Effect and mechanism of calcium ions on the astringency in green tea infusion and epigallocatechin gallate solution: An in vitro oral soft tribology study

In this study, the effect of calcium ions (Ca²⁺) on the astringency sensation in green tea infusion was explored using sensory evaluation, in vitro oral soft tribology, and targeted metabolomics. Ca²⁺ enhanced the astringency intensity (from 2 to 6) and the turbidity (from 10.0 to 83.3), and decreased the particle size (from 1468.0 to 817.65) in cold-brewing tea. Catechins influenced the astringent sensation in the presence of Ca²⁺ and the content of (−)-Epicatechin, (−)-Epigallocatechin, and (−)-Epigallocatechin gallate (EGCG) solution in green tea infusion after oral processing all reduced. The friction coefficient of hot-brewed tea (μ, 1.6–2.8) was greater than that of cold-brewed tea (μ, 1.0–2.6), and EGCG increased with the enlarged Ca²⁺ concentrations. Ca²⁺ increased the astringency mainly through catechins and saliva lubrication. The in vitro soft oral tribology could be usefully explored the enlarged astringency sensation by Ca²⁺, and applied to the astringency regulation of beverages.