Pomegranate ellagitannins inhibit alpha-glucosidase activity in vitro and reduce starch digestibility under simulated gastro-intestinal conditions

摘要

Pomegranate extract was tested for its ability to inhibit alpha-amylase and alpha-glucosidase activity. Pomegranate extract strongly inhibited rat intestinal alpha-glucosidase in vitro whereas it was a weak inhibitor of porcine alpha-amylase. The inhibitory activity was recovered in an ellagitannins-enriched fraction and punicalagin, punicalin, and ellagic acid were identified as alpha-glucosidase inhibitors (IC50 of 140.2, 191.4, and 380.9 mu mol/L, respectively). Kinetic analysis suggested that the pomegranate extract and ellagitannins inhibited alpha-glucosidase activity in a mixed mode. The inhibitory activity was demonstrated using an in vitro digestion system, mimicking the physiological gastro-intestinal condition, and potatoes as food rich in starch. Pre-incubation between ellagitannins and alpha-glucosidase increased the inhibitory activity, suggesting that they acted by binding to alpha-glucosidase. During digestion punicalin and punicalagin concentration decreased. Despite this loss, the pomegranate extract retained high inhibitory activity. This study suggests that pomegranate ellagitannins may inhibit alpha-glucosidase activity in vitro possibly affecting in vivo starch digestion.