The mechanism study of enhanced antioxidant capacity: Intermolecular hydrogen bonds between epigallocatechin gallate and theanine in tea

The interactions between various substances in foods have significant implications for their nutritional values. The antioxidant capacity of polyphenols in tea can also be modulated by interactions with other substances. In this study, the intermolecular hydrogen bonds between epigallocatechin gallate (EGCG) and theanine, as well as the antioxidant capacity, were both analyzed and demonstrated. The results showed that the antiradical activity against DPPH• increased by approximate 2.4 %, and the relative cellular activity of PC12 cells in hydrogen peroxide increased by approximate 3.4 %, when appropriate theanine was added to EGCG. This phenomenon could be interpreted by the intermolecular hydrogen bonds between EGCG and theanine, which activated the phenol hydroxyl group of EGCG, inducing the departure of proton and electron. Therefore, the antioxidant capacity was enhanced. The proposed mechanism was verified by electrochemical methods and density functional theoretical calculations. Electrochemical methods confirmed the interactions between EGCG and theanine, and exhibited the shift of the redox peaks before and after the formation of hydrogen bonds. The HOMO-LUMO energy gap of EGCG obtained by density functional theoretical calculation was reduced after hydrogen bonding with theanine.