In order to contribute to improve knowledge about the actions of Camellia sinensis extracts on starch digestion,
several varieties were compared. The latter were green, oolong, white, black, and purple teas. The results are
hoped to contribute to our understanding of the mode of action and potency of the various tea preparations as
possible adjuvants in the control of post-prandial glycemia. The extracts were prepared in way similar to their
form of consumption. All extracts decreased starch digestion, but the purple tea extract was the strongest inhibitor,
their inhibitory tendency started at the dose of 50 mg/kg and was already maximal with 250 mg/kg.
Maltose tolerance was not significantly affected by the extracts. Glucose tolerance was not affected by purple tea,
but black tea clearly diminished it; green tea presented the same tendency. Purple tea was also the strongest
inhibitor of pancreatic α-amylase, followed by black tea. The green tea, oolong tea, and white tea extracts tended
to stimulate the pancreatic α-amylase at low concentrations, a phenomenon that could be counterbalancing its
inhibitory effect on starch digestion. Based on chemical analyses and molecular docking simulations it was
concluded that for both purple and black tea extracts the most abundant active component, epigallocatechin
gallate, seems also to be the main responsible for the inhibition of the pancreatic α-amylase and starch digestion.
In the case of purple tea, the inhibitory activity is likely to be complemented by its content in deoxyhexosidehexoside-
containing polyphenolics, especially the kaempferol and myricetin derivatives. Polysaccharides are
also contributing to some extent. Cyanidins, the compounds giving to purple tea its characteristic color, seem not
to be the main responsible for its effects on starch digestion. It can be concluded that in terms of postprandial
anti-hyperglycemic action purple tea presents the best perspectives among all the tea varieties tested in the
present study.
This work was financially supported by grants from the Conselho
Nacional de Desenvolvimento Científico e Tecnológico (CNPq-304090/
2016-6), Coordenação do Aperfeiçoamento de Pessoal do Ensino Superior
(CAPES) and Fundação Araucária (53/2019). The authors are
grateful to the Foundation for Science and Technology (FCT, Portugal)
for financial support through national funds FCT/MCTES to CIMO
(UIDB/00690/2020) and through the institutional scientific employment
program-contract for L. Barros and M.I. Dias contracts. This work
was also funded by the European Regional Development Fund (ERDF)
through the Regional Operational Program North 2020, within the scope
of Project Mobilizador ValorNatural®: Norte-01-0247-FEDER-024479
and GreenHealth: Norte-01-0145-FEDER-000042.
