Comparative Microbiological And Physiochemical Analysis Of Locally And Laboratory Produced Yoghurt

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