Continuous extraction optimization, molecular structures and antioxidant activities of polysaccharide from Gracilariopsis lemaneiformis using liquid-phase pulsed discharge

The optimization of continuous extraction, molecular structures and antioxidant activities of polysaccharide from Gracilariopsis lemaneiformis using liquid-phase pulsed discharge (LPD) were investigated and compared with maceration extraction (ME). The maximum polysaccharide yield of LPD (147.94 +/- 2.95 mg/g) was obtained with 79 min using the single-factor experiments under the optimum conditions: Electric-field strength of 80 kV/cm, ratio of water to solid of 40 mL/g and flow velocity of 14 mL/min, which was more than that of ME (140.19 +/- 1.23 mg/g) with 300 min. The structural characteristics of GLP(LPD) and GLP(ME) such as the carbohydrate, protein and sulfuric radical contents, monosaccharide composition, molecular weight, FT-IR spectra, NMR spectra were determined, and their antioxidant activities were also studied by the assay of scavenging ability of hydroxyl radical and DPPH radical. The results indicated that the structural characteristics of GLP were not affected by LPD and GLP(LPD) had the better antioxidant activities than GLP(ME). This study showed that LPD could be considered an alternative way to improve the yields of active ingredients and antioxidant activities of extracts.