SHELF LIFE PROFILE OF SOYMILK BEVERAGE USING STARTER CULTURE (LACTOBACILLUS BULGARICUS AND STREPTOCOCCUS THERMOPHILUS).

ABSTRACT

Fermented foods are those processed through the activities of microorganisms. Soy milk is an aqueous extract from soybeans known for its nutritive health benefits. The aim of this work is to ferment soy milk product with starter culture (lactobacillus bulgaricus and streptococcus thermophilus) to prolong its shelf life. The soy bean was purchased from Ogbete main market located at Enugu North in Enugu state. It was immediately transferred to Godfrey Okoye University microbiology laboratory, where it was processed into soymilk. The processed product was pasteurized for 30mins, allowed to cool and added either milk or sugar as a carbon source before fermenting anaerobically with the starter culture (lactobacillus bulgaricus and streptococcus thermophilus) gotten from Aqua Rapha Company, Ninth mile, Enugu. Temperature and pH variations of fermented soymilk samples (soymilk with both organisms, mixed with milk and sugar respectively, soymilk with both organism mixed with either milk or sugar respectively) were determined. Sample containing both organisms with milk and sugar respectively, have the highest temperature (8⁰c) on day one and were slightly acidic (4.30), while sample containing both organism and sugar has the highest temperature (6⁰c) on the last day and are slightly acidic (4.25). Proximate analysis of this various soymilk samples were determined. Sample containing both organisms and sugar has the highest protein content (3.678%) while the control shows the least value (0.347%). Sensory evaluation showed that the product fermented with both organisms with milk and sugar was more acceptable than all other samples. Shelf life of these products were determined for 6 days. All the samples were acceptable from 0-3 days, but from the 4^–5^th day, sample 1 has a pungent smell and was not acceptable while sample 7 was able to retain its aroma and flavor. This is to show that starter culture fermentation was able to improve the shelf life and organoleptic properties for better acceptability.

