Water Chestnut (Trapa japonica Flerov.) Exerts Inhibitory Effect on Postprandial Glycemic Response in Rats and Free Radical Scavenging Activity in vitro

The α-glucosidase inhibitory and antioxidant effects of water chestnut (Trapa japonica Flerov.) were assessed to explore its possible use as an anti-diabetic agent. Methanol extracts of the fruit shell and meat of water chestnut were assayed for inhibitory activity against yeast α-glucosidase and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. Effect of fruit shell extract on postprandial glucose response was assessed. Compared with fruit meat, shell extract showed stronger inhibition against α-glucosidase with an IC?? of 273 ㎍/㎖. Oral administration of fruit shell extract (500 ㎎/㎏) significantly lowered the postprandial area under the glucose response curve to starch (1 g/㎏) in streptozotocin (STZ)-induced diabetic rats (p＜0.01). Compared with fruit meat, shell extract showed stronger scavenging activity against DPPH, with an IC?? of 27.1 ㎍/㎖. The results indicate that the fruit shell of water chestnut was effective in controlling postprandial hyperglycemia and exerted an antioxidant effect. Therefore, water chestnut may be useful in treating diabetes.