ABSTRACT

The microbial quality and shelf life of laboratory and commercially produced yoghurt were investigated. Six (6) laboratory prepared yoghurt, unsweetened (420) sweetened (421), unsweetened with sodium benzoate (422),sweetened with sodium benzoate(423), unsweetened with ginger (424), sweetened with ginger (425) and three (3) commercially produced yoghurt, Raph yoghurt (426) Nutri yo yoghurt (427) and Hollandia yoghurt (428) were used for this study. The bacterial genera; Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus and three fungal genera Saccharomyces cerevisae, Saccharomyces lactis and Pichia spp. were isolated. The Total Viable Count (TVC) ranged from 3.0 x 108 cfu/ml to 2.48109 cfu/ml. The Total Fungal Count (TFC) ranged from 4.0 x 107 cfu/ml to 2.6 x 108 cfu/ml while the Total Lactobacillus Count (TLC) ranged from 2.6 x 108 cfu/ml to 2.30 x 109 cfu/ml. A zero count was recorded for the Total Coliform Count (TCC) and the Total Staphylococcus Count (TSC). For the physiochemical parameters of the yoghurt samples the pH ranged from 4.02 ± 1.00 to 6.50 ± 0.48, Specific Gravity (SG) ranged from 0.6971 ± 1729 to 1.0751 ± 0.2051. The Total Titrable Acidity (TTA) ranged from 8.71 ± 2.96 to 17.80 ± 6.13, while the Total Soluble Solid (TSS) ranged from 5.70 ± 4.37 to 14.00 ± 3.93. The sensory gradually moved from liked extremely (1) on day 0 to neither liked nor disliked (5) on day 14, even though the general acceptability stopped at liked slightly (4).  The result of this study showed that refrigeration and deep freezing irrespective of the preservatives used prolonged the shelf life of yoghurt. 

TABLE OF CONTENTS

Title Page i

Certification ii

Dedication iii

Acknowledgements iv

Table of Contents v

Lists of Tables vii

List of Figures viii

Abstract ix

CHAPTER ONE

1.0 Introduction 1

1.1 Aims and Objectives 3

CHAPTER TWO

2.0  Literature Review 4

2.0.1 Microorganisms Involved In Yoghurt 6

2.1 Varieties and Types of Yoghurt 9

2.2 Types of Yoghurt 15

2.3 Yoghurt Manufacturing Process 17

2.3.1 Milk Standardization 17

2.3.2 Homogenization 18

2.3.3 Heat treatment 19

2.3.4 Fermentation process 21

2.3.5 Cooling 21

2.4 Production of Yoghurt 23

2.5 Probiotic Benefits of Yoghurt 25

2.6 Application of Probiotic Microorganisms in Functional Foods 25

2.7 Yoghurt Spoilage Microorganisms 27

2.7.1 Psychrotrophs 27

2.7.2 Coliforms 28

2.7.3 Lactic Acid Bacteria 28

2.7.4 Fungi 29

CHAPTER THREE

3.0 Materials and Methods 30

3.1 Sample Collection 30

3.2 Media and Media Preparation 30

3.3  Sterilization 31

3.4 Experimental Design 31

3.5 Sample Preparation 32

3.6 Laboratory Production of Yoghurt 33

3.7 Identification of Bacterial Isolates 34

3.7.1  Gram Staining 34

3.7.2 Motility Test 34

3.8 Identification of Fungal Isolates 35

3.9 Biochemical Cultural Characteristics 36

3.9.1  Catalase Test 36

3.9.2 Coagulase Test 36

3.9.3 Citrate Test 36

3.9. 4 Indole Test 37

3.9.5 Urease Test 37

3.9.6 Triple Sugar Iron Test 38

3.9.7 Oxidase Test 38

3.9.8  Methyl Red/ Voges Proskauer Test 38

3.9.9 Sugar Fermentation 39

3.10 Organoleptic Properties 39

CHAPTER FOUR

4.0 RESULTS 41

CHAPTER FIVE

5.0 Discussion, Conclusion and Recommendation 65

5.1 Discussion 65

5.2 Conclusion 67

5.3 Recommendation                                                                                                        68

      References                                                                                                                   69

LIST OF TABLES

Table Title Page

2.1: Manufacturing Process of Set- and Stirred-Yoghurt 11

2.2: A Schematic Presentation of the Production of Yoghurt 20

1: Characterization and Identification of Microbial Isolates 42

2: Occurrence of Microbial Isolates along Evaluation Time (In Day) 43

3: Microbial Count of the Yogurt Samples at 10-6 Dilution 46

Factor upon Storage at Different Temps. For 14 Days 

4: Physiochemical Characteristics of the Yoghurt Samples 54

5: Sensory Evaluation of the yoghurt Samples 57

LIST OF FIGURES 

Figure Title Page

1 Manufacturing process of set and stirred-yoghurt 22

2 A schematic presentation of the production of yoghurt 24