                                                           TABLE OF CONTENTS

TITLE PAGE   —   —   —   —    —     —     —   —     —-       —    —   —   —   —    —    i

APPROVAL PAGE —   —    —     —     —   —     —-       —  —   —    —   —  –  ii

DEDICATION —   —    —     —     —   —     —-       —    —    —    —-   —–  —iii

ACKNOWLEDGEMENTS   —   —    —     —     —   —     —-       —   —     —     iv

ABSTRACT —   —   —   —    —     —     —   —     —-       —   —–    —-     —-    —-      v

TABLE OF CONTENTS   —    —     —     —   —     —-    —   —   —-   —     vi-viii

LIST OF TABLES —   —     —     —   —     —-       —    —     —    —-  –      ix

LIST OF FIGURES —    —     —     —   —     —-       —     —-     —-    —       x

CHAPTER ONE

• INTRODUCTION —–    —     —     —   —     —-       —     —-      —–       1

1.1 PROBLEM STATEMENT —    —     —     —   —     —-       —     —-   —    2

• AIM —   —   —   —–   —     —-       —     —       —–    ——     —–         3

1.3 OBJECTIVES — —    —     —     —   —     —-       —       —–     —–    —        3

CHAPTER TWO

• LITERATURE REVIEW —   —    —     —     —   —     —-       —     —–    —   4

2.1   SOYMILK —   –   —     —     —   —     —-      —    —    —-     —-    —-   —  4

2.2   HISTORY OF SOYMILK —    —     —     —   —     —-       —   —-    —  5

2.3   CONTENT OF SOY —      —     —     —   —     —-       —    —   —-   —   6

2.4    HEALTH BENEFIT OF SOYMILK —  —    —     —     —   —     —-     — 10

2.5     MICROBIAL FERMENTATION ——    —     —     —   —     —-       — 14

2.6      LACTIC ACID BACTERIA —     —     —     —   —     —-       —       14

2.6.1    METABOLISM —   —   —-     —   —     —-       —     —    —     —  16

2.6.2   LACTIC ACID BACTERIA AS FUNCTIONAL STARTER CULTURE–  — 17

CHAPTER THREE

3.0 MATERIALS AND METHODS —   —     —     —   —     —-       —    — 21

3.1 SAMPLE COLLECTION —   —   —     —   —     —-       —   —   —   — 21

3.2 ISOLATION OF MICROORGANISMS FROM STARTER —   — —     —    21

3.2.1 ISOLATION OF PURE CULTURES OF ISOLATES. —       —     —     —  21

3.2.2 CHARACTERIZATION AND IDENTIFICATION OF ISOLATES. —   —   –  21

3.3 PREPARATION OF SOYMILK —   —  —     —     —   —     —-       —        22

3.3.1 LACTIC FERMENTATION —    —     —     —   —     —-       —   —      23

3.3.2 PH VALUE —   —   —   —-   —     —-       —   —   —    —    —    —    23

3.3.3 SENSORY EVALUATION —    —     —     —   —     —-       —   — — 23

3.3.4 PROXIMATE ANALYSIS —   —  —     —     —   —     —-       —    —–    24

3.3.5 EVALUATION OF SHELF LIFE —   —     —     —   —     —-       —     24

CHAPTER FOUR

RESULTS —   —   —   —    —     —    —-       —   —   —   —   —    —     —    25

CHAPTER FIVE

DISCUSSION —   —   —   —    —     —     —   —     —-       —      —-    —-   —      32

CONCLUSION —   —   —   —    —     —     —   —     —-       —     —-     —-   –       34

REFERENCES —   —   —   —    —     —     —   —     —-       —    —-      ——          35

APPENDIX —   —   —   —    —     —     —   —     —-       —    —-      ——    —        39

LIST OF TABLES

Table 1: Propagation temperature for lactic acid bacteria —   —    —   20

Table 2: Cell morphology of the isolate from freeze culture —   —   —   25

Table 3: Microscopic view and cell morphology of sub cultured isolates –26

Table 4: Temperature measurement of samples —   —   —   —   —     27

Table 5: pH measurements of samples —    —   — –   —   —    —   — —    28

Table 6: Mean value of the sensory evaluation after 17hrs — — — —     29

Table 7: Proximate analysis of soymilk — — — — — — —   —   —   —   —    – –    30

Table 8: Shelf life of soymilk at room temperature– — —   — — —–       31

   LIST OF FIGURES

Figure1: Soymilk during fermentation   –  —     —     —   —     —-       —41

Figure2: Soymilk before fermentation —   –    —     —   —     —-       —    42

Figure 3: Refrigerated soymilk —   —   —   —     —-       —    —    — 43

CHAPTER ONE

1.0  INTRODUCTION

Soymilk is a rich creamy liquid extract of soybean (Glycine max) (Tunde-Akintunde and Souley, 2009) and is the most available soy product. Soymilk is a popular nutritive beverage alternative to cow’s milk and is even cheaper(Soya-Agrodok, 2005). Soymilk has become a very interesting food due to its extraordinary nutritive value and health characteristics. It is a very rich source of highly valuable proteins, unsaturated fatty acids, soluble and insoluble dietary fibres, and isoflavones whose presence in everyday diet is very important (Boani, 2006). In some countries, soymilk is intended for the population who cannot digest milk due to lactose intolerance, allergy to milk proteins, or vegetarian way of diet. Soymilk has limited consumer acceptability due to its undesirable beanyflavour. to improve its acceptability due to reduction in objectionable flavour and oligosaccharides such as starchyose and raffinose that cause flatulence (Wang et al., 2002). (Akabandaet al. 2010) reported that fermentation of soymilk provides a possibility for modifying or improving its flavour and texture so that it becomes more acceptable. In western countries, soymilk is intended forpopulation who cannot digest milk for reasons like lactose intolerance, allergy to milk proteins, or vegetarian way of diet. Fermenting soymilk with lactic acid bacteria considerably increases its health value. Because of greater antioxidative actions (Wang etal. 2006), they are considered healthier than pure soymilk. The purpose of fermentation is to remove the undesirable beany taste which is mostly due to the presence of n-hexanal and pentanal , and to improve on the nutritional characteristics of soymilk. Several studies (Hong et al., 2004; Song et al., 2008) have reported numerous benefits of fermented soymilk including degradation of soybean allergens during fermentation by proteolytic enzymes. Due to the characteristics of milk that is highly perishable, the purpose of milk fermentation using lactic acid bacteria is to prolong its shelf life as well as to preserve the nutritious component of milk.

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