Molecular Weight Controllable Degradation of Laminaria japonica Polysaccharides and Its Antioxidant Properties

In this study, molecular weight controllable degradation of algal Laminaria japonica polysaccharides（LPS） was investigated by ultrasound combined with hydrogen peroxide. Three main factors, i.e., ultrasonic power（A）, ultrasonic time（B）, and H_2O_2 concentration（C） were chosen for optimizing parameters by employing three-factors, three-levels BBD. The influence of degradation on structure change and antioxidant activities was also investigated. A second-order polynomial equation including molecular weight（Y） of Laminaria japonica polysaccharides and each variable parameter, i.e., ultrasonic power（A）, ultrasonic time（B）, and H_2O_2 concentration（C）, was established： Y=20718.67-4273.13A-4000.38B-1438.75C＋2333.25AB＋1511.00AC＋873.00BC＋2838.29A~2 ＋ 2490.79B~2＋873.04C~2. The equation regression coefficient value（R~2 = 0.969） indicated that this equation was valid. The value of the adjusted determination coefficient（adjusted R~2 = 0.914） also confirmed that the model was highly significant. The results of selected experimental degradation conditions matched with the predicted value. FT-IR spectra revealed that the structures of LPS before and after degradation were not significantly changed. Antioxidant activities of LPS revealed that low Mws possessed stronger inhibitory than the original polysaccharides. The scavenging effects on superoxide radicals was the highest when IC50 of crude LPS was 4.92 mg mL~（-1） and IC50 of Mw 18.576 KDa was 1.02 mg mL~（-1）, which was fourfold higher than initial polysaccharide.