Lipid Stability in Soyflours Produced From Raw And Processed Soybeans
Date
2001-06
Authors
Journal Title
Journal ISSN
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Publisher
University of Ghana
Abstract
Soybean, a high protcin/oil legume is known (o contain high levels of
polyunsaturated fatty acids, which are susceptible to lipid oxidation and
hydrolysis. However, suitable processing methods and storage conditions can
enhance the stability o f lipid in soyflour.
The objective of the project was to investigate the effects of some processing
methods and storage conditions on the stability of lipid in soyflour and to define
the parameters for the prediction of the shelf life soyflour.
Some whole commercial soybeans were milled into raw soyflour. Some o f the
whole beans were cooked for one hour, and milled into cooked-dried soyflour.
The final portion was roasted in an open pan and then milled into roasted
soyflour. The raw, cooked-dried and roasted flours produced were stored at
temperatures of 5, 16, 30, 42, 68 and 80°C, and at water activities of 0.15, 0.23,
0.45, 0.68 and 0.75 for 12 weeks. Indices of lipid oxidation (peroxide value and
ihiobarbituric acid number) and an index of lipid hydrolysis (free fatty acids)
were determined at time intervals of 0, 2, 6, 10 and 12 weeks. Sensory
evaluation was performed on the samples stored at 5 and 30°C at storage times
of 4, 8,10 and 12 weeks. Results showed that the rates of lipid oxidation and hydrolysis were higher in
raw soy flour than in the heat-processed flours at the same storage temperature
and time and at (he same water activity. The rale of lipid hydrolysis was found to be minimal at 5°C and maximal at 3-0 °C in both raw and heat-processed
soy II ours. The rate of lipid oxidation was also found lo be minimal at water
activity corresponding to the average monolayer value of both raw and heatprocessed
soydours. The flavour of raw and heat-processed Hours began to
change significantly after 6 and 12 weeks of storage respectively; and this
occurred at peroxide value of 4.21 meq/kg and thiobarbituric acid number of
9.76 mg/kg. Hcat-treatment of soybeans prior to processing into Hours yield Hours with
lower rates o f chemical reactions, which result in minimal lipid oxidation and
hydrolysis. Storage of soy Hour under cold condition or maintaining (he moisture
content of soyllour at or close to the monolayer value of soy Hour results in
lower rates of chemical reactions, which increases the stability of lipids in
soyHour. The shelf life of soyllour can be predicted when the peroxide value
and the TBA Number of soyHour are known. It is possible to extend the shelf
life of soyHour by heat-processing the beans prior to milling into Hour and
storing the flour under cold conditions.
Description
Thesis (MPhil)-University of Ghana