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TITLE PAGE
PRODUCTION AND EVALUATION OF EXTRUDED SNACKS FROM COMPOSITE
FLOUR OF BAMBARA GROUNDNUT ( Voandzeia subterranea (L) Thoaur ),
HUNGRY RICE (Digitaria exilis Staph.) AND CARROT ( Daucus carota L.)
A THESIS SUBMITTED TO THE DEPARTMENT OF FOOD SCIENC E AND
TECHNOLOGY IN PARTIAL FULFILLMENT OF THE REQUIREMEN TS FOR THE
AWARD OF MASTER OF SCIENCE (M.Sc.) DEGREE OF THE UN IVERSITY OF
NIGERIA.
BY
OKAFOR, JANE NGOZI
PG/M.Sc./07/42659
DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY
UNIVERSITY OF NIGERIA, NSUKKA
FEBRUARY, 2010
ii
CERTIFICATION
OKAFOR , JANE NGOZI, a postgraduate student in the Department of Food Science
and Technology, Faculty of Agriculture, University of Nigeria, Nsukka, has satisfactorily
completed the requirements for the degree of Master of Science (M.Sc.) in Food
Science and Technology. The work embodied in this dissertation is original and has
not been submitted in part or full for any other diploma or degree of this or other
University.
______________________ ________________
Dr. (Mrs.) J. C. Ani Date Supervisor
______________________ ________________
Dr. (Mrs.) J. C. Ani Date Head of Department
iii
ACKNOWLEDGEMENT
My profound gratitude goes to the Almighty God for His mercies and graces. I wish to
thank Dr. (Mrs) J.C. Ani for her supervisory roles and tireless efforts that aided the
successful completion of this work. My sincere appreciation goes to my husband Dr.
G.I. Okafor for his love, support and encouragement.
I am very grateful to the entire Lecturers of the Department of Food Science and
Technology, University of Nigeria, Nsukka for enriching me academically.
I wish to thank my friends and well-wishers, who in no small measure have helped and
encouraged me in the course of this research work.
May the Almighty God bless and enrich you all abundantly.
Jane Ngozi Okafor
iv
ABSTRACT
Cleaned Bambara groundnut seeds were divided into four lots. Each lot was separately
pretreated thus: germinated, roasted, germinated and roasted, and unprocessed which
served as control. Each sample was ground, sieved, and extruded using single screw
extruder. Consumer preference test was done by a taste panel of 50 people who rated
the products on the attributes of colour, taste, flavour and overall acceptability using a
9-point hedonic scale. The treatment (roasting) given on the most preferred product
was adopted in producing composite of bambara and “acha” flour, which was mixed
with graded levels of carrot and other ingredients, and extruded. The product samples
were subjected to analyses for chemical composition, residual anti-nutrients, physico-
chemical and sensory properties using standard methods. The samples were stored for
six months under ambient conditions (28±2ºC) and analysed at 2 months interval for
moisture, texture, provitamin A (β-carotene) and sensory properties. Extruded snacks
from the composite of bambara groundnut, hungry rice and carrot had high protein (15-
16%), β-carotene (180-550.13mg/100g retinol) and minerals (iron and zinc) contents.
Inclusion of carrot to the composite increased (p≤0.05) the β-carotene content of the
product, when compared with the control. There were no significant differences
(p>0.05) between the sensory qualities of the control and products with 5% to 15%
carrot. Extrusion cooking significantly (p<0.05) reduced moisture content and brought
about concentration of other proximate components. It also significantly (p≤0.05)
reduced phytate from 91.01-81.11mg/100g to 36.75-30.58mg/100g, tannin from
0.16mg-0.26/100g to 0.06-0.09mg/100g. Trypsin inhibitor and haemagglutinin activities
were reduced from 6.81-8.32mg/100g and 4.01-6.50Hu/mg protein, respectively, to
undetectable levels. Extrusion cooking improved protein digestibility of the snacks. β-
carotene and minerals were not significantly (p>0.05) affected by the extrusion cooking,
while there was a significant reduction (p<0.05) of vitamin C from 6.21-8.96mg/100g to
2.51-4.05mg/100g in the extruded snacks. Significant (p<0.05) reductions were
observed in vitamin B1(40-50%), B2(15-24%), B3(15-24%) and B6(25-30%) content of
the extruded snacks. Storage for six months did not adversely influence the sensory
characteristics of the developed snacks. It is evident from the composition of the
developed products that protein-energy malnutrition and micronutrient deficiency
problems can be averted through dietary diversification and extrusion cooking
technology.
v
TABLE OF CONTENTS
Title Page - - - - - - - - - - i
Certification - - - - - - - - - ii
Acknowledgement - - - - - - - - - iii
Abstract - - - - - - - - - - iv
Table of Contents - - - - - - - - - v
Chapter One
1.0 Introduction - - - - - - - - - 1
1.1 Statement of the Problem - - - - - - - 2
1.2 Significance of the Study - - - - - - - 3
1.3 Objectives of the Study - - - - - - - 3
Chapter Two
2.0 Literature Review - - - - - - - - 4
2.1 Extruded Snacks - - - - - - - - 4
2.2 Legumes - - - - - - - - - 5
2.2.1 Bambara groundnut - - - - - - - 7
2.2.2 Processing of legumes - - - - - - 7
2.2.3 Milling and grinding - - - - - - - 7
2.2.4 Soaking, boiling and steaming - - - - - 8
2.2.5 Germination - - - - - - - - 8
2.2.6 Roasting - - - - - - - 9
2.2.7 Preparation of protein concentrate - - - - 9
2.2.8 Canning of legumes - - - - - - 10
2.2.9 Quick cooking legumes - - - - - - 10
2.2.10 Nutritional importance of legumes - - - - 10
2.2.11 Antinutritional constituents of legumes - - - - 12
2.2.11.1 Protease (Trypsin) inhibitor - - - - 12
2.2.11.2 Phytates - - - - - - - 13
2.2.11.3 Polyphenols (Tannins) - - - - - 13
2.2.11.4 Cyanogens - - - - - - 14
vi
2.2.11.5 Lectins - - - - - - - 14
2.2.11.6 Effect of processing on legume food quality - - 15
2.2.11.7 Effect of processing methods on anti-nutrients - 17
2.3 Extrusion cooking and its effect on food quality 18
2.3.1 Application of extrusion cooking 19
2.3.2 Advantages of extrusion cooking 19
2.3.3 Effect of extrusion cooking on protein quality 19
2.3.4 Effect of extrusion cooking on the anti-nutrients 20
2.3.5 Effect of extrusion cooking on amino acids 21
2.3.6 Effect of extrusion cooking on Maillard reaction 22
2.3.7 Effect of extrusion cooking on carbohydrates 23
2.3.8 Effect of extrusion cooking on vitamins 24
2.3.9 Effect of extrusion cooking on minerals 25
Chapter Three
3.0 Materials and Methods - - - - - - 26
3.1 Materials - - - - - - - - 26
3.2 Methods - - - - - - - - 26
3.2.1 Preparation of samples - - - - - 26
3.4.0 Analysis of Raw Material and Product - - - - 31
3.4.1 Proximate composition - - - - - 31
3.4.2.0 Mineral content analysis - - - - - 33
3.4.2.1 Determination of phosphorus - - - - 33
3.4.2.2 Determination of Iron - - - - - 34
3.4.2.3 Determination of calcium - - - - - 35
3.4.2.4 Determination of potassium - - - - 35
3.4.2.5 Determination of manganese - - - - 35
3.4.2.6 Determination of copper - - - - - 36
3.4.2.7 Determination of magnesium - - - - 36
3.4.3 In vitro protein digestibility - - - - - 36
3.4.4 Functional properties - - - - - 37
3.4.5 Determination of anti-nutritional factors - - - 37
3.4.6.0 Determination of vitamins - - - - - 40
3.4.6.1 β-carotene and Vitamin A - - - - - 40
vii
3.4.6.2 Vitamin B1 - - - - - - - 41
3.4.5.3 Vitamin B2 - - - - - - - 41
3.4.6.4 Niacin - - - - - - - 42
3.4.6.5 Vitamin C - - - - - - - 42
3.4.7.0 Experimental design/data analysis - - - 43
Chapter Four
4.0 Results and Discussion - - - - - - 44
4.1 Effect of Processing Treatment on the Proximate Composition of
Bambara Groundnut - - - - - - 44
4.2 Effect of Processing Method of Some Anti-Nutritional Factors 44
4.3 Effect of Processing Methods on the Functional Properties of
Bambara Groundnut - - - - - - 46
4.4 Effect of Treatment Method on Consumer Acceptability of
Extruded Snacks 47
4.5 Proximate Composition of Hungry Rice “acha” and Fresh Carrot 48
4.6 Effect of Extrusion on the Proximate Composition of Bambara/
Acha Blends Fortified with Carrot - - - - - 49
4.7 Sensory Qualities of Extruded Snacks - - - - 51
4.8 Effect of Extrusion on the Residual Anti-nutrients - - 51
4.9 Effect of Extrusion on in-vitro protein Digestibility - - 52
4.10 Effect of Extrusion on the Mineral Content of the Bambara
groundnut/Acha Blends Fortified with Carrot - - - 53
4.11 Effect of Extrusion on the Vitamin Content of the Snacks - 56
4.12 Effect of Storage on the Texture of the Extrudates - - 58
4.13 Effect of Storage on the Sensory Qualities of the Snacks - 59
4.14 Effect of Storage on the Vitamin Content of the Snacks - 60
Chapter Five
5.0 Conclusion and Recommendations - - - - 62
5.1 Conclusion - - - - - - - - 62
5.2 Recommendations - - - - - - - 62
References - - - - - - - - - 63
viii
LIST OF TABLES
Table 1: Trend in Total Distribution of Major Food Crops in Nigeria (‘000 tonnes) 6
Table 2: Energy and selected nutrients in some legumes - - - 11
Table 3: Essential Amino Acid Composition of Selected Legumes (g/16gn) - 11
Table 4: Effects of Antinutritional components of dry beans - - - 15
Table 5: Effect of Processing Method on the Composition of
Bambara Groundnut (BGN) - - - - - - 44
Table 6: Effect of Processing Methods on Some Anti-Nutritional
Factors in Bambara Groundnut - - - - - 45
Table 7: Effect of Processing Methods on Selected Functional
Properties of Bambara Groundnut - - - - - 46
Table 8: Consumer acceptance study of extrudates from treated bambara
groundnut. - - - - - 48
Table 9: Chemical Composition of “Acha” and Carrot (per 100g
sample) - - - - - - - 48
Table 10: Proximate Composition of Un-extruded & Extruded Bambara
- “Acha” Containing Graded Levels of Carrot - - - - 49
Table 11: Mean Sensory Scores of Bambara-“Acha” Extruded Snacks
Containing Graded Levels of Carrots - - -- 51
Table 12: Effect of Extrusion on Anti-Nutrient Content of BGN/Acha
Blends Containing Graded Levels of Carrot - - - 52
Table 13: Effect of Processing on In-vitro Protein Digestibility of
BGN-Based Extruded Snacks Containing Graded Levels of
Carrot - - - - - - 53
Table 14: Effect of Processing on the Mineral Content of Extruded Snacks 56
Table 15: Effect of Processing on ß-carotene and C Contents of the
Extruded Snacks - - - - - - - 56
Table 16: Effect of Extrusion on the Vitamin B Content of Bambara-“Acha”
Extruded Snacks Containing Graded Levels of Carrots (mg/100g) 58
Table 17: Effect of Storage Period on the Texture (Crunchiness)
of Extruded Snacks - - - - - - 58
Table 18: Effect of Storage on the Sensory Qualities of Extruded Snacks
(Stored for 6 Months) - - - - - - - 59
Table 19: Effects of Storage on the provitamin A Content of Extruded Snacks - 61
ix
LIST OF FIGURES
Fig. 1: Flow chart for the production of flour from germinated Bambara
groundnut - 28
Fig. 2. Flow chart for the production of flour from roasted Bambara groundnut - - 29
Fig. 3: Flow chart for the production of extruded snacks from BGN, “acha” and carrot composite flour - - 30 Fig. 4: Effect of storage period on the moisture content of the extruded snacks - 60
x
APPENDICES Page Appendix 1: Phosphorous standard curve -- --- -- -- 74 Appendix 2: Iron standard curve -- -- -- --- -- -- 75 Appendix 3: Magnesium standard curve -- -- --- -- -- 76 Appendix 4: Phytate standard curve -- -- --- -- -- 77 Appendix 5: Vitamin A standard curve -- -- -- -- -- 78 Appendix 6: Vitamin B1 standard curve -- -- --- -- -- 79 Appendix 7: Vitamin B2 standard curve -- -- --- -- -- 80 Appendix 8: Vitamin C standard curve -- -- --- -- -- 81 Appendix 9: Vitamin B6 standard curve -- -- --- -- -- 82
1
CHAPTER ONE
1.0 I N T R O D U C T I O N
In many developing countries such as Nigeria, malnutrition is an endemic dietary
problem characterized by protein-energy malnutrition and micro-nutrient deficiency
(Nnanyelugo, 1990; Bowley, 1995; Adelekan et al., 1997; WHO, 2005, 2006). In the
past few years, efforts have been made to reduce or eliminate the problem globally.
Dietary diversification has been suggested as the ultimate solution to malnutrition
challenges. Dietary diversification involves the use of commonly available or consumed
grains, legumes and other nutritious crops to meet the nutritional/dietary need of the
population. Consequently, there is a need for baseline research to identify and exploit
the potentials of locally available but under-utilized agricultural produce in nutritious
product formulations.
Among the locally available under-utilized agricultural produce are bambara groundnut,
hungry rice (“acha”) and carrot, whose utilization are presently limited to household
level, even though they have potentials for industrial application. Bambara groundnut is
an under-utilized indigenous African legume and one of the most important crops in the
continent. Total production has been estimated to be over 300,000 tons per year
(Poulter, 1981). It is an inexpensive source of high quality protein and the third most
important legume in Africa, after cowpea and groundnut (Obizoba and Egbuna, 1992;
Enwere and Hung, 1996). Despite this, its use is limited to household consumption in
most parts of Nigeria. In Eastern States, the seed is used in the preparation of a steam
gel popularly known as “Okpa” while in the Northern parts it is consumed in the form of
meal or roasted snack. According to Poulter (1981), bambara groundnut contains 24%
protein, 6-8% lysine, 1.3 methionine and 50% carbohydrate, it also contains reasonable
quantities of minerals and vitamins.
Hungry rice commonly referred to as “acha”, “fonio” or “finni” is another under-utilised
crop. It is estimated that over 101.3 tons is produced annually in Nigeria, mostly in the
Northern States (Bauchi, Plateau and Kaduna) (CBN, 2005). Hungry rice is processed
and consumed in a variety of ways such as “tuwo”, “kunnu”, “gote”, while whole grains
are used in preparation of soup and porridge (Jideani, 1999). Hungry rice is reported to
be uniquely rich in methionine and cystine (NRC, 1999). It also relatively evokes low
sugar release on consumption, which is an advantage for diabetics (Ayo et al., 2003).
2
Carrot (Daucus carota) is one of the traditional root crops of Northern Nigeria. It is very
rich in carotene the precursor of vitamin A, and contains appreciable amount of
thiamine and riboflavin (Pederson, 1980). Carrot is fast acquiring the status of “lost
crop” in the African continent because its local utilization is limited to direct eating in
unprocessed form as snack (Pederson, 1980). There is need to diversify and
popularize other means of utilizing carrot to derive maximum health benefit from its
nutrient particularly carotenoids(carotene/β- carotene).
Blends of these nutrient dense agricultural produce could be exploited to develop
nutritious shelf stable snacks, which could help in alleviating problems of protein-energy
malnutrition and micronutrient deficiency prevalent in the country. However, to get
maximum nutrient benefit from these crops, they need to be processed to reduce or
remove inherent anti-nutrients that may interfere with the biological availability of the
nutrients. Among the methods used in removing inherent anti-nutrients include roasting,
germination, frying, cooking and recently extrusion cooking (Siegal and Fawcett, 1976;
Rajawat et al., 1999, Nwabueze, 2006).
Extrusion cooking technology is a high temperature short time (HTST) technology. It
has been extensively used in producing varieties of food products, especially in creation
of novel food products and improvement of existing ones like snacks (Lowtan et al.,
1985; Lasekan et al., 1996). It is considered a beneficial food processing technique,
due to its effective destruction of growth inhibitors and contaminating micro-organisms
(Tarte et al., 1989; Chang et al., 2001). It has also been shown to improve the
nutritional quality of food products like snacks (Pham and Rosario, 1987, Rajawat et al.,
1999; Nwabueze, 2006).
1.1 Statement of the problem
Most developing countries experience high burden of protein – energy
malnutrition and severe micro-nutrient deficiencies, which have attracted the numerous
interventions by major stakeholders, to mitigate the challenges. Dietary diversification
involving the use of commonly available or consumed grains, legumes and other
nutritious crops to meet the nutritional needs of the population has often been
advocated. Consequently, the idea of production of nutrient dense ready-to-eat
extruded snacks from blends of bambara groundnut, hungry rice (“acha”) and carrot
3
appears to be a very attractive strategy to combat the observed nutritional challenges.
However, to get maximum nutrient benefit from these crops, processes like roasting,
germination and then extrusion were employed to reduce/eliminate the inherent anti-
nutrients that may interfere with the biological availability of the nutrients and enhance
acceptability.
1.2 Significance of the study
This research work has the capacity to address the twin problems of protein-energy
malnutrition and micronutrient deficiencies, which pose a challenge to meeting nutrition
related Millennium Development Goals (MGDs). It will stimulate establishment of
facilities for production of nutrient dense ready-to-eat extruded snacks, which could be
readily employed in nutrition intervention program like school feeding programmes,
community nutrition activities, nutrition support in emergency situations and promotion
of food security for vulnerable groups/households.
