulk density considers sample
weight and the three dimensional changes of the extrudate resulting from
expansion at the die. Bulk density is inversely proportional to expansion ratio.
The effect of extrusion variables on bulk density is shown in table 4.3. According
to our results, there was significant difference in bulk density for product moisture
content (p=0.05). Bulk density was higher for 36% moisture content. This is
possible because at higher moisture there is lower expansion ratio. High
moisture may have reduced pressure at the die that is believed to increase
expansion. There was no significant difference in bulk density for feed rate
(p=0.84) and screw speed (p=0.23). Although not significantly different (p=0.23).
bulk density increased slightly with increase in screw speed (from 118 to 253
rpm). Ferdinand et al. (1990) reported lowering moisture content lowered bulk
density. He also reported that bulk density decreased with increasing screw

speed.

49

Table 4.1. Expansion ratio and bulk density under different extrusion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

conditions
Sample Barrel Feed Moisture Screw Bulk Expansion
number Temperature rate content speed densi ratio
CC) (glmin) (%) (rpm) (glcm )
1 120/105 80 25 1 18 39.712.90 1.2310032
2 120/105 80 25 184 38.612.57 1.3010023
3 120/105 80 25 253 38.61078 1.3510035
4 120/105 120 25 118 41.011.29 1.2610071
5 120/105 120 25 184 40.41095 1.3410006
6 120/105 120 25 253 40.010.81 1 2910.011
7 120/105 80 36 118 40.710.57 1.1810044
8 120/105 80 36 184 40.710.50 1.1910002
9 120/105 80 36 253 38.810.57 1.2210003
10 120/105 120 36 118 40.210.99 1.3210142
11 120/105 120 36 184 40.210.76 1.3610114
12 120/105 120 36 253 40.711.19 1.3510110
13 130/115 80 25 118 40.510.49 1.2710037
14 130/115 80 25 184 39.310.66 1.2110006
15 130/115 80 25 253 37.411.40 1.2510066
16 130/115 120 25 118 36.71040 1.2410101
17 130/115 120 25 184 36.91101 1.2210002
18 130/115 120 25 253 37.21085 1.3710001
19 130/115 80 36 118 39.41081 1.1410092
20 130/115 80 36 184 40.310.61 1.1510002
21 130/115 80 36 253 39.111.20 1.2110084
22 130/115 120 36 118 40.110.85 1.2410062
23 130/115 120 36 184 40.110.71 1.2410021
24 130/115 120 36 253 38.411.53 1.3110026

 

 

 

 

 

 

 

Bulk density and expansion ratio are the average of 2 replicate values1standard deviation

50

 

4.4.3. Water Absorption Index (WAI)

The effect of extrusion variables: feed rate, product temperature, screw speed,
and moisture content moisture using a 7.0 mm die on Water Absorption Index
and Water Solubility Index are shown in Table 4.2. Feed rate (p=0.15), moisture
content (p=0.78) and screw speed (p=0.74) did not significantly affect water
absorption index. Although there was no significant difference, water absorption
index decreased with decrease in feed rate (809/min) and increase in moisture
content (36%). Colonna and Mercier, 1983 reported the same results. However,
this is contrary to what Njoki 8 Faller (2001) observed for extruded
plantain/com/soy blend. Increasing screw speed did not have a significant
difference (p=0.74) on water absorption index. However, water absorption index
increased slightly with increase in screw speed (118 to 253 rpm). Lower water
absorption index at lower screw speed may be attributed to severe degradation
of starch granules as a result of long residence time. The water absorption index
increased with increasing screw speed. This was probably caused structural
modification of fiber. Badrie and Mellows (1991) reported changes from a more
sheet-like micro-structure to a more disrupted appearance when shear was

increased.

51

4.4.4. Water Solubility Index

The water solubility index is related to the presence of soluble molecules, which
is related to dextrinisation (Colonna et al 1989). Table 4.2 shows the effect of
barrel temperature, feed rate, screw speed, and moisture content on water
solubility index. Increasing flour feed rate significantly (p=0.0001) increased
water solubility index. The average water solubility indices for 80 and 120 g/min
feed rate were 18.12 and 20.51 respectively. The increased water solubility index
under high feed rate is probably due to fully developed flow along the die which
also increases starch break down. Chang et al., 1998 reported the same findings
when they studied the effect of extrusion variables on rheological properties of
cornmeal. The average solubility indices for 25 and 36 % moisture contents were
21.26 and 17.36 respectively. Increasing extrusion moisture to 36 % decreased
product temperature and shear. This resulted in lower solubility index. Colonna et
al. (1984) reported that lower solubility indices for higher moisture and low
temperature extrusion conditions. The same results were reported by Sebio and
Chang (2000) when they extruded yam flour. Increasing screw speed from 118
to 253 rpm significantly increased (p=0.0001) water solubility index although
residence time was reduced. Increased solubility was probably due to sufficient
starch and/or fibre degradation during extrusion cooking. Hashimoto and
Grossman (2003) reported the same results when they extruded cassava
bran/cassava starch blend. Diosady et al. (1985) concluded that degradation of
starch is exclusively due to the product of the shear stress in the active zone of

the extruder barrel. Product properties depend mostly on the molecular

52

transformations, for example, disruption of starch granules, depolymerization of
amylose and amylopectin; these transformations are generated in the various

parts of the extruder by pressure, shearing and residence time (Colonna et al.

