Extraction and characterisation of sodium alginate from the southern African seaweed Ecklonia maxima

Abstract

Ecklonia maxima is an endemic South African seaweed with numerous commercially valuable compounds, including sodium alginate. This polysaccharide contains 1,4-linked β-D-mannuronic (M) and α-L-guluronic acid (G) residues, and has enormous health and food applications and benefits for biomedicine. In this study, acid extraction of sodium alginate from Ecklonia maxima was performed, and its chemical and physical properties were compared with commercial sodium alginate. A yield of 58.7 % (w/w of dry alga) sodium alginate was recovered from the seaweed. As expected, Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopic analyses of sodium alginate revealed the presence of M and G residues in the polysaccharide. Circular dichroism (CD) spectroscopy revealed an M/G ratio of 1.86 from the extracted sodium alginate. The viscosity average molecular weight of sodium alginate was 429 kDa using the Mark–Houwink–Sakurada equation. Three-dimensional conformational analysis by Congo red and CD spectroscopy suggested that sodium alginate exhibits a triple-helix conformation in solution. Furthermore, X-ray powder diffraction analysis confirmed that the alginate has an amorphous structure. Sodium alginate extracted from E. maxima found on the coasts of Southern Africa exhibits a high mannuronic content and high viscosity, potentially beneficial for drug delivery and biomedical applications.