ABSTRACT
The Scarcity of milk supply in developing countries perhaps led to the development of alternative milk from vegetable sources in Nigeria. The aim of this study was to produce yoghurt from blends of rice milk and soy milk and evaluate their proximate composition, mineral content, physico-chemical properties, microbiological quality and sensory properties using standard methods. The results obtained for proximate composition revealed the following range of values for moisture ( fat( ash( ),protein ( ) and carbohydrate ( ). Physico-chemical properties showed that MSNF ranged from ( ), total solids ( ±0.26%), pH ( ), %Acidity ( ), SG( ), RI ( ), Viscosity ( ). The results on mineral contents revealed that the yoghurts contained very low quantities of minerals and were below the level recommended by International Dairy Federation. Magnesium ranged from ( ), calcium ( ), potassium ( ), copper ( ), iron ( ), cadmium ( ), zinc ( ). Microbiological analysis revealed that the total viable count of the yoghurts ranged from 1.7 3.0 x 101 CFU/g and all the yoghurts showed zero results for coliform and fungal counts. The results on sensory evaluation showed that yoghurt containing 100 % rice was most preferred to other yoghurt. The appearance of the yoghurts ranges from (5.25c a), aroma (4.60b a), taste (4.60b a), mouthfeel (5.5a a), beany taste (0 5.75a), general acceptability (5.25b a); the lower preference for yoghurts containing soy milk was due to the beany flavor associated with soy foods. However, none of the yoghurt was found to be disliked. It was concluded that yoghurts containing 25 % rice milk: 75 % soy milk and 50 % rice milk: 50 % soy milk had higher nutrients compared to other samples and all the yoghurts were of high microbiological quality as they conformed with the standards recommended by International Commission on Microbiological Specifications for Foods. Addition of flavor to reduce the beany taste of the yoghurts and fortification of the yoghurts with minerals and protein were recommended.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgments v
Table of Contents vi
List of Tables ix
List of Figures x
Abstract xi
CHAPTER 1: INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement of Problem 5
1.3 Justification 7
1.4 Objective of Study 9
CHAPTER 2: LITERATURE REVIEW 10 2.1 Milk 10
2.1.1 Importance of milk and milk products 10
2.1.2
Fermented milk products 11
2.2 Yogurt 13
2.2.1 History of yogurt 15
2.2.2
Nutritional value of yogurt 18
2.2.3
Quality and shelf-life of yogurt 18
2.3
Vegetable Milk 19
2.3.1 Soybeans
and soymilk 20
2.3.1
Soy-yogurt 22
2.3.3 Milk
preparation and heat treatment 23
2.4
History and
Consumption of Soy Foods 24
2.4.1 Nutritional benefits of soy foods 26
2.5
Rice 27
2.5.1
Rice milk and rice yogurt 28
2.5.2
The nutritional value
of rice milk 29
CHAPTER 3: MATERIALS AND METHODS 31
3.1 Materials and Starter Cultures 31
3.2 Preparation of Rice Milk 31
3.3 Preparation of Soymilk 30
3.4 Rice-Soya Yogurt 31
3.5 Determination of Proximate Analysis 32
3.5.1
Moisture content 32
3.5.2 Nitrogen distillation 34
3.5.3
Total ash 34
3.5.4 Carbohydrates 36
3.5.5 Crude fat 36
3.6 Physiochemical Properties 38
3.6.1
pH measurement 38
3.6.2
Titratable acidity 38
3.6.3
Total solids 38
3.6.4
Solids-not-fat 39
3.6.5
Specific gravity 39
3.6.6
Milk solid non-fat (MSNF) 39
3.6.7
Mineral elements 40
3.6.8
Refractive index
40
3.6.9
Total aflatoxin analysis 40
3.6.10 Viscosity 41
3.7
Microbiological
Analysis 41
3.8
Sensory Evaluation 42
3.9
Statistical
Analysis of Data 42
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Proximate
Composition of Yogurt Produced from Blends of Rice Milk
and Soymilk 43
4.2 Physico-Chemical Properties of Yogurt Produced from blends of
Rice
Milk and
Soymilk 46
4.3 Mineral Content of Yogurt Produced from blends of Rice Milk
and
Soymilk 50
4.4 Microbiological
Quality of Yogurt Produced from blends of Rice Milk
and Soymilk 53
4.5 Sensory Evaluation of Yogurt Produced from blends of Rice Milk
and
Soymilk 55
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 58
5.1 Conclusion 58
5.2 Recommendations 58
References 59
LIST OF TABLES
4.1: Proximate composition of rice-soymilk
yogurts 45
4.2: Physico-chemical properties of rice-soymilk
yogurts 49
4.3: Mineral content of rice-soy milk yogurts 52
4.4: Microbial load (CFU/ml) of rice-soy milk
yogurts 54
4.5: Sensory attributes of rice-soy milk yogurt 57
LIST OF FIGURE
1: Flowchart of rice soya yoghurt production 33
CHAPTER ONE
INTRODUCTION
1.1
BACKGROUND OF STUDY
In the past few decades, extensive studies of lactic
acid fermentation of cereal and Legume have been researched. Extruded rice
flour, liquefied starch and cooked maize meal mixture are types of yoghurt-like
product produced from different kind of cereals. (Shin, 1989; Lee et al., 1992; Zulu et al., 1997). A product, so called Risogurt, was produced from
mixture of fermented rice and soy protein isolate (Mok et al., 1991). Mok et al.,
(1993), the further developed a method for producing a highly concentrated
lactic product from rice with improved quality by a secondary enzymatic
treatment during fermentation.