1989).

Table 4.2. Effect of extrusion variables on Water Absorption and Solubility

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

lndices
Sample Barrel Bean Moisture Screw WAI WSl
number Temperature flour content speed
(°C) (SJ/min) (W
1 120/105 80 25 118 5.331037 18.921028
2 120/105 80 25 184 5.351021 19.081017
3 120/105 80 25 253 7.861010 20.161011
4 120/105 120 25 118 5.791048 20.621014
5 120/105 120 25 184 6.5211 .07 22.421037
6 120/105 120 25 253 5.681080 23.081107
7 120/105 80 36 118 4.611071 16.021048
8 120/105 80 36 184 48811.51 15.301020
9 120/105 80 36 253 4.951022 17.181164
10 120/105 120 36 118 6.541067 16.341020
11 120/105 120 36 184 8.441109 17.881023
12 120/105 120 36 253 4.881001 19.721057
13 130/115 80 25 118 5.381055 18.141028
14 130/115 80 25 184 4.411037 20.841057
15 130/115 80 25 253 5.371085 21.561028
16 130/115 120 25 118 5.941173 220210.59
17 130/115 120 25 184 5.391058 24.541014
18 130/115 120 25 253 5.681083 23.761028
19 130/115 80 36 118 5.051006 16.561061
20 130/115 80 36 184 50610.22 17.861031
21 130/115 80 36 253 01911.56 16.101020
22 130/115 120 36 118 4.971015 16.081060
23 130/115 120 36 184 6.111046 18.921074
24 130/115 120 36 253 5.681054 20.901020

 

 

 

 

 

 

 

Water absorption and solubility indices are average of 2 replicate

values1standard deviation

53

 

4.5. Starch gelatinization

Gelatinization is an important physico-chemical change associated with the
cooking of starchy materials. Pasting properties of raw beans and extruded
samples are presented in figure 4.7, 4.8, and 4.9. The initial viscosity of extruded
samples was higher than that for raw beans. This was expected because
extruded samples are already gelatinized, which enables them to hydrate faster
and to a greater extent than raw sample. The viscosity of extrudate pastes
decreased with increasing temperature, in contrast to that of raw bean sample.
This behavior is not unexpected. Heating slurries of completely gelatinized
materials is known to cause a decrease in viscosity leading to the thinning of

starch sluny (Schwiezer et al., 1986).

Ungelatinized starch cannot absorb water at room temperature, and its viscosity
as measured by the Rapid Visco-Analyzer (RVA) is nearly zero. Gelatinized
starch, however, absorbs water rapidly to form a paste at room temperature
without further heating. The viscosity of the paste depends to a large extent on
the degree of gelatinization of the starch granules and the extent of their
molecular breakdown (El-Dash et al. 1983). The gelatinized starch is
characterized by lack of gelatinization peak, by a continuous decline in viscosity
for temperatures between 50 and 95°C, and by progressive increase in viscosity

during the cooling cycle.

54

The rise in viscosity at the end of cooling phase, that is, the difference between
the cold paste viscosity (CPV) and hot paste viscosity (HPV), gives an indication
of gelling properties due to retrogradation of starch molecules, especially
amylose and amylopectin. The final viscosity of extrudates was lower than that
for raw bean sample. This indicates that starch in extruded beans had undergone
thermal and mechanical degradation to an extent that was not conducive to
retrogradation and the slurry remained thin. Cia et al., (1995) also reported the

same trend for wheat extrudates.

Effect of screw speed on starch gelatinization

The effect of screw speed on pasting properties is illustrated in figure 4.7. The
cold-paste viscosity, that is, the viscosity of the paste at the end of cooling phase
of the extruded at 184 rpm. was higher than the viscosity of the sample
extruded at 253 rpm. The explanation for this phenomenon is that under high
screw speed there was more shear to break down starch granules that resulted
in sufficient gelatinization. The same results were reported by Guha et al. (1998)
when studying the effect of barrel temperature and screw speed on rapid
viscoanalyzer pasting behavior of rice extrudate. This demonstrates that the
proportion of partially cooked starch was slightly higher in samples extruded
under low shear. Shear is therefore a significant contributor to starch

gelatinization.

55

 

100 *

 

Raw bean sample

Viscosity (RVA units)
01
O

 

 

0 5 10 15 20 25
Time (min)

 

 

 

Figure 4.7. A representative set of curves showing the effect of screw
speed on starch gelatinization of raw and extruded light red kidney beans.

Temperature was 25° from 0 -7 min; 95° from 8 -10 min; and
25° from 11 —15 min

A: Screw Speed = 253 rpm; Feed rate = 80 glmin; Moisture Content = 25%
B: Screw Speed = 184 rpm; Feed rate = 80 glmin; Moisture Content = 25%

Effect of feed rate on starch gelatinization

The final viscosity of the sample extruded at a feed rate of 120 glmin was lower
(more gelatinized) than the sample extruded at 80 glmin (figure 4.8). There is a
possibility that increasing feed rate increased pressure at the die which, resulted

in mechanical and thermal degradation of starch crystalline structure.