1.3 Objectives of the study
• To produce high nutrient composite flour from blends of bambara ground nut,
hungry rice and carrot.
• To utilize the composite flour in the production of extruded snacks.
• To evaluate the nutritional quality and sensory properties/acceptability of the
products.
• To study the shelf life of the developed and packaged products.
4
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Extruded Snacks
Snack foods are foods which can be taken in place of or between meals. They are
convenient because they are quick and easy to eat. According to Lasekan et al., (1996)
snack foods add variety to the diet which partially explains their popularity. They may
also play a natural role on special occasions or when offered to visitors. Snack food
consumption has also been on the increase in Nigeria and other parts of the world
(Akpapunam and Darbe, 1994). This is as a result of urbanization and increase in the
number of working mothers. This development is being exploited by researchers and
food industrialists to develop innovative snack products that are nutritious - containing
increased protein, complex carbohydrates, and reduced fat (Shaw et al., 1994). Most
snacks are poor sources of protein, and often of poor nutritional quality. According to
Akpapunam (1984) this is because they are mostly prepared from plant food produce,
especially cereals, and cereal proteins are generally low in lysine and total protein
content, although high in sulphur containing amino acids. According to Bressani et al.
(1962), high protein and improved nutritional quality snacks could be produced by
combining cereals with animal food sources or, better with cheaper and more available
plant protein sources, such as legume and oil seeds.
Extruded snack foods have become an integral part of the eating habits of most of the
world’s population. Extrusion technology, at present, has become one of the major
processes of producing varieties of food or creating new food products and to improve
existing ones (Faubion and Hoseney, 1982; Lawton et al. 1985; Miller, 1993). Megard
et al. (1985), Tarte et al. (1989) and Chung et al. (2001) had applied high temperature
short time (HTST) extrusion processing in the development of snack foods, and
considered it a beneficial food processing technique due to its effective destruction of
growth inhibitors and contaminating microorganism. Texturized vegetable protein
products, which imitate that of muscle tissues have also been produced by extrusion
cooking (Chang et al., 2001). Yuryer et al. (1995) reported the use of isolated soybean
protein (ISP) in extruded snack products. With a model system of ISP and potato
starch, he showed that their blending was marked by improved textural and functional
properties of the extrudates. Camire et al. (1991) investigated the characteristics of
5
extruded mixtures of corn meal and glandless cotton seed flour, and reported that
snacks produced with 12.5% cotton seed flour were as acceptable as those containing
only corn, though extrusion reduced protein solubility and available lysine in the
samples. Bjorck and Asp (1989) observed that extrusion processing conditions have
been found to have a positive impact on nutrient retention. Chigumra (1992)
investigated the use of extrusion cooking technology in the production of maize,
sorghum and soybean based snacks, and reported the development of a nutritious
ready – to – eat high protein snack food products, which showed a marked
improvement on children’s health when consumed in Zimbabwe.
Rajawat et al. (2000) evaluated changes in the functional properties of faba beans flour
upon extrusion cooking at variable extrusion temperatures and feed moisture, and
reported that extrusion process reduced emulsification capacity, fat absorption capacity
and foaming capacity drastically, whilst foam stability was slightly affected. Nwabueze
(2006) studied the effect of hydration and screw speed on the nutritional qualities and
acceptability of extruded ready-to-eat African bread fruit snack, and reported that
acceptable products with adequate nutritional quality and anti-nutritional factors were
produced on extrusion cooking. There is a possibility and potential for making new food
products such as nutritious snacks by extrusion cooking of bambara, which is an
industrially under exploited or under utilised indigenous African legume, either alone or
in combination with other locally grown crops (cereals/tubers).
2.2 LEGUMES
Legume refers to the edible seeds of leguminous plants belonging to the leguminosae
family and they constitute an important source of dietary protein especially for most
people in developing countries (Siegel and Fawcet, 1976). The short fall in the
production of animal proteins and wide prevalence of protein malnutrition in developing
countries of the world have refocused the importance of legumes as source of protein in
human diets, especially in those countries where the consumption of animal protein is
limited by its low availability with its consequent high cost, cultural or religious habits
(FAO,1982). Apart from being an excellent and inexpensive source of dietary protein,
legumes have low sodium and high potassium contents, abundance of complex
carbohydrates, ability to lower serum cholesterol in humans, high fibre and low fat
6
contents, long shelf-life (in dried form) and diversity of the foods that can be made from
them (Sathe, 1996).
The history of grain legume production and consumption, shows that of the legumes
now being cultivated throughout the world, Pea (Psium spp), Cowpea (Vigna
unguiculata), Lentil pea (Cajanus cajan), Bambara groundnut (Voandzia subterranea)
and the Egyptian pea (Tritolium alexandrum) are indigenous to Africa (Idusogie, 1973).
Other legumes of the African continent are groundnut and soybean. The availability
and consumption of legumes in different regions of the world vary greatly. The
production of grain legumes in the world is around 52 MT (Table 1). The African
continent is characterized by moderate to intensive use of legumes. In some African
countries beans consumption is so large that about 65% of calorie intake is in the form
of legumes. Among those legumes, cowpea is grown and consumed most throughout
the continent with 90% of the world production (FAO, 1982). Nigeria accounted for
about 66% of the total world production of cowpea in 1972 (FAO, 1974), and represents
a cheap and important source of dietary protein for Nigerian populace (Apata and
Ologhoho, 1994).
Table 1: Trend in Total Distribution of Major Food Crops in Nigeria (‘000 tons) 1989 – 91 2000 2001 PULSES World 55856 54631 52385 Africa 6731 8000 8392 Nigeria 1363 2200 2200 CEREALS World 1903795 2063521 2086123 Africa 98735 114068 116503 Nigeria 18100 22891 22891 TUBERS World 577470 698169 677926 Africa 112994 164521 165719 Nigeria 35155 66578 66578 CASSAVA World 155264 176784 178868 Africa 72032 94676 95239 Nigeria 20821 33854 33854 Source: FAO (2002)
7
2.2.1 Bambara Groundnut
Bambara groundnut (Vigna subterranea) is an important indigenous Nigerian legume,
other names are: congo goober, earth pea, kaffir pea, ground bean, jungo bean,
Madagascan or stone groundnut or haricot pistache. It is the third most important
leguminous crop in Nigeria after cowpea and groundnuts (FAO, 1982; Doku and
Karikari, 1971; Alobo, 1999). Bambara groundnut (BGN) is one of the earliest grain
legume crops cultivated on the continent of Africa and is probably of West African origin
(Kay, 1979). It thrives in hot sunny climates on sandy loam soils but it is very adaptable
and grows on poor soils and is drought resistant. It is short lived, with 3-5 month
maturity period. It has branched stems and composed of leaves with three leaflet and
about 30 cm high. The pods are hard and wrinkled when dry, with each pod containing
one or two seeds. The seeds may be eaten raw when immature or the immature pods
and seeds may be boiled. The mature seeds are large and have high fat content with a
seed colour varying from black to white, red, cream, brown and may be mottled with
various colours (Oyenuga; 1968; FAO, 1982). The matured seeds are edible when
roasted or boiled or may be ground into flour and used in local dishes. Total production
has been estimated to be over 30,000 tons per year with Nigeria, Upper Volta, Niger,
Ghana, Togo and Ivory Coast, being the major producers (Doku et al., 1978). The
production of BGN in Nigeria has been on the increase. About 400,000 tons of BGN
were produced in Nigeria in 1981 (FAO, 1982). BGN has great potential in addressing
the protein energy malnutrition in Nigeria, if the technology of its industrial utilization is
effectively developed and applied.
2.2.2 Processing of Legumes
Legumes are generally consumed after some kind of processing like steaming,
sprouting, parching, roasting, puffing or along with cereals or tubers (FAO, 1982). Their
preparation techniques generally depend upon the structural and textural needs,
cultural food habits of the people (Siegel and Fawcet, 1976).
2.2.3 Milling and Grinding
Traditionally in Nigeria and other African countries, legumes are milled by mortar and
pestle, hand operated stones and chakkis are used at household level and in the
modern dhal mill respectively (Kurein, 1981). However with the advent of technological
advancement, grinders are commonly used in most localities. Powdered legumes are
8
used in a variety of dishes and savoury preparations. Grinding is done by wet or dry
methods. The relative proportion of particles of different mesh size is a major
influencing factor on the texture and quality of the product (Kurien, 1981).
2.2.4 Soaking, Boiling and Steaming
Soaking is the pretreatment that facilitates husk removal as well as to soften the
legumes and make them easier to cook. Cooking whole legumes in boiling water is the
most common method used in legume food preparation. According to Salunkhe et al.
(1985) soaking results in loss of ash, iron, copper and drastic reduction in flatulence
caused by oligosaccharides. Since excessive cooking repeatedly leads to a lowering of
digestibility, possibly due to the action of amino acid groups with carbohydrates and the
inactivation or destruction of certain essential amino acids, it is important that an
optimum cooking time be used, which will yield an acceptable textured bean product,
possessing the highest nutritive value (Siegel and Fawcett, 1976). Steaming is
primarily used as a secondary process for converting prepared legume flours and paste
into traditional products.
2.2.5 Germination
Germination process involves an initial soaking of the whole legume grain for 24 hours
to enable the grains to absorb enough moisture that would activate the growth
enzymes. This is followed by spreading the soaked grains on a damp cloth for up to 48
hours to provide appropriate condition for the process, and reduce the likelihood of
grains dry out, which will terminate the germination process. Seed constituents present
in an inert form are altered during soaking and germination and become more
assimilable for human nutrition (Kurien, 1981). Although germination doesn’t reduce
cooking time or improve texture, it brings about chemical changes, since it primarily
involves the carbohydrates of the grain, namely the conversion of some starch to lower
molecular disaccharides and dextrins by the action of amylases, which results in a
gradual decrease in the carbohydrate content of pulses during the course of
germination (Siegel and Fawcett, 1976; FAO, 1982). Similarly, protease activity also
increases during germination causing the degradation of high molecular weight protein
to lower ones leading to a noticeable increase in the concentration of amino acids.
Increase in some of the essential amino acids viz. lysine by 24%, threonine by 19%,
9
alanine by 29% and phenyl alanine by 7% has also been reported (Siegel and Fawcett,
1976).
2.2.6 Roasting
Legumes are sometimes roasted, toasted or heated to improve their nutritional value
and taste/acceptability (Kurien, 1981; Salunkhe et al., 1985). Roasted legumes are
generally consumed after mixing with parch or malted cereals or oil seeds. Roasting
brings about changes in aroma which are described as nutty, burnt and coffee -like due
to the formation of pyrazine compounds in the roasted food. It was reported (Powrie
and Nakai, 1981) that the level of pyrazine compounds also related to the extent of
browning. Roasting time is very important in enhancing PER in legumes, about 15
minutes of roasting at 200ºC was the optimum time to maintain maximum protein
quality considering available lysine.
2.2.7 Preparation of Protein Concentrate
Protein concentrates enjoy widespread commercial use in the fortification of foods and
beverages, which increase their nutritional value and improve functionality (Sosulki and
Young, 1979). They are generally prepared by wet extraction methods and their protein
contents normally range between 70-90% and 90-98% by weight. On the other hand,
protein rich flours could also be prepared by air classification, which is a means of
fractionating finely milled legume flour into protein and starch concentrates using a
spiral air stream (Heavier starch granules are separated from the finer protein – rich
particles) (Siegel and Fawcet, 1976). This dry separation technique is more promising
for starchy legumes (Sosulski and Young, 1979). The obtained protein fraction retains
good functional properties and there is no effluent to dispose of. The technique
involves finely milling the seeds by pin-milling and passing the flour into an air-classifier.
This separates (concentrate the protein) the smaller protein bodies from the larger
starchy granules by virtue of their different behaviour in the air flow (based on the
difference in size, shape, and density of the starch granules and the protein –
containing particle). In this way a protein concentrate (fine fraction) and a starch
concentrate (Coarse fraction) are produced. The hull is collected with the coarse
fraction, and the lipid material with the fine fraction (Vose et al., 1976). In a typical pilot
study, pea flour containing 21% fines (pea protein concentrate) with 60% protein
content and a coarse fraction (starch) with 8% protein were obtained. Repeated milling
10
gives an additional 10% pea protein concentrate with lower (45%) protein content
(Siegel and Fawcett, 1976).
2.2.8 Canning of Legumes
Canning represents another common method of preserving legumes especially in
developed countries. The most popular kinds of legumes that are canned are beans
(Phaseolus vulgaris L), navy or kidney beans, and Lima or buffer beans (Phaseolus
lunatus). They are consumed as vegetable side dishes or basic ingredient in salads.
Also, green or garden peas and black eye pea (Vigna unguiculata) are also canned.
Pre-cooked canned beans (Phaseolus vulgaris) are consumed in parts of Latin
America.
2.2.9 Quick Cooking Legumes
Quick cooking legumes are becoming popular since their preparation requires shorter
cooking time. More recent studies in the area of quick cooking dried beans include the
development of an intermittent vacuum treatment (Hydravac process) for 30-60 minutes
in a solution of inorganic salts (sodium chloride, tripolyphosphate, bicarbonate and
carbonate (Rockland and Metzler, 1976). The process consists of loosening the seed
coats by vacuum treatment, hot-water or steam blanching, soaking in solution of in-
organic salts, drying the processed beans under low velocity air stream of below 60ºC
for 24 hours. The overall advantage of this quick cooking process is its conversion of
dry beans to rehydrated product that cooks within 15 minutes, with about 80% reduction
in cooking time of 1-3 hours. Development of an inexpensive mechanical method for
producing quick cooking beans (California small white, Sanilac, Pinto) has been
reported by Kon et. al. (1973). The process of presoaking has been developed for
Pigeon pea by which the cooking time is reduced by 50% (Kon et. Al. 1973).
2.2.10 Nutritional Importance of Legumes
Legumes are important sources of many nutrients (Siegel and Fawcett, 1976; FAO,
1982), such as of protein, vitamins and minerals (Table 2). Their crude protein content
varies and ranges from 18 – 36%, and is of moderate quality, though deficient in
sulphur containing amino acids like methionine and tryptophan (Table 3). The use of
legumes makes a valuable contribution to the protein content of diets based
predominantly on root crops and cereals as staples.
11
TABLE 2: Energy and Selected Nutrients in Some Legu mes
(Composition Per 100g Edible Portion of Dried Matur e Whole Seeds)
Cowpea Bambara Groundnut
Black Gram
Chikpea Groundnut Soy bean
Water % 11.5 10.1 10.6 11.0 7.3 10.2 Protein (g) 22.7 16.0 21.0 19.4 23.4 35.1 Fat (g) 1.6 6.0 1.6 5.6 45.3 17.7 Carbohydrate (g) 61.0 65.0 63.4 60.9 21.6 32.0 Crude fibre (g) 4.2 ND 4.4 2.5 2.1 4.2 Dietary fibre (g) ND ND 19.5 25.6 6.1 11.9 Ash (g) 3.2 3.0 3.4 3.1 2.4 5.0 Energy (Kcals) 340 370 344 362 548 400 Calcium (g) 110 85 110 114 58 226 Iron (mg) 6.2 4.2 8.4 2.2 2.2 8.5 Thiamin (mg) 0.59 0.18 0.58 0.46 1.00 0.66 Riboflavin (mg) 0.22 ND 0.20 0.20 0.13 2.2 Nicotinic acid (mg) 0.22 ND 2.3 1.2 16.8 2.2
Source: FAO (1982)
Table 3: Essential Amino Acid (EAA) Composition of Selected Legumes (g/16g)
EAA Cowpea Bambara ground-
nut
Black gram
Chikpea Ground -nut
Soybean FAO scoring pattern
Isoleucine 3.8 4.4 4.3 4.4 3.5 4.5 4.0
Leucine 7.0 7.8 7.8 7.5 6.4 7.8 7.0
Lysine 6.8 6.4 7.4 6.8 3.5 6.4 5.0
Methionine 1.2 1.8 1.4 1.0 1.2 1.3
3.5 Cysteine 1.1 1.0 1.0 1.2 1.2 1.3
Phenyl alanine 5.2 5.6 6.6 5.7 5.0 4.9 6.0 Tyrosine 2.6 3.5 3.4 2.9 3.9 3.1
Threonine 3.6 3.3 3.7 3.8 2.6 3.9
4.0
Tryptophan 1.1 1.1 ND ND 1.0 1.3
1.0
Valine 4.5 5.3 5.9 4.5 4.2 4.8
5.0
Source: FAO (1982); ND = Not determined
Most of the legumes contain about 2% fat on the average though bambara groundnut
has up 5-7% fat. Soya beans, groundnut and some other legumes have up to 18-48%,
and are regarded as oil seeds. These legumes are also good sources of minerals such
12
as calcium, iron, copper, zinc, potassium and magnesium, which contributes 25-30% of
the total mineral content of legumes, and can be beneficially utilized in the diets of
people who take diuretics to control hypertension and who suffer from excessive
excretion of potassium through body fluids (Salunkhe et al., 1985). They also provide
variable quantities of most vitamins depending on the stage of maturity and state of
dryness. Beta-carotene, thiamine, riboflavin, niacin and ascorbic acid are present in
many legumes in appreciable amounts.
2.2.11 Antinutritional Constituents of Legumes
Although legumes are good source of protein, carbohydrates and minerals, they remain
under-exploited as human food due to the presence of several antinutritional
constituents, which lower the protein quality as compared to animal proteins. Some of
these anti-nutritional constituents and their deleterious effects are given in Table 4. The
major antinutritional constituents found in legumes are protease inhibitors, phytates,
lectins, amylase inhibitors, polyphenols, cyanogens and others. A brief description of
these are given below
2.2.11.1 Protease (trypsin) inhibitor
Enzyme inhibitors that can occur naturally in the human body include the pancreatic,
proteolytic inhibitors, blood clotting enzyme inhibitors, liver nicotinamide deamidase
inhibitors, and hyaluonidase inhibitors. Trypsin inhibitors are the most widely distributed
among the protease inhibitors. In addition to trypsin inhibitor chymotrypsin, subtilin,
elastase, plasmin, kallikrein and papain inhibitors are also present (Whitaker et al.,
1973). Two main trypsin inhibitors Bowman Birk and Kunitz are isolated from legumes.
