Natural rice protein was modified by enzymatic reaction(trypsin, pH 8.0, 55℃) at different times to prepare rice protein hydrolysates with different degrees of hydrolysis(2%, 4% and 8%). The effects of different degrees of hydrolysis on the secondary structure, micromorphology, thermal behaviors, intrinsic fluorescence, surface hydrophobicity, sulfhydryl content, solubility, emulsifying properties and in vitro antioxidant activity were investigated. The results showed that the content of β-turn in rice protein hydrolysates was increased, indicating a more stretchable and flexible secondary structure. The microstructure was observed to be porous, which is beneficial to improve solubility and emulsifying properties. When the degree of hydrolysis is less than 4%, the hydrolysates exhibited a good thermal stability; as the degree of hydrolysis increased, the heat resistance decreased. The enzymatic process also caused a change in the chromophore content of the protein molecule and a stronger fluorescence intensity as the degree of hydrolysis increased. In addition, the surface hydrophobicity and sulfhydryl content of rice protein decreased first and then increased after enzymatic hydrolysis, which may be related to the folding and unfolding caused by the change of disulfide bond of protein molecule. The study also found that the antioxidant activity of the enzymatic hydrolysates was significantly improved compared with the natural rice protein. The DPPH and ABTS free radical scavenging rate was the same as that of the BHT at the same concentration. As a mild, safe and efficient modification method, restrictive enzymatic hydrolysis can greatly improve the structure and functional properties of rice protein and significantly improve its antioxidant activity in vitro. © 2020, Editorial Office of Journal of CIFST. All right reserved.
