ABSTRACT
The
composite soymilk yogurt flavoured with pineapple as sweetener was produced
from composite blend of dano milk and soymilk. It was pasteurized at 850c
for 5 minutes. It was cooled , homogenized and inoculated with mixed yogurt
starter culture of Lactobacillus
bulgaricus, and Lactobacillus
acidophilus at 250c for 24 hours. The proximate, physicochemical
properties and sensory evaluation of the composite yogurt were determined. In
the proximate, the study reveals that the combination of dano milk and soymilk
increased the level of the protein content. This can be seen in the sample
50%S+M with the protein content of 13.23.The fat content of the product equally
decreased upon introduction of the sweetener (pineapple). The sensory score of
the yogurt samples reveal there was a significant difference (P>0.05) in terms
of the taste, texture, and overall acceptability between the sample
M100%(control) and the composite soy-yogurt sample (50%M+50%S+P,
100%S,100%S+Pand 100%m+p) except for sample 50%M+50%S that was not
significantly difference (P<0.05) from the control. Therefore soymilk can be
substituted up to 50% with dano milk yogurt preparation without affecting the
physicochemical and sensory properties of the yogurt.
CHAPTER ONE
1.0
INTRODUCTION
Interest
in functional foods has recently increased among consumers due to a greater
consciousness of health and nutrition; as well as the need to cure diseases and
also the increasing scientific evidence of their effectiveness. Fermented
products are a significant part of many indigenous diets.
Yoghurt
is a Turkish name for a fermented milk product. It is originated by early
normadic herdsman, especially in Asia, Southern and Eastern Europe. Yoghurt is
made by adding a culture of acid forming bacteria to milk that is usually
homogenized, pasteurized and fermented. Yoghurt is defined as a fermented milk
product that evolved empirically some centuries ago by allowing naturally
contaminated milk to sour at a warm temperature, in the range of 40-50 °C (Kwon
et al., 2011). The micro-organisms which are used conventionally in this
process are referred to as “Starter Culture”. They include Lactobacillus delbrueckii subsp. Bulgaricus and Streptococcus thermophilus. The average
size of Lactobacillus bulgaricus
ranges from 0.8 to 1.0μm in diameter (Rakis .,1978 , Sanfu. , 2009).
During the
fermentation, hydrolysis of the milk proteins occurs, the pH drops, the
viscosity increases and bacterial metabolites are produced that contribute to
the taste and possibly to the health promoting properties of yoghurt. The
sugars are fermented by the bacteria into lactic acid, which causes the
formation of the characteristic curd. The acid lowers the pH of the yoghurt and
restricts the growth of food poisoning bacteria (putrefactive or pathogenic).
Not only is
yoghurt a wonderful quick, easy and nutritious snack, but also research
evidence point to the fact that milk and yoghurt may actually add years to life
as found in some countries where fermented dairy products are a dietary (Wolf.,1978)
Several health benefits have been reported for traditional yoghurt and this
healthy image is enhanced by supplementation with probiotic bacteria ( ;
Magenis, et al 2006).
Soymilk is an
aqueous extract of soya beans (Glycine
max) and is quiet similar in appearance to cow milk (Agure-Dam, 1997). It
is commonly characterized as having a beany, grassy or soy flavor, which
reportedly can be improved by lactic acid fermentation, as in yoghurt-like products
Microorganisms possess endogenous β-glucosidases which can be utilized to
hydrolyze predominant isoflavone glucosides in soymilk to improve biological
activity.
It has been reported that probiotic organisms
including Bifidobacteria and some
other lactic acid bacteria hydrolyze isoflavone glycosides
into corresponding aglycones (Cheng., 1998).
Recent
reports indicate that some probiotic bacteria could better compete with yoghurt
cultures in a soy-based substrate. Soy has been examined as a substrate for the
Lactobacillus
species such as
L. Casei, L. helveticus, L. fermenti, L. fermentum and L. reuteri
(Garro et al., 1999; Murti et al., 1993b;( Chumchuere and Robinson, 1999; Garro
et al., 2004; Tzortzis et al., 2004).
The problems of which
is beany flavor can be improved by lactic fermentation, so production of
fermented soymilks such as soy yoghurt is important (Nsofor et al., 1992; AbdEl
Khair, , 2009).
