College of Food Science, South China Agricultural University, Guangzhou 510642, Guangdong, China.
College of Food Science, South China Agricultural University, Guangzhou 510642, Guangdong, China.
Food Chem. 2022 Aug 1;384:132533. doi: 10.1016/j.foodchem.2022.132533. Epub 2022 Feb 23.
Free radical grafting is a promising method that has been used to modify whey protein isolate (WPI) using polyphenol and provides desirable functionalities, but the reaction mechanism is unclear. This work investigated the grafting mechanism of WPI - (-)-Epigallocatechin-3-gallate (EGCG) through experimental techniques and molecular docking. The results showed that only the ascorbic acid radical anion (Asc) is generated in the Asc/ HO system. Asc removed hydrogen atoms from amino and sulfhydryl groups, resulting in a decrease in their content. Cystine, proline, methionine, and histidine were discerned to be the grafting sites between WPI and EGCG for more sensitiveness. Furthermore, Asc and •OH changed the secondary structure of WPI, but Asc further induced oxidative deamination of amino acids. Therefore, the grafting mechanism is presumed that the Asc catches hydrogen atoms in protein-sensitive amino acids and generates macromolecular radicals that induce the formation of WPI-EGCG graft.
自由基接枝是一种很有前途的方法，它被用来修饰乳清蛋白分离物（WPI），用多酚提供理想的功能，但反应机制尚不清楚。本工作通过实验技术和分子对接研究了 WPI-(-)-表没食子儿茶素没食子酸酯（EGCG）的接枝机理。结果表明，在 Asc/HO 体系中只有抗坏血酸自由基阴离子（Asc）生成。Asc 从氨基和巯基上除去氢原子，导致其含量下降。半胱氨酸、脯氨酸、蛋氨酸和组氨酸被认为是 WPI 和 EGCG 之间的接枝位点，因为它们更敏感。此外，Asc 和 •OH 改变了 WPI 的二级结构，但 Asc 进一步诱导了氨基酸的氧化脱氨。因此，接枝机制被认为是 Asc 在蛋白质敏感氨基酸中捕获氢原子，并生成诱导 WPI-EGCG 接枝形成的大分子自由基。
