Abstract: Rice bran protein was prepared from fresh rice bran subjected to stabilization and defatting after storage for different times with a view to investigating the effect of rice bran rancidity on structural characteristics of its in vitro pepsin digest. The results showed that as the extent of rancidity of rice bran increased, the time required for complete pepsin digestion of albumin subunits, glutelin acidic subunits, and globulin subunits firstly advanced, and then delayed, while glutelin base subunits and prolamin subunits became more difficult to digest by pepsin. The results of molecular mass distribution and particle size distribution indicated that oxidative aggregates of rice bran protein were formed as a result of rancidity, thereby inhibiting its in vitro pepsin digestion. In addition, as the extent of rancidity increased, the pepsin digest exhibited an increase followed by a decrease in the red shift in maximum fluorescence emission wavelength, while the surface hydrophobicity gradually decreased. In conclusion, protein oxidation caused by lipid rancidity in rice bran has important effects on the covalent cross-linking state, aggregation behavior and surface hydrophobicity of in vitro pepsin digest of rice bran protein.

Key words: rice bran rancidity, rice bran protein, in vitro pepsin digestion, structural characteristics