56

 

100 , 120.0 ’

 

 

 

 

90 Raw bean sample .
“ 80 -» 100.0 I
t m 6‘ l
= -+ 80.0 2. g
g 60 g l
5 50 ~» 60.0 E 5
E 40 3. l
3 A ~ 40.0 E
o 30 o
.2 2° '1 ‘1. .-
> B ~~ 20.0
t 10 N r .' ‘w“- _..-
l 0 M... - . . Y T 1 00 .
1 0 5 10 15 20 25 .
L Time (min) ‘

 

 

Figure 4.8. A representative set of curves showing effect of feed rate on
gelatinization in extruded and raw light red kidney beans.

Temperature was 25° from 0 — 7 min; 95° from 8 — 10 min; and
25° from 11 — 15 min

A: Screw Speed = 253 rpm; Feed rate = 80 glmin; Moisture Content = 25%
B: Screw Speed = 253 rpm; Fed rate = 120 glmin; Moisture Content = 25%

Effect of moisture content

The final paste viscosity was higher for samples extruded at higher feed moisture
(figure 4.9). The final paste viscosity is a measure of starch retrogradation, which
in extruded products, depends on the modifications that occur in the structure of
granules and molecules. The sample extruded at 25% moisture content was
characterized by a low degree of retrogradation, while the sample extruded at
36% moisture content resulted in high degree of gelatinization. It is possible that
increasing feed moisture to 36% percent reduced product temperature that to

some extent reduced starch gelatinization.

57

100

 

90 Raw bean sample

Viscosity (RVU)

 

 

o 5 1o 15 20 25
Time (min)

Figure 4.9. A representative set of curves showing effect of moisture
content on starch gelatinization in extruded and raw light red kidney beans.

Temperature was 25° from 0 - 7 min; 95° from 8 - 10 min; and
25° from 11 — 15 min

A: Screw Speed = 253 rpm; Feed rate = 80 glmin; Moisture Content = 25%
B: Screw Speed = 253 rpm; Feed rate = 120 glmin; Moisture Content = 25%

58

4.6. Sensory evaluation of extruded bean porridge

Extruded bean porridge that was used in this study was prepared by extruding
beans at 36% moisture content wet basis. The flour extruded at low moisture
content formed lumps in the porridge making it look unattractive. This may be
caused by severe degradation of starch extruded under high shear. The idea of
carrying out sensory evaluation came after preliminary evaluation by people
including Rwandan natives at Michigan State University, who evaluated extruded
bean porridge as delicious. A group of 70 trained panelists comprised mostly of
adult low income women at the National University of Rwanda, evaluated
extruded bean porridge and compared it with a local common porridge known as
Sosoma. Sosoma, considered to be a highly nutritious porridge by Rwandans,

is a blend of corn, sorghum, wheat, and soy.

Panelists liked extruded bean porridge. Frequency distribution of sensory score
for sosoma and extruded bean porridge for color, texture, flavor and overall
acceptability are shown in figure 4.10. A copy of the sensory questionnaire is
presented in appendix (Table A1 and A2 in English and Kinyarwanda

respectively).

59

 

 

 

L I Sosoma I Bean Porridgfl ‘

 

 

. .- xix/.5.; 1.5m»; xa.1zm~_'r‘r .WI 176" ' "Irv .: - wily-m" ‘n- 1" n a |
F

l Overall ' b

Flavor

 

 

 

Texture

Sensory Attributes

—‘

Color
a

 

 

 

l—

0.0 2.0 4.0 6.0 8.0 10.0
L Sensory Score

 

 

Figure 4.10 Sensory evaluation—of sosoma and extruded bean porridges.
Lower numerical values represent higher degree of acceptance

Means with different letters are significantly different (ps005)

There was no significant difference (p5 0.05) for color and texture. However,
some panelists liked sosoma flavor more than extruded bean porridge. In
general, panelists liked both porridges because all samples evaluated scored
lower than 5 (the lower the sensory score the higher the degree of acceptance)
for the sensory attributes tested. A score of 5 corresponds to neither like nor
dislike. In other words, a score above 5 means the panelists did not like product
while any score below 5 means the panelists like the product. Since this is

completely a new product and 100 % beans, the sensory results from this study

show that extruded bean porridge is a promising product.

60

4.7. Lectins as active phytohemagglutinins (PHA) activity

The PHA activity in dry beans was 0.55 ng/ uL. There was a significant reduction
between control (raw dry beans) and extrudated samples. Lectin activity in terms
of phytohemagglutinating activity (PHA) in light red kidney beans was effectively
reduced by all extrusion processing conditions used in this study (see Table 4.3
below). There was a significant difference (p=0.0031) between control (raw dry
beans) and extrudated samples. Extrusion conditions reduced
phytohemmaglutinin activity in all extruded samples by over 90%. This shows
that extrusion temperature was high enough to inactivate PHA activity. However,
there was no significant difference in phytohemagglutinin retention for feed rate
(p=0.6873), moisture (p=03910) and screw speed (p=09753). The explanation
for this phenomenon is that Iectins in extruded samples were inactivated at a
temperature lower than the product temperature at the die. Our result confirm
with Coffey and others (1992) who reported complete inactivation of Iectins at
93°C (wet heat) for 2 hr. Myer et al. (1981) and Myer and Froseth (1983) reported
90 % reduction of Iectins in red kidney bean and soybean mixes extruded at

barrel temperatures of 140°C.