These inhibitors lower the nutritional value of protein. Rackis (1974) and Liener and
Kakade (1980) have reviewed their nutritional implications in diets.
The trypsin inhibitors are present in some of the common foods like soyabean,
limabean, Phaseolus aureus, cowpea, navy bean, kidney and blackbean, broadbean
(Vicia faba), double bean, field beans, (Dolichos lablab), bambara groundnut, jackbean
(Canavalia ensiformis), pigeon pea (Cajanus cajan), other foods like cereals (wheat
flour), tubers, vegetables, nuts and eggs (Mathews, 1989). The trypsin inhibitors
adversely affect the digestion of dietary protein by proteolytic enzymes present in the
intestinal tract. The growth depression caused by the trypsin inhibitors may be the
13
consequence of an endogenous loss of essential amino acids being secreted by a
hyperactive pancreas, since pancreatic enzymes such as trypsin and chymotrypsin
particularly rich in sulfur containing amino acids resulted in pancreatic hypertrophy and
amino acid requirements (Salunkhe et al., 1985). Various processing methods such as
toasting, cooking, germination, fermentation, germination and extrusion decrease the
trypsin inhibitor activity (Bodwell and Hopkins, 1985; Kakade et. al., 1974, Apata and
Ologhoho, 1997; Wang et. al. 1997; Nwabueze, 2006; Singh, 2007).
2.2.11.2 Phytates
Phytic acid, the hexaphosphate of myoinositol is found in various legumes and also in
other foods which contain larger amounts of phytates. The phytate in seeds is
concentrated primarily in the bran and germ. Phytate has been generally regarded as
the primary storage form of both phosphorous and inositol in almost all seeds. In food
such as legumes and grains, a large proportion (60-80%) of phosphorous is present in
the form of phytic acid primarily as a complex salt of divalent minerals such as zinc,
calcium, magnesium and iron or as complexed with proteins. It has been shown that
phytate is involved in lowering the bioavailability of minerals (Salunkhe et al., 1985;
Oberleas, 1973). Phytate also interacts with protein resulting in reduced protein
solubility which affects their functional properties. It has been shown that phytate
inhibits several enzymes including pepsin, α-amylase and trypsin. Various processing
methods such as malting, germination and blanching reduce the phytic acid by 38-46%.
Reduction of phytic acid during blanching and malting may be due to leaching of
phytate ions into the soaking medium and increased activity of phytase enzyme during
germination (Archana and Kawata, 1998; Salunkhe et al. 1985).
2.2.11.3 Polyphenols (Tannins):
Polyphenols have been recognized as one of the antinutritional factors in legumes.
They are mainly located in seed coat with low or negligible amount in cotyledons.
Polyphenols are known to interact with proteins leading to either inactivation of
enzymes such as trypsin or chymotrypsin making the proteins insoluble. Polyphenolic
compounds inhibit other hydrolytic enzymes such as α-amylase and lipase, and are
known to decrease the digestibility of carbohydrates, protein and bio-availability of
vitamins and minerals (Salunkhe et. al. 1985). The major phenolic compounds of
concern are flavonoids, coumarins and furomarins, tannins and gossypols (Doyle et. al.
14
1994). Tea polyphenols, which were previously found to inhibit human salivary
amylase, have also been shown to inhibit sucrase and α-glucosidase. Dietary tannins
significantly decreased the digestion of protein and increased feed nitrogen extraction
but did not affect the biological value of nitrogen in the diet (Doyle et. al. 1994).
2.2.11.5 Cyanogens
These are substances capable of producing cyanide in plant foods. Cyanide
compounds are widespread throughout plant kingdom. They occur mainly in the form
of glycoside. They can be broken down to cyanide and the sugar residue by the action
of the enzyme glucosidase present in the plant (Montgomery, 1980). Lima bean has
the highest concentration of cyanogens (Linamarin) of all the food legumes (FAO,
1982), and cassava has the highest level of cyanogens among various fiber crops and
this is distributed throughout the plant (Balagopalan et. al., 1988). Large doses of
cyanide cause death by inhibition of cell respiration, but in small doses are converted
on ingestion into thiocyanate, a well known goitrogen. Although most food legumes
contain only low levels of goitrogens, the conversion of cyanogens into goitrogens may
explain some of the aetiology of goiter in certain areas of the world (FAO, 1982;
Mathews, 1989).
Legume seeds contain flatulence-producing oligosaccharides such as raffinose,
starchyose and verbascose. These sugars are not digested in the small intestine as
appropriate enzymes are lacking, so they pass to the large intestine where bacteria
fermentation result in gas production (Salunkhe et al., 1985; Augustine and Klien, 1989)
causing inconvenience. Rackis (1974) showed that the bacteria responsible for the
production of gas were spore-forming clostridia present in the colon. Flatulence is one
of the important factors limiting the consumption of bambara groundnut and other
legumes.
2.2.11.6 Lectins
Lectins are proteins that have the ability to clump or agglutinate and break down the red
blood cells in a way similar to antibodies. Lectins apart from causing food poisoning,
lower the protein quality of foods and cause reduction in rate of growth when they are
fed to experimental animals (FAO, 1982). However, the phyto haemagglutinins are
heat labile. Normal cooking destroys their specific action, cooking of beans for one
15
hour at 100oC destroys the toxicity and haemagglutinating activity completely (Jaffe,
1973).
Table 4: Effects of Antinutritional components of d ry beans
Components Effects
• Trypsin inhibitors Trypsin inhibition, pancreatic hyperotrophy, dietrary loss of lysine
• Chymotrypsin inhibitors Chymotrypsin inhibition
• α-amlyase inhibitors α-amylase inhibition, hinders carbohydrate utilization
• Subtilin inhibitors Subtilin inhibition
• Phyto-haemaglutinins (Lectins) Growth depression, fatal
• Phytates Reduced metal bioavailability, altered protein stability
• Flatulence factors Flatulence (Hydrogen, carbon dioxide and methane) production.
• Polyphenols Reduction in protein digestibility, inhibition of several enzymes.
• Off flavours Damage to amino acids, renders unacceptable to consumers
• Phytoalexine Hemolysis, uncouple oxidative phosphorylation
• Cyanogens Hemolysis, uncouple oxidative phosphorylation
• Goitrogens Inhibition of iodine binding to thyroid gland
• Lathyrism Nervous paralysis of lower limbs, fatal
• Favism Hemolytic anemia
• Allergens Several allergenic reactions bitter taste, foaming, hemolysis
• Saponins Growth inhibition, interference with reproduction performance.
• Estrogens Rachitogenic
Antivitamins of • Vitamin D • Viatamin E • Vitamin B-12 • Lysinoalanine
Liver necrosis, oxidation of vitamin E, muscular Dystroyphy Increased vitamin B-12 requirements Nephrotoxicity, reduction in available lysine, kidney cell, nucleus and cytoplasm enlargement. Generation of D-amion acids, act as synergist to lysinoalanine in the expression of nephrocytomegaly.
Source: Salunkhe et al. (1985)
2.2. 11. 7 Effect of processing on legume food qua lity
Processing conditions bring about changes in the nutritional quality of legume proteins,
their functional properties and anti-nutritional factors. The effect may be beneficial or
adverse depending on the conditions used. Some of the beneficial effects include
imparting attractive aroma, flavour, improvement of digestibility and palatability and
16
some functional properties and reducing/eliminating some of the antinutritional
components. On the other hand, processing may also have some deleterious effect on
legume proteins. The protein quality is primarily dependent on its essential amino acid
composition. Processing may result in the actual destruction of amino acids or binding
of amino acids due to the formation of linkages not hydrolyses by digestive enzymes
(Bender, 1972) or racemization of amino acids. Also processing methods which expose
the proteins to different conditions can cause changes in their structure/conformation
and may result in a loss or alteration of functional properties. The functional properties
are influenced by a number of factors such as the source of protein, method of isolation
and precipitation drying/dehydration, heating, concentration, chemical or enzymatic
modifications, environmental factors like temperature, pH and ironic strength.
Dry legume seeds normally require relatively long time to cook. Seeds of broadbean,
chickpea, bambara groundnut, common bean and to a lesser extent lentils are soaked
in water overnight before cooking as a means of reducing the cooking time. In some
instances small amounts of NaHCO3 is added while cooking to reduce it further. The
cooking process soften the hard legume seeds, improve the plasticity of the cell walls
thereby facilitate cell expansion and reduction of cellular adhesion. Some legume
seeds are very difficult to cook due to the presence of insoluble pectins in the form of
calcium and magnesium pectate. It has been reported that cooking quality may be
associated with the ratio of monovalent to divalent cations and with the phytic,
phosphorous, lignin and α-cellulose content of the seed. Cooking quality has been
found to be affected by storage conditions and moisture content of the seed.
Certain classes of legumes improve their protein value as a result of heat processing,
either through inactivation of trypsin inhibitors or increase the availability of certain
amino acids, particularly the sulphur containing ones. Processing at low temperature
treatments of protein may increase the digestibility (FAO, 1982). The processing
temperature and duration of heating and moisture content are the principal factors in
determining the degree of alteration. Dry heating is less effective than steaming
enhancing nutritive value (FAO, 1982). Negi et al. (2001) reported improved /increased
protein and starch digestibility in moth beans with soaking, dehulling, germination and
pressure cooking. Improved starch digestibility in fermented legumes (Bengal gram,
Cowpea and Green gram) due to breakdown of starch to sugars and reduction in
17
phytate levels has been reported (Urooj and Puttraj, 1994). However, when legumes
are roasted, a decrease in starch digestibility is noticed, perhaps, due to the presence
of enzyme inhibitors. Digestibility is affected by different methods of processing and
cooking. Products that are refined or isolated proteins and well processed have been
shown to have improved digestibility (Bodwell and Hopkins, 1985). El-Adawy et al.
(2000) reported increase in protein solubility, in-vitro protein digestibility and available
lysine and decrease in trypsin inhibitor, phytic acid, tannin and haemaglutinin activity
and carbohydrate with soaking of soybean, lupin seed, bean and black gram
respectively. Umoren et al. (1997) reported improvement in protein quality, reduction in
phytic, tannic acids and elimination of trypsin inhibitor, haemagglutinin and HCN in
cowpeas autoclaved for 30 mins at 105oC and 15 psi. Also germination of cowpeas
improved the in-vitro protein quality and starch digestibility but has little effect on the
overall amino acid profile (Jirapa et al., 2001)
2.2.11.8 Effect of processing methods on antinutr ients
Several methods of processing beans, which include dehulling, milling, soaking,
cooking, germination, fermentation, autoclaving, roasting, frying and parching, protein
extraction and extrusion will reduce/eliminate the antinutrients depending on the type of
bean. Generally adequate heat processing inactivates the protease inhibitors (FAO,
1982). Water soluble compounds such as the raffinose (oligosaccharides) can be
removed to a significant extent by discarding the soaked water, which helps to reduce
the flatulence potential of beans that contain them like bambara groundnut and cowpea
(Sathe, 1996; Smart, 1976). Heat stable compounds such as polyphenols and phytates
are however not easily removed by simple soaking. In such cases, other methods that
can hydrolyse these compounds may be more useful. According to Sathe (1996) after
4 days of germination of chickpea 91% of verbascose and stachyose and 88% of
raffinose were removed.
Soaking and dehulling reduced the phytic content up to 4% in faba bean. Soaking and
cooking, soaking, dehulling and cooking reduced the phytic acid content by 32-35% in
different varieties of faba bean. Autoclaving and germination reduced up to 55 and
69%, respectively (Sharma and Seighal, 1992).
The processing methods such as steaming and fermentation had been shown to
reduce the trypsin inhibitor activity of soybean (Doyle et al., 1994). Autoclaving of
18
cowpea for 30 minutes at 105oC and 15 psi resulted in total inactivation of the trypsin
inhibitor, haemagglutinin and HCN activities (Umoren et al. 1997). Total inactivation of
trypsin inhibitor had also been reported with autoclaving of black gram at 20 lbs for 20
minutes (Hajela et al, 1998). However, roasting showed only 6% destruction while
about 10% chymotypsin inhibitor activity remained. Inactivation of trypsin inhibitor is
greatly influenced by moisture content of food, time and temperature and methods of
heating and drying (Bodwell and Hopkins, 1985; Hajela et al. 1998).
Malting for 72 hours was found to be the most effective method in decreasing (40%) the
polyphenol content. Loss of polyphenol during malting was attributed to the presence
of polyphenol oxidase and to the hydrolysis of tannin protein and tannin – enzyme
complexes, which resulted in the removal of tannins. Germination has also been
reported to reduce the polyphenol content in Pearl millet (Doyle et al. 1994; Archana
and Kawata, 1998).
2.3.0 EXTRUSION COOKING AND ITS EFFECT ON FOOD QUAL ITY
Health and nutrition are the most demanding and challenging fields in this era and
would continue to be in the future as well. Maintaining and increasing nutritional quality
of food during food processing are always potentially important area for research.
Deterioration of nutritional quality, owing to high temperature, is a challenging problem
in most traditional cooking methods. Extrusion cooking is preferable to other food –
processing techniques in terms of continuous process with high productivity and
significant nutrient retention, owing to the high temperature and short time required
(Guy, 2001). Extrusion cooking is a high temperature, short-time process in which
moistened, expansive, starchy and/or proteinacious food materials are plasticised and
cooked in a tube by a combination of moisture, pressure, temperature and mechanical
shear, resulting in molecular transformation and chemical reactions (Havck and Huber,
1989; Castells et al. 2005). This technology has some unique positive features
compared with other heat processes, because the material is subjected to intense
mechanical shear. It is able to break the covalent bonds in biopolymers, and intense
structural disruption and mixing to facilitate the modification of functional properties of
food ingredients and/or texturizing them (Asp and Bjorck, 1989; Carvallo and Mitchelle,
2000).
19
In addition, the extrusion process denatures undesirable enzymes; inactivates some
antinutritional factors (trypsin inhibitors, haemagglutinins, tannins and phytates);
sterilizes the finished product; and retains natural colours and flavours of foods
(Fellows, 2000; Bhandari et al., 2001).
2.3.1 Application of Extrusion Cooking
The process had found numerous applications, including increasing numbers of ready-
to-eat cereals; salty and sweet snacks; co-extruded snacks; indirect expanded
products; croutons for soups and salad; an expanding array of dry pet foods and fish
foods; textured meat-like materials from defatted high-protein flours; nutritious
precooked food mixtures for infant feeding; and confectionery products (Harper, 1989;
Eastman et al., 2001).
2.3.2 Advantages of Extrusion Cooking
Parallel to the increased applications, interest has grown in the physico-chemical,
functional and nutritionally relevant effects of extrusion processing. Prevention or
reduction of nutrient destruction, together with improvements in starch or protein
digestibility, is clearly of importance in most extrusion applications. Nutritional concern
about extrusion cooking is reached at its highest level when extrusion is used
specifically to produce nutritionally balanced or enriched foods, like weaning foods,
dietetic foods, and meat replacers (Cheftel, 1986; Plahar et al., 2003). Many
researchers had reported the positive and negative effects of extrusion process on the
nutritional quality of food and feed mixtures using different extruder conditions
(temperature, feed moisture, screw speed and screw configuration) and raw material
characteristics (composition, particle size).
2.3.3 Effect of Extrusion Cooking on Protein
Protein nutritional value is dependent on the quality digestibility and availability of
essential amino acids. Digestibility is considered as the most important determinant of
protein quality in adults, according to FAO/WHO/UNU (1985). Protein digestibility value
of extrudates is higher than non-extruded products; the possible cause might be
denaturation of proteins and inactivation of antinutritional factors that impair digestion.
The nutritional value in vegetable protein is usually enhanced by mild extrusion cooking
conditions, owing to an increase in digestibility (Hakansson et al., 1987; Colonna et al.,
1989; Areas, 1992). It is probably as a result of protein denaturation and inactivation of
20
enzyme inhibitors present in raw plant foods, which might expose new sites for enzyme
attack (Colonna et al., 1989). All processing variables have different effects in protein
digestibility.
2.3.4 Effect of Extrusion Cooking on the Antinutr ients
An advantage of extrusion cooking is the destruction of antinutritional factors, especially
trypsin inhibitors, haemagglutins, tannins and phytates, all of which inhibit protein
digestibility (Bookwalter et al., 1971; Armour et al., 1998; Alonso et al., 1998, 2000a).
The destruction of trypsin inhibitors increases with extrusion temperature and moisture
content. At constant temperature, inactivation increases with increasing product
residence time and moisture content. The highest protein quality (as measured by
protein efficiency ratio), corrected for a value for casein of 2.5 is 2.15 in extruded soy
flour, obtained at a barrel temperature of 153°C, 20% moisture and 2 min residence
time, coinciding with 89% reduction of trypsin inhibitors(Bjorck and Asp, 1989).
