INFLUENCE OF STABILIZERS ON THE FERMENTATION RATE AND NUTRITIVE VALUE OF SET YOGHURT

ABSTRACT
Stabilized yoghurt samples were produced by reconstituting powdered milk in water along with sugar and 0, 0.5 and 1.0 % concentrations of carboxyl methyl cellulose (CMC), Corn starch and gum acacia before fermentation. The yoghurt samples were either produced as short set yoghurt by incubating at 42 oC for 5 hours or incubating at 30 ± 2 oC (room conditions) for 24 hours as long set yoghurt. Samples were analyzed at intervals of 1 h for 5 h for the short set yoghurt and at intervals of 4 h for 24 h for long set yoghurt. The proximate, physicochemical, niacin content, microbial and sensory evaluation were carried out in the yoghurt samples as fermentation progressed for both short set and long set yoghurt. Results showed that the addition of stabilizers reduced moisture content from 88.54 ± 0.02 % (no stabilizer) to 84.59 ± 0.02 % (CMC), 85.59 ± 0.02 % (corn starch) and 86.70 ± 0.02 % (gum acacia). Due to dilution effect, addition of stabilizers depressed protein contents from 3.37 ± 0.04 % (no stabilizer) to 3.28 ± 0.51 % (CMC), 3.08 ± 0.03 % (corn starch) and 3.32 ± 0.03 % (gum acacia). Total solids increased on addition of stabilizers from 11.64 ± 0.02 % (no stabilizer) to 15.41 ± 0.02 % (CMC), 14.47 ± 0.02 % (corn starch) and 13.30 ± 0.02 % (gum acacia). Increase in stabilizer concentration and fermentation time decreased moisture content but increased total solids, protein, fat, ash and sugars. The viscosity of the yoghurt samples significantly (p < 0.05) increased with addition of stabilizers from 1.48 ± 0.03 Cp (no stabilizer) to 78.03 ± 1.14 Cp (CMC), 2.74 ± 0.04 Cp (corn starch) and 1.99 ± 0.03 Cp (gum acacia), with CMC having the highest increase (p < 0.05) and gum acacia the least. Viscosity significantly increased (p < 0.05) as stabilizer concentration and fermentation time increased. Although CMC increased the pH from 6.19 ± 0.03 (no stabilizer) to 6.26 ± 0.02, corn starch did not affect pH (6.18 ± 0.02) while gum acacia reduced pH to 5.94 ± 0.03. Increase in stabilizer concentration and fermentation time increased pH. Addition of stabilizers increased the titratable acidity from 0.29 ± 0.01 % (no stabilizer) to 0.39 ± 0.01 %( CMC), 0.32 ± 0.01 % (corn starch) and 0.45 ± 0.00 % (gum acacia). Lactic acid production reduced as concentration of stabilizers increased, but increased as fermentation time increased. Vitamin B3 (niacin) increased with the addition of stabilizers from 0.15 ± 0.00 (no stabilizer) to 0.175 ± 0.02 mg/ml (CMC), 0.185 ± 0.01 mg/ml (corn starch) and 0.185 ± 0.00 mg/ml (gum acacia). Niacin production increased as stabilizer concentration and fermentation time increased. The total viable bacteria significantly (p < 0.05) reduced with increase in concentration of stabilizer and fermentation time, while lactic acid bacteria decreased with increase in stabilizer concentration it increased as the fermentation time increased. Significant (p < 0.05) interactions were observed between stabilizers and their concentrations for all parameters studied. Sensory results indicated that yoghurt produced with 1.0 % concentration of CMC gave the best mouth feel while yoghurt produced with corn starch produced the most desirable taste and flavor. Results showed that reaction rates were higher for the short set yoghurt for all parameters studied, resulting to achieving an equivalent effect in 5 h in short set yoghurt compared to the same effect achieved in 24 h in the long set yoghurt.

