Effect of an extract from evening-primrose seeds on postprandial blood glucose level and its active components

An ethanol extract (EPE) was prepared from defatted seeds of Evening-prim rose (Oenothera biennis L.). In this study, we examined the effect of EPE on postprandial blood glucose level and its active components. Detected polyphenol components of EPE were penta-O-galloyl-beta-D-glucose (PGG) 2.7%, gallic acid 3.1%, (+) -catechin 3.4%, procyanidin B1 and procyanidin B3 1.5%. 41.4% of the total proanthocyanidin (PAC) was contained in EPE. Then, we examined the effect of these components of EPE on inhibitory action against alpha-glucosidase in vitro and on the postprandial blood glucose level using rats. The results suggested that 1) the suppression of postprandial hyperglycemia was caused by inhibition of alpha-glucosidase activity due to EPE, 2) PAC was the main active component of EPE.