Abstract: In this paper, a polysaccharide from Porphyra yezoensis (PSPY) was prepared by water extraction followed by alcohol precipitation and was degraded by a combination of hydrogen peroxide and ascorbic acid. Based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, the optimum degradation conditions were established by one-factor-at-a-time method combined with response surface methodology as follows: both H2O2 and VC concentrations 4.1 mmol/L, temperature 52.4 ℃, and reaction time 2.1 h. The molecular masses of PSPY and the degraded polysaccharide (DPSPY) were 452 and 17 ku, respectively. The contents of total sugar and sulfate in DPSPY increased and protein content decreased relative to PSPY. Fourier transform infrared spectroscopic analysis revealed no significant structural different between PSPY and DPSPY. DPSPY was more biologically active than PSPY in terms of in vitro antioxidant activity, bile salt binding capacity and cellular immunoregulatory activity. This study provides the theoretical basis for the deep processing and product development of PSPY.

Key words: Porphyra yezoensis polysaccharide; degradation; bile salt; antioxidant activity; immunoregulatory activity