Effects of partial hydrolysis on structural, functional and antioxidant properties of oat protein isolate

Degree of hydrolysis (DH) plays important roles in the characteristics of food proteins. Herein, in order to explore the effects of partial hydrolysis on the structural, functional and antioxidant characteristics of hydrolysates, oat protein isolate was partial hydrolyzed by alcalase with different DH (2%, 4%, 6%, 8%, 12%, and 16%). Our results showed that hydrolysis could induce the significant structural changes of oat protein, mainly reflecting at amino acid pattern, molecular weight profile and protein conformation. Alcalase hydrolysis also resulted in hydrolysates with the emulsifying activity index of at least 19.83 m2/g, and the highest emulsifying stability was observed in the hydrolysate with DH of 6%, possibly due to its suitable molecular weight, exposed hydrophobic amino acid residues and high surface net charge. Besides, all hydrolysates exerted excellent DPPH radical scavenging activity with IC50 value ranging from 19.23 to 30.32 µg/mL, which was closely correlated with DH. The moderate alcalase hydrolysis (DH 6%) on oat protein isolate exhibited the strongest metal ion-chelating activity, with possessing the maximum amount of hydrophilic amino acids. More importantly, oat protein hydrolysate with DH 6% not only prolonged the induction period of sunflower oil, but also improved the stability of sunflower oil-in-water emulsion, as evidenced by the reduced TBARS production and the homogeneous droplet size. Therefore, partial hydrolysis can be advantageous for improving the functional and antioxidant characteristics of oat protein isolate, particularly the hydrolysate with DH 6%.