ABSTRACT

All the samples put together were higher in pH value by 0.75 showing less acidity than the 3 controls put together (524, 535, 526). The gravimetric values and viscousity of the laboratory product were found to be higher than the circulating commercial yoghurt in gravimetry and viscosity by 18.18% by approximately 18.20%. physiochemically, no significant differences existed among all the samples of yoghurt of the both laboratory produced and the commercially vended yoghurt when analyzed  statistically by analysis of variance at 0.005 confidence level. Proximately all the samples produced in the laboratory higher energy sources than those commercial ones (Percentage carbohydrates) by approximately16.66%.  All the samples both commercial are personally produced had approximately the same amount of percentage mean protein value of almost 7.3. All samples had low percentage fat content. Although the commercial ones were slightly higher than the laboratory products by 0.20%. All yoghurt samples showed high moisture content of between 66.99%- 87.94%. yoghurt not withstanding the source or location of make was found to contain the following proximate; ash, moisture, fat, protein and carbohydrates no fiber was found in any of them. All the yoghurt samples had low percentage ash composition differing from one another by 0.1% ash. Since ash proximate indicates the quantity of minerals, vitamins and other essential food nutrients for healthy living experimentation revealed that all yoghurt were low in ash content and by inference, low in mineral content. No significant differences existed in the proximate composition of all of them at p=<0.05. Experimentation revealed that the yoghurt starter culture considering microbial flora, showed higher stability. Keeping to only Lactobacillus acidophilus, Lactobacillus bulgaricus  and Streptococcus thermophillus, throughout the research with the laboratory yoghurt having the highest load of Lactobacillus spp. on the contrary, the commercial yoghurt samples, were found to contain other microbial flora than the standard starter ciulture. It was varied that these unwanted organisms came into them during processing either by cross contamination or by some opportunistic phenomenon. It was noticed in all the commercial available yoghurt used as control. They were contaminated by certain strains of Staphylococcus aureus which is pathogenic and Saccharomyces cerevisae, yeast, which is alcohol producing. Impacting more sour taste than necessary to commercial yoghurt. Sensory evaluation revealed that all the laboratory yoghurt product surpassed the vended commercial product in aroma, colour, mouth feel, taste, texture and general acceptability by 75% in quality attributes. No microbial succession occurred in the laboratory samples. Noticeably, microbial succession by either Sacharomyces cerevisaePitschai spp or Staphylococcus aureus  occurred in commercial yoghurt even with view to dominate the standard culture a trend which must be checked.

TABLE OF CONTENTS

Title Page i

Certification ii

Dedication iii

Acknowledgements iv

Table of Contents v

Lists of Tables viii

List of Figures  ix

Abstract x

CHAPTER ONE

1.0 Introduction    1

1.1 Aim and Objectives 3

CHAPTER TWO

2.0 Literature Review 4

2.1 Varieties and Types of Yoghurt 6

2.2 Types of Yoghurt  10

 2.3 Yoghurt Manufacturing Process 12

2.3.1 Milk Standardization 12

2.3.2 Homogenization  13

2.3.3 Heat treatment 14

2.3.4 Fermentation process 15

2.3.5 Cooling  15

2.4 Production of Yoghurt 17

2.5 Probiotic Benefits of Yoghurt 19

2.6 Application of Probiotic Microorganisms In Functional Foods 19

2.7 Yoghurt Spoilage Microorganisms  20

2.7.1 Psychrotrophs 20

2.7.2 Coliforms 21

2.7.3 Lactic Acid Bacteria  22

2.7.4 Fungi 22

CHAPTER THREE

3.0  Materials and Methods 24

3.1 Sample Collection  24

3.2 Media Used 24

          3.3   Sterilization 24

3.4 Sample Preparation 24

3.5 Laboratory Production of Yoghurt  25

3.6  Isolation And Enumeration Of Bacterial Isolates 26

3.6.1 Gram Staining 26

3.6.2 Spore Staining Technique 26

3.6.3 Motility Test 27

3.7 Biochemical Test 27

3.7.1 Catalase Test  27

3.7.2 Coagulase Test 27

3.7.3 Citrate Test 28

3.7.4 Oxidase Test 28

3.7.5 Indole Test  28

3.7.6 Urease Test 29

3.7.7 Methyl Red Test  29

3.7.8 Voges-proskaeur Test 29

3.7.9 Sugar Fermentation Test 30

3.8 Physiochemical Analysis 30

3.8.1 Determination of pH 30

3.8.2. Determination of T. T. A 31

3.8.3 Determination of total solids 31

3.8.4 Total Sugar 32

3.9 Proximate Analysis 32

3.10 Determination of Fungi 34

3.11 Sensory Evaluation  35

CHAPTER FOUR

4.0  Results 36

CHAPTER FIVE

5.0       Discussion, Conclusion and Recommendation 41

5.1 Discussion 41

5.2 Conclusion 43

5.3 Recommendation 44

References

LIST OF TABLES

Table    Title Page

1. Showing the physiochemical characteristics of both the laboratory    37

produced  test yoghurt  samples and the locally purchased yoghurt samples 

     2.       Showing proximate analysis result    38

     3       Sensory evaluation    39

     4       Biochemical test identification of microbial isolates from  40

    test samples evaluated