In 2010, there are about nine hundred and twenty nine
million people in the world who were affected by starvation with two hundred
and thirty nine million from sub-Saharan African. The most victims were the
children and the vulnerable groups. Deficiency of Protein calorie which is the
most deadly form malnutrition could be resolved if people could have daily
access to cost effective and balanced nutrition on their table.
The normal life of human may be extended to twice of 70
years, if people will learn how to
introduce a suitable flora in the intestine of children as soon as they are
weaned from the breast.” That rather statement by Metchnioff (1921) has
arguably never been achieved because there is no report to date that human can
normally live up to 140 years. However, the statement emphasizes maintaining
balanced intestinal flora to have a healthy life. More than few decades the
market for fermented dairy Yoghurt, has increased appreciably along with the
steadily increasing knowledge of the health benefits for fermented dairy products.
Semi-fermented dairy milk food, example yoghurt is preferred
and consumed by people all around the world. The possible use of fermented
dairy food is to prevent/control diarrhea because of its therapeutic effect.
The inflammatory response by carcinogen through increasing apoptosis is
modulated by the help of the food. Yoghurt protein is more digestible than cow
milk (Belewu et al., 2005). Yoghurt
can be defined simply as a dairy product from fermentation of milk. This
fermentation produces lactic acid from lactose that, combined with milk
protein, gives yoghurt its characteristic acidic taste and texture. Yoghurt is
further defined in the United States as an acidic-gelled product from culturing
of cream milk, partially skim milk, or skim milk either alone or in combination
by Streptococcus thermophilus and Lb. delbrueckii subsp. bulgaricus. Other
ingredients and other additional ingredients, and the micro-organisms used must
remain viable in the end product (FSANZ, 2007).
The type and characteristics of micro-organisms used as
starter cultures for milk fermentation are two of the most essential factors
that determine the overall quantity of the fermented products (Bouzar et al., 1997). A proper selection and
composition of starter culture can improve the product flavor, aroma,
stability, and texture. Therefore, it is significant to understand the
characteristics of the starter bacteria to obtain desirable, quality products.
The microorganisms used in milk fermentation can be
categorized into three groups: Mesoph8ilic, Thermophilic, and Artisanal. The
optimum temperatures for the first two groups are approximately 26˚C (79˚F) and
42˚C (108˚F) respectively, and they consist of different species of bacteria.
The artisanal who consumed yoghurt regularly in its native Balkan regions lived
longer (Metchikoff 1921, Van de water 2003). This knowledge of health benefits of yoghurt has helped to increase yoghurt
consumption. The trend is also enhanced by the increased palatability of yoghurt
due to the addition of sweeteners and fruits (Van de water 2003). Yoghurt is
usually made through fermentation by thermophilic microorganisms at a
relatively high temperature (slightly higher than 45˚C; 113˚F) (Walstra et al., 2006) and a shorter fermentation
time (5 hours or longer) at which the maximum pH of 4.5 is used as a guide to
stop the fermentation. Therefore, this limitation is used to distinguish yoghurt
from other fermented milk products. The term yoghurt is also used to cover
strained products from thermophilic fermentation of milk such as yoghurt
cheese, greek yoghurt and other yoghurt with cheese-like textures that retain
the acidic characteristics of yoghurt. Milk fermentation culminates in a product with different
textures ranging from liquid such as kefir and koumis to semi-solid or solid
such as yoghurt (Van de water 2003). Fermentation of milk with lactic Acid
Bacteria (LAB) also results in products with characteristic tastes and aromas.
LAB metabolism and interaction between selected strains produces lactic acid
and other compounds as well as coagulates milk protein. Fermentation conditions
such as temperature, pH, the presence of oxygen, and milk composition also
contribute to the characteristics of the end product (Nakazawa and Hosono1992).
The continued dairy milk shortage or absence in the
developing countries, therefore had led to the production of milk substitutes
from vegetable. Development of milk substitute generated from cereals and
legumes provide an alternative ways of producing an acceptable nutritious food
based on vegetable is increasing (Harkins and Sarret 1967).
Vegetable milk (analogue milk or plant milk) is a
general term for any non-dairy cream analogue that is derived from a plant
source (http://www.en.wikipedia/plantmilk,2015).
No formal or legal definitions for vegetable milk exist in
most countries. The most common varieties are soy milk, oat milk, coconut milk,
but there are also other varieties available which are rice or nut based.
