Abstract: Pu-erh tea is a unique fermented tea produced from the sun-dried leaves of large-leaf tea species (Camellia sinensis (Linn.) var. assamica (Masters) Kitamura) in Yunnan province of China. The special sensory characteristics and beneficial health effects of Pu-erh tea arise from the multitudinous chemical changes and transformations (oxidation, polymerization, condensation and decomposition) of polyphenolic constituents in sun-dried green tea leaves during the pile fermentation process. Recent studies have revealed that structural modification of polyphenols catalyzed by microbial extracellular enzymes during the pile fermentation of Pu-erh tea, such as methylation, glycosylation and other substitution patterns is an important pathway of polyphenol biotransformation in sun-dried green tea leaves, forming a wide variety of derivatives, which have been demonstrated in previous studies for their important influence on the flavor quality and bioactivity of Pu-erh tea. These compounds are marker ingredients and quality constituents in Pu-erh tea, and are of significant research interest. This paper reviews recent advances in research on chemical modification of polyphenols during the pile fermentation of Pu-erh tea.

Key words: Pu-erh tea, pile fermentation, polyphenols, derivatives, quality components