ABSTRACT
This research was done to determine the microbes present and the nutritional changes that occur when soybean is thermally processed to soymilk and then fermented to soy yogurt using starter cultures. The soybean was purchased from ubani central market in umuahia, Abia state. It was de-hulled, boiled and thermally processed to soymilk. The soymilk was then fermented to soy yogurt for 12 hours using starter cultures (lactobacillus spp and streptococcus thermophilus), sweetener (Glucose -D) and cassava stabilizer. Standard microbiological characterization of the isolates was carried out. Results revealed that the bacterial isolates from the raw soybean are: Staphylococcus aureus, Bacillus spp, Escherichia coli, and Lactobacillus spp. The fungal isolates from the raw soybean are Aspergillus spp and Saccharomyces spp. The soymilk had no microbial isolate because it was pasteurized for 20 minutes at 850C. The microbial isolates of the soy yogurt from the 0hr to the 12 hr were Lactobacillus spp and Streptococcus thermophilus. The moisture content determined by the AOAC method showed that soymilk had the highest value (82.16%) which was followed by the soy yogurt (80.35%) and the lowest was the raw soybean (8.00%). The crude protein determined by Kjeldalh method showed that raw soy bean had the highest value at (41.00%) which was followed by soy yogurt (7.87%) and soy milk (5.00%). The crude fiber determined showed that raw soy bean had the highest value (4.00%) which is followed by soy milk (0.07%) and the soy yogurt (0.02%). The fat was determined using the AOAC method showed that the raw soy bean had more fat content (19.00%) than the soymilk (4.00%) and the soy yogurt (3.35%). The ash content showed that the raw soybean had high ash value (19.00%) followed by the soymilk (0.77%) and the soy yogurt (0.55%). The carbohydrate using the AOAC method showed that the raw soybean had the highest value (21.00%) which was followed by the soymilk (8.00%) and then the soy yogurt (7.86%). The proximate composition showed that the soy yogurt had more protein content than soymilk. However, the soymilk had more crude fiber, moisture content, fat content, ash content and more carbohydrate. The %TTA was determined by the alkaline titrimetric method which showed that the soy yogurt (1.81) is more acidic than the soy milk (0.11). The pH was determined using Hana size pH meter which showed that the soy yogurt is more acidic (3.7) than the soy milk (6.4). The acidity of the soy yogurt prevents the activities of food spoilers and pathogens that might have access to the soy yogurt. From this study it can be concluded that fermented soy bean (soy yogurt) using starter cultures is more proteinous and has less fat than soy milk and also has comparable carbohydrate content with the soy milk. The fermented processed soybean seed (soy yogurt) contains lactobacillus spp and streptococcus spp which are classified as friendly bacteria and are beneficial to the human health.
TABLE OF
CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgements iv
Table of contents v
Lists of tables viii
Abstract ix
Chapter
One 1
1.0 Introduction 1
1.1 Aims
and Objectives 3
Chapter
Two
2.0 Literature
Review 4
2.1 Soybean 4
2.1.1 Origin
and History of Soybean 4
2.1.2 Importance
of Soybean 5
2.2 Chemistry
and Nutritional Composition of Soybean 9
2.2.1 Soybean
in Nutrition and Health 9
2.3 Bioactive Compounds Occurring In Soy 11
2.3.1 Isoflavones 11
2.3.2 Lectins
and Trypsin Inhibitors 12
2.3.3 Saponins 13
2.3.4 Phytates 15
2.4 Disease
Prevention 16
2.4.1 Cardiovascular Disease 17
2.4.2 Cancer 19
2.4.3
Osteoporosis 21
2.4.4
Alzheimer’s Disease 22
2.4.5 Other Beneficial Effects 23
2.5 Anti Nutritional Factors in Soybean 23
2.6 Processing Of Soybean 24
2.7 Soy Milk 24
2.8 Soy Yoghurt 24
2.8.1 Starter Cultures in Yogurt Manufacture 25
Chapter
Three
3.0 Materials
and Method 27
3.1 Collection of Samples 27
3.2 Sterilization of Materials 27
3.3 Media Used and Their Preparation 27
3.4 Production
of Soymilk 28
3.4.1 Production of Soy Yoghurt 30
3.5 Microbiological Analysis of Sample 32
3.5.1 Serial Dilution 32
3.5.2 Inoculation 32
3.5.3 Total Viable Count 33
3.5.4 Gram Stain 33
3.6 Proximate
Analysis of Fermented Soy Beans 34
3.6.1 Moisture Content Determination 34
3.6.2 Ash
Content Determination 35
3.6.4 Fat Content
Determination 35
3.6.5
Carbohydrate Determination 36
3.6.6 Crude Fiber 37
3.6.7 Protein Content Determination 38
3.6.8 Determination Of Total Titratable Acidity 39
3.6.9 Determination Of pH 39
3.7 Biochemical Test 39
3.7.1 Catalase Test 39
3.7.2 Coagulase Test 40
3.7.3 Citrate Utilization Test 40
3.7.4 Indole Test 41
3.7.5 Oxidase Test 41
Chapter Four
4.0 Results 42
Chapter
Five
5.0 Discussion, Conclusion and Recommendation 49
5.1 Discussion 49
