Identification of novel saponins from edible seeds of Japanese horse chestnut (Aesculus turbinata Blume) after treatment with wooden ashes and their nutraceutical activity.
Natural seeds of Japanese horse chestnut (Aesculus turbinata Blume) contain large amounts of mixed triterpenoidal saponins called escins. Recent studies have shown that escins have several biological activities including anti-inflammatory action and inhibitory effects on the absorption of ethanol and glucose. For the edible utilization of the seeds, natural seeds are usually treated with wooden ashes to remove harshness. Here, we found the novel compounds derived from escins in the edible seeds after the food processing with wooden ashes. The instrumental analyses revealed the chemical structures of escins and the derivatives. These compounds are identified as four types of deacetylescins Ia, IIa, Ib, and IIb as well as two types of desacylescins I and II. To determine their biological activity, the purified compounds were tested for their potential nutraceutical activity. The oral glucose tolerance test in mice revealed that a single oral administration of the isolated components of deacetylescins at a dose of 100 mg/kg was clearly effective in attenuating the elevation of blood glucose levels. The inhibitory effects of escins and their derivatives were in the order of escins>deacetylescins>desacylescins. Moreover, we found the inhibitory activity of those compounds on pancreatic lipase. Escins were the most potent in inhibiting the enzyme activity, and followed by desacylescins and then deacetylescins. Taken together, our results suggest the potential usefulness of novel saponins including deacetylescins and desacylescins from edible seeds as novel sources for nutraceutical foods with anti-obese effects.