|dc.description.abstract||The concentrated protein fractions of soyabeans, known as soya protein isolate, was produced
by three different methods from the same raw material namely defatted soya flakes.
Extraction of the soluble fraction of the raw material is common to all three methods. A
study was therefore undertaken to optimise the extraction process conditions in terms of time,
temperature, pH, extraction time, extraction volume and raw material particle size, thereby
maximising yields of soluble material.
The three different methods, namely isoelectric precipitation, ultrafiltration and swollen gel
technology were then used to separate the soluble and non-soluble protein fractions. Both the
isoelectric and ultrafiltration methods gave good yields of finished product, with the
ultrafiltration process giving the better overall yield, but the swollen gel method gave
disappointing results and was not feasible in practice.
Functional properties of the products from the isoelectric and ultrafiltration methods were
compared and found to be broadly similar although different in certain respects from those
of commercial soya isolates.
Levels of the anti-nutritional factors trypsin inhibitor and phytate in products from the three
processes were determined and the substantial differences observed in trypsin inhibitor levels
were further investigated. Determination of lysinoalanine levels was also attempted but the
results obtained were unsatisfactory. Amino acid composition and polyacrylamide gel
electrophoresis were used to compare the chemical composition of products from the three
processes. The comparative economics of the isoelectric and ultrafiltration processes for large
scale production of soya protein isolates were evaluated, taking into account the comparative
efficiencies of the two processes as determined during the study. It was established that,
while the isoelectric process initially appears more economical, it may be possible to modify
the ultrafiltration process in such a manner as to make it more economical than the isoelectric
process. Overall figures however indicate that the manufacture of soya protein isolate in
South Africa is not currently a viable economic proposition, due to high raw material costs.||en