MICROBIOLOGICAL ASSESSMENT OF COMMERCIALLY PREPARED YOGHURTS SOLD IN ABIA STATE, NIGERIA

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 34

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

LIST OF TABLES

Table 1:   Total microbial counts Cfu/ml of Yoghurt samples 35

Table 2 Identification and characterization of Bacterial Isolates 36

Table 3 Identification and characterize of Fungal Isolates 37

Table 4 Percentages occurrence of isolates from yoghurt sample 38

Table 5 Temperature, pH and Titratable acid values of the yoghurt samples 39

CHPATER ONE

2.0      INTRODUCTION

Yogurt is a widely enjoyed dairy product that is essentially an altered form of milk containing waste products from fermentation. The lactic acid that is produced from the fermentation of lactose contributes to the sour taste of yogurt by decreasing pH and allows for the characteristic texture by acting on the milk proteins (Zourari, Accolas, & Desmazeaud, 2004). Yogurt has been continually studied for its health benefits, particularly from the addition of probiotics. Current research has been investigating how to improve yogurt both in terms of its potential as a healthy food and as an appetizing product that appeals to the general population. Yogurt is also a means of preserving the nutrients in milk (Hui, 2000; Oyeleke et al., 2009). It is generally known as cultured milk, as it is derived from the action of bacterial on all or part of the lactose to produce lactic acid, carbon dioxide, acetic acid, diacetyl, acetaldehyde and several other components that gives the product its characteristic fresh taste (Tamine and Robinson, 2004). It is produced by the lactic fermentation of milk using a combination of bacteria such Lactobacillus bulgaricus and Streptococcus thermophilus (Hui, 2000) and is consumed both as a food and as a thirst quenching beverage (Alfa-Lawal, 2006). Yogurt has also been described as a notoriously balanced food containing almost the nutrients present in milk but in a more assimilable form and they can be produced from skimmed or whole milk and there is a large range of flavors available commercially (Anthar, 2006; Oyeleke et al., 2009). Fermented milks, like the fresh milk from which they are produced, are liable to contamination. Moulds and yeast are the primary contaminants in yogurt produced commercially in Nigeria (Suriyarachchi and Fleet, 2001; Oyeleke et al., 2009). Moulds and yeasts growing in yogurt utilize some of the acid and produce a corresponding decrease in the acidity, which may favor the growth of putrefactive bacteria (Oyeleke et al., 2009). Moulds and yeast are the primary contaminants in yogurt produced commercially in Nigeria (Suriyarachchi and Fleet, 2001; Oyeleke et al., 2009). Moulds and yeasts growing in yogurt utilize some of the acid and produce a corresponding decrease in the acidity, which may favor the growth of putrefactive bacteria (Oyeleke et al., 2009). Yogurts are ready to drink foods commonly taken for energy production and for health in Nigeria but there is paucity of studies done to evaluate their food safety.

The general objective of this study is to assess the microbiological quality of some commercially available yogurt retailed in Umuahia, Abia State, Southeast Nigeria. Dairy foods provide and ideal food system for the delivery of beneficial bacteria to the human gut. Given the suitable environment that milk and certain dairy products including yoghurt and cheese) provided, it promotes growth and support viability of these cultures. Dairy products such as yoghurt contain ‘probiotic” cultures, e.g. Lactobacilli and which are currently among the best known examples of functional food”. Their associated health claims range from alleviation of symptoms of lactose intolerance, treatment of diarrhea, cancer suppression and reduction of blood cholesterol (McDonough et al, 2007).

Yoghurt has also been described as a notoriously balanced food containing almost the nutrients present in milk but in a more assimilable form and they can be produced from skimmed or whole milk and there is a large range of flavours available commercially (Anthar, 2006).

Fermented milks, like fresh milk from which they are produced, are liable to contamination. The primary contaminants in yoghurt produced commercially in Nigeria are various bacteria general (Surriayarachchi and Fleet, 2001) which include Bacillus spp. which has been found to be the major contaminant of commercially prepared yoghurt. This could be probably be because of easy distribution of their spores in the environment. The spores can withstand harsh environment condition. Bacteria present in yoghurt utilize some of the acid and produce corresponding decreases in the acidity which may favour the growth of putrefactive bacteria (McDonagh et al., 2007).

1.1 OBJECTIVE OF THE STUDY

1. Assessment the microbiological quality of yoghurt

2. Isolation and identification of microorganism in yoghurt.

3. To determine the pH and titratable acidity of yoghurt

1.2 STATEMENT OF PROBLEM

Some yoghurt have been found to loose their taste and produce uncharacteristic odour before their expiry date which may be as a result of contamination through the processing line, packaging and or poor handling. Bacterial infestation has been reported among consumers of yoghurt leading to vomiting, diarrhea, stomach upset and flatulence.

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