Effect of Keratinase Modification on the Foaming Properties and Structural Characteristics of Rice Protein Hydrolysate

In this study, rice protein (RP) was hydrolyzed by keratinase, and partial functional properties (foaming properties, amino acid composition) and structural characteristics including SDS-PAGE, circular dichroism, and endogenous fluorescence of RP hydrolysate (RPH) with different degree of hydrolysis(DH) were determined. Results showed that the protein recovery rate of RP under neutral conditions was significantly improved by keratinase (P < 0.05). The foamability of RPH showed a trend of increasing first and then decreasing with the increase of DH. And there was no significant change in foaming stability among RPH. The contents of sweet amino acid, umami amino acid in RPH were significantly higher (P < 0.05) compared with RP without hydrolysis. The result of SDS-PAGE showed that RPH was mainly composed of polypeptides with a molecular weight of less than 20 kDa. There was significant increase in the proportion of random coils and significant decrease in the proportion of α-helix and β-fold in the secondary structure of RPH than those in RP without hydrolysis (P < 0.05), indicating that the secondary structure in RPH got more flexible and looser than that in RP without hydrolysis. The endogenous fluorescence results indicated that more contents of hydrophobic amino acids exposed in water phase after hydrolysis. This study would provide a theoretical basis for the development and utilization of RP products.