Extrusion (300-r.p.m. screw speed, 27kg/hour feed rate, 5/32 inches die size and 93-
97°C outlet temperature) causes complete destruction of trypsin inhibitor activity in
extruded blends of broken rice and wheat bran containing up to 20% wheat bran (Singh
et al., 2000). However, in blends containing bran beyond 20%, the inactivation of
trypsin inhibitor decreases from 92 to 60% (Singh et al., 2000). This may be correlated
to a lower degree of expansion of extrudates with an increased proportion of bran in the
blends, which probably reduced the effect of heat, resulting in a lower degree of
inactivation of trypsin inhibitor. Lectin (haemagglutinating) activity is relatively heat
resistant. An aqueous heat treatment, at 60 or 70°C for up to 90 min, does not alter the
lectin activity in soybean. Lectin activity is reduced, but not abolished by heating at 80
or 90°C. However, as found with kidney bean (Grant et al., 1982, 1994), the lectin
activity in the fully imbibed seed could be completely abolished by heating them for 5
min at 100°C. Extrusion has been shown to be very effective in reducing or eliminating
lectin activity in legume flour (Alonso et al., 2000b). Thus, extrusion cooking is more
effective in reducing or eliminating lectin activity compared with traditional aqueous heat
treatment. The enzyme hydrolysis of protein is improved after extrusion cooking as a
result of the inactivation of antitrypsin activity in extruded snacks. The higher
susceptibility of protein to pepsin, as compared with trypsin, further suggested the
presence of antitrypsin activity. The improvement in pepsin hydrolysis might be the
result of the denaturation of proteins during extrusion cooking, rendering the more
21
susceptible to pepsin activity. This suggests that extrusion considerably improved the
nutritive value of proteins (Singh et al., 2000).
2.3.5 Effect of Extrusion Cooking on Amino Acids
Among all the essential amino acids, lysine is the most limiting essential amino acid in
cereal-based products, which are the majority of extruded products. Thus a focus on
lysine retention during the extrusion process is of particular importance.
The available lysine in the extrudates of defatted soy flour and sweet potato flour
mixture ranged from 68 to 100% (Iwe et al., 2004). Increase in screw speed (80-
140r.p.m) and a reduction of die diameter (10-6mm) enhance lysine retention. Even
though an increase in screw speed increases shear, leading to more severe conditions,
the corresponding reduction in residence time (as a result of increase in screw speed)
limits the duration of heat treatment, resulting in high lysine retention. An increase in
level of sweet potato increases lysine retention, which can be attributed to the lower
levels of lysine in the sweet potato raw material, as the losses are more pronounced at
increasing levels of soy addition, which apparently has higher lysine content. Optimum
available lysine was estimated at a feed composition of 98.49%, screw speed 118.98
r.p.m, mixtures of defatted soy flour and sweet potato flour (Iwe et al., 2004). In the
extrusion of wheat flour (150°C mass temperature, 5mm die diameter, 150-r.p.m screw
speed), an increase in feed rate (from 200-350g min-1) significantly improved lysine
retention (Bjorck and Asp, 1989).
A number of studies suggests that higher moisture content (15-25%) significantly
improved lysine retention (Noguchi et al., 1982; Bjorck and Asp, 1989). It was found
that, at a given process temperature during extrusion cooking of cowpea and mung
bean, the available lysine decreased with increasing feed moisture content at 93 -
167°C barrel temperature, 30-45% feed moisture and 100 to 200-r.p.m. screw speed
(Pham and Del Rosario, 1984). Owing to the complex nature of interactions between
extruder conditions, these changes might not be related to a single factor.
Apart from lysine, a few other amino acids have been affected by a decrease in
moisture content during extrusion. Cysteine decreases below 14.5% moisture content
during the extrusion (181-187°C mass temperature, 12-25% feed moisture, 35 to 79 –
Nm torque) of maize grits (Iwe et al., 2001). Biological evaluation also revealed a
22
decrease in the availability of aspartic acid, tyrosine and arginine with decreasing
moisture content. With increasing energy input to the extruder, a significant reduction in
the availability of several amino acids was found. The loss of available arginine (21%),
histidine (15%), aspartic acid (14%) and serine (13%) was significant at 135-160°C
mass temperature and 150 or 200-r.p.m. screw speed (Iwe et al., 2001). Extrusion
cooking of a cereal blend resulted in a considerable loss of arginine, and to a lesser
extent also of histidine (170°C mass temperature, 10% feed moisture and 40-r.p.m
screw speed). Lysine and methionine availability was not affected below 149°C during
extrusion cooking of soybeans (127-154°C mass temperature, 12% feed moisture and
20-s residence time). At the highest temperature, lysine showed the greatest loss
(31%), although a 13% decrease in methionine was noted (Bjorck and Asp, 1989).
2.3.6 Effect of Extrusion Cooking on Maillard Rea ction
Maillard reaction is a chemical reaction involving amino groups and carbonyl groups,
which are common in foodstuffs, and leads to browning and flavour production. The
nutritional significance of Maillard reaction is most important for animal feeds and foods
intended as the sole item in a diet (Fukui et al., 1993). Maillard reaction occurs between
free amino acid groups of protein and carbonyl groups of reducing sugars, and lead to a
decrease in the availability of amino acids involved and in protein digestibility. Pentoses
are most reactive, followed by hexoses and disaccharides. For hexoses, the order of
reactivity is D-galactose> D-mannose> D-glucose. Reducing disaccharides are
considerably less reactive than their corresponding monomers. Basic amino acids are
more reactive than natural or acid amino acids (Kroh and Westphal, 1989). Lysine
appears to be the most reactive amino acid, owing to the fact that it has two available
amino groups (O’Brien and Morrissey, 1989). Furthermore, lysine is limiting in cereals,
and loss in availability would immediately result in a decrease in protein nutritional
value. Lysine may thus serve as an indicator of protein damage during processing.
However, arginine, tryptophan, cysteine and histidine might also be affected (Iwe et al.,
2001).
The process conditions used in extrusion cooking – high barrel temperatures and low
feed moistures are known to favour the Maillard reaction. In the extrusion cooking of a
cereal mixture, the loss of available lysine range from 32% to 80% at 70°C mass
temperature, 10-14% feed moisture and 60-r.p.m. screw speed (Beaufraud et al.,
23
1978). There was a substantial loss (32%) of available lysine without addition of sugars
in the cereal mixture, which might be the result of hydrolysis of starch. Free sugars
might be produced from starch hydrolysis during extrusion to react with lysine and other
amino acids with free terminal amines. It was found that retention of available lysine
during processing of a cereal/soy-based mixture containing 20% sucrose ranged from
0% to 40% at 170°C mass temperature, 10-14% feed moisture and 60-r.p.m. screw
speed (Noguchi et al., 1982). The loss depends on extrusion conditions, increasing with
temperature and decreasing with moisture content of the feed. In order to keep lysine
losses within an acceptable range, it is necessary to avoid extrusion cooking above
180°C at water contents below 15%, and/or avoid the presence of high amount of
reducing sugars during the extrusion process. Apart from lysine, limited data are
available about the effects of the Maillard reaction on other essential amino acids
during the extrusion process. It is known that the loss of amino acids, owing to the
Maillard reaction is affected by the degree of reactivity of different sugars.
2.3.7 Effects of Extrusion Cooking on Carbohydrates
Carbohydrates range from simple sugars to more complex molecules, like starch and
fibre. Sugars, such as fructose, sucrose and lactose are great sources of quick energy.
They provide sweetness and are involved in numerous chemical reactions during
extrusion. Control of sugars during extrusion is critical for nutritional and sensory quality
of the products. Extrusion conditions and feed materials must be selected carefully to
produce desired results. For example, a weaning food should be highly digestible, yet a
snack for obese adults should contain little digestible material (Camire, 2001).
Several researchers (Noguchi et al., 1982; Camire et al., 1990; Borejszo and Khan,
1992) have reported sugar losses in extrusion. In the preparation of protein enriched
biscuit, 2-20% of the sucrose was lost during extrusion at 170-210 °C mass
temperature and 13% feed moisture (Noguchi et al., 1982; Camire et al., 1990). It may
be explained based on the conversion of sucrose into glucose and fructose (reducing
sugars), and loss of these reducing sugars during Maillard reaction with proteins.
Oligosaccharides (raffinose and stachyose) can induce flatulence and therefore impair
the nutritional utilization of green legumes (Omueti and Morton, 1996). Raffinose and
stachyose contents decreased significantly in extruded high starch fractions of pinto
beans (Borejszo and Khan, 1992).
24
2.3.8 Effect of Extrusion Cooking on Vitamins
The daily vitamin intake might be small compared with other nutrients but the small
quantities consumed are crucial to good health because of the role of vitamins as co-
enzymes in metabolism. The increase in the consumption of extruded infant foods and
similar products which may form the basis of an individual’s diet has focused concern
on the effect of extrusion on the retention of vitamins and minerals that are added prior
to extrusion. As vitamins differ greatly in chemical structure and composition their
stability during extrusion is also variable. The extent of degradation depends on various
parameters during food processing and storage e.g. moisture, temperature, light,
oxygen, time and pH. Among the lipid soluble vitamins, vitamin D and K are fairly
soluble. Vitamin A and E and related compounds- carotenoid and tocopherols
respectively, are not stable in the presence of oxygen and heat (Killeit, 1994). Thermal
degradation appears to be the major factor contributing to β-carotene losses during
extrusion. Higher barrel temperatures (200°C compared with 125°C) reduce all trans-β-
carotene in wheat flour over 50% (Guzman-Tello and Cheftel, 1990).
Ascorbic acid (vitamin C) is also sensitive to heat and oxidation. This vitamin decreased
in wheat flour when extruded at a higher barrel temperature at fairly low (10%) moisture
(Anderson and Hedlund, 1990). Blue-berry concentrate appeared to protect 1% added
vitamin C in an extruded breakfast cereal compared with a product containing just corn,
sucrose and ascorbic acid (Chaovanalikit, 1999). When ascorbic acid was added to
cassava starch to increase starch conversion, retention of over 50% occurred at levels
of 0.4-1.0% addition (Sriburi and Hill, 2000).
In summary, the retention of vitamins in extrusion cooking decreases with increasing
temperature, screw speed and specific energy input. It also decreases with decreasing
moisture, feed rate and die diameter. Depending on the type of vitamin, considerable
degradation can occur, especially in products with high sensory appeal. The following
options for the nutritional enrichment of extruded products with vitamins are possible:
1. The usage of specific vitamin compounds or forms of application with improved
stability;
2. Addition of extra amount to compensate for losses during extrusion and storage;
3. Post extrusion application, e.g. by dusting, enrobing, spraying, coating or filling
together with other ingredients.
25
2.3.9 Effect of Extrusion Cooking on Minerals
Extrusion cooking generally affects macromolecules. Smaller molecules may be
impacted upon by either the extrusion process itself or by changes in larger molecules,
which in turn affect other compounds present in the food. Despite the importance of
minerals for health, relatively few studies have examined mineral stability during
extrusion because they are stable in other food processes (Camire et al., 1990).
Minerals are heat stable and unlikely to become lost in the steam distillate at the die.
Extrusion can improve the absorption of minerals by reducing other factors that inhibit
absorption. Phytate may form insoluble complexes with minerals and eventually affect
mineral absorption adversely (Alonso et al., 2001). Extrusion hydrolyses phytate to
release phosphate molecules. Extrusion of peas and kidney beans resulted in phytate
hydrolysis, which explains the higher availability of minerals after processing (high
temperature extrusion) (Alonso et al., 2001). Extrusion does not significantly affect
mineral composition of pea and kidney bean seed, except for iron. Iron content of the
flours is increased after processing and it is most likely due to the leaching of metallic
pieces, mainly screws, of the extruder (Alonso et al., 2001).
26
CHAPTER THREE
MATERIALS AND METHODS 3.1 Materials
The seeds of Bambara Groundnut (BGN) were purchased from Nsukka market together
with other needed raw materials like “acha”, carrots, sugar, fat, salt and spices. High
density polyethylene for packaging the products was purchased from Polyproducts Ltd,
Ilupeju, Lagos.
3.2. Methods
3.2.1 Preparation of Samples
Bambara groundnut seeds (12kg) were cleaned by sorting and winnowing prior to
sharing into four lots designated A, B, C, and D and were either germinated, roasted,
germinated and roasted, and unprocessed, respectively as described below.
Germination (A) : Germination of BGN seeds was carried out by soaking 4kg BGN
seeds which has been washed with water and soaked for 12hrs at an average room
temperature of 28±20C. After soaking, the grains were spread on wet jute bags and
covered with moistened muslin cloth to germinate. Germinated seeds were removed
after 48hrs, and dried in an air oven (Gallenkamp) at 600C for about 12hrs. The
vegetative parts of the dried BGN were removed by rubbing between palms and
winnowed. The cleaned BGN were milled using Apex mill to pass through 0.4mm mesh
size.
Roasting (B) : The BGN seeds were roasted at 140°C for 40min in an oven (Memmert
GmBH model KG 8540), cooled and milled using Apex mill to pass through 0.4mm
mesh size.
Germination and Roasting (C): Germination and roasting of the BGN seeds were
carried out as described above.
Unprocessed Raw BGN (D): The lot D sample of the BGN was left unprocessed, to
serve as control.
27
Extrusion: Sample (3.6kg) from each lot was mixed with fat (0.36kg), sugar (0.6kg),
salt (0.12kg), spices (0.12kg), and extruded using a single screw extruder (Brabender
PL2001, Germany) at 150°C with screw speed of 170rpm and feed moisture of 20%.
Consumer Acceptance Study
Consumer preference test was done - to select the best treatment for composite flour
production and fortification - by a taste Panel of 50 people to ensure a more accurate
representation of the most preferred treatment. They rated the products attribute of
colour, taste, flavour and overall acceptability on a 9-point hedonic scale, where “9”
represents extremely acceptable while “1” represents extremely unacceptable score.
From preliminary consumer preference test, the roasted sample was then adopted in
producing composite of bambara and “acha” flour, which was mixed with graded levels
of carrot.
Preparation of “Acha” Flour : “Acha” grains (3kg) were sorted, thoroughly washed and
strained to remove sand and other extraneous materials, dried in a Gallenkamp oven at
60°C for 6hrs, cooled and milled using Apex mill to pass through 0.4mm mesh size.
Preparation of Carrot Powder : Cleaned carrots (6kg) were manually grated, dried
(55°C for 8hrs), cooled and milled using Apex mill to pass through 0.4mm mesh size.
Extruded Snacks Formulation and Extrusion : Roasted BGN milled into flour (3.6kg)
and acha flour (1.2kg) composite, were fortified with carrot powder at 0%, 5%, 10%,
15% and 20% level on replacement basis. The samples were mixed with fat (0.36kg),
sugar (0.6kg), salt (0.12kg) and spices (0.12kg), and extruded under similar condition
as previously described. The extruded samples were cooled and packaged in high
density polyethylene sachets for analyses and storage study.
Texture Analysis : The objective texture analysis of the extruded snacks was
conducted with the aid of a Universal Testing Machine (Testometric AX, M500-25KN
England). Each sample was placed on the compression plate and the lever carrying a
suitable mouthpiece was lowered till the sample was crushed. The maximum
compression force attained by each sample, which was displayed on the panel was
recorded.
28
Sensory Evaluation
Organoleptic properties of the samples were evaluated by 20 semi trained panelist for
various sensory attributes using a 9-point hedonic scale questionnaire (Larmond,
1977), where “9” represents extremely acceptable while “1” represents extremely
unacceptable score. The attributes evaluated were crispiness/crunchiness, taste,
flavour, texture, colour and overall acceptability. Data were analysed statistically using
analysis of variance (ANOVA) and mean separation was done by Duncan (1955)
multiple range tests at 5% level of probability.
Storage Study: Samples were stored for six months under ambient conditions
(28±2ºC) and analysed at 2 months interval for moisture, vitamin A and sensory
properties (as described above). The texture of stored samples was also determined
using the Universal Testing Machine (Testometric AX, M500-25KN).
Bambara groundnut (BGN) Seeds
Sorting/Washing
Soaking
Germination (48hrs)
Drying
Derooting/Dehulling
Milling
Sieving
Flour
Fig. 1: Flow chart for the production of flour from germinated BGN
29
Bambara groundnut (BGN) Seeds
Sorting/Washing
Weighing
Roasting (140°C for 40min)
Cooling
Milling
Sieving
Flour
Fig. 2: Flow chart for the production of flour from roasted BGN
30
Composite flour
(Bambara groundnut (BGN), “acha” and carrot)
Weighing
Mixing of ingredients (Sugar, fat, spices)
Conditioning
Extrusion
Cooling
Packaging
Storage
Figure 3: Flow chart for the production of extruded snacks from BGN, “acha” and carrot composite flour
31
3.4.0 ANALYSIS OF RAW MATERIAL AND PRODUCT Chemical, microbial, physical and sensory analyses were performed on the raw
materials and the products as described below.
3.4.1 Proximate Composition
Proximate composition was determined by using standard method (AOAC, 1995). This
involved the determination of fat, moisture content, crude fibre and protein, ash and
carbohydrate content.
Fat
The Soxhlet extraction method AOAC (1995) was used in determining fat content of the
samples. Each of the sample (2.0g) was weighed out using Mettler- HAS balance, and
put in the extraction thimble and plugged. It was then placed back in the Soxhlet
apparatus. Weighed flat bottom flask (B) was thereafter filled to about three quarters of
its volume with petroleum ether of 40-600C boiling point range. The apparatus was then
set up and the experiment was carried out for a period of 4-8 hours after which
complete extraction was made. The petroleum ether was recovered by evaporation
using water bath (Technicol England) and the remaining sample in the flask was dried
in the oven (Gallenkamp) at 800C for 30 minutes and cooled in a dessicator and finally
weighed using Mettler HAS. The difference in the weight of the empty flask and the
flask with oil gave the oil content, which was calculated as percentage fat content as
follows;
F =C - B x 100 A 1 Where,
A = Weight of sample B = Weight of empty flask C = Weight of flask + oil Protein
The crude protein content of the samples was determined by the semi-micro Kjeldahl
technique described by AOAC (1995). The sample (1.0g) was put into a Kjeldahl flask
and 3.0g of hydrated cupric sulphate (catalyst) were added into the flask. Twenty
mililiters (20ml) anhydrous sodium sulphate and concentrated sulphuric acid (H2SO4)
were added to digest the samples, stoppered and swirled. The flask with its content
was then swirled occasionally until the liquid was clear and free from black or brown
32
colour. The clear solution was then cooled and made up to 100ml with distilled water
and a digest of about 5ml was collected for distillation.
