ABSTRACT

Yogurts are ready to drink foods commonly taken for energy production and for health in Nigeria. Therefore this study was carried out to determine the microbial and microbiological assessment of commercially prepared yogurts sold in Umuhaia to evaluate their food safety. The commercially prepared yogurt products were purchased from vendors and transported for microbial and microbiological analyzed using standard laboratory methods. A total of 26 bacterial strains and 4 fungi were isolated from ten (10) samples of yoghurt for microbiological assessment of yoghurt. The isolate were identified by morphological characteristics, pigmentation on media, microscopy, biochemical and sugar fermentation methods. The details of these isolates and their percentage occurrence comprising Bacillus subtilis (5), Escherichia coli (4), Staphylococci aurues (2), Lactobacillus species (8), Klebsilla species (3),  Aspergillus flavus (1), Mucor alternaria (1) and Saccharomyces cerevisiae (2) The Lactobacillus species bacterial has the highest number of bacteria isolates (26.67%) while the lowest isolates were recorded in aspergillus flavus and Mucor alternarian with (3.33%) respectively. There were significant decline in pH, temperature and titratable acid. This study has shown that most yogurts contain probiotics isolates including Lactobacillus and Saccharomycess which are therefore beneficial for human consumption, therefore all effort should made to sustain the standard of yogurt.

TABLE OF CONTENTS

Title page i

Certification ii

Dedication iii

Acknowledgements iv

Table of Contents v

List of Tables vii

Abstract viii

CHPATER ONE

1.0 INTRODUCTION

1.1 Objective of the Study 3

1.2 Statement of Problem 3

1.3 Significance of the Study 3

1.4 Limitation of the Studies 3

CHAPTER TWO

2.0    LITERATURE REVIEW

2.1    Yoghurt Potentials 4

2.1.1 The Biochemistry behind Yogurt 4

2.2 Yogurt Production 7

2.3 Benefits of Yogurt 8

2.4 Probiotics 10

2.5 Current Problems 12

2.6 Improving Functionality of Yogurt 14

2.6.1 Towards a "Superior" Yogurt 16

2.6.2 Temperature and pH control of yoghurt 17

2.6.3 Mechanical Rationale for Potential Benefits of Yoghurt on 

Gut Function and Health 18

2.7 Laxation 19

2.7.1 Yoghurt and diseases of the gastrointestinal tract 19

2.7.2 Diarrheal diseases 21

2.7.3 Colon cancer 22

2.7.4 Inflammatory Bowel Disease 23

2.7.5 Helicobacter pylori 24

CHAPTER THREE

3.0    MATERIALS AND METHODS 

3.1   Sample collection 26

3.2    Media Preparation 26

3.3    Microbiological Analysis 26

3.4 Identification of Isolates 27

3.5 Gram Staining Techniques 27

3.6 Motility Test 27

3.7       Biochemical Tests        27

3.7.1 Catalase Test        27

3.7.2    Coagulase Test (Slide test)                                                                                         28

3.7.3    Oxidase Test        28

3.7.4    Citrate Utilization Test        29

3.7.5     Indole Test        29

3.7.7     Voges-Proskauer Test        29

3.7.8     Methyl Red Test        30

3.7.9     Sugar utilization test         30

3.8 Lactophenol Cotton Blue Staining 31

3.9 Physiochemical Analysis  31

3.10 Measurement of pH  31

3.11 Determination of Titratable Acidity 32

CHAPTER FOUR

4.0 RESULTS

4.1 Total microbial counts Cfu/ml of Yoghurt samples 33

4. 2 Identification and characterization of Bacterial Isolates 33 

4.3 Identification and characterize of Fungal Isolates 33

4.4 Percentages occurrence of isolates from yoghurt sample 33

4.5 Temperature, pH and Titratable acid values of the yoghurt samples 34

CHAPTER FIVE

5.0 DISCUSSION, CONCLUSION AND RECOMMENDATION

5.1 Discussion 40

5.2 Conclusion 42

5.3 Recommendation 42

References 43