Due to continuous increase in the population
and inadequate supply of animal milk protein leading to malnutrition in Nigeria
many research works have been geared finding alternative protein source from
legume.
Soymilk can serve as a very good alternative to
the expensive cow milk as it contains all the essential amino acid even though
some are in a low concentration
It is well known from experiment that diets
containing containing casein or other animal protein could induce elevation of
plasma total LDL cholesterol concentration but this can be prevented by
vegetable protein such as soy protein (caroll and kurowska 1998)
1.2 HISTORY OF THE YOGURT MAKING
Milk
fermentation is one of the oldest methods practiced by the human beings to
preserve milk with an extended shelf life. The exact origination of milk
fermentation is not clear; however, it seems that it is dated back to the dawn
of the civilization.
It
has been reported that the early civilizations such as the Samarians,
Babylonians, Pharoes and Indians were well advanced in agricultural and animal
husbandry practice. This can be supported by the findings of Copley et al.,
2003 in which the dairy fat residues were found in pottery fragments from Neolithic
Bronze-age and Iron-age settlements, which suggests that the practice of
dairying had existed in Britain approximately 6500 years ago.
However,
it is questionable that the milk fermentation was practiced during this period.
Therefore, the origin of the fermented milk products including yogurt remains
unsolved. It has been reported that the Anatolian goatherds conserve their milk
by thickening as they used to dry it in the sun and transport in animal
stomachs. It is generally accepted among the historians that the fermentation
of milk is discovered accidentally by the Neolithic people of Central Asia when
they stored milk in primitive methods such as in sheep-skin bags in warm
climates.
With reference to yogurt, it can be suggested
that it has been evolved in Turkey as the term “yoghurt” has been derived from
a Turkish verb, “jugurt” that means “to be curdled or coagulated”.(Belleville,
2002)
The
earliest writings about yogurt can be found from those of Pliny who lived in
the first century A. D. and wrote about ancient barbarous nations that knew how
to thicken the milk into a substance with an agreeable acidity. According to
the literature,(Douglass et al.,2006) the founder of the Mongol empire, Genghis
Khan and his armies lived on yogurt and spreading of this news among the people
had made the yogurt consumption to spread throughout the East.
Moreover, according to the Persian tradition,
Abraham owed his fecundity and longevity to the regular ingestion of yogurt,
and the emperor Francis I of France was said to be cured of severe diarrhea by
consuming yogurt made of goat milk leading to introduce the health benefits of
yogurt into the western world in 1542(Howell and Caldwell, 1978)
The
first industrialized production of yogurt took
place in 1919, in Barcelona, Spain at a company named Danone. Yogurt was
firstly introduced to the USA in the early 20th century in the form of tablets
especially designed for those with digestive intolerance. However, it became
popular in the North America when Danone, a small-scale yogurt factory started
manufacture of yogurt in New York in 1940(Fennel, 1966)
Even
though, yogurt has been evolved for centuries, it was subjected to a
significant and dynamic evolution process in the 20th Century to originate a
vast array of products. For instance, fruit yogurts, yogurts with fruit on
bottom and blended yogurts were introduced in 1937, 1947 and 1963 respectively.
It seems that the evolution process of yogurt has taken place in different
regions of the world once it had been originated in the Central Asia. This
might be the reason of having different types of yogurts and yogurt-like
products in different names.
1.3 STATEMENT OF THE PROBLEM
Animal protein
(milk) are more expensive in Nigeria and
not easily affordable by all for yogurt production necessitates the need to seek for ways of producing yogurts
from plant protein (soy beans).Combination animal protein provides more
complete amino acid , hence better nutrition .
Improving
product nutrient value by fruit addition and increased new product variety.
Reduce postharvest losses of soybean due to underutilization in Nigeria.
Therefore
, many researches have been carried out on yogurt but none have being
established on using pineapple as sweetener, aimed at achieving the
aforementioned solution.
1.4 AIM/OBJECTIVES
To
produce yogurt from plant protein (soymilk)
To evaluate the sensory attributes of yogurt made
from soymilk and cow milk using pineapple as sweetener.
To
determine the proximate composition attributes of the yogurt made from soymilk
and cow milk using pineapple as sweetener.
To check if there is a significant difference in
the texture, appearance, colour, taste and general acceptability of the yogurt
produce using ANOVA
To check the proximate contents of the samples
produced
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