61

Table 4.3. Percent reduction of Iectins in light red kidney extruded at
different conditions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Barrel Product PHA
Run Temperature temperature at Moisture retention
(°C): Zone 1 die (°C) Bean Screw content (ng/uL)
(nearest flour Speed (%), wet
die)/Zone 2 (glmin) (rpm) basis
Raw N/A 055010.094
beans N/A N/A N/A N/A

1 120/105 123.0 80 118 25 0.04010017
2 120/105 127.3 80 184 25 005410.003
3 120/105 130.0 80 253 25 005210.005
4 120/105 124.0 120 118 25 005510006
5 120/105 129.3 120 184 25 005510.003
6 120/105 128.3 120 253 25 0.04210004
7 120/105 119.3 80 118 36 0.04410004
8 120/105 118.0 80 184 36 005110.004
9 120/105 1 17.3 80 253 36 0.04710.004
10 120/105 126.0 120 118 36 004110.003
11 120/105 129.4 120 184 36 004210.001
12 120/105 124.0 120 253 36 005110.004
13 130/115 126.0 80 118 25 0.05210.002
14 130/115 123.2 80 184 25 0.04410.003
15 130/115 135.1 80 253 25 0.04710.004
16 130/115 137.2 120 118 25 005410.003
17 130/115 135.5 120 184 25 0.04910.003
18 130/115 127.2 120 253 25 005310.014
19 130/115 123.3 80 118 36 0.05210.003
20 130/1 15 124.8 80 184 36 0.03710.006
21 130/1 15 126.6 80 253 36 003010.009
22 130/115 127.8 120 118 36 0.03710.013
23 130/1 15 127.0 120 184 36 003810.006
24 130/1 15 126.1 120 253 36 004710.005

 

PHA retention is a mean of triplicate valueststandard deviation

62

 

4.8. Calculation of energy requirement by the extruder

Efficiency has always been a major concern for engineers. Extrusion cooking is
an energy efficient process because a substantial amount of the mechanical
energy from the extruder motor is dissipated during the viscous flow within the
channels of the extruder screws (Harper, 1980). Table 4.4 shows the total energy

and cost (US dollars) that was used for all extrusion runs.

63

Table 4.4. Energy and cost consumption for the extruder

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample SME SME Cost*/ton in Cost**/t
Number fl'otal feed (kWh/ton) US dollars on in
rate (kg/hr) Screw (kJ/kg) Rwanda;
speed Power(kW)
1 5.534 118 1.83 1193.1 4294.7 386.52 1073.66
2 5.534 184 2.04 1329.9 4787.5 430.87 1196.87
3 5.534 253 2.43 1584.1 5702.7 513.25 1425.68
4 7.934 118 1.74 754.2 2715.2 244.37 678.80
5 7.934 184 2.05 888.6 3199.0 287.91 799.74
6 7.934 253 2.53 1096.7 3948.0 355.32 987.00
7 5.905 118 1.64 912.1 3283.6 295.53 820.91
8 5.905 184 1.98 1101.2 3964.4 356.80 991.10
9 5.905 253 2.39 1329.3 4785.3 430.68 1 196.33
10 8.305 118 1.57 580.8 2091.0 188.19 522.75
11 8.305 184 2.30 850.9 3063.3 275.69 765.82
12 8.305 253 2.53 936.0 3369.6 303.26 842.40
13 5.534 118 1.72 1121.3 4036.5 363.29 1009.11
14 5.534 184 2.41 1571.1 5655.8 509.02 1413.95
15 5.534 253 2.72 1773.1 6383.3 574.50 1595.83
16 7.934 118 1.86 806.2 2902.5 261.22 725.62
17 7.934 184 2.48 1075.0 3870.0 348.30 967.49
18 7.934 253 2.78 1205.0 4338.1 390.43 1084.53
19 5.905 118 1.76 978.9 3523.9 317.15 880.98
20 5.905 184 2.23 1240.3 4465.0 401.85 1116.24
21 5.905 253 2.59 1440.5 5185.8 466.72 1296.44
22 8.305 118 1.82 673.3 2424.0 218.16 605.99
23 8.305 184 2.12 784.3 2823.5 254.12 705.88
24 8.305 253 2.67 987.8 3556.0 320.04 889.01
*based on $0.09/kWh
“based on $0.25/kWh

The most important extrusion variable that affected the power used by the

extruder was screw speed.

Increasing screw speed

increased energy

requirement from the motor. As an example of estimating energy requirements,

the lowest-cost extruded product was at 118 rpm; 36% moisture content; 8.3

64

kglhr total feed rate and the cost per ton was approximately $188 in the United

States or $522 in Rwanda (sample no.10 Table 4.4).

Figures 11 below shows percent of operating expenses (electricity, raw beans,
labor, and packaging) required to produce 1 kg of extruded bean flour in Rwanda

and United States.

1 IL- United States I Rwanda I I
80 .__ 1
l
60 ~
50 1
40 1
30 ~
20 —
10 1

0 J
1 Electricity Beans labor Pkg

 

 

Percent of operating cost

 

 

 

 

 

l

_ __.__._ _ ___1 . ._ J

 

 

Figure 11. Percent of total operating expenses to produce 1 kg of extruded
bean flour in United States and Rwanda

The total operating costs to produce 1 kg of extruded bean flour were estimated
to be $1.37 in the United States and $1.20 in Rwanda. The most expensive
operating cost is labor and electricity for the United States and Rwanda

respectively.

