Extraction and characterization of sodium alginate from Moroccan Laminaria digitata brown seaweed

Sodium alginate from Moroccan Laminaria digitata brown seaweed were extracted under different conditions. The extraction yield was affected by the extraction temperature and the samples’ size. Alginates were purified by re-precipitation with ethanol and characterized by 1H NMR, fluorescence spectroscopy and infrared spectroscopy, in order to determine their structural and physicochemical properties. Viscosimetric measurements gave an intrinsic viscosity of 2.542 dL/g which permits to calculate the average molar mass value (1.14 × 105 g/mol). By analyzing 1H NMR spectra, Moroccan L. digitata alginates showed a high quantity of both homopolymeric mannoronic and guluronic blocks (FMM = 0.47) and (FGG = 0.41) respectively, while the alternating block fractions (FMG = 0.06 and FGM = 0.06) showed low values than those previously described in the literature. The M/G ratio value is 1.12 allowing the preparation of alginates suitable to form soft and elastic gels more than brittle ones. The characteristics obtained for Moroccan Laminaria digitata may be useful to obtain polyelectrolyte complexes for the production of drug delivery micro- and nanoparticles. In some cases, a charged polysaccharide with low viscosity is needed.