Effects of galloyl group on the astringency perception of epigallocatechin gallate and epigallocatechin

The astringency in green tea primarily originates from gallate-type and non-gallate-type catechins. Epigallocatechin gallate (EGCG) is a gallate-type catechin, which has a strong astringency and is the most abundant catechin in tea. Unlike EGCG, epigallocatechin (EGC) has one fewer galloyl group on the C3 oxygen atom and exhibits a weaker astringency. Taking EGCG and EGC as representative catechins, this study investigated the effects of the galloyl group on their astringency. The interactions of EGCG and EGC with salivary proteins were qualitatively and quantitatively analyzed using fluorescence spectroscopy, isothermal titration calorimetry, and molecular docking. The surface roughness and viscoelasticity of the salivary film were then studied to relate the molecular interactions and perceived astringency. Additionally, the bindings of EGCG and EGC to astringency receptor proteins were also simulated. The results revealed that the galloyl group enabled the EGCG-promoted aggregation of salivary proteins, resulting in a stronger astringency through both tactile and gustatory pathways. In contrast, EGC exhibited a weaker astringency only through the gustatory pathway.