过氧自由基氧化对大米蛋白结构的影响

Effect of Oxidative Modification by Peroxyl Radical on the Structure of Rice Protein

采用不同浓度2,2’-盐酸脒基丙烷(AAPH)在有氧条件下热分解产生的过氧自由基代表脂质氧化过程中的脂质自由基,研究过氧自由基氧化对大米蛋白结构的影响。结果表明,当AAPH浓度从0增加至25 mmol/L,大米蛋白羰基和二硫键含量分别由3.77和13.88 nmol/mg增加至7.26和15.73 nmol/mg,游离巯基由7.32 nmol/mg下降至1.97 nmol/mg,表明过氧自由基诱使大米蛋白发生了氧化;傅里叶红外分析表明蛋白质氧化导致大米蛋白α-螺旋和β-折叠含量下降,β-转角和无规卷曲含量上升。随着大米蛋白氧化程度的增加,大米蛋白粒径从126 nm增加到216 nm,表面疏水性从1053下降到568,内源荧光最大荧光峰位蓝移,内源荧光强度下降,并且在分子量分布图中高分子量聚集体含量逐渐增加。表明过氧自由基氧化修饰导致大米蛋白结构改变和形成氧化聚集体。

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.