ABSTRACT
Lactic Acid Bacteria (Lactobacillus acidophilus, Lactobacillus plantarium, and Bifidobacterium) isolated from fermented Ogi and Breast milk using MRS agar medium and a commercially acquired lactic acid bacteria (LAB) were used to produce yoghurt samples. Fermented Ogi and breast-milk samples was appropriately diluted and plated out on the MRS Agar using pour plate method. The plates were incubated under 35oC-37oC and at different pH for 48 hours under Micro aerophilic condition using excello anaerobic jar. The effect of varied temperature and pH on the growth of the isolates was investigated to determine the optimum temperature and pH for the growth of the organism. The isolates and the commercially acquired Lactic acid bacteria were used to produce Yoghurt samples A-D from DANO powdered milk in an 8 hours fermentation process. The fermented product was used to compare favourably against the commercial product in terms of both nutritional and sensory attributes. The three LAB isolates were used singly as starter culture. The optimum pH for the Yoghurt production was 5.5 while the optimum temperature is 40oC. The Yoghurt sample C had the highest pH (6.60 ± 0.00; p<0.05) and highest moisture content (88.10 ± 0.04; p<0.05), the highest protein content was from sample A and D (control). Sample A has the highest crude fat (0.85 ± 0.00; p<0.05) ash content was highest in sample D (control) (3.29 ± 0.05; p<0.05) and the fibre content of the Yoghurt was: 0.14 ± 0.02; p<0.05. It was therefore concluded that L. acidophilus, L. plantarium and Bifidobacterium can be used in Yoghurt production as a starter culture which are sourced from breast-milk and fermented Ogi. However, Bifidobacterium are more suitable for use as starter culture than the others.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgements iv
Table of Contents v
List of Tables viii
List of Figures ix
Abstract x
CHAPTER
ONE
1.0 Introduction 1
1.1 Aims
and Objectives 2
CHAPTER
TWO: LITERATURE REVIEW
2.1 Lactic
Acid Bacteria 3
2.1.1 Sources
of Lactic Acid Bacteria 4
2.1.2 Conditions that favour
the growth of Lactic Acid Bacteria (LAB) 5
2.1.3 Classification and
Uses of Lactic Acid Bacteria 7
2.1.4 Uses of Lactic Acid
Bacteria 8
2.2 Yoghurt and Its
Components 9
2.2.1 Other Components of
Yoghurt 11
2.3 Milk and Its
Constituents 11
2.3.1 Water in Milk 12
2.3.2 Fat of Milk 12
2.3.3 Protein 12
2.3.4 Lactose 13
2.3.5 Ash or Mineral Matter
(Salts of Milk) 13
2.3.6 Vitamins in Milk 14
2.3.7 Microorganisms in Milk 14
2.3.7.1 Lactic Acid Bacteria 14
2.3.7.2 Coliforms 15
2.3.7.3 Spoilage Microorganisms
in Milk 15
2.3.7.4 Pathogenic
Microorganisms in Milk 15
2.4 Significance of
Microorganisms in Milk 16
2.5 Yoghurt Starter
Cultures 16
2.5.1 Selection of Pure
Culture 17
2.6 Classification of
Yoghurt 17
2.7 Health Benefits
Effect of Yoghurt 19
2.8 Uses of Yoghurt 21
CHAPTER
THREE: MATERIALS AND METHODS
3.1 Sample
Collection 22
3.2 Sample
Preparation 22
3.3 Bacterial
Strains and Growth Conditions 22
3.4 Isolation
of Lactic Acid Bacteria (LAB) 23
3.5 Determination
of Bacterial load at Different Temperature and Pressure Using
Direct
Plate Count 23
3.6 Identification
and Characterization of Bacterial Isolates 23
3.6.1 Macroscopic
Examination 24
3.6.2 Gram
Staining Reaction (Microscopic Examination) 24
3.6.3 Biochemical
Reaction Test 24
3.7 Measurement
of pH 28
3.8 Determination
of Titratable Acidity 28
3.9 Proximate
Analysis 28
3.9.1 Determination
of Moisture Content 28
3.9.2 Ash
Determination 29
3.9.3 Determination
of Protein 30
3.9.4 Determination
of Carbohydrate Content 31
3.9.5
Determination of Fat Content 31
3.10 Sensory Properties of Yoghurt Samples 32
CHAPTER FOUR
4.0 Results 33
CHAPTER FIVE: DISCUSSION,
CONCLUSION AND RECOMMENDATION
5.1 Discussion 42
5.2 Conclusion 45
5.3 Recommendation 46
References 47
LIST
OF TABLES
Table 4.1: Characterisation
of Lactic Acid Bacteria isolated from both Ogi and Breast Milk 33
Table 4.2: (%) Occurrence of LAB isolates in ogi and bread milk as sources for starter culture development 34
Table 4.3: Quality Characteristics of Yoghurt Produced with LAB starter