60% sodium hydroxide solution (5ml) was put into the distillation flask and distilled for
some minutes. The ammonia that distilled off was absorbed by boric acid indicator,
which was titrated with 0.1ml hydrochloric acid (HCl). The titre value of the end point,
at which the colour changed from green to pink was taken. The crude portion was
calculated as percentage crude protein thus:
Percentage crude protein = 0.0001410 x 6.25 x 25 x T x 100
W x 5
Where W = weight of sample T = Titre value A factor of 6.25 was used to convert nitrogen to protein.
Soluble protein
Nitrogen solubility was determined according to the method of Mattil (1971). One gram
of sample was mixed with 15ml of water and pH adjusted to 7.0 by the addition of dilute
alkali or acid. The volume was adjusted to 20ml with water and shaken for one hour at
room temperature and centrifuged at 5000rpm for 20 min. The solublized nitrogen was
expressed as per cent of total nitrogen of the sample. A factor of 6.25 was used to
convent soluble N to protein.
Crude Fibre
The crude fibre content of the sample was determined using the method described in
AOAC (1995). Two grams (2.0g) W1, of samples was weighed using Mettler HAS
balance, and put in a 250-ml beaker, and boiled for 30 minutes with 100ml of 0.12ml
H2SO4 and filtered through a funnel. The filtrate was washed with boiling water until the
washing was no longer acidic. The solution was boiled for another 30 minutes with
100ml of 0.012M NaOH solution, filtered with hot water and methylated spirit three
times. The residue was transferred into a crucible and dried in the oven (Gallenkamp)
for 1 hour. The crucible with its content was cooled in a dessicator and then weighed
(w2) using Mettler HAS balance. This was taken to a furnace for ashing at 6000C for 1
hour. The ashed sample was removed from the furnace and put into a dessicator to
33
cool and later weighed (w3) using Mettler, HAS.balance. The percentage crude fibre
was calculated thus:
%Crude fibre = loss of weight on ignition/weight of sample x 100
Ash
The crucibles were washed thoroughly, dried in hot oven (Model: Gallenkamp, size: 3
OV165) at 1000C, cooled in a dessicator and their empty weights were recorded.
Sample weighing 3g each was weighed into the labeled porcelain crucible. Initial
carbonization was conducted by placing the dish over a Bunsen flame and heated
gently until the content turned black. The samples were then subjected to burning in a
muffle furnace at 550oC for 5 hours. The ashed samples were removed from the muffle
furnace, moistened with a few drops of water to expose the unashed carbon, and re-
ashed at 550 oC for another hour. The resulting samples were removed from the
furnace, cooled in a dessicator and weighed soon after reaching room temperature.
The percentage ash was calculated using the expression;
Percentage ash content = 100×−B
AC
Where: A= Weight of empty dish B= Weight of sample in g C= Weight of dish + ash
Carbohydrate Content
The carbohydrate content of each sample was determined by difference. The difference
between 100 and the sum of the percentages of moisture, protein, fat, fibre and ash of
each sample was found, and expressed as percentage carbohydrate.
3.4.2.0 Mineral Content Analysis
Determination of minerals like Ca, P, Na, Mg, K, Fe, Cu and Mn were carried out
according to AOAC (1995). Sample weighing 10g was transferred into a crucible, and
heated over flame to volatilize as much of the organic matter as possible, before
34
transferring into a muffle furnace to burn at 450°C for 5-7hours. To the ash was added
10ml of dilute HCl, boiled for a few minutes, and made up to 100ml with distilled water.
This was used for the mineral analysis as described below.
3.4.2.1 Determination of Phosphorous
Determination of phosphorous was done according to the method of AOAC (1995).
Twenty five grams (25g) of ammonium molybdate and 1.25g of ammonium
metavanadate were added to 300ml of distilled water, warmed to dissolve, cooled and
made up to 500ml with water. Concentrated HCl (215ml) was diluted to 500ml with
water and mixed with ammonium molybdate-ammonium metavanadate reagent.
Phosphorous stock was prepared by dissolving 0.879g of dried phosphorous
dihydrogen orthophosphate (dried at 105oC for one hour) with water and 1ml of conc.
HCl added. It was diluted to 200ml with the first reagent, and 2ml of toluene was added
to give 1mg/ml. The working standard was prepared by measuring 2ml of phosphorous
to 0, 2, 4, 6, 8, and 10ml of standard phosphorous solution into six 200-ml volumetric
flasks and diluted to mark with water.
Each phosphorous standard solution (5ml) was pipetted into a 500-ml graduated flask.
Molybdate mixture (10ml) was added and diluted to the mark with water. It was allowed
to stand for 15 minutes for colour development, and the absorbance measured at
400nm against blank. A calibration curve (see appendix 1) relating absorbance to mg of
phosphorous was used to read the phosphorus content of the sample solution in mg/ml,
and the number of phosphorous equivalent to the absorbance of the sample blank
determined was calculated.
3.4.2.2 Iron Determination
Phenanthroline method as described in AOAC (1995), was used. Phenanthroline
solution was prepared by dissolving 100mg I,10-phenanthroline molybdate in 100ml
distilled water by stirring and heating to 80oC. Hydroxylamine solution was prepared by
dissolving 10g in 100ml of distilled water, while ammonium acetate buffer solution was
prepared by dissolving 250g in 150ml distilled water. 5ml of the digested sample was
added in a test-tube. Then, 3ml of phenanthroline solution and 2ml of HCl was added.
Hydroxylamine solution (1ml) was added to the mixture and boiled in a steam bath at
600oC for 2 minutes. Then, 9ml of ammonium acetate buffer solution was added and
35
diluted to 50ml with water. The absorbance was taken at 510nm. Calibration curve (see
appendix 2) was prepared by pipetting 2, 4, 6, 8, and 10ml standard iron solution into
100ml volumetric flasks to prepare a solution of known concentrations. The curve
obtained was used to read off the value of iron.
3.4.2.3 Determination of Calcium
Titrimetric method was used for calcium determination as described in AOAC (1995).
The test solution (10ml) was added into 250-ml conical flask. Potassium hydroxide
(25ml), water (25ml) and a pinch of calcium indicator were added, and titrated against
Ethylene Diamine Tetra Acetate (EDTA) dissolution salt solution to an end point. The
volume of EDTA is the volume equivalent of calcium in the solution. The value of
calcium was calculated as shown below:
% Ca = 10.1000
100...
××××××
edofsampleuswt
DFofcalciumwtAtEDTAmolTAvolumeofED.
Where EDTA- Ethylene Diamine Tetra Acetate
DF- Dilution factor
3.4.2.4 Determination of Potassium
Determination of potassium was done according to the method of AOAC (1995). The
ashed sample (2ml) was pipetted and transferred into 3 test tubes and 3ml of water
added; 2ml of sodium cobalt nitrite reagent was added, shaken vigorously and allowed
to stand for 45 minutes and centrifuged 15 minutes. The supernatant was drained off
and to the residue was added 2ml of ethanol and shaken vigorously, centrifuged and
the supernatant drained off. The residue was further washed twice with ethanol and
centrifuged respectively. 2ml of water was added to the residue, boiled for 10 minutes
with frequent shaking to dissolve the precipitate, cooled and 1ml of 1% choline
hydrochloride, 1ml of 2% sodium ferricyanide added, and made up to 6ml with water.
The absorbance was taken at 620nm against a blank.
3.4.2.5 Determination of Manganese
Determination of manganese was done according to the method of AOAC (1995).
Ashed sample (2ml) was transferred into 3 test tubes and 3ml of water added; 0.5ml of
conc. sulfuric acid was added and boiled for 1 hour. 0.1g of sodium m-periodate was
36
added and boiled for 10 minutes, cooled and made up to 10ml with water. The
absorbance was taken at 570nm against a blank.
3.4.2.6 Determination of Copper
Determination of copper was done according to the method of AOAC (1995). Ashed
sample (2ml) was transferred into 3 test tubes and 3ml of water added; 1ml of
versanate-citrate solution was added. The mixture was made alkaline with ammonia
and 0.1ml of 1% sodium diethyldithiocarbamate added. 5ml of carbon tetrachloride was
added and shaken vigorously; allowed to separate and the absorbance of the lower
layer taken at 440nm against a blank.
3.4.2.7 Determination of Magnesium
Determination of magnesium was done according to the method of AOAC (1995).
Ashed sample (2ml) sample was transferred into 3 test tubes and 3ml of water added;
2ml of 10% sodium tungstate, 2ml of 0.67N sulfuric acid were added, centrifuged for 5
minutes. 5ml of the supernatant was taken added 1ml water, 1ml of 0.05% titan yellow,
and 1ml of 0.1% gum ghatti. 2ml of 10% sodium hydroxide was added and the
absorbance taken at 520nm against a blank.
3.4.3. In Vitro Protein Digestibility
The in vitro protein digestibility was determined by the method described by Akeson
and Stahman, (1964). Pepsin followed by pancreatin digest was prepared by incubating
100 mg of protein equivalent sample with 1.5 mg pepsin in 15ml of 0.1N HCl at 37oC for
3 hours. After neutralization with 0.2 N NaOH, 4 mg pancreatin in 7.5 ml of phosphate
buffer (pH 8.0) was added. One ml of toluene was added to prevent microbial growth
and the solution was incubated for additional 24 hours at 37oC. The enzyme was
inactivated by the addition of 10 ml 10% trichloro acetic acid (TCA) to precipitate
undigested protein. The volume was made up to 100 ml and centrifuged at 5000 rpm
for 20 min. The protein content of the clear solution was calculated as the percentage of
the total protein solubilised after enzyme hydrolysis.
37
3.4.4 Functional Properties
Water absorption capacity
This was determined by the method of Sosulski (1962). To 1g of flour in a weighed
centrifuged tube 10 ml of water was added and the material suspended in water by
mixing with a thin glass rod and vortexed for 1 minute. After a holding period of 30 min.,
the suspension was centrifuged at 3000 rpm for 25 min. The supernatant was
discarded and the tube kept mouth downwards at an angle of 45o in an oven at 50oC for
25 min, before keeping it in a dessicator and weighing. The difference in two weights
gave the amount of water absorbed by the material. Water absorption capacity was
expressed as the amount of water absorbed by 100 g of material.
Fat absorption capacity
This was determined by the method of Sosulski et al (1976). To 1g of meal, 10ml of
refined groundnut oil was added and the material suspended in oil by mixing with a thin
glass rod and vortexed for 1 min. After 30 min standing, the suspension was
centrifuged at 300 rpm for 25 min. Volume of free oil was measured. Fat absorption
capacity was expressed as the amount of oil (in ml) absorbed by 100g of meal.
Foam Capacity
Two grams of bambara groundnut flour was mixed with 90ml of water in a Blender, and
whipped at low speed for 5 mins and mixture poured into a 250-ml measuring cylinder
and the total volume was recorded after 30 sec. Foam capacity was expressed as %
volume increase (Lawton and Carter, 1971).
Foam stability was determined by measuring the volume of foam at 2, 5, 10, 15, 30, 60
and 120 mins after pouring the mixture into the cylinder. Foam stability was expressed
as foam volume after the lapse of a particular time interval.
3.4.5 Determination of Anti-Nutritional Factors
Trypsin inhibitor activity
Trypsin inhibitor activity was determined according to the method of Kakade et al.
(1974). One gram of the finely ground defatted flour sample was extracted with 50ml of
0.01N NaOH for 3 hours at room temperature and centrifuged at 10,000 rpm for 20min.
The supernatant was used for estimation after addition of 2-5ml distilled water. Aliquots
38
ranging from 0.2 to 1.0 ml were pipetted into duplicate test tubes and volume adjusted
to 2.0 ml with distilled water. To each tube 2.0 ml of trypsin solution was added, placed
in water bath at 39oC and 5 ml of previously warmed (37OC) N-Benzoylarginine-p-
nitroanilide (BAPNA) solution added. Exactly after 10 min, the reaction was terminated
by adding 1.0 ml of acetic acid (30%), and the absorbance measured at 410 nm against
the reagent blank. The reagent blank was prepared by adding 1.0 ml of acetic to test
tubes containing trypsin and water (2.0 ml) followed by addition of 5.0 ml of BAPNA.
The rest of the procedure was same. Sample blanks were prepared using sample
extract. Trypsin inhibitory unit per ml (TIU/ml) vs. volume of extract was plotted and
extrapolated to zero (see appendix 3). One trypsin unit was defined as an increase in
0.01 absorbance units at 410 nm per 10ml of reaction mixture under condition used.
Trypsin inhibitor activity was expressed in terms of trypsin inhibitor units (TIU) and the
value expressed as TIU/mg of sample.
Phytate
The phytate content of the flour was determined by Maga (1982) method. Two (2g)
grams of each finely ground flour sample was soaked in 20ml of 0.2 N HCl and filtered.
After filtration, 0.5 ml of the filtrate was mixed with 1ml ferric ammonium sulphate
solution in a test tube, boiled for 30 min in a water bath, cooled in ice for 15min and
centrifuged at 3000 rpm for 15 min. One millimeter of the supernatant was mixed with
1.5ml of 2,2- pyridine solution and absorbance measured in a Spectrophotometer at
519nm. The concentration of phytic acid was obtained by extrapolation from a standard
curve using standard phytic acid solution. For plotting the standard curve (see Appendix
4) different concentrations (0.2-1.0ml) of sodium phytate solution containing 40-200µg
phytic acid were taken and made to 1.4ml with water (0.4OD corresponding to 70µg
phytic acid).
Tannin
Tannin content was determined by the Folis- Denis calorimetric method described by
Kirk and Sawyer (1998). Five-gram (5g) bambara groundnut sample was dispersed in
50ml of distilled water and shaken. The mixture was allowed to stand for 30min at 28°C
before it was filtered through Whatman No.42 grade filter paper. Sample containing 2ml
extract was dispersed into a 50-ml volumetric flask. Similarly 2ml standard tannin
39
solution (tannic acid) and 2ml of distilled water were put in separate volumetric flask to
serve as standard and reagent was added to each of the flask and the 2.5ml of
saturated Na2CO3 solution added. The content of each flask was made up to 50mls with
distilled water and allowed to incubate at 28ºC for 90min. Their respective absorbance
was measured in a spectrophotometer at 260nm using the reagent blank to calibrate
the instrument at zero.
Haemagglutinin
The method described by Pull et.al. (1978) was used. Fresh blood was collected from a
student (blood group B) using a 5-ml syringe. The red blood cells (erythrocytes) were
extracted from the whole blood suspension in a clinical tube centrifuged at 2000rpm for
10 minutes. One volume of the red blood cells was diluted with 4 volumes of cold 0.9%
saline solution, centrifuged at 2000rpm for 10min and the supernatant fluid discarded.
The sedimented cells were washed with saline in this manner at least three times, until
the supernatant fluid was colourless. The washed red blood cells were introduced to
phosphate buffered saline (0.006M phosphate buffer pH 7.4 in saline) about 4ml of cells
per 100ml of phosphate buffered saline. To 10 parts of this suspension was added 1
part of 2% trypsin solution and the mixture incubated at 37°C for 1hour. The trypsinized
red blood cells were then washed 4 to 5 times with 0.9% saline as earlier described to
remove traces of trypsin. About 2g of bambara groundnut flour was dissolved in 20ml
distilled water, 2ml of the solution was centrifuged at 2000rpm for 10 minutes in order to
obtain a clear solution. The supernatant which was collected and used as crude
agglutinin extract was diluted 2 fold increase to a final dilution of 1:640 in phosphate
buffered saline portions. Each dilution (25ml) was transferred to wells in a microtitre
plate and 25ml volume of 3% suspension of trypsinized type “B” human erythrocytes
was added to each well. The titres were recorded after 3hours at room temperature.
Trypsinized type “B” human erythrocyte was prepared by treatment of a 3% (v/w)
suspension of cells in phosphate-buffered saline for 1hour with Sigma type ix porcine
pancreatic trypsin. One haemagglutinin unit (HU) - defined as the least amount of
haemagglutinin that will produce evidence of agglutination of 25FI of a 3% suspension
of washed, trypsinized type “B” human erythrocytes after 3 hours incubation at room
temperature. Da x Db x S
Hu/g= --------------------------------- V
40
Where V= volume of extract in tube; Da= Dilution factor of extract in tube 1; Db= Dilution factor of tube containing 1Hu; S = ml original extract/gcal
3.4.6.0 Determination of Vitamins
Determination of vitamin A - Biological method for assessment of vitamin A in form of β-
carotene status was used (IVACG, 1982), while determination of vitamins B1, B2,
B3 and
B6 were carried out using Snell and Snell (1953) methods.
3.4.6.1 ββββ-carotene and Vitamin A
Sample weighing 1gm each was macerated with 100ml of distilled water, and 2ml was
pipetted in duplicate into a glass stoppered test tube. An equal volume (2ml) of ethanol
was added drop wise with mixing to give 50% solution (v/v). At this concentration the
protein precipitated and free from retinol and retinyl esters was extracted by addition of
3ml hexane. The tube was stoppered and the contents mixed rigorously on the vortex
for 2 minutes to ensure complete extraction of carotene for 5 – 10 minutes at 600 -1000
x g to obtain a clean separation of phases. Two (2)ml of the upper hexane extract was
pipetted. Absorbance due to carotenoids at 450nm was read against a hexane blank
(A450).
After determining A450, the cuvettes were removed and the hexane was evaporated to
dryness under a gentle stream of nitrogen at 40 – 50oC water bath, while avoiding
splashing on the test tube wall. At the point of dryness during evaporation, the residue
was immediately re-dissolved and rehydrated by addition of 0.01ml of a mixture of
chloroform – acetic anhydride (1.1v/v). The cuvettes or tubes were cupped to minimize
evaporation and was protected from light to avoid oxidation.
