Study On β-conglycinin In Vitro Digestibility And Its Relation To Immunogenicity Of Protein Hydrolysates

β-conglycinin is one major soybean anti-nutritional factor which hampers the usage ofsoybean in feed industry. The stability and immunoreactivity variation of β-conglycinin afterhydrolysis with pepsin, aspergillus niger acid proteas or subtilisin were evaluated in order toprovide some theoretical foundation for the manufacture of hypoallergenic soybean products.β-conglycinin was isolated from defatted soybean powder and purified through theSephrose CL-6B system. The concentration of β-conglycinin was detected by BCA kit while itspurity (>90%) was analyzed by SDS-PAGE.Then subtilisin or pepsin or aspergillus niger acid proteas was mixed with β-conglycinin atthe ratio of1:50(E/S) and these mixtures were incubated in water bath (37℃,100rpm) for0、0.5、1、15、30、60or120min, respectively.The results of SDS-PAGE showed that the а′and а subunit were easily degraded by pepsinand aspergillus niger acid proteas at the ratio of1:50(E/S), whereas the β subunit was still stableeven after hydrolysis with these two enzymes together for120min. Subtilisin orpepsin+subtilisin can digested these three subunits in the following order α′> α> β, but notcompletely.From the data of the degree of hydrolysis (TNBS method) we can found that the hydrolysisability of these these enzymes were, in order, subtilisin, pepsin and aspergillus niger acid proteas.When combination, the orders were subtilisin+pepsin (12.96%)> subtilisin (9.83%)> pepsin+aspergillus niger acid proteas (8.61%)> pepsin (7.64%)> aspergillus niger acid proteas(7.04%).The FT-IR data demonstrated that the change of the second structure of β-conglycinin wasdepended on the type of the proteases. The alpha-helix and β-pleated sheet were reduced by7.63%and1.87%,4.31%and7.20%,10.04%and5.17%after hydrolysis with pepsin oraspergillus niger acid proteas or subtilisin, respectively, whereas the β-turn and random coilwere increased by2.78%and8.24%,6.23%and3.84%,10.04%and5.17%, respectively.The ELISA data indicated that the immunoreactivity of β-conglycinin was reduced byabout51.50%,47.03%,55.84%after hydrolysis with pepsin, or aspergillus niger acid proteas orboth of them together for120min, individuality. Subtilisin has a better performance to reducethe immunoreactivity of β-conglycinin (70.19%) than those of the pepsin and aspergillus nigeracid proteas; especially when the β-conglycinin was hydrolyzed with subtilisin and pepsin together (79.84%).In conclusion, our data demonstrate that the β subunit of β-conglycinin was very stable tohydrolysis with pepsin or aspergillus niger acid proteas individually or together whereassubtilisin can reduce the immunoreactivity of β-conglycinin well.