Phenolic Composition and alpha-Glucosidase Inhibition of Leaves from Chilean Bean Landraces

The MeOH:H2O (7:3) extracts of leaves from Chilean bean landraces were assessed for total phenolic (TP), total flavonoid (TF), total proanthocyanidin (TPA) content, antioxidant capacity (ORAC, FRAP, TEAC, CUPRAC, DPPH) and the inhibition of enzymes associated with metabolic syndrome (alpha-glucosidase, alpha-amylase, pancreatic lipase). The chemical profiles were analyzed by HPLC-DAD. Higher antioxidant activity in the ORAC and CUPRAC assay was found for the landrace Coscorron, and the best effect in the TEAC for Sapito, respectively. The main phenolics were flavonol glycosides and caffeic acid derivatives. The extracts presented strong activity against alpha-glucosidase, but were inactive towards alpha-amylase and pancreatic lipase. The leaf extract from the Sapito landrace was fractionated to isolate the main alpha-glucosidase inhibitors, leading to caffeoylmalic acid with an IC50 of 0.21 mu g/mL. The HPLC fingerprints of the leaves differentiate three groups of chemical profiles, according to the main phenolic content. A significant correlation was found between the alpha-glucosidase inhibition, the content of caffeoylmalic acid (r = -0.979) and kaempferol 3-O-beta-D-glucoside (r = 0.942) in the extracts. The presence of alpha-glucosidase inhibitors in the leaves of Chilean beans support their potential as a source of bioactive compounds.