5.2 Conclusion 52
5.3 Recommendation 52
References 53
LIST OF TABLES
Table Title Page
4.1: Morphological and Biochemical
characteristics of Bacterial isolates 43
4.2: Bacteria succession from
different Agar. 44
4.3: Morphological characteristics
of fungal isolate 45
4.4: Fungal succession on Sabouraud
dextrose agar 46
4.5: Proximate composition of the
raw soybean, soymilk and soy yogurt 47
4.6: Total titratable acidity and
ph values of soymilk and soy yogurt 48
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Soybean
(Glycine max) is a member of the
family Leguminosae, sub family pailionacae. It is an annual plant of varying
heights. The number of pods and seeds are strongly influenced by environmental
factors. Soy bean is a high protein legume grown as food and are common in the
orient and other part of the world. Glycine
soja is the wild ancestor of Glycine
max, and grows wild in china, Japan, Korea, Taiwan and Russia. The subgenus
Glycine consists of at least 16 wild perennial specie, for example, Glycine canascens. (Rachael and
Oluwamodupe, 2012).
Soybean
is a top vegetable protein source and it is particularly valued for its high
protein content. Aside from protein they contain good amounts of carbohydrates
and fats. They contain antioxidants and phytonutrients that have been linked
with various health benefits. Recently, in Nigeria, a stimulated interest
appears to have developed in the use of soybean for human food. One of such
steps is commercial production of soy-ogi, a protein fortified Nigeria made
beverage, which was derived, perfected and produced at the Federal Institute of
Industrial research, Oshodi Nigeria. (Rachael and Oluwamodupe, 2012).
The
main products from soybeans are meal and oil in the orient, alongside a variety
of fermented soy foods and non-fermented soy foods. Fermented soy is a form of
soy that has gone through a lengthy fermentation process that makes it
digestion- friendly. Examples are soy yoghurt, tempeh, natto and miso. Unfermented
soy comes in the form of tofu, soymilk, fresh raw or cooked soybeans, soy
chips, soy flour and the countless number of processed foods that contain soy
derivatives or soybean oil.
Soy
contains high levels of toxins or anti-nutrients that can cause gastric
distress, growth depression, pancreatic hypertrophy, hyperplasia and adenoma in
experimental animals. These anti-nutrients include potent enzyme inhibitors
that block the action of trypsin, an enzyme needed for protein digestion (Atli,
2017). Excessive amount of these anti-nutrients can lead to stomach upset and a
deficiency of nutrients, especially amino acids. When soy is fermented, these
compounds are deactivated. Fermented soy has a wide range of health benefits
like anti cancer effects, reduction of menopausal syundrome frequency
osteroprosis protection, coronary heart disease prevention due to
antiatherogenic properties and high amounts of vitamin K2. (Atli, 2017).
The
methods of processing and heat treatment of soybeans also combats anti-nutritional
factors. Soybeans have been used in human and animal nutrition because of their
favourable agronomic characteristics, relatively low price, high quality and
quantity of protein and oil as well as their important functional properties
for the development of different types of foods for humans (Siulapwa and
Mwambungu, 2014)
Despite
the benefits derived from soybean, it can be an easy medium or route for
transmitting food borne bacteria and enteric bacteria pathogens as well as
fungal pathogen, identified with food poisoning, gastric enteritis, dysentery
and enteric fever. These pathogens can be balanced by probiotics which are
constituents of fermented milks and yoghurt. Diary milk used in the production
of yoghurt contains lactose and since soymilk made from soybean is milk
alternative for vegans and people who are lactose intolerant, therefore , it
was necessary to use soymilk in yoghurt production, knowing that soybean comes
from plants, making it naturally free of cholesterol and low in saturated fat.
The
microbial load and proximate composition of soybean present prior to thermal
application and fermentation definitely differs from the microbial load and proximate
composition after thermal processing and fermentation. This study would
highlight and state the difference in microbial load and proximate composition
of the soybean during its stages of processing which could justify or cause a
review in its processing stages.
1.2 AIM AND OBJECTIVES
1. To
determine the effect of fermentation on the microbial load and nutritional
status of the soybean
2. To
isolate and characterize the microbes associated with the fermentation of soybean
derivative (soy yoghurt) after fermentation.
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