Enzymatic modification of the extractability of protein from soybeans (Glycine Max)

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Virginia Polytechnic Institute


Six fungi, Pestalotiopsis westerdijkii QM:381, Myrothecium verrucaria QM:460, Aspergillus terrus QM:72f, Chaetomium globosum QM:459, Basidiomycetes sp. QM:806, Trichoderma viride QM:6a were screened according to their ability to elaborate an extracellular enzyme system which has the highest soy fiber-degrading activity and the highest carboxymethylcellulase activity. Pestalotiopsis westerdijkii QM:481 gave the most potent extracellular enzyme system.

When Pestalotiopsis westerdijkii was grown on a wheat bran medium at a temperature of 31.5°C for ten days, it elaborated the most potent extracellular enzyme system.

It was found that the optimum conditions for this extracellular enzyme system, acting on soy residue for the purpose of making soy residue protein available for extraction, were pH 4.6 and 38°C.

Treating one gram of soy residue, 40 ml (32 mg Nitrogen) enzyme preparation, at the optimum pH and temperature for 20 hours caused the most efficient extraction of protein.

There was an increase in the amount of soluble carbohydrates, reducing sugars, glucose and galactose due to the action of enzyme on soy residue. The amount of non-protein nitrogen in the extractable fraction of soy residue after treatment with enzyme preparation or water increase with the increase of incubation time even in the presence of toluene which prevents bacterial contamination. This is probably due to the action of proteases from the soybean and enzyme preparation.

In large scale experiments, when 40 ml (32 mg Nitrogen) of the enzyme preparation per gram of soy residue were used, about 60% of the soy residue protein was made available for water extraction and the yield of extractable protein in soy milk was increased by 20%.

Feeding experiments using treated or untreated soy residue and soy milk showed that the treated milk contains protein of higher quality and better digestibility when compared to untreated soy milk or treated residue. The most limiting amino acid in these products is methionine. The amino acid composition of these products was very much the same.