The extraction of polysaccharide from Laminaria japonica residue by citric acid and study on antioxidant activities and structural characteristics

Laminaria japonica residue was used as the material to obtain polysaccharide by the citric acid extraction, and the antioxidant activities and structural characteristics of the polysaccharide had been compared with those of polysaccharide obtained by direct citric acid extraction. The results showed that the yield of the polysaccharide was 7. 00%±0. 03%, and the antioxidant activities were similar with those of polysaccharide obtained by direct citric acid extraction, with the values of oxygen radical absorbance capacity, DPPH radical scavenging activity, ABTS radical scavenging activity and reducing power of 130. 13μmol Trolox/g, 18. 89μmol Trolox/g, 53. 58μmol Trolox/g and 37. 56μmol Trolox/g, respectively. Moreover, the value of ORAC was 2 times higher than that of BHT. Gel permeation chromatography analysis indicated that the polysaccharide comprised two components, the molecular weights were 310182u (2. 73%) and 30515u (97. 27%) separately. The infrared (IR) spectra analysis demonstrated that the polysaccharide had resemblant structure with that obtained by direct citric acid extraction.