ABSTRACT

This work studied the in vitro inhibitory effect of bacteriocin from lactic acid bacteria (LAB) from Ugba against spoilage bacteria of carrot (Daucus carrota). Seven bacteria species were isolated from randomly selected spoilt carrot tubers from five (5) locations. The isolates and their respective occurrences Staphylococcus aureus (100%), Pseudomonas spp (75%), Proteus spp (40%), Serratia spp (80%), Bacillus spp (80%), Corynebacterium spp (15.3) and Escherichia coli (40%). Two lactic acid bacteria, Lactobacillus fermenti and Lactobacillus plantarum were isolated from Ugba and their crude bacteriocin extracts were used for tests. Result of pathogenecity test of the spoilt carrot bacteria isolates, showed only three isolates, Corynebacterium, Pseudomonas and Serratia species were confirmed to be pathogens of fresh healthy carrot tubers. The inhibitory effects of the crude bacteriocin extracts of the lactic acid bacteria isolates showed inhibitions of varied sizes against the pathogens in vitro. L. casei crude extracts generated inhibition zones of diameters in the range of 11.67mm (Corynebacterium) to 13.67mm (Serratia) while L. fermenti cause inhibitions of 10.67mm (Pseudomonas) to 12.67mm (Serratia). The inhibitory of L. plantarium crude bacteriocin extracts was in the range of 10.67mm (Corynebacterium) to 13.67mm (Serratia). The inhibitory activities of the lactic acid bacteria extracts were all lower than that of a standard antibiotic (control) which ranged between 18.67mm (Serratia) 22.0mm (Pseudomonas). The potentials of the crude bacteriocin extracts from lactic acid bacteria controlling carrot spoilage bacteria was observed in spite of the relatively low level of inhibitions.

TABLE OF CONTENTS

Title Page   i

Certification iii

Dedication iv

Acknowledgement v

Table of Contents vi

List of Tables vii

Abstract ix

CHAPTER ONE

1.0 Introduction 1

1.1 Aim and Objectives 3

CHAPTER TWO

2.0 Literature Review 5

2.1 Importance and Description of the African Oil Bean Tree 5

2.2 Preparation of Ugba 5

2.3 Lactic Acid Bacteria 6

2.3.1 Taxonomical Classification of Lactic Acid Bacteria 7

2.3.2 Occurrence of Lactic Acid Bacteria in Nature 7

2.4 Bacteriocins 8

2.4.1 Antimicrobial Property by Bacteriocin Production 9

2.4.2 Range of Activity 10

2.5 Classification of Bacteriocins 11

2.5.1 Class I 11

2.5.2 Class II 12

2.5.3 Class III 13

2.5.4 Nisin 13

2.6 Bacteriocin-Like Substances 14

2.7 Isolation and Purification 15

2.8 Methods of Purification 16

2.8.1 Purification of Class I Bacteriocins 18

2.8.2 Purification of class II bacteriocins 19

2.8.3 Purification of class III bacteriocins 22

2.9 Bacterial Resistance to Bacteriocins 22

2.10 Bacterial Pathogens Associated with Fruit Contamination 22

2.10.1 Campylobacter 20

2.10.2 Pathogenic Escherichia coli 23

2.10.3 Salmonella spp 23

2.10.4 Shigella spp 24

2.10.5 Staphylococcus 25

2.10.6 Vibrio 25

2.10.7 Listeria monocytogenes 26

2.10.8 Sporeformers 26

2.11 Sources of Contamination 27

2.11.1 Production Environment 27

2.11.2 Postharvest Handling 28

2.11.3 Human Hygiene 29

2.12 Pathogen Prevention 30

2.12.1 Processing Strategies 30

2.12.2 Handling Parameters 32

2.12.3 Alternative Technologies 33

CHAPTER THREE

3.0 Materials and Methods 35

3.1 Source of Materials 35

3.2 Sample Preparation 35

3.3 Isolation of Bacteria 35

3.4 Characterization of Isolates 36

3.4.1 Characterization of Bacteria Isolates 36

3.4.2 Microscopic Features 36

3.5 Identification of Isolates 36

3.5.1 Gram Staining 37

3.5.2 Biochemical Reaction Tests 37

3.5.2.1 Sugar Utilization Tests 38

3.5.2.2 Catalase Test 38

3.5.2.3 Indole Test 38

3.5.2.4 Citrate Utilization Test 38

3.5.2.5 Hydrogen Sulphide (H2S) Production Test 39

3.5.2.6 Voges-Proskauer Test 39

3.5.2.7 Urease Test 39

3.5.2.8 Methyl Red Test 39

3.5.2.9 Oxidase Test 40

CHAPTER FOUR

4.0 Results 41

CHAPTER FIVE

5.0 Discussion, Conclusion and Recommendations 47

5.1 Discussion 47

5.2 Conclusion 49

5.3 Recommendations 50

References