Abstract: Polysaccharides from blackcurrant fruit (BFPs) were prepared by enzymatic treatment with a mixture of papain and pectinase. Two degraded polysaccharides (UM-15 and UM-30) were obtained by ultrasonic treatment of BFPs at a power of 700 W for 15 and 30 min, respectively. The physiochemical properties showed that the viscosity-average molecular mass and dynamic viscosity of the degraded polysaccharides were reduced compared to BFPs. However, their reducing sugar and uronic acid contents were increased, with UM-30 being higher than UM-15. Structural characterization by Fourier transform infrared spectroscopy, Congo red and iodine-potassium iodide tests showed that the natural and degraded polysaccharides exhibited similar characteristic absorption peaks, and they had no triple helix structure and possessed a complex chain structure. Antioxidant assays indicated that the degraded polysaccharides exhibited higher scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radical and nitrite ion and stronger lipid peroxidation-inhibitory activity than those of BFP, and the antioxidant activity of UM-30 was greater than UM-15. Within the experimental concentration range, the highest scavenging rates of DPPH, superoxide anion radical and nitrite ion by UM-30 were (90.18 ± 0.66)%, (71.43 ± 0.25)%, and (84.46 ± 1.43)%, respectively, and the maximum inhibition rate of lipid peroxidation was (65.83 ± 0.67)%. Thus, ultrasonic irradiation is an efficient and green method to improve the physicochemical properties and bioactivity of polysaccharides.

Key words: blackcurrant, polysaccharide, ultrasonic degradation, properties, bioactivity