The spectrophotometer at 620nm was preset consisting of 0.1ml chloroform –acetic
anhydride mixture and 1.0ml of trichloro acetic acid (TCA) – chloroform chromagen
reagent, 1.0ml of trifluro acetic acid (TFA) could also be used. The cuvette containing
the sample was placed in the spectrophotometer and 1.0 TCA chromagen reagent
added to the cuvete from a rapid delivery pipette. These steps were carried out rapidly
and with care since the blue colour fades quickly and chromagen reagent is highly
corrosive. Absorbance reading was recorded (A620) at exactly 15 seconds (t15) and at
30 seconds (t30) after addition of reagent. A standard curve (see Apendix 5) was plotted
from the A620 values on ordinary rectangular coordinate paper where the ordinate was
41
the A620 value and the abscissa was the µg vitamin A/tube and a factor (FA620)
calculated as shown below:
FA620= 620
/min
A
tubeAvitagµ
Vitamin A was calculated using this formular
Total carotenoids (as β-carotene/dl) = A620 x FC450 x 150
Where, FC450 = constant determined in the laboratory
150 = dilution factor
Likewise vitamin A was calculated (as µg retinol/dl) = A620 x FA620 x 75
Where F A620 = 1/slope of standard curve=1/0.0228=35.7
3.4.6.2 Vitamin B 1 (Thiamin)
The content of Vitamin B1 in the samples was determined according to the Colorimetric
method (Snell and Snell, 1953), of Analysis. Thiamine hydrochloride (50mg) was
weighed using Mettler-HAS balance into a 100-ml volumetric flask, and dissolved in
100ml of water. Sample weighing 1gm each was macerated with 100ml of distilled
water. Each sample solution (2ml) was pipetted separately into 100-ml separation
funnels, 2ml reagent solution was added, and mixed for 1minute, before allowing it to
separate. Isobutyl alcohol (15ml) was added, the mixture was shaken for 2 minutes,
moving the funnels up and down to separate the isobutyl alcohol layer. It was dried by
passing through anhydrous sodium sulphate, then the absorbance was determined at
367nm (Spectro 21D PEC Medicals USA) using isobutyl alcohol as blank. A standard
curve (see Appendix 6) was plotted and the slope used in calculating vitamin B1 as
shown below:
Vitamin B1 = (A x DF)/slope of std. Curve
Where, A – Absorbance
DF- Dilution factor =50
3.4.6.3 Vitamin B 2 (Riboflavin)
The Vitamin B2 content of the snacks was determined using Colorimetric method (Snell
and Snell, 1953). Riboflavin (6mg) was weighed into a 100-ml volumetric flask and
made up to mark with distilled water. The solution (20ml) was diluted in 100ml of
distilled water. The solution was pipetted separately into 2 volumetric flasks (25-ml).
42
Denigee’s reagent solution (5ml) was diluted in 100ml of water. Five (5ml) of each
standard solution was pipetted separately into 2 volumetric flasks (25ml) and 5ml of
denigee’s reagent was added. The flasks were shaken and allowed to stand for 15
minutes before reading their absorbance in 525nm (Spectro 21D PEC Medicals USA)
against a blank solution of 10ml and 5ml of the denigees reagent. A standard curve
(see Appendix 7) was plotted, and the slope used to calculate vitamin B2 as shown
below:
Vitamin B2 = (A x DF)/slope of std. curve
Where, A – Absorbance
DF- Dilution factor =5
3.4.6.4 Niacin
The colometric method (Snell and Snell, 1953) was used to determine niacin content of
the samples. Volumetric flask (100-ml) was weighed using Mettler, HAS balance and
50mg of niacin amide added, dissolved and made up to mark with distilled water. Ten
(10) ml of the solution was put into another 100-ml volumetric flask and made up to
mark with distilled water.
The standard (5ml) was measured into a test tube. Separately 2ml of ammonia buffer
solution and 1ml of distilled water were added, after which 1ml of 2, 6 dichloroquinone
chlorimide solution was added. The solution was shaken vigorously and the
absorbance was taken immediately at 60 to 80nm against a blank.
AT x WS x 3.3 x 100 x 25 x 5 x 5 = mg/5ml AS 100 100 TV 5 25
Where AT = Absorbance of test solution AS = Absorbance of standard solution WS = Weight of standard taken VT = Volume of syrup taken
3.4.6.5 Vitamin C The direct calorimetric method as described by Kalia (2002) was used to determine the
vitamin C content of the samples. It was based on the extent to which a 2,6-
43
dichlorophenol-indephenol solution is decolourized by ascorbic acid in sample extracts
and in standard ascorbic acid. The sample (50g) was blended with an equal weight of
6% HPO3, and an aliquot of the macerate was made up to 100ml.
Plotting of standard curve : The requisite volume of standard ascorbic acid solution-1,
2, 2.5, 4 and 5ml- was pipetted into dry cuvettes, and made up to 5ml with 2% HPO3.
Dye solution (10ml) was added with a rapid delivery pipette and the cuvette shaken
prior to taking the reading within 15-20 sec. The Calorimeter was set to 100%
transmission using a blank consisting of 5ml of 2% HPO3 solution and 10ml of distilled
water. The absorbance of the red colour of the standard solution was measured at
518nm, and absorbance plotted against concentration (see Appendix 8).
The sample extract (5ml) was placed in a cuvette, 10ml of dye was added and
the reading was taken as in standard. The concentration of ascorbic acid was read from
the standard curve and used to calculate the ascorbic acid content as shown below:
(mg of ascorbic acid per 100g of sample)
Ascorbic acid content x Vol. made up x 100 =-------------------------------------------------------------------------------- ml of sol. taken for estimation x 1000 x wt. of sample taken
3.4.7.0 Experimental design/data analysis
The experiment was designed using Completely Randomized Design (CRD). SPSS
version 13 was used to analyse the data obtained statistically using analysis of variance
(ANOVA), and mean separation was done by Duncan(1955) multiple range test at 5%
level of probability.
44
CHAPTER FOUR
4.0 RESULTS AND DISCUSSION
4.1 Effect of Processing Treatments on the Proximat e Composition of Bambara Groundnut
The result of proximate composition of bambara groundnut (BGN) and effect of different
processing treatments like roasting, germination and a combination of both is presented
in Table 5. The moisture (10.30%), crude protein (21.85%), fat (6.90%), ash (3.64%),
fibre (3.42%) and carbohydrate (53.93%) of the raw bambara were comparable to
values reported by Poulter (1981), and Obizoba and Egbuna (1992). No significant
changes were observed in protein, fat and ash content of the germinated BGN flour.
However, roasting on the other hand brought about significant reduction in the moisture
content. The slight increase in the protein (21.85% to 23.09%) and fat (6.9% to 7.33%)
contents noticed in the roasted flour could be probably due to concentration of nutrients
as a result of moisture lost during roasting (FAO, 1982).
Table 5: Effect of Processing Method on the Composi tion of Bambara Groundnut (BGN)
Sample Code
Moisture (%)
Protein (%) Fat (%) Ash (%) Fibre (%) *Carbohydrate (%)
Energy (KCal)
BGN 10.30a±0.91 21.85b±1.34 6.90a±1.02 3.64a±0.98 3.42a±0.76 53.89b±1.30 365.06 RBGN 7.01b±0.73 23.09a±0.99 7.33a±1.25 3.76b±0.70 3.21a±1.08 55.60b±1.50 380.73 GBGN 10.79a±0.67 22.18b±0.54 6.73a±0.54 3.58a±0.50 3.60a±0.79 53.12b±0.86 361.57 G/RBGN 7.24b±0.79 23.20a±1.80 7.16a±0.48 3.85a±1.11 3.52a±0.90 55.03ab±0.16 377.36
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). *Carbohydrate calculated by difference. SD= Standard deviation BGN = Raw Bambara Groundnut; RBGN = Roasted Bambara Groundnut GBGN= Germinated Bambara Groundnut; G/RBGN =Germinated/Roasted Bambara Groundnut
4.2 Effect of Processing Method on Some Anti-Nutrit ional Factors Table 6 shows the effect of processing method on some anti-nutritional factors. Just like
other legumes, bambara nut contains anti-nutritional factors such as trypsin inhibitor,
tannins (polyphenols), phytate, haemagglutinins. Processing methods such as
dehulling, milling, soaking, cooking, germination, fermentation, autoclaving/roasting and
frying have been found to reduce or eliminate these anti-nutritional factors (FAO, 1982).
The result of this experiment is in agreement with this observation. The processing
treatments given had significant (p<0.05) effect in reducing the anti-nutritional factors.
Roasting reduced the concentration of trypsin inhibitor by 37.5% (from 17.94mg/g to
45
11.21mg/g), germination reduced it by 17% (from 17.94mg/g in the raw bambara to
14.85mg/g) while a combination of germination and roasting brought the highest
reduction of 68% (from 17.94mg/g to 8.73mg/g). The nutritional implication of these
reductions in the concentration of trypsin inhibitor is that it will lead to improvement in
protein and digestibility. Negi et al. (2001) and Archana et al. (2001) reported higher
protein digestibility/quality after heat treatment (autoclaving and roasting), which they
attributed to destruction of heat labile protease inhibitor and opening up of protein
structures by denaturation, leading to increased accessibility of the protein to enzymatic
attack. Germination/malting has also been reported to improve protein digestibility
(Nnanna and Philips, 1990). Increased protein quality/digestibility upon germination
may be probably due to decrease in the anti-nutritional factors like tannin, phytate and
trypsin inhibitors, modification and degradation of storage proteins by the action of
proteolytic enzymes. Tannins are generally defined as soluble astringent, complex and
phenolic substances of plant origin, which play significant role in the reduction of dietary
protein digestibility by complexing either with dietary protein or digestive enzyme.
Table 6: Effect of Processing Methods on Some Anti- Nutritional Factors in Bambara Groundnut
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). SD= Standard deviation Tannin content was significantly reduced by the roasting process to 56.5% (from
0.62mg/100g in the raw sample to 0.35mg/100g). Germination reduced tannin by 21%,
while a combination of roasting and germination caused 55% reduction of tannin
content in the sample (from 0.62 to 0.28mg/100g). This reduction brought about
improvement in nutritional quality. Phytate level reduced from the initial content of 100%
(255mg/100g) in raw bambara to 69.8% (178mg/100g) in roasted sample, 75.3%
(192mg/100g) in germinated sample and 47% (120mg/100g) in the germinated and
roasted samples. The Haemagglutinin activity was also reduced from 100%
Processing Treatments on Bambara-Nut
Trypsin Inhibitor Units
(TIU) mg/g
Tannic acid (equivalent)
mg/100g
Phytate (mg/100g)
Haemagglutinin (Hu/mg protein)
Raw 17.94a±0.58 0.62a±0.89 255d±0.36 6.50a±0.78 Roasted 11.21c±1.23 0.35c±1.01 178b±1.42 3.80c±65 Germinated 14.85b±0.69 0.49b±0.22 192c±0.98 5.20 b±1.32 Germinated & Roasted
8.73d±1.24 0.28d±0.05 120a±0.73 2.10d±0.96
46
(6.50Hu/mg/protein) in raw bambara flour to 58.5% (3.80Hu/mg/protein) in roasted
sample, 80% (5.20Hu/mg/protein) in germinated sample to 32.3% (2.10Hu/mg/protein)
in germinated and roasted sample. Reduction in trypsin inhibitor, tannin content, phytic
acid, and haemagglutinin contents of some tropical legumes processed by cooking,
autoclaving and roasting had been reported by Igbedioh et al. (1994) and Apata and
Ologhobo (1994). Similarly Obizoba and Egbuna (1992) reported reduction in
haemagglutinin content of germinated bambara groundnut. Phytate reduction by 38 –
46% after germination had been reported by Archana and Kawata (1998) and Salunkhe
et al. (1985). The reduction was attributed to leaching of phytate ions and increased
activity of phytase enzyme during germination.
4.3 Effect of Processing Methods on the Functional Properties of Bambara Groundnut
The effect of processing methods on the functional properties of Bambara groundnut is
presented in Table 7.
Table 7: Effect of Processing Methods on Selected F unctional Properties of Bambara Groundnut Treatments Water
binding capacity
(g/g)
Oil binding capacity
(g/g)
Foaming capacity (vol/ml)
Nitrogen solubility (%)
Raw 1.7b±0.63 1.3a±0.42 33.3c±0.25 85.40b±0.66 Roasted 1.6b±0.70 1.3a±0.01 24.0a±0.06 46.80d±0.73 Germinated 1.0a±0.29 1.1a±0.83 41.7d±0.41 92.10a±1.32 Germinated /Roasted
1.2a±0.44 1.2a±0.92 28.9b±0.11 49.20c±0.95
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). SD = standard deviation
The functional properties of food proteins determine their behaviour in food systems
during processing, storage, preparation and consumption. These functional properties
and the interaction of proteins with other components directly and indirectly affect
processing applications, food quality and ultimate acceptance. Germination process
was found to significantly (p< 0.05) affect the water binding capacity of bambara flour
(see Table 7). Roasting on the other hand did not have any significant (p>0.05) effect on
the water absorption capacity. Padmashree et al. (1987) reported that polar amino
acids of proteins had an affinity for water and denatured proteins bind less water. Fat
binding capacity has been attributed to the physical entrapment of oil. This is important
47
since fat improves taste, texture and mouth feel (Kinsella, 1976). Processing methods
did not have significant (p>0.05) effect on the fat binding capacity 1.3g/g (raw), 1.3g/g
(roasted), 1.1g/g (germinated) and 1.2g/g for (germinated/roasted). Roasting
significantly (p<0.05) reduced the foaming capacity by 28%, while germination
significantly (p<0.05) increased it by 25.2%. Nitrogen solubility profile over a range of
pH is used as a guide to protein functionality since this relates directly to many
important properties of protein (Lin et al.1974; Sosulki et al. 1976; Mc Waters and
Holms, 1979). Roasting reduced Nitrogen solubility of bambara flour from 85.40%
solubility in the raw samples to 46.80% in the roasted flour, and 49.20% in the
germinated and roasted flour. Padmashree et al. (1987), observed that heat treatment
(roasting, puffing, boiling and pressure cooking) significantly(p<0.05) reduced protein
solubility in the pH range of 2 – 10. Reduction in Nitrogen solubility with heat processing
had also been reported for sunflower, rapeseed, groundnut and soyabean
(Padmashree et al. 1987). However, there seem to be slight increase in the solubility
with germination, as the protein solubility increased from 85.40% in the raw flour to
92.10% in the germinated flour.
4.4 Effect of Treatment Methods on the Consume r Acceptability of the Extruded Snacks from Treated Bambara Groundnut .
The effect of treatment methods (roasting, germination, roasting & germination) on the
consumer acceptability of the extrudates is presented in Table 8. There were
significant differences (p< 0.05) among the extrudates in colour, taste, flavour and
overall acceptability, while there were no significant difference (p> 0.05) among them in
texture and mouthfeel. The extrudates from roasted bambara groundnut had
significantly (p<0.05) higher mean score in colour, taste, flavour and overall
acceptability. This relatively higher mean score of the roasted samples could be
probably due to the roasted flavour and aroma imparted on the bambara groundnut
during roasting. Controlled roasting of nuts brings about development of desirable
roasted aroma in foods, which are described as nutty, burnt and coffee like, due to the
formation of pyrazine compounds that also reflects the extent of browning colour
development in the product (Powrie and Nakai, 1981). The relatively lower mean
sensory scores recorded in the germinated extrudates could be probably due to the
slight bitter after taste observed in germinated samples.
48
Despite the low mean scores, the samples were not however rejected. Roasting was
found to improve the organoleptic qualities of the extrudates, and hence it was
subsequently adopted for formulation of the blends with acha and graded levels of
carrot.
Table 8: Consumer Acceptability Study of the Extrud ates from Treated Bambara Groundnut
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (P< 0.05). *BGN-Bambara Groundnut. SD = standard deviation 4.5. Proximate Composition of Hungry Rice “Acha” an d Fresh Carrot
The chemical composition of carrot used as a source of ß-carotene is presented in
Table 9. Carrot contains (for each 100g) 9.80g carbohydrate, 0.9g protein, 0.10g fat,
1.9 fibre, very rich in ß-carotene (840.8mg/100 retinol) 0.80mg iron, 38.3mg Ca, 2.96mg
Zinc. It also contains a good source of vitamin B1, B2, B6, vitamins C and naicin. The
composition of carrot in this study compares with the values reported by Chan (2007).
Table 9: Chemical Composition of “Acha” and Carrot (per 100g of sample) Parameters Acha Carrot Moisture, % 10.92±0.95 87.50±2.34 Protein, % 9.85±0.56 0.90±0.12 Ash, % 1.21±0.04 0.80±0.20 Fat, % 1.34±0.05 0.10±0.01 Fibre, % 2.24±0.6 1.90±0.15 Carbohydrate, % 74.44±2.21 9.80±1.13 Energy (Kcal) 349.22±5.55 42.60±2.33 Ca (mg) 64.2±3.21 38.34±1.56 Potassium (mg) ND 328.0±2.78 Magnesium (mg) 4.51±0.93 15.40±0.98 Zinc (mg) ND 2.986±0.45 Iron (mg) 23.01± 1.11 0.80±0.11 Vitamin A in form of ß-carotene (In mg/100 retinol) ND 840.8±6.32 Vitamin C (mg) 28.60±2.01 10.7±1.05 Vitamin B1 (mg) 0.10±0.01 0.06±0.01 Vitamin B2 (mg) 0.05±0.02 0.05±0.02 Vitamin B3 (mg) 2.00±0.37 0.96±0.12 Vitamin B6 (mg) ND 0.04±0.01
Values are mean of triplicate determination ±SD. ND – Not determined
Treatments Colour Taste Texture Flavour Mouthfeel Overall Acceptability
Raw BGN* 6.6±0.96b 6.8±0.71ab 7.1±0.19a 6.8±0.86ab 7.0±0.52a 6.8±0.92b Roasted BGN* 7.5±1.01a 7.7±0.86a 7.3±0.90a 7.6±0.66a 7.4±0.45a 7.7±0.50a Germinated BGN* 6.5±0.73b 6.0±0.61b 7.2±0.30a 6.5±0.25b 7.1±0.84a 6.3±0.80b Roasted/Germinated 7.0±0.20ab 6.7±1.14a 7.2±0.79a 6.9±0.60ab 7.3±0.88a 6.6±0.38b
49
The chemical and energy composition of “acha” revealed 10.92% moisture, 9.85%
protein, 1.21% fat, 1.34% ash, 2.24% fibre, 74.44% carbohydrate, and 349.22Kcal of
energy per 100g (dry weight basis). It also contains appreciable quantities of
micronutrients such as Ca, Mg, Fe and vitamins (B1, B2, B3 and C). These values
compare with those reported by Nnam (2000) and Ayo et al. (2007).
