Influence of preparation methods on the yield, components and antioxidant activities of polysaccharides from Palmaria palmata

The aim of this study was to clarify the influences of extraction methods and ethanolconcentrations of precipitation on the extraction ratios, components and antioxidant activities ofpolysaccharides from Palmaria palmate. Based on the DPPH/hydroxyl radicals scavenging tests, the order of antioxidant activities of extracts was A75 (microwave-assisted extraction (MAE) with 75% ethanol precipitation) > A0 (MAE without precipitation) > B75 (hot reflux extraction (HRE) with 75% ethanol precipitation) > B0 (HRE without precipitation). A75 was purified by anion-exchange chromatography and three fractions (F1 to F3) were obtained, and their antioxidant activities decreased in the order: F3 > F2 > F1. But F4 (the lyophilized supernatant of 75% ethanol precipitation of A0) showed the strongest activities among the crude polysaccharides and their fractions. The weaker activities of B0 than A0 (purity was50.97 ± 0.86% and the content of F3 was 23.21 ± 0.88%) was due to the coactions of lowerpurity (39.55 ± 0.70%), total lack of F3, and the stronger activity of A75 was owed to the higherpurity (60.31 ± 1.42%). The results indicated that MAE with ethanol precipitation possessed higher selectivity for polysaccharides from P. palmate than HRE and it was necessary to attach importance to study the bioactivities of minor components.   Key words: Palmaria palmata, polysaccharides, microwave-assisted extraction, heat-reflux extraction, ethanol precipitation, antioxidant activity.