65

T
l
l
l
I
l
I
l
‘
l
l

 

1200.0 « MC=25%

NK3=3696
MC=25%

 

 

500.0 , MC=36%"" ;

Specific mechanical energy (kJIkg)
8
O
.0
O

50 100 150 200 250 300
: Screw speed at barrel temp 130M150 1
L _ _ -___l

Figure 4.12. Effect of screw speed on SME at different moisture contents
and feed rates at barrel temperature 1301115°C

 

Cost of charcoal and firewood in Rwanda

Charcoal and firewood are the main source of energy for cooking dry beans and
other food stuff in Rwanda. A bag of charcoal costs FRW 5,000 (USD 9.00) and
is not available all the time. This bag of charcoal can last for 10 days if you are
cooking 2 kg of beans, an amount that feeds a typical Rwandan family per day.
Therefore, to cook 20 kg of dry beans, Rwandans spend $9.00. For 1 ton (1000
kg) Rwandans would pay around $450.00. Using charcoal is more expensive
(table 4.5) compared to using a low-cost extruder (Table 4.5, $ 197-$482/ton),
and there are several advantages linked to extrusion processing. Extrusion
cooking is a High-Temperature-Short-Time so one does not need to spend hours
on a simmering pot of beans. This reduces the amount of smoke produced by
cooking fires which are detrimental to human health and can also cause global

warming problems. Extruded beans are shelf-stable and are ready-to-eat. This

66

prevents loss of beans by bean weevils during storage. Extrusion technology can
be used to make novel extruded bean-based products. Using extruders in
Rwanda may reduce the amount of trees cut for firewood and charcoal making.
This in turn would reduce soil erosion and increase agricultural yields. Reduction

in tree cutting would also protect natural habitats.

A

1400.0

1300.0 — p=0.001
1200.0 . = .
MC=25°/ p=0.086 FR 809lm1n

1100.0 -

 

 
 
   
 

1
1000.0 — i
900.0 1 ”0:35” p=0.029 |

 

 

 

Specificlf Mechanical Energy (lekg

 

 

800.0 « MC=25°
700,0 - .8 FR=1209/min
600.0 - ”0:35” p=0.885
500.0 «
400.0 . 1 . .
y 50 100 150 200 250 300
L“ Screw speed at barrel temp 120I1OSC

 

 

Figure-4.713. Effect of screw speed on SME alt-different moisture contents
and feed rates at barrel temperature 120l105°C

Increasing barrel temperature from 120l105°C to 130l115°C did not have a
significant effect (p=0.1496) on specific mechanical energy (figures 4.11 and
4.12). The extrusion parameters screw speed (p=0.0001); feed rate (p=0.0001);
and moisture content (p=0.0001) significantly affected specific mechanical
energy. Increasing screw speed increased power dissipated by the extruder

motor that increased specific mechanical energy. Increasing flour feed rate and

67

moisture content increased total mass flow rate that decreased specific

mechanical energy.

68

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS
In developed countries, extrusion processing has become on of the important
new technologies that is assuming an increasing role in the food industry in an
effort to provide an unprecedented array of novel products to satisfy consumer
preferences, especially in the ready-to-eat cereals. Little work on extrusion has
been done on dry beans. Much work on extrusion processing has been
accomplished using expensive extmsion equipment with high production
capacity. This type of extmsion equipment is not suited to the context of
developing countries. Therefore, the use of low-cost extrusion would be of great

potential interest for countries with low income.

In the present study physical, chemical and sensory characteristics of extruded
light red kidney beans were investigated. Raw ground bean flour was extruded
at 120 and 130°C barrel temperature; 25 and 36% moisture content wet basis;

screw speeds of 118, 184 and 253 rpm; and flour feed rate of 80 and 120 g/min.

Degree of fill increased with increase in mass flow rate and decreased with
increase in screw speed. This was expected because higher fill levels result in a
tighter residence time distribution (RTD) and less shear, and lower fill levels are

associated with wider RTD and more shear.

69

Feed rate is the one of the extrusion variables that had a pronounced effect on
residence time most. Mean residence time and residence time distribution

decreased with increase in feed rate.

In general extrusion variables did not significantly affect expansion ratio of
extruded light red kidney beans. Low expansion ratio may be attributed by the

presence of high protein in dry beans.

Flour feed rate, screw speed and moisture content did not significantly affect
water absorption index (WAI). However, percent water solubility index was

affected only by feed rate, and moisture content.

According to Rapid Visco Analyzer pasting curves, starch was completely
gelatinatized under all conditions studied. However, more gelatinatization was

observed in samples extruded under low screw speed and moisture content.

There was significant reduction of phyohemagglutinins (Iectins) in extruded

beans compared to raw beans.

Sensory evaluation results show that extruded bean porridge is promising.

Rwandans who evaluated the product liked it very much compared to sosoma, a

wheat-com-sorghum-soy-based porridge.

7O

The cost of energy for running an extruder appeared to be low under increased

mass flow rate and screw speed. Cooking dry beans using an extruder is up to

43% less expensive than using charcoal and firewood, and there are many

advantages associated with extrusion technology. These advantages may

include reduced environmental degradation.

5.1. Conclusions

1.

The results from our experiments indicate that the low-cost Chinese
extruder resulted in total starch gelatinization, which is required if the flour

is to be used as instant flour;

Extrusion conditions inactivated phytohemagglutinins in light red kidney

beans by over 90%;

The cost of using extruder to cook dry beans was estimated to be

approximately 43% lower than using charcoal;
Extrusion cooking technology may result in products with extend shelf-life
because of the reduced moisture (approx. 5%) compared to raw beans

(approx. 14%) stored in open conditions;

Using extrusion cooking technology in Rwanda may prevent

environmental degradation caused by deforestation and erosion.

