Abstract: Three extraction methods, including hot water extraction (HWE), ultrasonic-assisted extraction (UAE) and multiple enzymatic extraction (MEE), were used to extract polysaccharides from Laminaria japonica. Extraction conditions were optimized using one-factor-at-a-time and orthogonal array design methods, and the physicochemical properties and antitumor activity of the polysaccharides were comparatively analyzed. The results showed that the optimized HWE conditions were as follows: temperature 85 ℃, extraction time 5 h, and solid to solvent ratio 1:80 (g/mL); the optimized UAE conditions were ultrasonic power 500 W, extraction time, 10 min, and solid to solvent ratio 1:90 (g/mL); the optimized MEE conditions were papain 75 U/g, pectinase 15 000 U/g, cellulase 108 000 U/g, pH 5, temperature 50 ℃, solid to solvent ratio 1:70 (g/mL), and extraction time 3 h. Under the above conditions, the average yield of polysaccharides was 5.97%, 5.81% and 14.29%, respectively. There were significant effects of different extraction methods on the polysaccharide composition. The solubility of the polysaccharides obtained by MEE was significantly better than those obtained with HWE and UAE. All the polysaccharides contained a small amount of protein or polypeptide, and had three-strand helical structures. MTT assay showed that the three polysaccharides exhibited different antitumor activities, among which the polysaccharides obtained by UAE showed the strongest inhibitory effect on human lung cancer cell A549 while the polysaccharides extracted by CEE displayed the strongest inhibitory effect on human breast cancer cell line MCF-7.

Key words: Laminaria japonica, polysaccharide, extraction methods, physicochemical characteristics, antitumor activity