Extraction and Isolation of 7S and 11S from Low-Temperature Defatted Soybean Draff

A semi-works production method which the extraction and isolation of 7S and 11S was improved. The method of isoelectric point and cooling precipitation was developed for extraction and isolation of 7S and 11S fractions from low-temperature defatted soybean draff, based on the indices of the extraction yield which was determined by the Kjeldahl method and purity which was determined by SDS-PAGE. Compared the optimum parameters of five kinds of extraction methods that phosphate buffer's effect is better than others, its extraction yield is 89.55%. The optimal isolation parameters of 7S are as follows: pH 4.7, sedimentation time 1 h, the stirring rate of acid 40r/min, its purity and yield are 73.25% and 50.6% respectively. The optimal isolation parameters of 11S are as follows: pH 6.2, cooling precipitation 12h, temperature 4 degrees C, the stirring rate of acid 30r/min, its purity and yield were 76.37% and 41.2% respectively. With the improvements, the extraction yield of 11S and 7S fractions were significantly increased. They may be widely used as a source of highly functional soybean protein in more food products.