cultures 36
Table 4.4: Proximate composition of 2 Yoghurt produced with LAB starter
cultures (%) 38
Table 4.5: Mean Sensory scores of acceptability of yoghurts produced with LAB starter cultures 40
LIST
OF FIGURES
Figure 3.1: Flow
chart of Yoghurt Production 27
CHAPTER ONE
1.0 INTRODUCTION
Many
Lactic bacteria strains, characterized as probiotics, have been proven to
beneficially affect humans or animals by improving the properties of their
indigenous gut flora (Fuller 2011; Havenaar and Huis int Verd, 2012). The
incorporation of potentially probiotic lactic acid bacteria of human origin in
traditional fermented foods has been established in the dairy industry, leading
to the production of different types of fermented milks and yoghurts (Gomes and
Malcata, 2014). Strains of the lactobacillus genus, such as Lactobacillus
acidophilus, Lactobacillus caseiand Lactobacillus paracasei, Lactobacillus
bulgaricus constitute significant proportion of the lactic acid bacteria
used in commercial probiotic-based milk products (Shorrt, 2014). New applications
of probiotic microorganisms in foods have been introduced into the market or
are still in the developmental phase such as frozen yoghurt, soy yoghurt, ice
cream bread and chocolate (De Vuyst, 2010).
Probiotic
products are usually standardized, based on the presumption that culture
viability is a reasonable measure of probiotic activity, thus the ability the
strain to attain high cell population is of primary importance. A concentration
of approximately 107 ml-1at the time of consumption is
considered functional (Gomes and Macata, 2014; Shortt, 2014). High cell growth
and acidification would also result in the reduction of fermentation time and
enhance the viability of the specific strain by preventing of undesirable
microorganism present in the raw material (Mark Linder and Lonner, 2012). A
starter culture are those microorganism that are used in the production of
cultured products such as yoghurt and cheese. The natural microflora of the
natural substrate is either inefficient, uncontrollable and unpredictable or is
destroyed altogether by the heat treatments given to the substrate. Traditional
methods are still used in producing some products but advances in starter
technology, especially in selection, maintenance, freezing and lyophilisation
of commercial starter, have brought starter availability, flexibility and
reliability to product manufacturers (Cogan and Accolas, 2016). Lactobacilli
are very fastidious microorganisms that require fermentable carbohydrates,
vitamins and nucleic acids and minerals to grow regardless of the specific
nutrient requirements of the strain (Gomes and Macata, 2014). Thus the
substrate composition and nutritional requirements of the strain considerably
affect the overall performance of the fermentation. A number of studies on the
development of food fermentation process based on the use of cereal and
vegetable substrates have been reported (Caralampopoulos et al., 2014; Yoon et al.,
2016; Demir et al., 2017). Microbial
growth on these substrates depends on the environmental factors such as pH,
temperature and accumulation of metabolic end products. However, as natural
fermentation rely on microbial populations present in the raw material, these
products exhibits substantial variations in flavor and quality (Giraud et al., 2011). The good adaptation of
lactic acid bacteria in cereals and vegetables suggests that utilization of a
potentially probiotics strains as starter culture in these substrate other than
milk would produce a fermented food with defined and consistent characteristics
and possibly health promoting properties.
1.1 AIMS
AND OBJECTIVES
The
objectives are:
1. To
isolate, identify and characterize different genera of lactic acid bacteria
from fermenting milk capable of being used as probiotic strains.
2. To
study the key factors influencing the growth and embolic activity of the
strains.
3. To use the isolated organism as starter
culture to produce yoghurt as probiotic food
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