Inhibitory characteristics of flavonoids from soybean (Glycine max [L.] Merr.) leaf against pancreatic lipase

Several reports on obesity have targeted to determine inhibitors of pancreatic lipase (EC 3.1.1.3, PL), which plays a major role in the digestion of dietary lipids, from natural sources. This study aimed to suggest soybean leaf, a soybean by-product, as a novel source of PL inhibitors and investigate PL inhibitory characteristics of the active constituents. Fluorometric lipase assay revealed that the soybean leaf extract has inhibitory activity against PL. UPLC-MS/MS analysis identified flavonoids (genistein, daidzein, formononetin, taxifolin, diosmetin, and glycitein) as active constituents. Among them, diosmetin and glycitein were novel PL inhibitors with half-maximal inhibitory concentrations of 131.9 ± 8.4 and 127.5 ± 7.4 μM, respectively. The inhibition mode of diosmetin and glycitein were deteremined as competitive type from the enzyme kinetic study, supported by molecular docking simulation. Their bindings to PL were confirmed to follow the static quenching process in fluorescence analysis. Collectively, the results of present study indicates soybean leaf and its flavonoids as a promising natural source for antiobesity functional food.