Cocoa brew inhibits in vitro α-glucosidase activity: The role of polyphenols and high molecular weight compounds

Cocoa brew showed a dose-dependent inhibitory activity against α-glucosidase (IC50 7.87 mg/mL). The cocoa brew was fractionated by ultrafiltration in a low molecular weight fraction (LMW <10 kDa) and two melanoidin-rich fractions called high molecular weight (HMW > 30 kDa) and intermediate molecular weight (IMW 10-30 kDa) fractions. All fractions tested caused some inhibition with IMW that was the most active (IC50 2.37 mg/mL). LMW fraction was separated with Sephadex LH-20 in an unbound (containing monomeric and dimeric catechins) and a bound fraction. All the inhibitory activity was recovered in the unbound fraction. All the phenolic compounds identified with HPLC showed α-glucosidase inhibitory activity. IMW and HMW fractions were fractionated by ethanol precipitation. The fractions from IMW precipitated with 75 and 25% ethanol were found to contain power inhibitors of α-glucosidase activity (IC50 0.87 and 1.01 mg/mL, respectively). In the HMW sample, the fractions precipitated with 50 and 75% ethanol were found to be active against α-glucosidase activity. Most of the inhibitory activity against α-glucosidase of cocoa brew was due to the LMW fraction (56%) whereas IMW and HMW contributed for about 47% of the inhibitory activity. This study suggests that different components of cocoa may influence α-glucosidase activity.