DETERMINATION OF EXOPOLYSACCHARIDES FROM LACTIC ACID BACTERIA ISOLATED FROM FERMENTED FOODS

ABSTRACT

Exopolysaccharides were determined from lactic acid bacteria isolated from fermented foods. Foofoo, Ogiri, Ugba, and Yoghurt were the fermented foods used. Five lactic acid bacteria including species of Lactobacillus, Streptococcus, Bacillus, Micrococcus and Leuconostoc. The occurrence of the isolates were Lactobacillus (78%), Leuconostoc (50%), Micrococcus (66.7%), Streptococcus (50%) and Bacillus (66.7%). The distribution of the isolates in the fermented foods vary significantly. Tests on EPS production shsow that the quanitity of EPS produced by the different lactic acid bacteria vary between the organisms. The yield was highest 486.67 mg/l from Lactobacillus, and least 130.0 mg/l in Leuconostoc while Streptococcus, Micrococcus and Bacillus yielded 413.3 mg/l, 133.3mg/l, 320.0 mg/l respectively. Test on optimization of conditions for maximum EPS production show that temperature, pH and fermentation time affected the production of EPS but the optimum conditions show that fermentation at pH 5.0 at 40°C for 96 hours yielded the best results in all the test lactic acid bacteria. Although variations were needed in the preferences of the isolates which includes Bacillus, Streptococcus, and Lactobacillus were used in the optimization test which gave the same result irrespective of the organisms involved. It was recorded that EPS production should be conducted at the above found optimum conditions for maximum yield. 

TABLE OF CONTENTS

Title page                                                                                                                        i

Certification                                                                                                                   ii

Dedication                                                                                                                       iii

Acknowledgement                                                                                                          iv

Table of Contents                                                                                                           v

List of Tables                                                                                                                  vii

List of Figures                                                                                                                 viii

Abstract                                                                                                                           ix

CHAPTER ONE

1.1  Introduction                                                                                                         1

1.2 Objective of study                                                                                                      2

CHAPTER TWO

2.0    Literature Review                                                                                                   3

2.1    Exopolysaccharides                                                                                                3

2.1.1 Exopolysaccharides from Lactic acid bacteria                                                       3

2.1.2 Application of Exopolysaccharides in foods                                                          4

2.2.   Lactic acid bacteria                                                                                                5

2.2.1 Application  of Lactic acid bacteria                                                                       5

2.3    Fermented foods                                                                                                                 6

2.3.1 Purpose and benefits of food fermentation                                                             7

2.3.2 Nutritional benefits of food fermentation                                                              7

CHAPTER THREE

3.0   Materials and methods                                                                                             9

3.1   Sources of materials                                                                                                9

3.2   Sample preparation and media preparation                                                             9

3.2.1 Preparation of sample                                                                                             9

3.2.2 Media preparation                                                                                                  9

3.2.3 Preparation of MRS media                                                                                    10

3.3    Isolation of lactic acid bacteria                                                                             10

3.4    Identification of isolates                                                                                        11

3.5    Screening for exopolysaccharide Production                                                        11

3.6    Extraction of exopolysaccharide                                                                           12

3.7    Optimization of EPS production                                                                           12

CHAPTER FOUR

Results                                                                                                                            14

CHAPTER FIVE

Discussion                                                                                                                       24

Conclusion                                                                                                                      26

References                                                                                                                     26

              LIST OF TABLES                         

Table        Title                                                              Pages

1:                     Characterization and identification of bacterial isolates from samples  16

2:                    Occurrence of lactic acid bacteria in test samples                                          17

3:                     Preliminary test for EPS yield by isolates                                                      18

4:                     Optimization of EPS production by pH                                                          19

5:                     Optimization of EPS production by Temperature                                          20

6:                     Optimization of EPS production by fermentation time                                    21

LIST OF FIGURES

Figure     Title                                                          Pages

1.                     Formation of mucoid colony                                                                       22

2.                     Exopolysaccharide determined after drying                                                23

CHAPTER ONE

INTRODUCTION

1.0    BACKGROUND OF THE STUDY

Lactic acid bacteria are associated with many fermented foods; particularly milk based products such as curd, yoghurt, sour cream, cheese and buttermilk where they contribute to develop taste, flavour and shelf life of fermented food (Shah and Prajapati 2013).

 Most of the lactic acid bacteria producing exopolysaccharide belong to the genera Streptococcus, Lactobacillus, Lactococcus, Leuconostoc, and Pediococcus. Lactic acid bacteria are able to produce mainly two types of polysaccharides according to their location in the cell, intracellular polysaccharides and extracellular polysaccharides (Deegest et al., 2001).

 Exopolysaccharide impart highly desirable rheological changes in the food matrix such as increased viscosity and improved texture (Badel et al., 2011).

 Exopolysaccharide may induce positive physiological responses including lower cholesterol levels (Levrat-Verny et al., 2000) reduced formation of pathogenic biofilms, (Kim 2009) modulation of adhesion to epithelial cells (Ruas-Madiedo et al., 2006)

The beneficial effects of bacteria to human health, with respect to the development of functional food, have largely been attributed to its exopolysaccharides. Some of these bacteria are referred to as probiotics; a concept Salminen et al. (1998) describes as live microbial food ingredients which are of benefit to human health. The health promoting effects of probiotics has been attributed partly to exopolysaccharides. Antitumor, antiulcer, immunomodulatory, antiviral and cholesterol lowering activities (Ruas-Madiedo et al., 2002) are some of the health benefits attributed to these exopolysaccharides. Lactobacillus lactis sub specie cremoris, enjoys wide application in dairy industries for yogurt production due to the special rheological properties that it impacts on products; however, this same organism is thought to possess some health-promoting properties.

Looking at the various utility of exopolysaccharide from lactic acid bacteria, it is essential to raise the yield and improve efficiency of exopolysaccharide. A crucial strategy to achieve this will be to precisely understand the interaction between different exopolysaccharide producing lactic acid bacteria and the best condition the optimum yield. Lactic acid bacteria cannot bulk synthesize the exopolysaccharide without altered fermentation conditions. Screening the spontaneous diversity in lactic acid bacteria will increase the chances of picking genetically stable strains of lactic acid bacteria and discover the ones capable of providing large quantities of functionally efficient exopolysaccharide (Monsan et al., 2001).

1.1       Objective Of Study

a)     To determine the exopolysaccharide productivity of selected lactic acid bacteria

b)    To determine the growth condition necessary for the optimum yield of exopolysaccharide by the selected lactic acid bacteria. 

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