ABSTRACT

Several strains of lactic acid bacteria secrete extracellular polysaccharides in favourable environment such as milk. Exopolysaccharides (ESP) is used to describe extracellular polysaccharides either attached as capsule with bacterial cell wall or liberated into the medium as ropy polysaccharides. LAB exopolysaccharides is economically important because it impacts functional effects on food and confer beneficial health effects on the consumers such as antioxidant, cholesterol lowering effects and immune modulation. Lactic acid bacteria have been used for thousands of years in dairy products and food industries, they play crucial role in food fermentation processes. A wide variety of strains are routinely used as starter cultures to manufacture dairy products. These bacteria produce Lactic acids, hydrogen peroxides and several enzymes during fermentation. Growth of spoilage and pathogenic bacteria in the fermented food are inhibited due to the production of antimicrobial substances by LAB as their competition for nutrients. Test confirmed all the isolates to be gram positive, catalase negative, non-motile and non-spore forming rods and cocci in shape. Carbohydrates fermentation test confirmed Lactobacillus acidophilus, Lactococcus lactis, Lactobacillus fermentum, Leuconostoc messentoriodes as the probable organisms. These LAB all produced exopolysaccharides with mucoid and ropy colonies. These exopolysaccharides produced were used for the antimicrobial activity against staphylococcus aureus and Escherichia coli. The results showed zones of inhibition on EXO A, EXO L, EXO M and EXO F for Staphylococcus aureus as 18mm, 28mm, 25mm, 20mm and for   E. coli 20mm, 25mm, 30mm, and 22mm respectively which implied the ESP inhibited the growth of the test organisms.    

TABLE OF CONTENTS

Title page i

Certification ii

Dedication iii

Acknowledgement iv

Table of content v

List of table vii

Abstract viii

CHAPTER ONE: INTRODUCTION

1.2 Lactic Acid Bacteria (Lab) 1

1.3 Aim and Objectives of Study 2

CHAPTER TWO: LITERATURE REVIEW

2.1 Fermented Foods 3

2.2       Purpose and Benefits of Food Fermentation 3

2.3 Lactic Acid Bacteria (Lab) 4

2.4 What Is Lactic Acid Bacteria? 4

2.5 History of Lab 5

2.6  Exopolysccharides 6

2.7 Exopolysaccharide Producing Lab 7

2.8 Types of Exopolysaccharide  7

2.9 Exopolysaccharide Production, Isolation And

Characterization 8

CHAPTER THREE:     MATERIALS AND METHODS

3.1 Source of Material 9

3.2 Sample Preparation 9

3.3 Media Preparation 9

3.4 Preparation of MRS Broth  10

3.5 Isolation of LAB 10

3.6 Colony Count of Isolates 11

3.7 Identification of Isolates 11

3.8 Determination of Colony Features 12

3.9 Microscopy 12

3.10 Gram Staining 12

3.11.1 Catalase Test 13

3.11.2 Motility Test 13

3.11.3  Coagulase Test 13

3.12 Growth at Different Temperature 14

3.13 Growth at Different PH 14

3.13.1 Growth at PH 3 14

3.13.2 Growth at PH 9 14

13.14 Salt Tolerance Test 15

3.15 Sugar Fermentation Tests 15

3.16 Test Organisms 15

3.17  Anti-Bacterial Activity of EPS Producing Lab 15

3.18  Screening for ESP Production 16

3.19 Extraction of Exopolysaccharides 16

CHAPTER FOUR: RESULTS 17

CHAPTER FIVE: DISCUSSION, CONCLUSION AND RECOMMENDATION

5.0 Discussion 22

5.1 Conclusion 23

5.2 Recommendation 23

REFERENCES 24