College of Chemistry and Chemical Engineering, Neijiang Normal University, Neijiang 641100, China.
Sichuan Science and Technology Resources Sharing Service Platform of Special Agricultural Resources in Tuojiang River Basin, Neijiang 641100, China.
J Agric Food Chem. 2021 Feb 24;69(7):2306-2315. doi: 10.1021/acs.jafc.0c07337. Epub 2021 Feb 12.
In the present study, soy protein isolate (SPI) was noncovalently modified by (-)-epigallocatechin-3-gallate (EGCG), and its foaming, emulsifying, and antioxidant properties were all significantly increased. Fluorescence analysis revealed that the fluorescence quenching of SPI by EGCG was static quenching. EGCG mainly changed the folding state of SPI around Trp and Tyr residues, and the binding site was closer to Trp. UV-vis spectra further proved that more hydrophobic residues of SPI were exposed to a hydrophilic microenvironment. Circular dichroism spectra indicated that the contents of ordered structures were transforming into random coils with the reduce of α-helix, β-sheet, and β-turns by 3.8%, 2.0%, and 1.2%, respectively. Meanwhile, the binding stoichiometry of two molecules of EGCG per one molecule of SPI was obtained from isothermal titration calorimetry, and the interaction was a spontaneous endothermic process with a noncovalent complex preferentially formed. According to thermodynamic parameters and molecular docking model, hydrophobic force and hydrogen bonds were considered to be the main interaction forces between SPI and EGCG. Overall, after modification through the high affinity to EGCG, the structure of SPI became looser and exposed more active groups, thus resulting in an improvement of its foaming, emulsifying, and antioxidant properties.
在本研究中，大豆分离蛋白（SPI）通过（-）-表没食子儿茶素-3-没食子酸酯（EGCG）进行非共价修饰，其起泡、乳化和抗氧化性能均显著提高。荧光分析表明，EGCG 对 SPI 的荧光猝灭是静态猝灭。EGCG 主要改变了 SPI 中色氨酸和酪氨酸残基周围的折叠状态，结合部位更接近色氨酸。紫外可见光谱进一步证明，更多的 SPI 疏水性残基暴露在亲水微环境中。圆二色光谱表明，有序结构的含量随着α-螺旋、β-折叠和β-转角的减少分别转化为无规卷曲，分别减少了 3.8%、2.0%和 1.2%。同时，从等温热滴定实验中获得了两个 EGCG 分子与一个 SPI 分子的结合计量比，并且该相互作用是一个自发的吸热过程，优先形成非共价复合物。根据热力学参数和分子对接模型，疏水作用力和氢键被认为是 SPI 和 EGCG 之间的主要相互作用力。总的来说，经过与 EGCG 的高亲和力修饰后，SPI 的结构变得更加松散，暴露出更多的活性基团，从而提高了其起泡、乳化和抗氧化性能。
