Abstract: Low-fat soybean flakes were used to evaluate the effects of some operating conditions for glycinin (11S) extraction such as pH, reducing agent type and cold precipitation duration on the extraction rate and purity of glycinin. The pH adjustment of protein extract from 6.2 to 6.6 could decrease the extraction rate of glycinin by 16.71%, while the purity of the protein exhibited an increase by 4.60%. The contents of sulfhydryl and disulfide in proteins increased as the pH increased. Addition of sodium bisulfite (SBS) instead of dithiothreitol (DTT) or β-mercaptoethanol (ME) to the protein extract at pH 6.4 could increase the extraction rate of glycinin. The effect of DTT on the extraction rate of glycinin was the lowest among the reducing agents. The highest extraction rate and purity of glycinin were obtained after 10 h of cold precipitation. No significant difference was observed in the total content of sulfhydryl and disulfide as the precipitation duration was prolonged from 12 to 16 h (P ≥ 0.05), while the content of free sulfhydryl decreased as a result of partial oxidation to disulfide bonds.

Key words: glycinin(11S), operating conditions, extraction rate, purity