Ultrasonic degradation, purification and analysis of structure and antioxidant activity of polysaccharide from Porphyra yezoensis Udea

The chemical structure and antioxidant of natural and ultrasonic degraded polysaccharides from Porphyra yezoensis Udea was investigated. The degraded polysaccharide (PYPS_UD) was purified, and F2 (a homogeneous fraction) was obtained. FT-IR, ¹H and ¹³C NMR spectral analysis revealed that F2 have typical porphyran structure. It has a backbone of alternating (1 → 4)-3,6-anhydro-α-l-galactopyranose) units and (1 → 3)-linked β-d-galactose or (1 → 4)-linked α-l-galactose 6-sulfate units. The result ascertained ultrasound degradation did not change the main structure of polysaccharides in the test conditions. Antioxidant proved that the activity of scavenging superoxide and hydroxyl radical is F₂ > V_C > PSPY_UD > PSPY. It was possible that ultrasonic treatment is an effective way for enhancing PSPY's antioxidant activity ascribing to decreasing molecular weight of polysaccharides.