Properties of Polyphenols in Hot Water Extract of Water Chestnut Husk and Suppressive Effect on Postprandial Blood Glucose Elevation in Humans

Abstract

In this study, we aimed to investigate the properties of polyphenols in the husk of the "water chestnut", which is an aquatic plant, and effects on postprandial blood glucose levels in humans. We prepared a hot water extract of the husk of the Japanese water chestnut ( Trapa japonica ) , and investigated the content of polyphenols in the extract and their stability against heat. The result showed that the total polyphenol content in the hot water extract of water chestnut was approximately ２ ０ ０!/１ ０ ０!, and the total content of polyphenols (eugeniin, １, ２, ３, ６-tetra-O-galloyl-β -Dglucopyranose ( TGG ) and trapain ) exclusive to water chestnut was approximately ２ ０! /１ ０ ０! . Eugeniin and TGG were observed to be stable against heat ; however, trapain was sensitive to heat (８ ０℃ or higher) . Twenty-one healthy volunteers drank water or the hot water extract of water chestnut husk(２ ０ ０!) , and were subjected to a cooked rice load test. The group that consumed the hot water extract of water chestnut exhibited significant suppression in blood glucose elevation ２ ０ and ３ ０ minutes after meal. This was speculated to be due to the inhibitions of carbohydrase activity and glucose uptake into the small intestine by the polyphenols of water chestnut husk.Key words：water chestnut, polyphenols, suppressive effect on blood glucose elevation, inhibitory effect of carbohydrase, Caco-2 cells ヒシ，ポリフェノール，血糖値上昇抑制作用，糖質分解酵素の阻害活性，Caco-２細胞

Effects of Polyphenols from Water Chestnut (Trapa japonica) on Lipid Metabolism

“…Trapain, which is named after the scienti c name of water chestnut, is a rare polyphenol that was previously believed to be found only in castor beans [12]. We have previously investigated the functionalities of water chestnut polyphenols (WCPs) and revealed their high antioxidant activities and inhibition of postprandial blood glucose elevation [11,13]. However, their functionality against metabolic syndrome has not been reported to date.…”