YOGHURT PRODUCTION OF POWDERED MILK USING LACTIC ACID BACTERIA AS STARTER CULTURE

ABSTRACT

Lactobacillus bulgaricus, Streptococcus thermophilus and Lactobacillus fermentum isolated from fermented foods: yoghurt, “ugba” and “kunu-zaki” using MRS agar and a commercially acquired lactic acid bacteria (LAB) were used to produce yoghurts samples A-H from Milksi Powered milk in a 5 hour fermentation process. The three LAB isolates were used singly and in combinations as starter cultures. There was a maximum drop in pH (4-4.8) between the second and third hour of fermentation while the yoghurt produced using S. thermophilus had the lowest pH (5.2) at the temperature of 40oC. The optimum pH for the yoghurt production was 5.5 while the optimum temperature was 40oC. Yoghurt samples B and F had the highest moisture level (P<0.05) while Samples C, E and G had the highest dry matter content. The highest ash content (0.8 ±0.01; P<0.05) was from sample F while Samples D and E had the highest crude fibre content. Sample A had the highest crude fat value (3.95a±0.01; P<0.05), Sample F the highest crude protein content (3.95a±0.01; P<0.05) while the highest carbohydrate content was from Samples C, E, G and H (control). The control Sample (H) had the highest and Hedonic test for sensory properties of the eight yoghurt samples showed that the eight yoghurt samples were acceptable to the panelist indicating that the samples would compete favourably in the market with commercially sold yoghurts.

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                                                                                      11

2.3.1 Milk Standardization                                                                                                     12

2.3.2 Homogenization                                                                                                            13

2.3.3 Heat treatment                                                                                                               13

2.3.4 Fermentation process                                                                                                     14

2.3.5 Cooling                                                                                                                          14

2.4 Production of Yoghurt                                                                                                      16

2.5 Probiotic Benefits of Yoghurt                                                                                          18

2.6 Application of Probiotic Microorganisms In Functional Foods                                       18

2.7 Yoghurt Spoilage Microorganisms                                                                                  19

2.7.1 Psychrotrophs                                                                                                                19

2.7.2 Coliforms                                                                                                                       20

2.7.3 Lactic Acid Bacteria                                                                                                      21

2.7.4 Fungi                                                                                                                              21

CHAPTER THREE

3.0  Materials and Methods                                                                                                    23

3.1 Sample Collection                                                                                                            23

3.2 Media Used                                                                                                                       23

          3.3   Sterilization                                                                                                                      23

           3.4  Isolation And Enumeration Of Bacterial Isolates                                                                      23

            3.5. Characterization of isolates                                        24

            3.5.1 Gram Staining                                                                                                                           24

            3.5.2 Spore Staining Technique                                                             25

3.5.3 Motility Test                                                                                                                 25

3.6 Biochemical Test                                                                                                              25

3.6.1 Catalase Test                                                                                                                  25

3.6.2 Coagulase Test                                                                                                              27

3.6.3 Citrate Test                                                                                                                    28

3.6.4 Oxidase Test                                                                                                                  28

3.6.5 Indole Test                                                                                                                     28

3.6.6 Urease Test                                                                                                                    29

3.6.7 Methyl Red Test                                                                                                            29

3.6.8 Voges-proskaeur Test                                                                                                    29

3.6.9 Sugar Fermentation Test                                                                                               30

3.7 Physiochemical Analysis                                                                                                  30

3.7.1 Determination of pH                                                                                                      30

3.7.2. Determination of T. T. A                                                                                              31

3.7.3    Determination of total solids                                                                                      31

3.7.4 Total Sugar                                                                                                                    32

3.8 Proximate Analysis                                                                                                           32

3.9 Determination of Fungi                                                                                                    34

3.10 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.     Identification of Lactic acid bacteria isolated from fermented foods   37

     2.       Showing proximate analysis result                                                              38

     3       Sensory evaluation                                                                                       39

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 milk product and is one of the famous fermented milk preparations. The word yoghurt is derived from the Turkish word “jugurt” which means dense thick (Adams and Moss, 2015). However, yoghurt is known by other name in many other countries such as Turkey, India and the Balkan States. It is the most widely available fermented milk in western world where its popularity derives more from its flavour and versatility. Yoghurt is a dairy product produced by bacteria fermentation of milk sugar (lactose) into lactic acid. This gives yoghurt its gel-like texture andcharacteristics taste. It is often sold with a fruit vanilla or chocolate flavour but can be unflavoured. Its nutritional and therapeutic functions have been known in the middle east, far east and Eastern Europe for hundreds years, but it has only been appreciated in the west in the last decades. Yoghurt is made by introducing two bacteria: Lactobacillus bulgaricusand Streptococccusthermophilusinto either whole or skimmed milk. The milk is first heated to a temperature between 85 C to 95 C for 30 minutes for pasteurization and proper viscosity and cooled to incubating temperature before inoculating the starter culture. These bacteria feed on milk, sugar, producing an acid in return, which coagulates the milk protein, resulting to a semi-solid consistency and a flavour. The Lactobacillusbulgaricusand Streptococcus thermophilusused as yoghurt starters has been found in such foods and fermented products as meat, milk products, vegetables, beverages and bakery products (Aukrust and Blom, 2012).

The optimum conditions for the growth of these organisms includes anaerobic conditions, temperature of about 35 C to 45 C and a pH of 3.5 to 5.5 when cultured in DeManRogosa and Sharpe Media (MRS). Yoghurt is rich in protein and several vitamins and essential minerals. It contains much fat than the milk form. It is made from starter culture that contains enzymes that help break down lactose inside the intestine; therefore, it is enjoyed by people with lactose intolerance. Yoghurt therefore helps to fight war against death because of hunger, malnutrition and famine in all aspect of life of an individual and of a community. Although milk of various animals has been used for yoghurt production in various parts of the world, most of the industrialized yoghurt production uses cow milk. Whole milk, partially skimmed milk, skim milk or cream milk may be used. The milk used for yoghurt manufacture should be of the highest bacterial quality available and should be free from any material that will impede or prevent the growth of the starter organism (antibiotics, preservative, disinfectant and bacteriophages).Fermentation of milk brings about many changes in its chemical constituents, which have bearing on its nutritive value. Yoghurt has been found to contain proteins, carbohydrate, fats, and high percentage of lactic acid than other fermented milk produce and it is rich in vitamin B complex. Yoghurt proteins are more digestible than that of fresh milk and that the partial hydrolysis of milk constituents in yoghurt contributes to their increase digestibility. Cow’s milk is preferred for preparing yoghurt as having low fat. This provides immunity; protects the consumer from cold, cough and strengthens body’s defense mechanism as well as strengthens the collagen in the skin. It lowers the blood pressure, bad cholesterol and risk of heart attack. Yoghurt is one of the major sources of vitamins and minerals and contains higher vitamins(vitamins B12) than fresh milk. Recently, there is a growing interest to develop a variety of fermented milk products for other beneficial purposes, particularly for health purposes and preventing of toxins produced by food- borne pathogens and spoilage bacteria that enter human body (Shah, 2007). The beneficial effects of fermented milk products are produced by a variety of bioactive compound of lactic acid bacteria  (Griffiths and Tellez, 2013).

1.1 AIM AND OBJECTIVES

The aim of this study is the production of several yoghurt samples from powdered milk using LAB isolates recovered from fermented foods.

1.2 OBJECTIVES

1.     To identify and characterize LAB isolates recovered from fermented foods.

2.      To determine the optimum conditions for the production.

3.     To determine the proximate composition of yoghurt samples.

4.     To determine the sensory evaluation of produced yoghurt.

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