Abstract: Oat protein isolate hydrolysates with different degrees of hydrolysis (DH, 2%–7%) were prepared by limited enzymatic hydrolysis with papain, and their structural and antioxidant properties were investigated. Our results showed that papain hydrolysis could favor the formation of low-molecular-mass peptides, demonstrating changes in protein structure. This was further confirmed by the results of ultraviolet absorption and fluorescence spectroscopy. Also, the enzymatic hydrolysis could change the secondary structure of oat protein, as demonstrated by a decline in α-helical structure and an increase in random coil and β-turn structures. This implied that the enzymatic hydrolysis might be beneficial to the antioxidant potential of oat protein hydrolysates. Interestingly, papain hydrolysis (particularly at DH of 4%) led to an increase in 1,1-dipheny1-2-picrylhydrazyl (DPPH) radical scavenging activity and metal ion chelating activity of oat protein hydrolysates, demonstrating half-maximum inhibitory concentration (IC50) of 36.83 μg/mL and 33.42 μg/mL, respectively. More intriguingly, the hydrolysate at 4% DH could not only prolong the induction period of sunflower oil, but also improve the oxidative stability of sunflower oil-in-water emulsion. Therefore, limited hydrolysis with papain could result in the improved antioxidant activities of oat protein, which was closely associated with the changes in protein structure.

Key words: oat protein isolate; papain; structural properties; antioxidant activity; limited hydrolysis