Plastein reaction enhanced bile-acid binding capacity of soybean protein hydrolysates and whey protein hydrolysates

Plastein reaction is a modification reaction that can improve the functional properties of protein hydrolysate. The product of the reaction is a thixotropic aggregation of peptides. This study investigated the formation condition of soybean-whey plastein and bile acid binding capacity of plastein. Soy protein and whey protein were hydrolyzed by pepsin. The mixture (1:1, w/w) of two hydrolysates was modified by pepsin again. After the reaction, the decrease in free amino groups and the turbidity of the modified hydrolysate were measured to obtain appropriate reaction condition. Results showed that the concentration of hydrolysates 40% (w/v), enzyme ratio of 2.0 KU/g protein, pH 5.0, 37 °C, reaction time of 3.0 h respectively, were showed maximum changes in protein hydrolysates. Tricine SDS-PAGE analysis under denaturing conditions revealed that whey protein was more sensitive to pepsin and yielded different polypeptides (PPs) of molecular weight ranged from 3.5-17 kDa. However, a high molecular weight PP was completely hydrolyzed while PPs of 14.2-26 kDa were partially digested after pepsin treatment. Native page analysis further revealed the presence of a high-molecular weight PP in crude and purified plastein product. The bile acid binding capacity was improved by the plastein reaction. The amount of binding sodium deoxycholate, sodium taurocholate, and sodium cholate were 0.75, 2.0 and 1.87 μmol/100 mg respectively.