Abstract: This study was implemented in order to explore the effect of ultrasound-assisted H2O2-Vitamin C (VC) degradation on ginseng polysaccharides (GPS). GPS were extracted from ginseng by water extraction followed by alcohol precipitation and separated and purified by DEAE-52 cellulose and Sephadex G-100 column chromatography. Fraction GPS-1A was degraded into a low-molecular-mass polysaccharide DGPS-1A under the following conditions: sample concentration 4.2 mg/mL, H2O2-VC concentration 10.3 mmol/L and ultrasound power 1 006 W. Meanwhile, the structural characteristics of GPS-1A and DGPS-1A, their inhibitory effects on major starch digestive enzymes and their antioxidant activities were studied. The results showed that the relative molecular masses of GPS-1A and DGPS-1A were 135 and 77.8, respectively, but the composition of monosaccharides did not change after ultrasound-assisted H2O2-VC degradation. The Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra also showed that the major functional groups of the polysaccharide were not damaged after degradation. In addition, DGPS-1A showed stronger in vitro antioxidant and hypoglycemic activities than did GPS-1A. At the maximum concentration (6 mg/mL), the inhibition rates of α-glucosidase and α-amylase and the scavenging rates of 1,1-diphenyl-2-trichrophenylhydrazine radical (DPPH) and hydroxyl radical by DGPS-1A were (90.83 ± 3.04)%, (78.03 ± 2.29)%, (89.56 ± 1.17)% and (76.85 ± 1.63)%, compared to only (65.16 ± 2.53)%, (54.04 ± 1.97)%, (31.77 ± 2.42)% and (30.85 ± 2.29)% with GPS-1A, respectively. Moreover, the reducing power of DGPS-1A was 2.03 times higher than that of GPS-1A. These results indicate that ultrasound-assisted H2O2-VC degradation of ginseng polysaccharides has potential application in the development of functional foods with antioxidant and hypoglycemic activities.

Key words: ginseng polysaccharides; extraction and purification; degradation; structure; biological activities