Effect of microwave plasma processing on the structure, physicochemical properties and functional properties of rice bran protein

Abstract

To investigate the effects of microwave plasma treatment on rice bran protein (RBP), various power levels (150, 160, 170, 180, and 190 W) and processing times (1, 3, 5, 7, and 9 min) were examined for their impact on the conformation, physicochemical properties, and functional properties. The results showed that high-energy active particles generated by microwave plasma could oxidize modify the spatial structure of RBP, thus affecting its functional characteristics. The primary structure of RBP, as revealed by SDS-PAGE, remained unchanged. While the content of β-sheet structures initially decreased and then increased, the random coil content first increased and then decreased, the spatial structure first unfolded and then folded again. The intrinsic fluorescence spectrum showed that hydrophobic amino acids buried within the protein's interior were initially exposed but later reburied. The disulfide bond was first broken to sulfhydryl group and then reformed due to excessive oxidation, which promoted the intermolecular aggregation of RBP. Compared with its natural counterpart, the average particle size decreased from 519.6 nm to 186.7 nm at a power of 160 W and a treatment time of 5 min. Consequently, the emulsification activity index and the stability index increased by factors of 2.18 and 1.40, respectively. The foaming capacity index and foam stability index reached maximum values of 73.07% and 43.34%, respectively. These results provide theoretical evidence for the application of microwave plasma technology to modify plant proteins.