Changes In Allergenicity And Functional Property Of Soy Protein Isolates Hydrolyzed With Different Enzymes

In this paper,the soy protein isolate was extracted from low-temperature defatted soybean meal by the method of "alkali dissolution and acid precipitation".The effect of the ratio of material to liquid,extraction time,temperature,and pH on the extraction effect of soy protein isolate was investigated.The extraction process was optimized.SPI was hydrolysised by Alcalase,flavourzyme,pepsin and Trypsin.The analysis of the degree of hydrolysis and SDS-PAGE showed the changes of main antigen protein molecules of SPI.The antigenicity of the soy protein after hydrolysis was determined by ELISA and the changes of the emulsifying properties and foaming properties of the soy protein during the hydrolysis were measured simultaneously.We also exploring the changes of molecular structure,antigenic characteristics and physicochemical properties during the process of soybean proteolysis.In addition,changes of glycoproteins in the hydrolysates of soy protein were determined by PAS(periodic acid-schiff),and the hydrolysates were deglycosylated to show the relationship between glycoprotein and soybean protein antigenicity.1.The four factors have a certain influence on the protein extraction rate and protein content.The optimized condition was carried out as the following: substrate concentration 1g/m L,temperature 50?,hydrolysis time 60 min,pH8.0.The protein extraction rate and protein content reached 84.2% and 94.7%,respectively.2.The solubility and degree of hydrolysis of the soy protein isolate after enzymatic hydrolysis have been greatly improved.The emulsifying properties and foaming properties of the hydrolysates also improved.The emulsifying properties,emulsifying stability,and foam expansion rate of the Alcalase protease,flavor protease,pepsin,and trypsin hydrolysates all increased first and then decreased.The values reached maximum at 30 minutes after enzymatic hydrolysis,while the foam stability gradually decreased,but was not significant.3.The enzymatic hydrolysis contributes to the improvement of the emulsifying properties of the trypsin hydrolysate,but it has little effect on the change of the foaming performance.The degree of hydrolysis and SDS-PAGE analysis showed that the major antigenic proteins of soybean 7S globulin and 11 S globulin were degraded by Alcalase,flavourzyme and pepsin,and the degradation effect of trypsin was weak.4.Three new protein bands(29ku?23ku?27ku)were generated from the enzymatic treatment by alcalase,pespin and flavourzyme,and showed strong resistance to enzymatic hydrolysis.It has also been found that 33 ku can be digested by alcalase and flavourzyme,but cannot be digested by pepsin and trypsin.The reason why these components are resistant to enzymatic hydrolysis and its significance are worthy of further study and discussion.The results of ELISA showed that the antigenic residual ratio of soybean protein isolate was greatly reduced after being hydrolysised with alcalase,pepsin,flavourzyme and trypsin for 30 min.When time was reached for 120 min,the remaining antigen rate were 28%?57%?30%?75%,respectively.5.The results showed that the three subunits of ?-conglycinin(7S)and both acidic and basic polypeptides of glycinin(11S)were glycoprotein and the antigenicity of the soy protein after enzymatic hydrolysis is reduced,which proves that the soybean antigen protein contains glycoprotein components that cannot be digested by the protease.