Antioxidant activities and structural characterization of flavonol O-glycosides from seeds of Japanese horse chestnut (Aesculus turbinata BLUME)

We attempted to evaluate the contents and distribution of antioxidants in the whole seeds, seed shells, and peeled seeds of the Japanese horse chestnut. The seed shells exhibited the highest antioxidant activities due to the presence of highly polymeric proanthocyanidins as we have reported recently. On the other hand, the peeled seeds predominantly contained flavonols such as quercetin and kaempferol at a high level of 66.7% of total polyphenols, also contributing to the predominant antioxidant activities. The instrumental analysis of the extract from the whole seeds revealed the identification of eight flavonol O-glycosides, including six compounds with quercetin and two species with kaempferol as aglycones. The isolated species exhibited different antioxidant activities depending on the types of aglycones, glycosides, and acylated moieties. The results indicate that the peeled seeds are a good source of flavonol O-glycosides serving as antioxidants to be used for food additives and dietary supplements.