Carboxymethyl-kappa-carrageenan derivatives synthesized from kappa-carrageenan of the red alga Kappaphycus striatus cultivated in Vietnam: Characterization, structure and biological activity

Carboxymethyl-kappa-carrageenans (CMKCs) were synthesized from kappa-carrageenan extracted from the red alga Kappaphycus striatus with different molar ratios of monochloroacetic acid (MCA) in the presence of sodium hydroxide. The structural and physicochemical characteristic of products were evaluated by FT-IR, ¹³C and ¹H NMR spectra, degree of substitution, molecular weight, zeta potential and biological activity. Degree of substitution of carboxymethyl group in kappa-carrageenan ranged from 0.24 to 1.12. FT-IR and ¹³C NMR spectra proved the substitution of carboxymethyl group in kappa-carrageenan disaccharide unit. Molecular weight of CMKCs increased slightly while their zeta potential was lower compared to the parent kappa-carrageenan. CMKCs exhibited a slight difference in the lowest hemagglutination concentrations on native human blood group types and showed an increase in antioxidant activity. The results indicate that carboxymethyl-kappa-carrageenan derivatives from kappa-carrageenan of the cultivated red alga K. striatus could be a good source of materials for application.