Characterisation of the hypoglycaemic activity of glycoprotein purified from the edible brown seaweed, Undaria pinnatifida

Seaweed has been reported to control postprandial hyperglycaemia in various ways. We recently reported the characterisation of a glycoprotein from Undaria pinnatifida (UPGP) with antioxidant activities. In this study, we characterised the hypoglycaemic effect of UPGP through monitoring alpha-glucosidase inhibition and glucose transport across yeast cell. Dose-dependent inhibitions of UPGP against yeast and rat intestinal alpha-glucosidase were observed with IC50 values of 0.11 and 0.29 mg mL(-1), respectively. UPGP showed stable inhibition following incubation at different temperatures and metal ions. Regarding bioaccessibility, the inhibition was decreased slightly during the gastric phase compared to undigested UPGP, with an increase during the duodenal phase. Kinetics and membrane dialysis revealed mixed and reversible inhibition, respectively. Furthermore, UPGP with acarbose showed synergistic inhibition against alpha-glucosidase, and UPGP increased the rate of glucose transport across the yeast cell. In conclusion, our study demonstrated that UPGP may be used as bioaccessible food additives for controlling postprandial hyperglycaemia.