Inhibitory effects of polyphenolic compounds from seed shells of Japanese horse chestnut (Aesculus turbinata blume) on carbohydrate-digesting enzymes

Abstract

Polyphenolic compounds were extracted with hot water from the seed shells of Japanese horse chestnut (Aesculus turbinata Blume) and then fractionated and separated into three fractions, Fl, F2 and F3 by a multi-step column chromatography procedure. The structures of the isolated fractions were analyzed by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry. Fl contained mainly low-molecular weight phenolic substances, whereas F2 and F3 consisted of polymeric proanthocyanidins (tannins) with the polymerization degrees of 19 and 23, respectively. To determine the type of interflavan linkage of polymeric tannins, F2 and F3 were subjected to thiolytic degradation with 1-dodecanethiol to give their dodecylsulflde derivatives. The resulting derivatives were analyzed by high-performance liquid chromatography followed by electrospray-ionization mass spectrometry. The tannins had doubly linked A-type interflavan linkages in addition to single B-type bonds. The isolated polyphenolic compounds inhibited α-glucosidases including maltase and sucrase, as well as α-amylase, in a dose-dependent manner. In particular, compared to the low-molecular weight F1 substances, the highly polymerized F2 and F3 were more potent inhibitors of α-amylase. Taken together, polyphenolic compounds from seed shells of Japanese horse chestnut are potentially useful as constituents for developing functional foods that suppress an abrupt increase in blood glucose level after eating due to the appreciable ability of these compounds to inhibit digestive enzymes of carbohydrates.