Carboxymethyl Kappa Carrageenan Derivatives Synthesized from Kappa Carrageenan of the Red Alga Kappaphycus Striatus Cultivated in Vietnam: Characterization, Structure and Biological Activity

Abstract Carboxymethyl kappa carrageenans (CMKCs) have been 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 wase evaluated by FT-IR, 13 C and 1 H 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 13 C 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 red alga K. striatus cultivated could promise be a good source of materials for application as carriers.