71

5.2. Recommendations for future research

1.

The present study is characterized by less expanded products. Future
research should focus on mnning extrusion experiments on an extruder
with bigger motor using smaller dies, for example, less than 4mm under

low moisture (<25% wet basis);

Conduct bean extrusion runs with other types of foods, for example, corn,
tapioca, wheat, oats. This may improve the texture and overall acceptance

of extruded bean based products;

“Beany” flavor is one of the factors that limit consumption of dry beans.
Extrusion is believed to create new flavor in extruded beans. Future
research should investigate the effect of extrusion variables on the

reduction of “beany” flavor;
Dry bean is of the legumes loaded with antioxidants. Further research
studies should investigate the effect of extrusion cooking variables on

phytochemical (antioxidant) bioavailability and stability in dry beans;

Investigate the effect of extrusion on beans with dried fruits and

vegetables to make vegetable snack;

72

6. Conduct sensory evaluation studies of extruded bean porridge for

Americans;

7. Our results show that extrusion cooking inactivated phytohemmaglutinin
activity was inactivated by at least 90%. Studies should be conducted by
normalizing extruded beans by canned beans to find out if the remaining

percentage is a residual or not.

73

APPENDICES

Appendix 1. Water pump calibration

 

 

 

 

 

 

 

0.12 1
O
0.1 y= 0.0475x- 0.0331
R2=099
. 0.08
I E
I 5 0.06
I §
‘ 3
, 0.04
i 0.02 .
0 l I 7* I T
0.5 1 1.5 2 2.5 3 3.5 l
I Pump settlng
I__ _ _ ___ _

 

 

Figure 5.1.—51513515 curve 12,—r0519: pump used in all extrusion runs

74

Appendix 2. Screw speed calibration curve

2m, ___.W 1 WI

Screw Speed calibration

300 .. — Hi- __~_ 1 -1- _1 . .

i y = 2.5456x- 35.072
250 I, R2 = 0.99

N
O
C

150 .

Actual reading (rpm)

_L
O
O

 

 

50I

 

Extruder read (rpm) J

 

Figure A.2. Standard curve for screw speeds used in all extrusion runs

75

 

Appendix 3. Extruder feeder calibration

I 0.18 - V 5 i- . 1-. _ ___ -1 ,,;__ __

 

    

y = 0.0335x- 0.0032
R2 = 0.98

O
_ I...
N
_._ __ _.L___ 1

Flour (kg/min)

 

_ V .

1 1 .5 2 2.5 3 3.5 4 4.5 5 5.5

 

Feeder settlng
Lfi

Figure A3. Standard curve for extruder feeder calibration U

 

 

76

 

Appendix 4. Consent form for extruded bean porridge

Consent Form-Consumer Panel: Evaluation of
extruded bean products (porridge)

Dear Participant:

Several Michigan State University researchers are investigating consumer perceptions of bean porridge
made from extruded dried beans. We would like you to take about 15 minutes (including the time you
spend reading this letter) to help us evaluate 2 samples of porridge. We are asking for volunteers, over the
age of 18, taste these samples. If you have a known food allergy dried beans and sugar, please do not
volunteer for this study.

If you meet the above requirements, we would like you to look at and taste the bean products. You will be
give 2 samples to look at, taste and answer questions related to the product quality. If you agree to taste
these and provide your evaluation based on the survey questionnaire, please sign the consent form below.
You will be given a bottle of soda and/or food treats that are worth less than $5 for your evaluation and
completion of the survey.

If you believe there is a potential of an allergic reaction upon sniffing and tasting, notify the on-site
sensory evaluation coordinator and/or principle investigator immediately. You will be released from
participating in this study. Please note if you are injured as a result of your participation in this research
project, Michigan State University will assist you in obtaining emergency care, if necessary, for your
research related injuries. If you have insurance for medical care, your insurance carrier will be billed in the
ordinary manner. As with any medical insurance, any costs that are not covered or in excess of whatever
are paid by your insurance, including deductibles, will be your responsibility. Financial compensation for
lost wages; disability, pain or discomfort is not available. This does not mean that you are giving up any
legal rights you may have. You may contact George Nyombaire with any questions (08432228).

Your response is confidential and we will protect your confidentiality to the full extent of the law. We
have no way to connect you, as an individual, to this completed survey form You are free to not answer
any question you choose, but please try to answer every question. We are not able to use incomplete
responses nor are we able to provide the incentive for incomplete responses.

If you have any questions during your reading this consent form, or during or after your participation,
please do not hesitate to contact the on-site sensory evaluation leader and/or the principle investigator. Feel
free to contact George Nyombaire, the principle investigator, via phone at 08432228 or
nyombair@msu.edu for any inquiry you might have due to your participation in our study.

In case you have questions or concerns about your role and rights as a research participant, please feel free
to contact Dr. Peter Vasilenko, Ph.D., Director of Human Research Protections, (517)355-2180, fax
(517)432-4503, e-mail irb@msu.edu, mail 202 Olds Hall, Michigan State University, East Lansing, MI
48824-1047.

