Preparation Of Special Soy Protein Isolates By Enzyme Modification

Enzymatic modification is an effective way to improve soy protein's functionality. Past enzymic modification research focused on effects of reaction conditions. In this paper,"trasition state SPI"which means partly denatured proteins were made and hydrolyzed. We tried to find out substrate's effect on enzyme hydrolysis and choose the appropriate SPI for reaction. On the basis of these results, we could optimize the right technologic conditions with a view of functionality of the product.It showed the properties of different"trasition state"SPI heating in pH 4.5 and pH 7.0 for different time respectively were various. Solubility in buffer of the latter is better than the former and the aggregations were bigger. With the SDS-PAGE results of their hydrosates, it's found that subunit of"trasition state SPI"was obviously selectively hydrolyzed. In pH 4.5"transition SPI",α',αsubunits ofβ-conglycinin were firstly hydrolyzed,βsubunit ofβ-conglycinin secondly, acid subunit of glycinin thirdly, and alcaline subunits of glycinin lastly. However, the subsequence were changed betweenβsubunit ofβ-conglycinin secondly and acid subunit of glycinin in pH 7.0"transition SPI".The results based on the single factor experiment indicated the optimum processing condition as follows: for product injected in meat, the"trasition state"protein of heating at pH 7.0 and at 100℃for 30 seconds, when hydrolysis, the solids content was 10%, the dosage of Alcalase was 0.1% based on the solids content, keeping the solution at 50℃and the pH value ranged from 7.0 to 7.5, inactivating enzyme at 100℃for 30 seconds, freeze-drying at pH 7.5; for product of good dispersibility, the"trasition state"protein of heating at pH 4.5 and at 70℃for 10 minutes, when hydrolysis, the solids content was 10%, the dosage of Bromelain was 0.2% based on the solids content, keeping the solution at 50℃and at pH 7.0, inactivating enzyme at 120℃for 30 seconds, spray-drying at pH 7.0, and covering with phospholipid was better. The final product properties were more or less or even better than the properties of the same kind of home or oversea ones.