Severe diseases like PKU, makes animal proteins (especially casein) found in dairy
milk difficult to digest are diverse reasons that lead to the consumption of
vegetable milk (approximately 3% of people are allergic) (http://www.foodintol.com/dairy.asp,2015).
Vegetable milk can be used for babies in communities
where babies are not given dairy milk for ethical reasons and galactosemia
(Obizoba and Egbuna 1992). Communities where babies are not given dairy milk
for ethical reasons and galactosemia are feed with vegetable milk (Obizoba and
Egbuna 1992). The most common legume and cereal grain, soybeans and rice will
be used alternatively as a milk substitute in the production of yoghurt.
Improvement of quality soymilk are still researched (Sun-young et al., 2000) but rarely on rice milk.
Therefore in this study, rice milk will be substituted with soymilk to produce
yoghurt in order
to complement its
nutrient deficiency. The sweet
taste in most rice milk varieties
are produced by a natural enzymatic process, generating sugars by the cleavage
of carbohydrates, especially glucose similar to the Japanese amazake (http://www.bnet.com/ricemilk). Some rice
milk may nevertheless be sweetened with sugar cane syrup or other sugars. Rice
milk contains more carbohydrate, but does not contain significant amounts of
calcium, vitamin B12, vitamin B3 and iron compared to cow’s milk. It is often
consumed by people who are lactose intolerant, allergic to soy or have PKU. It
is also used as dairy substitute for vegetarians, and rice milk does not
contain cholesterol or lactose (http://www.en.wikipedia/wiki/ricemilk).
Soymilk is a fine emulsion of soybeans flour or water
extract of wet ground soybean. Among the sources of vegetable milk, soybean has
received high research attention and more research is still designed to improve
the quality of soymilk (Sun-young et al.,
2000). Though the soybean is classified among the leguminous plants, it differs
from other legumes in containing far more proteins and fats than ordinary peas
and beans.
Emphasizes of scientific studies concludes the fact that
soybean contains vitamins in substantial quantities and is a valuable source of
B-complex vitamins. Soya beans protein contains essential amino-acids and is
therefore a complete protein which satisfies the human requirements for protein
metabolism. Soya milk is a complete protein and has about the same protein as
cow’s milk; it can substitute animal protein and other sources of dietary
fiber, vitamins and minerals (Sack et al.,
2006). Soymilk contains little digestible calcium because calcium is bound to
the bean’s pulp, which is indigestible by humans. Soymilk has little saturated
fat and no cholesterol compared to cow’s milk.
Sucrose seen in soy products as basic disaccharide, are
broken down into glucose and fructose. Since soy does not contain galactose, a
product of lactose breakdown soy-base formulas can safely replace breast milk
in children with galactosemia. Soy milk contains no lactose, which makes it a
substitute for those who are lactose-intolerant. The composition of soymilk
varies with the varieties of soybean used and the method of production (Wang et al., 1978).
-
To produce bacteriocins that may have potential uses
as food preservatives;
-
To enhance the perceived sensory
properties of the product (e.g. due to the production of organic acids,
carbonyl compounds and partial hydrolysis of protein and/or fat);
-
To improve rheological properties
of fermented milk products (i.e. viscosity and firmness);
-
To contribute
dietetic/functional/nutraceutical properties of fermented milks, such as occurs
with the use of probiotic micro-organisms.
Yoghurt is semi-fermented milk consumed by people all
over the world. It is classified into different types and variations probably
due to the various types of live and active culture used, plain or fruit flavor
and most importantly the different sources of milk (animal/plant) (Belewu et al., 2005; Belewu, 2006). Rice milk
is considered the best hypoallergenic form of milk. The milk enhances immune
system and provides resistances to bacteria and viruses invading the body due
to high level of antioxidant, selenium and magnesium (http://www.healthiro.com/diet.food/rice-milk).
A wide range of fermented milks are manufactured
throughout the world and, according to Kurnmann et al., (1992), around 400 generic names are applied to traditional
and industrialized products. In UK, for an example, the economic value of yoghurt
and drinking yoghurt sold in 2002 was around £814 million. (Anon, 2003). For
those people who cannot or do not want to consume dairy yoghurt. Rice-Soya yoghurt
might be an acceptable replacement considering the low protein content in rice
milk; rice milk will be complemented with soy milk which contains same amount
and quality protein as that in cow’s milk (Sacks et al., 2006) in the production of yoghurt. Therefore, properties
of rice- soya yoghurts made from rice milk and soy milk are tested because
texture and mouth feel are the most important characteristics for yoghurts.
1.4 OBJECTIVE OFSTUDY
The main objective of this research is to produce yoghurt from
locally available raw materials from rice milk and soymilk.
The specific
objectives of the research are to:
i.
To produce plant yoghurt from rice milk and soymilk.
ii.
To evaluate the physicochemical properties of
rice-soy yoghurt.
iii.
To determine mineral contents of the rice-soy yoghurt.
iv.
To evaluate its general acceptability.
v.
To carryout microbial analysis on the yoghurt samples.
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