OPTIMAL CONDITIONS FOR THE PRODUCTION OF YOUGHURTS FROM POWDERED MILK USING LACTIC ACID BACTERIA AS A STARTER CULTURE

ABSTRACT

Six species of lactic acid bacteria Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus fermentum, Lactobacillus acidophilus, Lactobacillus brevis, Lactococcus lactis, was isolated from the various samples yoghurt, orange, kunu, MRS medium was used for the isolation for 48 hours at 37°C incubation temperature. The use of colony forming unit per quality of sample was adopted to attain the actual number of viable cells. The colonies obtained was further subcultured to get a pure culture. Identification, characterization and biochemical properties of isolates obtained was performed on the different species of lactic acid bacteria. Three species of the LAB isolated L. buglaricus, S. thermophilus and L. fermentum was further used as starter culture to produce yoghurt using powdered milk (Milksi).The quality parameters of the product was determined by laboratory analysis and compared within the different yoghurt sample produced from A-H (control) in terms of nutritional and sensory attributes. The result of the various fermented milk at 0 to 5 hours of production were noted, the result obtained showed that the initial pH of the yoghurt during fermentation were slightly acidic during fermentation, all the sample tended to be more acidic due to fermentation and had lower pH values even at different degree censius when pH of yoghurt sample where check (38°C, 39°C, 40°C).The other yoghurt produced had more protein 3.95%, ash 0.85% and moisture content 85.50% than the (control) protein 2.97%, ash 0.73, moisture content 86.39% . The value at (P<0.05 ) showed that there was a significant different in the values above. The optimal conditions for the production of yoghurt using these species of lactic acid bacteria (Lactobacillus bulgaricus, Streptoccus thermophilus and Lactobacillus fermentum) was found to be 40°C and pH 5.5. The result of the hedonic test of sensory properties showed that product has more sour taste, this indicates that the quality of the products was pleasant. It was therefore concluded that lactic acid bacteria could be sourced from yoghurt, orange, and kunu. 

TABLE OF CONTENTS

Title page ﾿ i

Certification ﾿ ii

Dedication ﾿ iii

Acknowledgement ﾿ iv

Table of content ﾿ v

List of tables ﾿ viii

List of figures ﾿ ix

Abstract ﾿ x

CHAPTER ONE

1.1 ﾿ Introduction ﾿ 1

1.2 ﾿ Aims and Objectives of study ﾿ 3

CHAPTER TWO

2.0 Literature Review ﾿ 4

2.1 Lactic acid bacteria ﾿ 4

2.1.1 Sources of lactic acid bacteria ﾿ 5

2.1.2 Conditions that favours the growth of lactic acid bacteria ﾿ 5

2.1.3 Classification of lactic acid bacteria ﾿ 8

2.1.4 Uses of lactic acid bacteria ﾿ 8

2.2.1 Yoghurt and its components ﾿ 9

2.2.2 Milk and its constituents ﾿ 11

2.2.3 Yoghurt starter cultures ﾿ 16

2.2.4 Other components of yoghurt ﾿ 17

2.2.5 Selection of pure culture ﾿ 17

2.2.6 Classification of yoghurt ﾿ 17

2.2.7 Nutritional quality of yoghurt ﾿ 19

2.2.7.1 Health benefits effects of yoghurt ﾿ 19

2.2.8 Uses of yoghurt ﾿ 21

CHAPTER THREE

3.0 Materials and methods ﾿ 23

3.1 Sample collection ﾿ 23

3.2 Lactic acid bacteria culture preparation ﾿ 23

3.3 Isolation of lactic acid bacteria ﾿ 23

3.4 Determination of bacteria load at suitable temperature using direct plate count ﾿ 24

3.5 Identification and characteristics of bacterial isolates ﾿ 24

3.5.1 Macroscopic examination ﾿ 24

3.5.2 Gram staining reaction (microscopic examination) ﾿ 25

3.5.3 Motility Test ﾿ 25

3.5.4 Biochemical Reaction ﾿ 25

3.6 Measurement of pH ﾿ 28

3.7 Determining of titratable acidity ﾿ 28

3.8 Proximate analysis ﾿ 28

3.8.1 Determination of moisture content ﾿ 29

3.8.2 Ash content determination ﾿ 29

3.8.3 Determination of protein ﾿ 30

3.8.4 Determination of carbohydrate ﾿ ﾿ 31

3.8.5 Determination of fat content ﾿ 31

3.9 Sensory properties of youghurt samples ﾿ 32

CHAPTER FOUR 

4.0 Results ﾿ 33

CHAPTER FIVE

5.0 Discussion, Conclusion and Recommendation ﾿ 53

5.1 Discussion ﾿ 53

5.2 Conclusion ﾿ 57

5.3 Recommendation ﾿ 57

References

Appendix