Effect of Oxidative Modification by Peroxyl Radical on the Structure of Rice Protein
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Abstract:
The peroxyl radicals derived from the thermal decomposition of different concentrations of 2,2’-azobis (2-amidinopropane) dihydrochloride (AAPH) under aerobic conditions were selected to be representative of lipid peroxidation-derived lipid radicals, and the effect of oxidative modification by peroxyl radicals on the structure of rice protein was studied. The results showed that when the concentration of AAPH increased from 0 to 25 mmol/L, the protein carbonyl and disulfide contents of rice protein increased from 3.77 and 13.88 nmol/mg to 7.23 and 15.73 nmol/mg, respectively, while the free sulfhydryl content of rice protein decreased from 7.32 to 1.97 nmol/mg, indicating that the peroxyl radical induced the oxidation of rice protein. Fourier transform infrared spectroscopy indicated that the oxidation of the protein led to a decrease in α-helix and β-sheet motifs, and an increase in β-turn and random-coil motifs. As the extent of rice protein oxidation increased, the particle size of rice protein increased from 126 nm to 216 nm and the surface hydrophobicity decreased from 1053 to 568. Meanwhile, the wavelength of the maximum emission peak of intrinsic fluorescence was blue-shifted, and the intrinsic fluorescence intensity was decreased. Besides, the content of high-molecular aggregates in the molecular weight distribution of rice protein gradually increased. The results indicated that the oxidation of rice protein induced by peroxyl radicals changed the structure of rice protein, and formed oxidative aggregates.
