EGCG与乳清蛋白相互作用的光谱分析

Spectral Analysis of the Interaction between EGCG and Whey Protein Isolate

探究表没食子儿茶素没食子酸酯(epigallocatechin gallate,EGCG)与乳清分离蛋白(whey protein isolate,WPI)间的相互作用。测定不同pH值与不同离子浓度条件下WPI的紫外吸收光谱、导数光谱和荧光光谱,利用SternVolmer方程判断荧光猝灭机制,采用位点结合模型公式计算结合常数和结合位点数。结果表明,紫外吸收光谱和导数光谱结果显示EGCG改变了WPI中酪氨酸和色氨酸残基所处的微环境,使WPI的分子构象发生了变化。荧光光谱结果显示EGCG可以有规律地猝灭WPI的内源荧光,猝灭机理为静态猝灭,EGCG与WPI结合常数在pH 2.0~9.0范围内随pH的增大先减小后增大,在离子浓度0.10 mol/L^0.20 mol/L范围内随离子浓度的增大而增大,结合位点数约为1。EGCG与WPI间存在静电相互作用。

The interaction between epigallocatechin gallate(EGCG)and whey protein isolate(WPI)were studied. The UV absorption spectra,derivative spectra and fluorescence spectra of WPI at different pH and ion concentration were measured. The fluorescence quenching mechanism was determined by Stern-Volmer equation. The binding constants and the number of binding sites were calculated by the site binding model formula. UV absorption spectra and derivative spectra showed that EGCG changed the microenvironment of tyrosine and tryptophan residues in WPI and altered the molecular conformation of WPI. The fluorescence spectra showed that EGCG could regularly quench the intrinsic fluorescence of WPI. The quenching mechanism was static quenching. The binding constant of EGCG and WPI decreased first and then increased with the increase of pH value in the range of 2.0-9.0,and increased with the increase of ion concentration in the range of 0.10 mol/L-0.20 mol/L,and the number of binding sites was about 1. The above results indicated that there was an electrostatic interaction between EGCG and WPI.