Effect of Rice Bran Storage Time on the Structure of Rice Bran Protein
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Abstract:
Rice bran stored for different periods before defatting and preparing rice bran protein were used to analyze the effect of storage time on the structure of rice bran proteins. The results showed that, as storage time increased, rice bran lipids were gradually hydrolyzed and oxidized. The protein carbonyl and disulfide content of rice bran protein increased from 1.76 and 5.69 nmol/mg and 9.16 and 8.25 nmol/mg, respectively, while free sulfhydryl content decreased from 7.58 to 1.22 nmol/mg, which indicated that storage of rice bran caused oxidation of the rice bran proteins. As storage time of rice bran increased from zero to ten days, a decrease in the intrinsic fluorescence intensity of rice bran protein was accompanied by a blue shift of the wavelength of maximum emission. A gradual decrease in surface hydrophobicity and an increase in the ratio of protein aggregates in molecular weight distribution profiles of rice bran proteins were also observed, which indicated that storage of rice bran led to the aggregation of rice bran proteins. Fourier transform infrared spectroscopic analysis indicated that the α-helix and β-sheet content decreased, while the β-turn and random-coil content increased during storage. The results of electrophoresis also indicated that protein oxidation led to the formation of oxidative aggregates of rice bran proteins, and that disulfide as well as non-disulfide covalent bonds participated in the formation of these aggregates. The results of this study indicated that the rancidity-induced oxidation of rice bran proteins changed their structure and caused the formation of oxidative aggregates.
