ABSTRACT
Fermented
foods are those processed through the activities of microorganisms. Soy milk is
an aqueous extract from soybeans known for its nutritive health benefits. The
aim of this work is to ferment soy milk product with starter culture (lactobacillus bulgaricus and streptococcus
thermophilus) to prolong its shelf life. The soy bean was purchased from
Ogbete main market located at Enugu North in Enugu state. It was immediately
transferred to Godfrey Okoye University microbiology laboratory, where it was
processed into soymilk. The processed product was pasteurized for 30mins,
allowed to cool and added either milk or sugar as a carbon source before
fermenting anaerobically with the starter culture (lactobacillus bulgaricus and streptococcus thermophilus) gotten
from Aqua Rapha Company, Ninth mile, Enugu. Temperature and pH variations of
fermented soymilk samples (soymilk with both organisms, mixed with milk and
sugar respectively, soymilk with both organism mixed with either milk or sugar
respectively) were determined. Sample containing both organisms with milk and
sugar respectively, have the highest temperature (80c) on day one
and were slightly acidic (4.30), while sample containing both organism and
sugar has the highest temperature (60c) on the last day and are
slightly acidic (4.25). Proximate analysis of this various soymilk samples were
determined. Sample containing both organisms and sugar has the highest protein
content (3.678%) while the control shows the least value (0.347%). Sensory
evaluation showed that the product fermented with both organisms with milk and
sugar was more acceptable than all other samples. Shelf life of these products
were determined for 6 days. All the samples were acceptable from 0-3 days, but
from the 4-5th day, sample 1 has a pungent smell and was
not acceptable while sample 7 was able to retain its aroma and flavor. This is
to show that starter culture fermentation was able to improve the shelf life
and organoleptic properties for better acceptability.
CHAPTER ONE
1.0 INTRODUCTION
Soymilk is a rich creamy liquid extract of soybean (Glycine max)
(Tunde-Akintunde and Souley, 2009) and is the most available soy product.
Soymilk is a popular nutritive beverage alternative to cow’s milk and is even
cheaper(Soya-Agrodok, 2005). Soymilk has become a very interesting food due to
its extraordinary nutritive value and health characteristics. It is a very rich
source of highly valuable proteins, unsaturated fatty acids, soluble and
insoluble dietary fibres, and isoflavones whose presence in everyday diet is
very important (Boani, 2006). In some countries, soymilk is intended for the
population who cannot digest milk due to lactose intolerance, allergy to milk
proteins, or vegetarian way of diet. Soymilk has limited consumer acceptability
due to its undesirable beanyflavour. to improve its acceptability due to
reduction in objectionable flavour and oligosaccharides such as starchyose and
raffinose that cause flatulence (Wang et al., 2002). (Akabandaet al. 2010)
reported that fermentation of soymilk provides a possibility for modifying or
improving its flavour and texture so that it becomes more acceptable. In
western countries, soymilk is intended forpopulation who cannot digest milk for
reasons like lactose intolerance, allergy to milk proteins, or vegetarian way
of diet. Fermenting soymilk with lactic acid bacteria considerably increases
its health value. Because of greater antioxidative actions (Wang etal.
2006), they are considered healthier than pure soymilk. The purpose of
fermentation is to remove the undesirable beany taste which is mostly due to
the presence of n-hexanal and pentanal , and to improve on the
nutritional characteristics of soymilk. Several studies (Hong et al., 2004; Song et al.,
2008) have reported numerous benefits of fermented soymilk including
degradation of soybean allergens during fermentation by proteolytic enzymes.
Due to the characteristics of milk that is highly perishable, the purpose of
milk fermentation using lactic acid bacteria is to prolong its shelf life as
well as to preserve the nutritious component of milk.
1.1 PROBLEM STATEMENT
Development of a beanyflavour
during processing of soy milk has limited its use amongst populations. Thus
much effort has been directed toward elimination of beanyflavour in processing
of soy milk. Heating of the soybeans either before or during initial processing
to inactivate lipoxygenase and the use of fermentation has been used to stop
undesirable flavours in soymilk. The heating process during
conventional soy milk making considerably destroys most of the anti-nutritional
factors in soy milk and improves the digestibility of soy protein, as well.
However, compounds, like phytic acid, which interferes with the availability of
calcium, is not reduced effectively (Onourahet
al., 2007). At the same time, over-heating to eliminate trypsin inhibitor
activity to a great extent can cause damage to amino acids, as well as loss in
the overall nutritional value of soy milk. Incorporating the fermentation
process into soy milk production has become a popular method to improve the
acceptability and health properties of soy milk.
1.2 AIM
• The aim of this study is to examine the effect of
starter culture (lactobacillus bulgaricus and streptococcus thermophilus)
in the fermentation of soymilk.
1.3 OBJECTIVES
• To examine the effect of Lactobacillus bulgaricus
and Streptococcus thermophilus in the soymilk mixed with milk respectively.
• To know the effect of Lactobacillus bulgaricus and
Streptococcus thermophilusin the soymilk mixed with sugar respectively.
• To
know the effect of both
organisms (lactobacillus bulgaricusand streptococcus thermophilus)in
the soymilk mixed with sugar and milk respectively.
• To examine the proximate analysis of both fermented and
non-fermented soymilk
• To examine the sensory evaluation of the fermented
soymilk product.
• Determination of shelf life of the final product.
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