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

The 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 partially hydrolyzed with alcalase at different DHs (2%, 4%, 6%, 8%, 12%, and 16%). Our results showed that hydrolysis could induce significant structural changes in oat protein, mainly reflecting at the 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-1, and the highest emulsion stability was observed in the hydrolysate with a 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 an IC50 value ranging from 19.23 to 30.32 μg mL-1, which was closely correlated with DH. The oat protein isolate with moderate alcalase hydrolysis (DH 6%) exhibited the strongest metal ion-chelating activity and possessed the maximum amount of hydrophilic amino acids. More importantly, the oat protein hydrolysate with a DH of 6% not only prolonged the induction period of sunflower oil, but also improved the stability of the 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 a DH of 6%.