Effect and characterization of polysaccharides extracted from Chlorella sp. by hot-water and alkali extraction methods

This study characterized and compared the physicochemical properties and antioxidant activity of polysaccharides from Chlorella sp. extracted by hot-water extraction method at different temperatures (60–180 °C) and alkali extraction method at different alkali concentrations (0–4 %). Results showed that the dissolution percent of polysaccharides of the two methods reached maximum values of 71.19 % and 58.79 % at 120 °C and 4 % alkali concentration, respectively. All these polysaccharides contained the same monosaccharide components at different proportions. The molecular weight of polysaccharides extracted by alkali method were larger than that extracted by hot-water method. High temperature and alkali concentration both degraded polysaccharides into the lower molecules and destroyed the carboxyl group in polysaccharides. The polysaccharides from alkali method showed the better antioxidant activity, and the polysaccharide extracted by 1 % alkali concentration showed the highest antioxidant activity with 85.17 % (4 mg/mL) and 96.75 % (1 mg/mL) scavenging rates of DPPH and OH, respectively. This study concludes that the determination of the extraction condition of Chlorella polysaccharides should consider the great effect of physicochemical properties and antioxidant activity.