PLEASE NOTE UPON YOUR SIGNING THIS CONSENT FORM, YOU VOLUNTARILY AGREE To
PARTICIPATE IN OUR STUDY. YOUR SIGNATURE INDICATES YOU HAVE READ THE
INFORMATION PROVIDED ABOVE AND THAT YOU HAVE HAD AN ADEQUATE
OPPORTUNITY To DISCUSS THIS STUDY WITH THE PRINCIPLE INVESTIGATOR AND HAVE
HAD ALL YOUR QUESTIONS ANSWERED TO YOUR SATISFACTION. YOU WILL BE GIVEN A
COPY OF THIS CONSENT FORM WITH YOUR SIGNATURE FOR YOUR RECORDS UPON YOUR
REQUEST.

SIGNED DATE

 

 

77

1"

 

Appendix 5. Formula for calculating moisture for extrusion runs

751 flour MC flour + If! water

 

MC =
".1 flour + m water
Where MC = Moisture Content wet basis, decimal
n'r no... = Mass Flow Rate of flour (g/min)
MC no”, = Moisture Content of Flour, wet basis, decimal

tit ware, = Mass Flow Rate of water (g/min)

Appendix 6. Flour moisture determination

Bean flour moisture was determined by drying 2 g of bean flour in a convection oven at
1350C for 2 hours. Percent moisture was determined as loss of moisture/weight 0 wet
sample multiplied by 100.

78

Appendix 7: Sensory evaluation questionnaire for extruded bean porridge

(Kinyarwanda)

IGERAGEZWA KUBIKOMA BYUBWOKO BUBIRI
Soma kuri bun' gikoma hanyuma usubize ibibazo bikurikira (hitamo igisubizo

kikubereye).

 

Nimero y’igikoma # -)

N
W

(D
N
(D

 

A. Ukuntu ukunze ibara ryigikoma?

9—Ndarlkunze birenze
8—Ndarikunze cyane
7—Ndarikunze
bigereranlje
6—Ndarikunze buhoro
5—Sindikunze kandi
sindyanze
4—Ndaryanze buhoro
3—Ndaryanze bigeraranije
2—Ndaryanze cyane
1—Ndaryanze birenze

dNQhUIQNNCDN

Hari ikindi wumva
wavuga

.........................

Sanwemmflmo

Hari iklndl wu

va wavuga

 

B. Ukuntu ukunze igikoma mukanwa?

9—Ndagikunze birenze
8—Ndagikunze cyane
7—Ndagikunze
bigereranije
6—Ndagikunze buhoro
5—Sinkikunze kandi
sinkyanze
4—Ndacyanze buhoro
3—Ndacyanze
bigereranije
2—Ndacyanze cyane
1—Ndacyanze birenze urugero

JMU‘MONO‘D

Harl Iklndl wumva
wavuga

Ana-AMONGCD

Harf Iklndl wumva wavuga

 

C. Agahumuro?

9—Ndagakunze birenze
8—Ndagakunze cyane
7—Ndagakunze
bigereranlje
6—Ndagakunze buhoro
5—Sinkakunze kandi sinkanze
4—Ndakanze buhoro
3—Ndakanze bigereranlje
2—Ndakanze cyane
1—Ndakanze birenze
urugero

 

Ana-hmmfleoto

Hari iklndl wumva
wavuga

 

 

de-FOIONGO

Harl iklndl wumva wavuga

 

79

 

 

 

D. Ukuntu ukunze igikoma muri rusange? 9 9
8 8
9—Ndagikunze birenze 6 ;
8—Ndagikunze cyane
7—Ndagikunze 5 5
bigeraranije 4 4
6—Ndagikunze buhoro 3 3
5—Sinkikunze kandi 2 2
sinkyanze 1 1
4—Ndacyanze bu horo Harl Iklndl wumva Harl iklndl wumva wavuga
3—Ndacyanze WW9! ............................
bigeraranije -----------------------------------------------------
2—Ndacyanze cyane ...............................
1_Ndacyanze birenze ........................
urugero ........

 

 

 

80

 

Appendix 8: Sensory evaluation questionnaire for bean porridge (English)

Please evaluate the bean porridge samples and answer the following questions
(circle the appropriate response).

 

N
b)

8

0

Sample # -)

 

A. How do you like the texture ?

9—Like Extremely

8—Like Very Much

7—Like Moderately
6—Like Slightly

5—Neither Like nor Dislike
4-Dislike Slightly
3-Dislike Moderately
2"Dis'ike Very MUCh Comments ............... Comments...
1—Dislike Extremely

ANU-hOIONQON
ANW4hUIO‘IQON

 

B. How do you like the

sweetness?

9—Like Extremely

8--Like Very Much

7--Like Moderately
6—Like Slightly

5-Neither Like nor Dislike
4—Dislike Slightly Comments ............... Comments ...............
3--Dis|ike Moderate|y ..................................................
2—Dislike Very Much ..................................................
1--Dislike Extremely

 

C. How do you like the flavor?

9-Like Extremely

8-Like Very Much

7--Like Moderately
6--Like Slightly

5--Neither Like nor Dislike
4—Dislike Slightly
3--Dislike Moderately
2-Dislike Very MUCh Comments ............... Comments ...............
1--Dislike Extremely

de-FUIO'DNQO
ANQPMGNQO

 

 

 

 

 

81

 

D. How do you rate

OVERALL acceptability?

