Biochemical activities of N,O-carboxymethyl chitosan from squid cartilage

Chitosan was prepared by alkaline N-deacetylation of squid cartilage β-chitin and carboxymethylated derivatives with different degrees of substitution (DS) were synthesized. The DS of the derivatives calculated by pH titration were 0.64, 0.81, 1.0, 1.33 and 1.59. The antioxidant properties and bile acid binding capacity of the derivatives were studied in vitro. The carboxymethylation of chitosan caused enhancement of bile acid binding capacity. At 1 mg/mL, carboxymethyl chitosan (CMCS) showed a stronger scavenging effect than chitosan towards DPPH radicals. The CMCS scavenging effect on superoxide radicals was stronger than that of chitosan, and EC50 values were below 5.6 mg/mL. The effectiveness of reducing power correlated with the DS of CMCS. At 1.2 mg/mL, the ability of CMCS to chelate ferrous iron was 100%, whereas that of chitosan was only 22.34%. This suggested that carboxymethylation is a possible approach to obtain chitosan derivatives with desirable biological properties.