CHEMICAL EVALUATION AND ELECTROPHORETIC PATTERN OF SOY PROTEINS

Abstract

ABSTRACTThree varieties of soybean (Bragg, Punjab‐1 and Lee) were chemically evaluated for their protein quality from the amino acid data, solubility classes of proteins, chemical score, essential amino acid index, requirement index and electrophoretic pattern of proteins. Cotyledon, the major component of seed, accounted for about 93% of tryptophan and methionine of the whole seed. Glycinin as the predominant fraction of soy protein (about 63% of total protein) contained 73% and 71% of the amount of methionine and tryptophan of the whole seed, respectively, but was deficient in methionine. Albumin, constituting about 12% of total soy protein, was also deficient in methionine but was quite rich in tryptophan. Prolamine fraction of soy protein was rich in methionine and tryptophan. On the other hand, glutelin was the poorest in these amino acids. Soy protein contained a balanced amino acid pattern with the exception of methionine which was found to be the main limiting amino acid. The electrophoretic pattern of albumin fraction of Punjab‐1 and Bragg differed from that of Lee while there were no varietal differences in the pattern of whole seed proteins and glycinin. Punjab‐1 appeared to be better in its protein quality based on its higher values of chemical score, essential amino acid index and requirement index. The present investigation has revealed that chemical evaluation is comparable to biological evaluation and can serve as a good index in the assessment of protein quality of food grain.