4.6 Effect of Extrusion on the Proximate Compositio n of Bambara/”Acha” and Carrot flour Blend
The proximate composition of blend of bambara/”acha” and carrot flour before, and
after extrusion is presented in Table 10. Expectedly, extrusion cooking reduced the
moisture content from 10.52% in the bambara/acha blend to 4.05% in the extruded
sample. Equally, the moisture content of the 5 – 20% carrot fortified blends reduced
from 9.61 – 10.06% in the blends to 4.05 – 4.61% in the extruded products. The
moisture reduction could be probably due to the loss of moisture on extrusion as a
result of high temperature in the extruder and subsequent drying of the extruded
products. There was also a slight increase in the protein and ash contents after
extrusion. These could be probably due to concentration of these nutrients, as a result
of moisture loss.
Table 10: Proximate Composition of Un-extruded & Ex truded Bambara- Acha Containing Graded Levels of C arrot
Sample Code
Moisture (%) Protein (%) Fat (%) Ash (%) Fibre (%) Carbohydrate (%)*
Energy (KCal)
BEFORE EXTRUSION Before BAB
10.12a±0.93
15.19b±0.31
3.24a±0.32
2.73a±0.65
1.96b±0.44
66.76b±0.22
356.96
BAC5 10.06a±0.74 14.68bc±0.90 3.03a±0.7c 2.90a±0.85 2.02b±0.81 67.31b±0.65 355.23 BAC10 9.8a±0.85 14.11c±0.18 2.87a±0.45 2.82a±0.77 2.69a±1.08 67.71b±0.88 353.11 BAC15 9.9a±0.12 13.61cd±1.05 2.92a±0.32 2.89a±0.15 2.95a±0.92 67.73b±0.34 351.56 BAC20 9.61a±0.11 13.09d±0.99 2.48a±0.83 2.68a±0.07 3.03a0.21 69.11c±0.17 3501.12
AFTER EXTRUSION After BAB
4.05b±0.74
16.25a±0.65
6.80b±0.08
3.47ab±0.82
1.89b±201
67.54b±1.08
396.88
BAC5 4.23b±0.49 15.99a±0.38 6.31b±0.08 3.83ab±0.82 2.34b±0.25 67.30b±0.21 388.71 BAC10 4.61b±0.32 15.32ab±0.18 6.39b±0.63 3.78ab±1.62 2.78a±0.71 67.12b±0.98 387.27 BAC15 4.00b±0.91 15.15b±1.08 6.73b±0.12 3.99b±0.99 2.90a±1.04 67.23b±0.35 390.09 BAC20 4.18b±0.78 15.02b±0.77 6.46b±0.96 3.93b±1.18 3.06a±0.21 67.35b±0.67 387.22
CEP 4.10b±0.33 6.00e±055 1.00c±0.25 1.80c±0.67 1.00c±0.33 86.10a±0.88 383.4 Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). *Calculation by difference BAB=Roasted bambara/Acha blend without carrot (control); BAC5=Roasted bambara/Acha blend with 5% Carrot; BAC10=Roasted BGN/Acha with 10% Carrot; BAC15=Roasted bambara/Acha with 15% Carrot; BAC20=Roasted bambara/Acha with 20% Carrot; CEP= Commercial Extruded Product
50
However, the bambara/acha blend with zero carrot fortification (BAB) as well as its
extrudate had significantly higher protein content than the 15 and 20% carrot fortified
samples. This could probably due to the fact that replacement of the bambara
groundnut/”acha” blend with carrot gradually reduced the protein content of the
resultant composite flour, because bambara groundnut naturally contains higher
proportion of protein than carrot. The commercial extruded snack sold in the market
was found to contain 6% protein, which was less than the protein content of the
extruded snacks in this study.
The BGN based blends had relatively high protein content that reflected in the extruded
snacks, making them nutrient dense food products that would be children friendly.
According to US Committee on Dietary Allowance (1980), children between 5 and 14
years old require 34 – 46g of protein/day for body building, repairs, metabolism and
proper functioning of the body for better health benefit. These extruded snacks would
provide between 30 and 50% Recommended Dietary Allowance (RDA) for protein
requirements of 5-14 years old school age child, if 100g of it is consumed daily. The
Protein content of snack containing 5% added carrot flour was 15.99%, which satisfies
about 48% RDA protein requirement of a child if 100g of it is consumed. Snacks with
10% carrot inclusion had 15.32% of protein (which satisfies 44.5% RDA), 15% carrot
containing samples had 15.15% protein content (which satisfies 43% RDA) and 20%
carrot added samples had 15.02% protein content (which satisfies also about 43%
RDA).
There was significant (p<0.05) increase in the fat content of the blends from a range of
2.48% – 3.34% to 6.06% – 6.80% in the extruded products. This increase could be
attributed to the vegetable fat added to the formulation. Also noticeable was a slight
increase in the fibre with increasing addition of carrot in the blends, and this follows the
same trend after extrusion. The fibre content of the product satisfies 40 – 69% of a
child’s daily RDA (5g of dietary fibre). The caloric value of the extruded product is
significantly (p<0.05) higher than that of the blends, which rose from 351.12 –
356.96Kcal in the blends to 387.27 – 396.88Kcal in the extruded samples. These
increases could be probably due to the increase in the fat content as a result of the
added vegetable oil. The high caloric values will provide adequate energy for children
who need a lot of it for their daily activities.
51
4.7 Sensory Qualities of Extruded Snacks
The sensory properties of the extruded snacks from BGN/”Acha” fortified with carrot
(BAC5 – BAC20) and the control sample without carrot (BAB) are presented in Table
11. Carrot addition was found to decrease the ratings of all the sensory attributes
(colour/appearance, taste, mouthfeel, flavour, crunchiness/texture and overall
acceptability) analysed. The extruded snack with 0% carrot inclusion was the most
acceptable followed by 5% carrot addition, 10% carrot addition, 15% and 20% carrot
addition. The lower sensory mean score/acceptability of the carrot-fortified extrudates
may be probably because people are not used to this type of product. The carrot taste,
colour and composition may also have affected some of the organoleptic properties,
and may have contributed to the formation of new flavours in the products. However,
there was no significant difference (p>0.05) between the control sample (BAB) and
samples with 5 and 10% carrot in all the sensory attributes analysed, therefore they
were further used for the storage studies.
Table 11: Mean Sensory Scores of Bambara-Acha Extru ded Snacks Containing Graded Levels of Carrots
Sample Code
Colour/ Appearance
Taste Mouthfeel Flavour/ Aroma
Crunch -iness
Texture Overall Acceptability
BAB 7.5a±0.130 7.4a±0.85 7.0a±0.98 7.1a±1.06 7.6a±1.04 7.0a±0.71 7.4a±1.27 BAC5 7.3a±0.71 7.5a±1.34 7.1a±0.39 7.3a±0.73 7.4a±0.85 7.3a±0.92 7.3a±0.99 BAC10 7.4a±0.99 7.19b±0.55 6.5ab±0.54 7.0a±0.84 7.0ab±0.76 7.0ab±0.22 7.0ab±1.26 BAC15 7.0ab±1.01 6.9ab±0.71 6.0b±0.89 6.8ab±1.14 6.9ab±1.91 6.2b±0.35 6.2bc±1.10 BAC20 6.2b±0.46 6.4b±0.84 6.1b±1.17 6.0b±1.47 6.3b±0.77 6.0b±0.41 5.6c±0.53
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). SD = standard deviation BAB=Roasted bambara/”acha” blend without carrot (control); BAC5=Roasted bambara/”acha blend with 5% Carrot; BAC10=Roasted BGN/”acha” with 10% Carrot; BAC15=Roasted bambara/”acha” with 15% Carrot; BAC20=Roasted bambara/”acha” with 20% Carrot;
4.8 Effect of Extrusion on the Residual Anti-Nutrie nts
Table 12 shows the level of residual anti-nutrients in the extruded snacks. Extrusion
had significant (P<0.05) effect on the anti-nutritional properties, particularly on trypsin
inhibitor and haemagglutinin. This effect is attributed to moist heating occasioned by
flour hydration and extruder temperature and pressure conditions. Trypsin inhibitor
activities are known to be protease inhibitor, and is destroyed by heat, the extent of the
52
destruction depends on the process temperature, duration of heating, particle size,
moisture content, buffer, pH and screw speed (Pham and Del Rosario, 1987).
Table 12: Effect of Extrusion on Anti-Nutrient Cont ent of BGN/Acha Blends Containing Graded Levels of Carrot
*Not Detected. Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). BAB=Roasted bambara/”acha” blend without carrot (control); BAC5=Roasted bambara/”acha” blend with 5% Carrot; BAC10=Roasted BGN/”acha” with 10% Carrot; BAC15=Roasted bambara/”acha” with 15% Carrot; BAC20=Roasted bambara/”acha” with 20% Carrot;
In this study, trypsin inhibitor activity and haemagglutinin were not detected, while the
phytate level was reduced to 81.11mg/100g from 91.01mg in the raw blend and to
30.58 from 36.75mg/100g in the extruded samples. Similarly, the tannin content
decreased from 0.16 – 0.26mg/100g to 0.06 – 0.09 mg/100g. This result agreed closely
with the values reported by Nwabueze (2006) for extruded breadfruit snacks.
4.9 Effect of Extrusion on In-Vitro Protein Digesti bility
The effect of extrusion on in-vitro protein digestibility of the BGN/”acha” blends with
added carrot is presented in Table 13. According to FAO/WHO/UNU (1985), protein
nutritional value is dependent on the quantity, digestibility and availability of essential
amino acids, while digestibility is considered as the most important determinant of
protein quality. From the result, there was increase in the invitro-protein digestibility of
the samples after extrusion. Roasted bambara/”acha” blend without carrot (control-
BAB) was found to increase from 84.62% to 86.74%, BAC5 increased from 86.73-
89.05%, BAC10 increased from 86.92-88.62%, BAC15 (87.01-89.08), while BAC20
increased from 86.57 to 89.89%. The increase in the protein digestibility after extrusion
Sample Code
Trypsin Inhibitor Uni ts (TIU) mg/g
Tannin (Tannic acid equivalent mg/100g)
Phytate (mg/100g)
Haemagglutinin (HU/mg protein)
Before Extrusion BAB 8.33a±0.93 0.26a±6.54 91.01a±1.08 5.12 BAC5 7.94a±0.40 0.19b±1.01 86.29b±0.94 4.85 BAC10 7.01b±1.26 0.16b±0.77 81.11c±0.84 4.01 BAC15 6.81b±0.79 0.19b±0.91 83.31c±0.66 4.35 BAC20 6.87b±0.85 0.18b±0.26 85.73b±1.54 4.30
After Extrusion BAB ND* 0.06c±0.03 34.01e±0.11 ND* BAC5 ND 0.09c±0.69 30.58d±0.83 ND BAC10 ND 0.09c±0.12 32.14d±0.25 ND BAC15 ND 0.08c±0.01 36.75e±0.90 ND BAC20 ND 0.08c±0.36 33.68d±0.29 ND
53
might be due to denaturation of proteins, as well as inactivation of enzyme inhibitors
present in raw plant foods, which expose new sites for enzyme attack (Colonna et al.
1989; Nwabueze 2006; Singh et al. 2007). Similar finding had been reported by
Hakansson et al. (1987), Colonna et al. (1989) and Areas (1992), who observed that
the nutritional value in vegetable protein is usually enhanced by mild extrusion cooking
conditions, owing to an increase in digestibility.
Table 13: Effect of Processing on In-vitro Protein Digestibility of BGN- Based Extruded Snacks Containing G raded Levels of Carrot
Sample Code
In-vitro protein Digestibility (%) Before Extrusion After Extrusion
BAB 84.62a±0.52 86.74b±0.95 BAC5 86.73b±0.90 89.05cd±1.52 BAC10 86.92b±0.74 88.62c±b0.84 BAC15 87.01b±0.12 89.08cd±1.01 BAC20 86.57b±0.66 89.86d±0.72
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). SD = standard deviation BAB=Roasted bambara/Acha blend without carrot (control); BAC5=Roasted bambara/Acha blend with 5% Carrot; BAC10=Roasted BGN/Acha with 10% Carrot; BAC15=Roasted bambara/Acha with 15% Carrot; BAC20=Roasted bambara/Acha with 20% Carrot;
4.10 Effect of Extrusion on the Mineral Content of the BGN/Acha Blends with added Carrot.
Table 14 shows the effect of extrusion on the mineral content of the BGN/”Acha” blends
with carrot. There was a slight increase in the mineral contents of the blends on
extrusion. The extrudates had slightly higher mineral content than the flour blends,
which was more noticeable in the calcium, phosphorus, potassium, magnesium and
manganese contents. The increase in the mineral content after extrusion also follows
the same trend with the level of carrot incorporation as in the blends before extrusion.
The slight increase in the mineral composition of the extrudates could be probably due
to concentration of nutrients as a result of moisture loss during extrusion. Extrusion
cooking had been found to improve the absorption of minerals by reducing other factors
that inhibit its absorption, but does not significantly (p>0.05) affect mineral composition
of pea kidney bean seeds (Alonso et al. 2001).
55
Table 14: Effect of Processing on the Mineral Conte nt of Extruded Snacks Macro-Minerals (mg/100g) Micro-Minerals (mg/100g)
Sample code Ca P Na K Mg Zn Fe Cu Mn
BEFORE EXTRUSION
BAB 73.92a±2.01
161.33e±1.04
2.08a±0.60
1239.75a±1.09
83.89a±1.80
3.18a±1.03
7.81a±0.90
0.42a±0.38
5.60a±0.44
BAC5 76.85b±0.95 159.94d±1.36 3.61b±1.05 1241.08±1.55 82.68a±0.39 3.42a±0.73 7.58a±1.31 0.35a±0.52 5.03b0.89
BAC10 80.04bc±1.09 155.95c±0.96 3.75b±0.84 1244.17bc±0.68 82.36ab±1.10 3.68ab±0.62 7.35±1.08 0.31a±0.47 4.96b±0.25
BAC15 83.19c±0.98 153.27b±0.78 3.69b±1.31 1246.34c±1.00 82.04ab±0.94 3.89b±1.01 7.12bc±0.74 0.36a±0.59 4.30c±0.12
BAC20 85.98c±0.77 150.52a±0.99 3.84b±1.08 1249.01d±0.88 81.72b±1.21 4.05b±0.78 6.90c±0.52 0.30a±1.01 4.01c±0.63
AFTER EXTRUSION
BAB 78.70bc±0.91 181.05i±0.38 2.32a±0.88 1338.40e±1.10 94.16c±0.44 3.95b±1.72 7.95a±1.03 0.40a±0.21 5.80a±0.24
BAC5 81.63bc±0.67 178.98h±0.40 3.56b±1.05 1330.73f±0.71 93.81c±0.97 4.17b±0.95 7.87a±0.78 0.39a±1.05 5.66a±0.38
BAC10 84.56c±1.18 173.29g±0.72 3.85b±0.23 1364.02g±0.56 93.64c±0.82 4.36bc±0.74 7.69a±1.09 0.39a±0.79 5.35ab±0.11
BAC15 87.89cd±2.03 172.93g±0.72 3.80b±0.48 1369.87h±0.85 93.03cd±0.91 4.04b±0.63 7.26ab±0.45 0.40±1.30 5.01b±0.96
BAC20 90.22d±0.70 170.01f±0.12 3.97b±1.26 1392.561±1.00 92.88d±0.60 4.61c±0.51 7.20ab±0.61 0.33±0.82 5.23b±0.69
*RDA for children 4-10 yrs 800 800 2-5 4-6 250 10 10 50-250mg 2.5-3.8
*% RDA Met 10-12 18-23 78-100 40-100 33-38 32-46 69-79 Above 50 Above 50
. Column means with different superscripts are significantly different at 5% probability level (P< 0.05). Values are mean ± SD of triplicate determination. SD = standard deviation. RDA-Recommended Dietary Allowance (*Source: US Committee on Dietary Allowances (1980)) BAB=Roasted bambara/”acha” blend without carrot (control); BAC5=Roasted bambara/”acha” blend with 5% Carrot; BAC10=Roasted BGN/”acha” with 10% Carrot; BAC15=Roasted bambara/”acha” with 15% Carrot; BAC20=Roasted bambara/”acha” with 20% Carrot;
56
4.11 Effect of Extrusion on the Vitamin Content of the Snacks
Effect of extrusion on the ß-carotene and C contents is presented in Table 15. There
was a significant (p<0.05) increase in vitamin A(as ß-carotene) with increase in carrot
inclusion in the blends.
