Abstract: The physicochemical properties and structure of Ulva pertusa polysaccharides before and after complexation with zinc ions were determined by gas chromatography-mass spectroscopy, gel permeation chromatography-multi-angle laser light scattering-refractive index detection, Congo-red test, ultraviolet-visible (UV-VIS) spectroscopy, infrared spectroscopy, X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy. The inhibitory effect of the polysaccharide-zinc complex on α-glucosidase and α-amylase was investigated. Results showed that Ulva pertusa polysaccharides were composed of rhamnose, fucose, xylose, mannose, glucose and galactose, with a molar ratio of 1.00:0.06:0.93:0.45:2.29:0.07. After the complexation reaction, the molecular mass and total sugar content of the polysaccharides were decreased, and the triple-helical structure disappeared. Zn2+ reacted with –COO-, –CH3, –OSO3- in the polysaccharides. The surface morphology of Ulva pertusa polysaccharides changed apparently, the molecular size was decreased, and the molecular aggregation ability was enhanced after complexation with zinc ions. The inhibitory effect of Ulva pertusa polysaccharides-zinc complex on α-glucosidase and α-amylase was stronger than that of the native polysaccharides. These results confirmed that the structure of Ulva pertusa polysaccharides changed obviously after complexation with zinc ions, and the hypoglycemic activity in vitro was enhanced.

Key words: Ulva pertusa polysaccharide-zinc complex, structural characterization, hypoglycemic activities in vitro