TABLE OF CONTENTS

Title Page
Table of Contents
List of Tables
List of Figures
Abstract

CHAPTER ONE: INTRODUCTION
1.0       Background of the Stud
1.1       Statement of Research Problem
1.2       Justification
1.3       Objectives
1.4       Significance of the Study

CHAPTER TWO: LITERATURE REVIEW
2.1       Yoghurt as a Fermented Dairy Product
2.2       Fermentation
2.3       Fermented Foods
2.4       Yoghurt Production
2.5       Processing of Yoghurt
2.5.1  Modifying the composition of milk
2.5.2 Pasteurization and Homogenization
2.5.3    Homogenization
2.5.4    Fermentation
2.6       Factors that affect fermentation rate of yoghurt
2.6.1    Temperature
2.6.2    Sugar content
2.6.3    Starter culture concentration
2.7       Types of Yoghurt
2.7.1    Set style yoghurt
2.7.2    Stirred style Yoghurt
2.7.3    Drinking Yoghurt
2.7.4    Flavoured Yoghurt
2.7.5    Frozen Yoghur
2.7.6    Dried Yoghurt
2.7.7    Bio – Yoghurt
2.7.8    Fat-substituted Yoghurt
2.7.9    Chemically acidified Yoghurt
2.8       Raw Material/Ingredients in Yoghurt Production
2.8.1    Milk
2.8.2    Sweeteners and Sugar
2.8.3    Stabilizers
2.8.4    Fruits and Flavours
2.8.5    Starter culture
2.9       Role of stabilizers in Yoghurt Production
2.10   Nutritional and Health Benefits
2.11     Yoghurt and Health
2.12   Vitamin metabolism in yoghurt
2.13     Biosynthesis of Niacin

CHAPTER THREE: MATERIAL AND METHODS
3.1       Raw Materials
3.2   Source of Raw materials
3.3       Methods of Production/Processing
3.3.1    Preparation of yoghurt mix
3.3.2    Production of Fresh Yoghurt Samples
3.4       Analysis of Samples
3.4.1    Determination of pH
3.4.2    Determination of Titratable Acidit
3.4.3 Determination of Apparent Viscosity
3.4.4    Determination of Total solids
3.4.5    Determination of Ash content
3.4.6    Determination of Moisture Content
3.4.7    Determination of fat conten
3.4.8    Determination of crude Protein
3.4.9    Determination of Niacin (Vitamin B3)
3.5       Microbial Analysis
3.6       Sensory Evaluation
3.7       Data Analysis

CHAPTER FOUR: RESULT AND DISCUSSION
4.1       Effect of Stabilizers on the Physicochemical Characteristics of short set and long set Yoghurt
4.1.1    Moisture Content of Short Set and Long Set Yoghurt
4.1.2    Fat Content of Short Set and Long set Yoghurt
4.1.3    Protein Content of Short set and Long set yoghurt
4.1.4    Ash Content of Short Set and Long Set Yoghurt
4.1.5    Total Solids Content of Short Set and Long Set Yoghurt
4.1.6    Viscosity (Cp) of Short Set and Long Set Yoghurt
4.1.7    Total Titratable Acidity (%) of Short Set and Long Set Yoghurt
4.1.8    pH of Short Set and Long Set Yoghurt
4.2       Vitamin B3 (Niacin) (mg/ml) Content of Short Set and Long Set Yoghurt
4.3       Microbial Count (cfu/ml) of Short Set and Long set Yoghurt
4.4       Sensory Evaluation of short set and long set yoghurt

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
5.1       Conclusion
5.2       Recommendation
References
Appendix

CHAPTER ONE

INTRODUCTION

1.0 BACKGROUND OF THE STUDY
Dairy products are generally defined as foods produced from commercially domesticated cows, goats or buffalo’s milk (United Kingdom food Standard Agency, 2009). They are usually high energy-yielding food products. Raw milk for processing of dairy products comes mainly from cows and to a lesser extent from other mammals such as goats, sheep, yaks, camel or horses. Dairy products are commonly found in the European, middle-Eastern and Indian cuisines, whereas they are almost unknown in Eastern cuisines. The United Kingdom Food Standards Agency defined Dairy as “foodstuffs” made from mammalian milk (Bandler and Singh, 2009). Most dairy products contain large amounts of saturated fat and most of them are usually fermented. Examples of dairy products include Cheese, Kefir, yoghurt, etc.

