ANTI-DIABETIC POTENTIAL OF PHENOLIC COMPOUNDS: A REVIEW

Starch is the main carbohydrate in human nutrition. Starch digestibility can vary from a rapid digestion to indigestibility. Therefore, postprandial glycaemic control in type 2 diabetics is of great interest in the context of worldwide health concerns. Although powerful synthetic inhibitors of starch digestive enzymes, such as acarbose, are available to control postprandial hyperglycemia, plant-based enzyme inhibitors are potentially safer. Natural enzyme inhibitors, such as wheat albumin, the Phaseolus vulgaris alpha-amylase inhibitor, and several phenolic compounds, have the potential to serve as a remedy against hyperglycemia-induced chronic diseases. The inhibition of alpha-amylase and alpha-glucosidase is mediated by different phenolics found in varieties of raspberry. Maltase inhibitory activities of chebulagic acid and chebulinic acid from fruit of Terminalia chebula are comparable to that of acarbose. The Nepalese herb Pakhanbhed (Bergenia ciliata) phenolics, (-)-3-O-galloylepicatechin and (-)-3-O-galloylcatechin, showed effective inhibition against starch digesting enzymes. In separate studies, oral administration of starch and maltose with persimmon (Diospyros kaki) leaf tea proanthocyanidins [containing (-)-epigallocatechin-3-O-gallate] and black/bitter cumin (Centratherum anthelminticum) seed phenolics, respectively, resulted in a significant and dose-dependent decrease in the blood glucose level in Wistar rats. Co-application of phenolics with synthetic enzyme inhibitors may reduce the effective dose of synthetic inhibitors required in the regulation of starch digestion. Several phenolic compounds might be useful functional food components and could contribute to manage both hyperglycemia and proper cellular redox status. Human dose-selecting studies and well-controlled long-term human studies would help to optimize the beneficial effects of phenolic compounds.