Carboxymethylation of polysaccharides from Auricularia auricula and their antioxidant activities in vitro

The chemical carboxymethylated polysaccharide (CMAAP), which is derived from the poorly water-soluble, crude polysaccharide from Auricularia auricula (AAP), was prepared. The degree of substitution of CMAAP was 0.857, and its solubility in water reached 0.6 mg/mL, much higher than that of AAP (0.1 mg/mL). One fraction, CMAAP22, was purified. Chemical analysis indicated that CMAAP22 was composed of mannose and glucose in a ratio of 1.06:1 with a molecular weight of 3.4 × 10(6)Da. IR spectra and (13)C NMR spectra indicated that the C2, C4 and C6 positions were partially substituted by -CH(2)COOH. AFM revealed that CMAAP22 was spherical particle structure with a diameter of 80-300 nm. Moreover, the antioxidant activity of CMAAP22 was improved, nearly twice as much as that of the AAP, especially in the scavenging of DPPH and ABTS+.