Fermented dairy products, also known as cultured dairy foods or cultured milk products, are dairy foods that have been fermented with lactic acid bacteria such as Lactobacillus, Lactococcus and Leuconostoc. The fermentation process increases the shelf-life of the product as well as adds to the taste and improves the digestibility of milk (Canadian dairy Commission, 2007). There is evidence that fermented milk products have been produced since around 10,000 B.C, and a range of different Lactobacilli strains has been grown in laboratories for a wide range of cultured milk products with different tastes.


Fermented milk products are sour tasting milk products which have been made by either fermenting the milk naturally or by the use of starter culture to produce the desirable milk product. Examples of fermented milk in Africa, Syria, Asia and America are Cheese, nono, buttermilk, yoghurt, irgo, kadam, laban, shenineh, dahi, shirkand, mahi, etc (Ajayi, 2006).
Yoghurt, as a fermented dairy product, is a semi-solid milk product and the best known of all fermented milk products. It is obtained by souring of milk using a pure culture of Lactobacillus bulgaricus and Streptococcus thermophilus (Chandan and Shahani, 1993). It can be manufactured from liquid cow milk, powdered milk and vegetable milk (Soy milk) as base material (Adolfsson et al., 2004). Lactic acid and the other molecules that are formed during fermentation of milk make yoghurt a food product that is both acidic and creamy, appreciated for its taste and nutritional qualities notably for its calcium content (Buttriss, 1997). Yoghurt is thus a very convenient food as compared to milk which is very fragile. Due to the health benefits and taste, it is known to constitute an appreciable proportion of total daily food consumption or even just as a refreshing beverage in several countries (Khan et al., 2008). It is regarded as a nutritionally balanced food, containing almost all the nutrients present in milk and in a more assimilable form (Younus et al., 2002). Yoghurt is a source of highly nutritive protein, energy from added cane sugar, milk fat and unfermented lactose as well as vitamins (Ihekoronye and Ngoddy, 1985). It is actually considered to be more nutritive than milk in terms of vitamins content, digestibility and as a source of calcium and phosphorus (Foissy, 1983). It is believed that yoghurt has valuable “therapeutic properties” and helps in curing gastro intestinal disorders (Adolfsson et al., 2004). It also prevents and controls diarrhoea, capable of modulating the inflammatory response produced by carcinogens, helps in reducing the inflammatory response through an increase in apoptosis.


Yoghurt is characterized as a smooth viscous gel with specific taste of sharp acid and green apple flavor (Bodyfelt et al., 1988). Some yoghurts exhibit a heavy consistency that closely resembles custard of milk pudding, in contrast to others that are purposely soft boiled and are essentially drinkable (Connolly et al.,1984). The most important textural characteristics of yoghurt are firmness and the ability to retain water which is a factor of the type and concentrations of stabilizers used. The type of culture used is also an important factor affecting microstructure and the textural properties of yoghurt (Hussan et al., 1999).

Stabilizers and thickeners are important in several manufactured products and dairy products such as chocolate dressing, milk drinks, ice-cream and yoghurt. These substances prevent separation of various ingredients, increase the viscosity and inhibit the formation of large crystals. Substances used as stabilizers and thickeners include vegetable or tree gums such a gum tragacanth and gum Arabic, agar, cornstarch, gelatin and pectin. Cellulose compounds like methylcellulose and CMC (sodium carboxyl methyl cellulose) are also used (Awan, 1995).

Yogurt is mainly classified based on its chemical composition (full-fat, reduced fat and low-fat), manufacturing method (set and stirred yogurt), flavour type or post incubation process. Yoghurt on the basis of method of production prior to incubation, cooling and final packaging exists as set and stirred yoghurt. Set yoghurt is a type of yoghurt which when produced is incubated and cooled in the final retail package and it is characterized by a firm jelly-like texture (White, 1995). On the other hand, stirred yoghurt is a type of yoghurt that is produced and incubated in a tank and the final coagulum is “broken” by stirring prior to cooling, addition of flavours and packaging (Skriver et al., 1993; White, 1995).


1.1       STATEMENT OF RESEARCH PROBLEM
From previous researches, it is noteworthy to say that fermentation increases the vitamin content of products, more especially some B-complex vitamins due to microbial activities during fermentation where synthesis and breakdown of substances occur (Ochanda et al., 2010). Yoghurt starter cultures utilize some vitamins present in milk during fermentation for their growth. However, this increment depends on the rate of the inoculation, the strain of yoghurt starter...

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