Abstract: The purpose of this study was to investigate the chemical composition and α-amylase inhibitory activity of the crude ethanol extract of tartary buckwheat and its fractions obtained by successive extraction with organic solvents of different polarities including petroleum ether, ethyl acetate and N-butyl alcohol. An ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) method in the negative ion mode was established to analyze the major constitutions in the extracts. Results showed that the majority of the extracts were the flavonoids rutin, quercetin, quercetin-3-rutinoglucoglucoside, isoquercetin and kaempferol-3-O-rutinoside as well as some phenols such as hydroxybenzoic?acid. The inhibition rate against α-amylase and the inhibition type were determined and fluorescence quenching experiments were used to study the α-amylase inhibitory activity of the extracts. Results revealed that the crude extract, and the ethyl acetate-soluble and N-butyl alcohol-soluble fractions all significantly inhibited α-amylase activity whereas the petroleum ether-soluble fraction could not. Therefore, it can be inferred that the inhibition of α-amylase by tartary buckwheat extracts likely resulted from the combined action of different fractions in a noncompetitive manner, as indicated by the kinetic analysis. Fluorescence quenching experiments revealed that the fluorescence of α-amylase was statically quenched as it formed a complex with the extracts of tartary buckwheat.

Key words: UPLC-Q-TOF-MS, extracts of tartary buckwheat, α-amylase, inhibition, fluorescence quenching