High Performance Liquid Chromatography and Metabolomics Analysis of Tannase Metabolism of Gallic Acid and Gallates in Tea Leaves

Tannase
(E.C. 3.1.1.20) is hypothesized to be involved in the metabolism
of gallates and gallic acid (GA) in pu-erh tea fermentation. In this
work, we measured tannase in Aspergillus niger fermented
tea leaves and confirmed the production of fungal tannase during pu-erh
tea fermentation. A decrease in catechin and theaflavin gallates and
a significant increase in GA content and the relative peak areas of
ethyl gallate, procyanidin A2, procyanidin B2, procyanidin B3, catechin-catechin-catechin,
epiafzelechin, and epicatechin-epiafzelechin [variable importance
in the projection (VIP) > 1.0, p < 0.05, and
fold
change (FC) > 1.5] were observed using high performance liquid
chromatography
(HPLC) and metabolomics analysis of tea leaves fermented or hydrolyzed
by tannase. In vitro assays showed that hydrolysis
by tannase or polymerization of catechins increased the antioxidant
activity of tea leaves. In summary, we identified a metabolic pathway
for gallates and their derivatives in tea leaves hydrolyzed by tannase
as well as associated changes in gallate and GA concentrations caused
by fungal tannase during pu-erh tea fermentation.