Table 15: Effect of Processing on Vitamins A(as ß-c arotene) and C Contents of
the Extruded Snacks
Sample Code
Vitamin A (as ß-carotene) (µg/100g retinol)
Vitamin C (mg/100g)
BEFORE EXTRUSION BAB 53.08a±0.99 6.21a±0.25 BAC5 180.08b±0.85 7.60b±0.73 BAC10 278.46c±0.28 8.11b±1.01 BAC15 417.79d±0.74 8.67b±0.98 BAC20 548.52e±0.92 8.96b±0.65
AFTER EXTRUSION BAB 56.62a±1.10 2.54c±0.25 BAC5 181.33b±0.67 2.51c±0.44 BAC10 289.96c±0.54 3.92d±2.10 BAC15 419.00d±1.30 3.70d±0.86 BAC20 550.13e±0.22 4.05d±1.09 CEP 46.7 ND *RDA 700 45 *% RDA 25-80 6-9 ND –Not Detected. Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). (*Source: US Committee on Dietary Allowances (1980)). RDA= Recommended Dietary Allowances
BAB=Roasted bambara/”acha” blend without carrot (control); BAC5=Roasted bambara/”Acha” blend with 5% Carrot; BAC10=Roasted BGN/”Acha” with 10% Carrot; BAC15=Roasted bambara/”Acha” with 15% Carrot; BAC20=Roasted bambara/”Acha” with 20% Carrot; CEP= Commercial extruded product
The formulation with 20% carrot (BAC20) had the highest level of ß-carotene (548.32
µg/100g retinol), while the BAB had 53.08µg/100g retinol content. The blends with 5%
carrot (BAC5) had 181.33µg/100g retinol, 10% (BAC10) had 278.46 µg/100g retinol
and 15% inclusion (BAC15) had 417.79µg/100g retinol. The ß-carotene content of the
CEP was found to be 46.7µg/100g, which was comparable to bambara-acha blend
without carrot (BAB) but much lower than the extruded samples with carrot that were in
the range of 180.08-550.13µg/100g. However, there was no significant difference
(p>0.05) in the ß-carotene content of these blends on extrusion, though there was a
slight increase in vitamin A after extrusion. Extrusion did not overtly affect the ß-
carotene level of the products. Rowe et al. (2009) reported similar observation. The ß-
carotene content of the extruded snacks in this study will would meet about 25 – 80% of
57
the RDA for ß-carotene in children, which would make it an ideal snack for vitamin A
Deficiency (VAD) feeding program. The observed stability of ß-carotene in this work
agrees with the report of Atwood et al. (1995) who noted that vitamin A exhibits good
stability during cooking. Vitamin C on the other hand is sensitive to heat and oxidation.
There was a significant reduction in the vitamin C content of the blends after extrusion.
In this study, over 50% of the vitamin C content was lost after extrusion. Vitamin C was
reduced from 6.21mg/100g in the control to 2.54mg/100g after extrusion. Sample BAC5
was reduced from 7.60mg/100g to 2.51mg/g, BAC10 from 8.11 to 3.92mg/100, BAC15
from 8.67 to 3.70 and BAC20 from 8.96 to 4.05mg/100g after extrusion. Vitamin C is
known to be extremely heat labile in a neutral pH and liquid matrix. Cooking losses
depend on the degree of heat, surface area exposed to water and oxygen, pH,
presence of transition metals and other factors that enhance oxidation (Anderson and
Hedlund, 1990; Eitenmiller and Landen, 1999). Anderson and Hedlund (1990) equally
reported that vitamin C decreased in wheat flour when extruded at fairly low (10%)
moisture. Gregory (1996) noted that it was not unusual for vitamin C cooking losses to
reach 100%. Ranum and Chome (1997) reported vitamin C levels of below detectable
limits in five of nine cooked Corn Soy Blend (CSB) samples collected in the field.
The vitamin B1 content of the blends ranged from 0.54 to 0.61mg/100g, B2 (0.39-
0.44mg/100g), vitamin B3 content ranged from 2.34 to 2.59mg/100g, while B6 was in the
range of 0.56 to 0.68mg/100g. The bambara /”acha” blends without carrot had slightly
higher content of all the B vitamins (B1,B2,B3 and B6) analysed. This could be probably
due to the higher content of these vitamins in bambara groundnut and acha compared
to carrot. However, extrusion cooking brought about significant reduction in these
vitamins, with vitamin B1 being the most affected, followed by vitamin B6. Extrusion
brought about between 40-50% reductions in vitamin B1, while about 25-30% reduction
was recorded in B6. Vitamins B2 and B3 recorded about 15-24% reductions in their
contents. Athar et al. (2006) reported a decrease in the levels of B group of vitamins
after extrusion of corn-pea blends, with thiamine and pyridoxine being the most affected
with over 50% reduction in thiamine content. Camire et al. (1990) and Killeit (1994)
obtained similar results. They reported that thiamine and pyridoxine were the most
thermolabile on extrusion and that the levels decreased linearly with temperature that
riboflavin was less sensitive to heat but more sensitive to shear. Compared to the
(commercial extruded product) (CEP) the extruded snacks had relatively lower
58
quantities of vitamins B1,B2,B3 and B6 probably because the market brand had been
fortified with these vitamins to meet specific needs as mandated by the Standard
Organization Nigeria (SON). The extruded snacks in this study were not fortified with
vitamin B complex.
Table 16: Effect of Extrusion on the Vitamin B Cont ent of Bambara-“Acha” Extruded Snacks Containing Grad ed Levels of Carrots (mg/100g) Samples B1
(Thiamin) B2
(Riboflavin) B3
(Niacin) B6
(Pyridoxine) Before Extrusion
BAB 0.61a±0.79 0.44a±0.38 2.59a±0.28 0.68a±0.65 BAC5 0.60a±0.41 0.42a±0.71 2.48a±0.03 0.64a±0.24 BAC10 0.55b±0.08 0.40a±0.55 2.53a±0.36 0.60b±0.46 BAC15 0.58ab±0.15 0.42a±0.86 2.45a±0.11 0.56b±0.18 BAC20 0.54b±0.50 0.39b±0.42 2.34a±0.70 0.61b±0.02
After Extrusion BAB 0.37c±0.32 0.35bc±0.11 2.04b±0.79 0.58b±0.04 BAC5 0.35cd±0.71 0.34c±0.85 2.00b±0.19 0.56b±0.01 BAC10 0.35cd±0.18 0.53bc±0.08 1.96c±0.82 0.50c±0.45 BAC15 0.36c±0.24 0.32c±0.40 1.92b±0.64 0.44c±0.21 BAC20 0.32d±0.53 0.33c±0.25 1.90b±0.05 0.46bc±0.33 CEP 0.99 1.08 12.36 1.41 *RDA 1.20 1.40 16.00 1.60
*% RDA 26-31 23-25 12-13 28-33
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). *Source: US Committee on Dietary Allowances (1980). RDA= Recommended Dietary Allowance BAB=Roasted bambara/Acha blend without carrot (control); BAC5=Roasted bambara/Acha blend with 5% Carrot; BAC10=Roasted BGN/Acha with 10% Carrot; BAC15=Roasted bambara/Acha with 15% Carrot; BAC20=Roasted bambara/Acha with 20% Carrot; CEP= Commercial extruded product
4.12 Effect of Storage on the Texture of the Extrud ates
The effect of storage period on the texture (crunchiness) of three extruded snack
samples (BAB, BAC5 and BAC10), which were selected for storage studies based on
their nutrient composition and sensory acceptability is presented in Table 17.
Table 17: Effect of Storage Period on the Texture ( Crunchiness) of Extruded Snacks
Sample Code
Storage Period (Months)
O 2 4 6
Compression force (N)
Energy (N/m)
Compression force (N)
Energy (N/m)
Compression force (N)
Energy (N/m)
Compression force (N)
Energy (N/m)
BAB 230.17a±0.25 0.36±0.81 214.48a±0.11 0.32±0.05 189.45b±1.23 0.28±0.09 176.21b±1.39 0.25±0.91
BAC5 218.09a±1.22 0.33±0.25 206.32a±0.81 0.29±0.64 190.82b±1.11 0.28±0.65 178.34b±0.43 0.24±0.50
BAC10 228.32a±0.88 0.34±0.211 210.05ab±0.99 0.31±0.02 198.11b±0.77 0.29±0.31 180.77c±1.07 0.26±0.22
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05).BAB=Roasted bambara/”acha” blend without carrot (control); BAC5=Roasted bambara/”acha” blend with 5% Carrot; BAC10=Roasted BGN/”Acha” with 10% Carrot.
59
There were significant differences (p<0105) in the compression force (force required to
compress or break the extruded snacks) of the extruded snacks with increase in
storage period. The compression force decreased (p<0.05) after 4 months, which could
be attributed to softening due to slight increase in moisture content of the samples with
storage.
4.13 Effect of Storage on the Sensory Qualities of the Snacks
The sensory quality scores of the extruded snacks stored over a 6-month period under
ambient conditions (28±2°C) are presented in Table 18. There was no significant
difference (p>0.05) in colour/ appearance, taste, mouthfeel, flavour, crunchiness and
acceptability over the 6 months period of storage. The result however, revealed gradual
decrease in the mean scores of the attributes, though the changes were not significant
(p>0.05). The assessors were not able to detect any significant difference (p>0.05) in
crunchiness within the storage period, inspite of the slight increase in their moisture
content that ranged from 5.17 to 5.50% after 6 months. After 6 months of storage,
samples BAB and BAC5 had high sensory ratings for most of the quality attributes and
compared well with freshly prepared samples.
Table 18: Effect of Storage (6 months at 28±2°C) on the Sensory Qualities of
Extruded Snacks Samples Colour Taste Mouthfeel Flavour/
Aroma Crunchiness Overall
Acceptability 0 Month
BAB 7.5a±0.130 7.4a±0.85 7.0a±0.98 7.1a±1.06 7.6a±1.04 7.4a±1.27 BAC5 7.3a±0.71 7.5a±1.34 7.1a±0.39 7.3a±0.73 7.4a±0.85 7.29±0.99 BAC10 7.4a±0.99 7.19b±0.55 6.5a±0.54 7.0a±0.84 7.0a±0.76 7.0ab±1.26
2 Months BAB 7.4a±0.09 7.5a±0.45 7.1a±1.25 7.0a±0.85 7.5a±0.77 7.0a±0.99 BAC5 7.5a±0.22 7.2a±0.38 7.0a±0.49 6.8a±0.66 7.5a±0.52 7.0a±0.11 BAC10 7.2a±0.36 7.0a±0.69 6.9a±0.88 6.9a±0.21 7.0a±0.13 6.8a±0.41
4 Months BAB 7.0a±2.00 7.1a±0.99 6.8a±0.01 6.9a±0.94 7.0a±0.85 6.8a±0.74 BAC5 7.1a±0.45 7.0a±0.12 6.7a±0.36 7.0a±0.86 6.9a±92 6.4a±0.59 BAC10 7.0a±1.20 6.7a±1.09 6.3a±.81 6.6a±1.11 6.9a±0.91 6.5a±1.02
6 Months BAB 6.9a±1.27 7.0a±0.98 6.7a±0.46 6.2a±0.69 6.8a±0.76 6.7a±0.91 BAC5 7.1a±0.93 6.8a±0.56 6.5a±0.52 6.5a±1.20 6.9a±0.34 6.8a±0.86 BAC10 7.0a±1.01 6.7a±0.88 6.5a±1.35 6.7a±0.23 6.8a±0.45 6.6a±0.11 Column means±SD with different superscripts are significantly different at 5% probability level (p< 0.05). BAB=Roasted bambara/Acha blend without carrot (control); BAC5=Roasted bambara/Acha blend with 5% Carrot; BAC10=Roasted BGN/Acha with 10% Carrot.
Fig. 4 shows the effects of storage period under ambient conditions (28±2°C) and carrot
inclusion on the moisture content of the packaged extruded snacks. There was
60
significant difference (p<0.05) in the moisture content of the samples with increase in
storage period. The moisture content of sample BAB increased from 4.05% at O month
to 5.26% after 6 months storage, recording about 29.9% increase in moisture. The
moisture content of sample BAC5 increased from 4.25 to 5.17% with 22.20% moisture
absorption, while BAC10 increased from 4.31 to 5.50% recording 27% moisture
absorption. Shaw et al. (1994) also recorded increase in moisture content for extruded
snacks containing mechanically separated beef and potato flour. Samples stored for 6
months had significantly (p<0.05) higher moisture content than the freshly prepared
samples. The decrease in breaking strength or compression force could be attributed to
the effect of moisture absorbed by the samples during storage.
Fig.4: Effect of storage under ambient conditions (2 8±2°C) on the moisture content of packaged extruded snacks
0
1
2
3
4
5
6
0 2 4 6
Storage period, months
Moi
stur
e co
nten
t, %
BAB-Roasted BGN/"acha" withoutcarrot"
BAC5- Roasted BGN/"acha" with 5%carrot
BAC10- Roasted BGN/"acha with10% carrot
4.14 Effect of Storage on the Vitamin Content of th e Snacks
Table 19 shows the effect of storage period on ß-carotene content of the extruded
snacks. There was a gradual decrease or reduction in the ß-carotene content of the
extruded snacks during the storage period. At the 4th month of storage, the ß-carotene
content of all the samples was significantly (P<0.05) lower than the ß-carotene content
of the fresh samples. After 6 months storage, the ß-carotene content of extruded
bambara/”acha” without carrot was 19.0% lower than the fresh sample, the 5% (BAC5)
containing carrot samples was 23.8% lower while the 10 (BAC10) carrot containing
61
sample was 26.6% lower than the fresh sample. The decrease in ß-carotene content
during storage could be due to long exposure of the product to light, and also probably
due to the antioxidant properties/activities of ß-carotene in the product during storage
that may have reduced/affected ß-carotene composition of the product. Light has been
reported (Krause and Hunschar, 1972) to affect stability of ß-carotene.
Table 19: Effects of Storage (6 months) at 28± oC on the Vitamin A(as ß-carotene )
Content of Extruded Snacks
Sample Codes
O 2 4 6 % Loss (After
6 months) BAB 56.62a±1.10 54.01b±0.75 50.62c±1.84 45.89d±0.32 19.0 BAC5 180.78d±0.85 176.41c±0.25 169.95b±1.81 141.76a±0.99 21.6 BAC10 289.96d±0.54 283.20c±2.36 270.11b±1.55 212.43a±0.87 26.7
Values are mean±SD of triplicate determination. Column means with different superscripts are significantly different at 5% probability level (p< 0.05). BAB=Roasted bambara/”acha” blend without carrot (control); BAC5=Roasted bambara/”acha” blend with 5% Carrot; BAC10=Roasted bambara/”acha” with 10% Carrot.
62
CHAPTER FIVE
5.0 CONCLUSIONS AND RECOMMENDATI ONS
5.1 CONCLUSIONS
The work revealed that bambara groundnut, hungry rice and carrot, are rich in different
nutrients, which when combined/blended in the right proportions to make composite
flour, would produce nutrient dense flour and consequently food products rich in
protein, Vitamin A and other vitamins and minerals. The products would help to
alleviate the twin problems of protein energy malnutrition and micro-nutrient malnutrition
(hidden hunger) in Nigeria.
From the study it was established that:
1. Blending of bambara groundnut, hungry rice and carrot produced composite flour
rich in protein (12-15%), Vitamin A (181.33-548 µg/100g retinol) and Iron (6.90-
7.81mg/100g), which could be used for different food applications;
2. The composite flour produced very acceptable extruded snacks with high protein
(13-15%), vitamin A (180-550.13mg/100g retinol) and minerals (Iron and Zinc) that
could be exploited for school feeding programme;
3. Extrusion cooking of the blends brought about significant (p<0.05) increase in
protein digestibility and improvement on other nutrients such as minerals;
4. Extrusion cooking did not have significant (p>0.05) effect on the vitamin A and
mineral content of the extruded snacks. However, the treatment brought about
significant (p<0.05) reduction in phytate and tannin contents of the extruded snacks,
and totally destroyed trypsin inhibitor and haemagglutnin activities;
5. Extrusion cooking also brought about significant (p<0.05) reduction in vitamin C and
other heat labile B vitamins like thiamin and riboflavin;
6. Storage for 6 months at room temperature did not have adverse effect on vitamin A
and moisture contents, as well as on the sensory attributes (taste,
colour/appearance, flavour, crunchiness and overall quality).
5.2 RECOMMENDATIONS
Dietary diversification and blending of agricultural produce rich in different nutrients
should be encouraged in food product formulations and development, because it
reduces nutritional imbalance associated with diet from single produce.
The use of extrusion cooking should be encouraged and adopted in the production of
cereal-legume based snacks, because it improves protein quality and digestibility,
drastically reduces anti-nutritional factors and enhance product acceptability.
63
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Appendix 1
PHOSPHORUS STANDARD CURVE
y = 0.0186x
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 10 20 30 40 50 60 70 80 90
CONC(mg/100ml)
AB
S
75
Appendix 2
IRON STANDARD CURVE
y = 0.1306x
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 2 4 6 8 10 12 14
CONC(µg/ml)
AB
S
76
Appendix 3
Mag nes ium s tandard c urve
y = 0.475x
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 1 2 3 4 5
C onc entration (µg /ml)
Ab
so
rba
nc
e
77
Appendix 4
PHYTATE STANDARD CURVE
y = 0.1283x
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 2 4 6 8 10 12 14
CONC(µg/ml)
AB
S
78
Appendix 5
79
Appendix 6
Appendix 7
VITAMIN B1 STANDARD CURVE
y = 0.5604x
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
CONC(mg/100ml)
AB
S
80
Appendix 7
VITAMIN B2 STANDARD CURVE
y = 3.7041x
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.05 0.1 0.15 0.2 0.25CONC(mg/100ml)
AB
S
81
Appendix 8
Vitamin C standard curve
y = 18.585x
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 0.02 0.04 0.06 0.08 0.1 0.12
Concentration(mg/ml)
Abs
orba
nce
82
Appendix 9
VITAMIN B6 STANDARD CURVE
y = 0.0526x
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12
CONC(mg/100ml)
AB
S