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

LIST OF FIGURES

Figure                                 Title                                     Page

1      Manufacturing process of set- and stirred-yoghurt                                        16

2      A schematic presentation of the production of yoghurt                                 18

CHAPTER ONE

1.0  INTRODUCTION

Yoghurt is a fermented dairy product, having several health benefits. Yoghurt is mainly of two types i.e. set yoghurt and stirred yoghurt. Yoghurt properties can be enhanced by the addition or treatment with various additives. Yoghurt can be supplemented with various useful ingredients. Addition of herbs or their active components like oils could be effective strategy to improve functionality of milk and milk products with respect to the health benefits, food safety and bio preservation (Whitt and Salyers, 2002).

 Yoghurt is a very versatile product that suits all palates and meal occasions (Isleten and Karagul-Yuceer, 2006). It is one of the most popular fermented milk products (Lucey et al., 2009). Its attractiveness has grown and is at this time used in most parts of the world (Lee and Lucey, 2010). Fermented milk, like the fresh milk from which they are produced, is liable to contamination. Knowledge of the behavior of yoghurt during storage is important, because its shelf life is based on whether the product displays any of the physical, chemical, or sensory characteristics that are unacceptable for consumption (Salvador and Fiszman, 2004). Changes in the chemical, physical and microbiological composition of yoghurt determine the storage and shelf life of the product (Sofu and Ekinci, 2007). The pH values of yoghurt immediately after production range between 4.5 and 4.2 (Holec, 2000).  The microbiological quality assessment of yoghurt is mainly concerned with protection of the consumers against exposure to any health hazard and ensuring that the material is not suffering microbiological deterioration during its anticipated shelf-life (Caballero, 2003). In addition to deterioration in sensory quality, microbiological counts have been used as indices for the end of shelf life of dairy products (Muir and Banks, 2000).

Coliforms detection or enumerating is often used as parameters for evaluating the yoghurt quality in different countries (Tamine and Robinson, 2007). Presence of Coliforms in dairy products is an indication of faecal contamination when the hygiene is poor (Thatcher and Clark, 2008). Some members of Coliforms are responsible for the development of objectionable taints in milk and its products rendering them of inferior quality or even unmarketable (Yabaya and Idris, 2012).

Escherichia coli (E. coli) frequently contaminate food and it is considered a good indicator of fecal contamination (Singh and Prakash, 2008), its presence in milk products indicates presence of other entero-pathogenic microorganisms which constitute public health hazard (Singh and Prakash, 2008). Enterococci may have a distinctive role as indicators of poor factory sanitation owing to their relatively high resistance to drying, detergents, as well as freezing temperature. Moreover, these organisms are also implicated in food poisoning outbreaks (Yabaya and Idris, 2012). Enterococci organisms have been proposed for hygienic condition inspections in process lines of fermented products (Vanos, 2011). The presence of enterococci in dairy products has long been considered an indication of inadequate sanitary conditions during the production and processing of milk (Giraffa et al., 2007).

Staphylococcus aureus (S. aureus) in food article is an index of its contamination from personnel sharing in production and handling. Moreover, Enterotoxigenic Staphylococcus aureus strains may find opportunity to grow and multiply in the food leading to food poisoning among consumers (Abdel Hameed and El-Malt, 2009). Yeasts are a major cause of spoilage of yogurt and fermented milks in which the low pH provides a selective environment for their growth (Fleet, 2000). Yeast and mold are the major contaminants in yoghurt (Nwagu and Amadi, 2010).

Micotoxigenic fungi and pathogenic bacteria are able to grow at refrigeration temperature to numbers, which can result to an infection (Potter and Hotchkiss, 2005). Presence of yeasts and moulds in milk and dairy products are undesirable even when found in few numbers as they result in objectionable changes that render the products of inferior quality (Abdel Hameed 2011). Moulds and yeasts growing in yoghurt utilize some of the acid and produce a corresponding decrease in the acidity, which may favour the growth of putrefactive bacteria (Oyeleke, 2009).

1.1   AIM AND OBJECTIVES

The aim of this study is to evaluate the comparative microbiological and physiochemical analysis of locally and laboratory produced yoghurt.

The objectives are

1.     To identify microorganisms associated with locally and laboratory produced yoghurt.

2.     To determine the physiochemical characteristics of locally and laboratory produced yoghurt.

3.     To determine the sensory evaluation of locally and laboratory produced yohurt.

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