Preparation and Biological Activities of Low Molecular Weight Brown Algae

The polysaccharide was degraded by ascorbic acid and hydrogen peroxide, and the optimal degradation conditions were obtained by the index of DPPH free radical scavenging rate. Then the degradation products were classified by ultrafiltration to obtain different molecular weight components, and their activities were analyzed. The optimal degradation conditions were H₂O₂-V_C 20 mmol/L, 45 ℃ and 3 h. Under these conditions, the DPPH free radical scavenging rate reached 61.23%, and the yield of degradation products was 73.16%. Electrophoretic results showed that the bands of the degraded polysaccharides were obviously in the low molecular weight region. Then the degradation products were classified into four different molecular weight fractions, as <5 kDa, 5~10 kDa, 10~30 kDa and >30 kDa by ultrafiltration. There were significant differences among the molecular weight segments (P<0.05), especially the <5 kDa component (main component 2.140×10³ Da, 29.6%) had the best biological activity. The DPPH free radical scavenging rate was 59.27%, and the moisture retention rate was 75.75% after 60 h, the tyrosinase inhibition rate was 65.28%. The content of uronic acid of the <5 kDa component decreased slightly compared with polysaccharides. The results could provide theoretical basis for the application of polysaccharides in functional food and other fields.