pH值偏移处理对油莎豆蛋白结构及乳化性质的影响

Effect of pH-shifting Treatment on the Structure and Emulsifying Properties of Cyperus esculentus L.Protein

采用傅里叶变换红外光谱、荧光光谱、紫外光谱探究pH值偏移处理对油莎豆蛋白结构的影响,同时结合表面疏水性、溶解度、浊度及粒径的变化进一步探究pH值偏移处理对油莎豆蛋白乳化性质的影响。结果表明:随pH值升高,油莎豆蛋白二级结构中β-折叠相对含量降低,α-螺旋相对含量显著增加,β-转角和无规卷曲相对含量也略有增加。蛋白平均粒径在碱性条件下随pH值升高而减小,蛋白粒度分布逐渐从双峰分布转变为单峰分布,表明蛋白质可以更均匀地分散在溶液体系中。通过荧光光谱与紫外光谱分析可知pH值偏移处理使蛋白分子构象发生了改变,在碱性条件下蛋白分子内部多肽链部分展开,疏水基团暴露,蛋白结构变得更加舒展。随pH值升高,蛋白浊度显著降低,说明蛋白粒子更加分散。蛋白表面疏水性及乳化性质随pH值升高先降低后增加,说明碱性条件下pH值升高,蛋白结构展开,包裹在蛋白分子内部的疏水基团暴露出来,表面活性增强,乳化性升高。研究结果说明pH值偏移处理能够导致油莎豆蛋白结构改变,同时引起其乳化性质的变化。

The effect of pH-shifting treatment on the structure of Cyperus esculentus L.protein was studied by Fourier infrared spectroscopy,fluorescence spectroscopy,UV absorption spectroscopy and 8-anilino-1-naphthalene sulfonate(ANS)fluorescence probe emission spectroscopy.Furthermore,the effect on the emulsifying properties of C.esculentus L.protein was analyzed by measuring changes in the surface hydrophobicity,solubility,turbidity and particle size.The results showed that the content ofβ-sheet decreased,the relative content of a-helix increased significantly and the contents ofβ-turn and random coil increased slightly as the pH increased.The average particle size of the protein decreased with increasing alkaline pH,the particle size distribution gradually changed from bimodal to monomodal,indicating that more uniform dispersion of the protein.Fluorescence and UV absorption spectroscopy showed that pH-shifting treatment resulted in protein conformational changes;the polypeptide chains in the protein molecule were partially folded,hydrophobic groups were exposed,and the protein structure became more stretched under alkaline pH conditions.As the pH increased,the turbidity decreased significantly,indicating that the protein molecule became more dispersed.The surface hydrophobicity and emulsion stability of the protein first decreased and then increased with increasing pH,indicating that the protein structure was unfolded with increasing alkaline pH.In addition,hydrophobic groups buried inside the protein molecules became exposed,accompanied by an increase in the surface activity and emulsifying activity.These results showed that pH-shifting treatment could change the structure and emulsifying properties of C.esculentus L.protein.