1-Like Extremely
2-Like Very Much
3--Like Moderately
4--Like Slightly

5-Neither Like nor Dislike
6--Dislike Slightly
7-Dislike Moderately
8-Dislike Very Much

‘ 94:. II E | |

 

the

 

dNb’hUIONOD

Comments ...............

 

ANthIQNGCD

Comments ...............

 

82

 

Appendix 9: Extrusion variables with mean residence time

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample Screw Flour Mean
Number Barrel Moisture Speed F eedrate Residence
Temperature (°C) Content (%) (rpm) (glmin) time (s)

1 120/105 25 118 80 70.7
2 120/105 25 184 80 66.4
3 120/105 25 253 80 57.0
4 120/105 25 118 120 62.6
5 120/105 25 184 120 52.7
6 120/105 25 253 120 50.0
7 120/105 36 118 80 64.2
8 120/105 36 184 80 59.4
9 120/105 36 253 80 49.8
10 120l105 36 118 120 60.5
11 120/105 36 184 120 58.3
12 120l105 36 253 120 44.2
13 130/115 25 118 80 62.3
14 130/115 25 184 80 62.7
15 130/115 25 253 80 56.0
16 130l115 25 118 120 61.8
17 130l115 25 184 120 52.9
18 130/115 25 253 120 49.7
19 130/115 36 118 80 65.4
20 130/1 15 36 184 80 62.9
21 130/115 36 253 80 53.2
22 130/115 36 118 120 63.0
23 130/115 36 184 120 58.5
24 130/1 15 36 253 120 53.4

 

 

 

 

 

 

 

 

83

Appendix 10: Extrusion variables with extruder percent fill

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample Barrel Flour Percent fill
Number Temperature Moisture Screw Speed Feedrate
(°C) Content (%) (rpm) (glmin)
1 120/105 25 118 80 46.9
2 120/105 25 184 80 44.0
3 120/105 25 253 80 37.9
4 120/105 25 118 120 61.8
5 120/105 25 184 120 52.9
6 120/105 25 253 120 50.4
7 120/105 36 118 80 50.0
8 120/105 36 184 80 46.3
9 120/105 36 253 80 38.8
10 120/105 36 118 120 70.8
11 120/105 36 184 120 64.3
12 120/105 36 253 120 51.7
13 130/115 25 118 80 41.8
14 130/115 25 184 80 41.7
15 130/115 25 253 80 37.2
16 130/115 25 118 120 61.7
17 130/115 25 184 120 52.9
18 130l115 25 253 120 49.7
19 130/115 36 118 80 54.7
20 130/115 36 184 80 49.0
21 130l115 36 253 80 41.4
22 130/115 36 118 120 74.2
23 130l115 36 184 120 69.2
24 130l115 36 253 120 62.6

 

 

84

 

Appendix 11: Calculation of void volume of twin-screw extruder JS30A

 

1

4

I”
I

I

 

 

----q —_---—

 

 

 

R b R

9/ 2
/9\ an
>

P

ie slice
Area of area, C
crescent, d

 

9/2

 

 

°‘——-N———°‘——>

 

 

Appendix 11 con’t”

Cos g: (a/2)/R

= cos'1 (a/2)/R

Q

2

b . (6?)
R 2

Area of triangle = l/2 (b)(a/2)

Area of two triangles = (b a/2)
Pie slice area, C = GRz/Z

Area of crescent, d = l/2(GR2 — ba)

Diameter of extruder screw, D = 30 mm

Radius of extruder screw, R = 15 mm

Diameter of extruder barrel, P = 56.5 mm

Length of extruder screw, L = 425 mm

Volume of2 screws = 0.0003838 m3

Volume of barrels = barrel volume * Screw length

Void volume = Volume of barrels — Volume of 2 screws

86

Appendix 12: Analysis of variance tables

Analysis of Variance for Bulky density

 

 

Source Degree of Sum of Squares Mean Square F Ratio
Freedom

Model 4 10.99 2.75 1.90

Error 19 27.48 1.45 Prob > F

Total 23 38.46 0.15

 

Analysis of Variance for Expansion Ration

 

 

Source Degree of Sum of Squares Mean Square F Ratio
Freedom

Model 4 0.05 0.013 4.72

Error 19 0.05 0.0027 Prob > F

Total 23 0.10 0.008

 

Analysis of Variance for Water Absorption Index

 

 

Source Degree of Sum of Squares Mean Square F Ratio
Freedom

Model 4 2.79 0.69 0.74

Error 19 17.90 0.94 Prob > F

Total 23 20.69 0.57

 

Analysis of Variance for Water Solubility Index

 

 

Source Degree of Sum of Squares Mean Square F Ratio
Freedom

Model 4 145.46 36.36 31.48

Error 19 21.95 1.16 Prob > F

Total 23 167.40 0.001

 

87

Appendix 12 can’t”

Analysis of Variance for Phytohemagglutinins

 

 

 

Source Degree of Sum of Squares Mean Square F Ratio
Freedom
Model 4 0.00027 0.000069 1 .63
Error 19 0.00081 0.00043 Prob > F
Total 23 0.0011 0.21
P:
2"

88

 

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cultivars of cowpeas (Vigna sinensis). J. Food Sci. 44: 1317.

Altomore, RE, and Ghoss, P. 1986. An Analysis of residence time distributions
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Anderson R A, Conway H F, Pfeifer V F, Griffin E L. 1969. Gelatinization of corn
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Anderson, AK. 1998. The Impact of Twin-Screw Extrusion Processing on
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