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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