Large yellow tea (LYT) belongs to yellow tea, which is made of mature tea leaves (<i>Camellia sinensis </i>(L.) O. Kuntze) with branches harvested by machine in the summer and autumn. It has a special manufacturing process of high-temperature (140-150 °C, 15 min) roasting. Scarce research concerned the chemical composition and bioactivities of LYT. The effects of roasting process on tea polyphenols and α-glucosidase inhibition were evaluated. Chemical analysis showed contents of epi-catechins decreased after roasting, while nonepi-catechins had several times elevation. The roasted tea sample was prior to untreated one in α-glucosidase inhibition. The inhibition effect on α-glucosidase weakened sharply after removing catechins from LYT infusion by polyvinylpolypyrrolidone (PVPP). As the main heat-epimerized catechin, (-)-gallocatechin gallate (GCG) exhibited higher inhibitory effect and stronger affinity for α-glucosidase than its corresponding epimer [(-)-Epigallocatechin gallate, EGCG]. This outcome also confirmed by molecular docking, GCG had lower binding energy with α-glucosidase. These results suggested that roasting process is critical for improving the hypoglycemic effect of LYT by epimerization of epi-catechins.

Roasting process improves the hypoglycemic effect of large yellow tea by enhancing the inhibition effect of epimerized catechins on α-glucosidase

256th National Meeting (2018)

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