Extraction and physicochemical characterization of Sargassum vulgare alginate from Brazil

Alginate fractions from Sargassum vulgare brown seaweed were characterized by 1H NMR and fluorescence spectroscopy and by rheological measurements. The alginate extraction conditions were investigated. In order to carry out the structural and physicochemical characterization, samples extracted for 1 and 5 h at 60 °C were further purified by re-precipitation with ethanol and denoted as SVLV (S. vulgare low viscosity) and SVHV (S. vulgare high viscosity), respectively. The M/G ratio values for SVLV and SVHV were 1.56 and 1.27, respectively, higher than the ratio for most Sargassum spp. alginates (0.19–0.82). The homopolymeric blocks FGG and FMM of these fractions characterized by 1H NMR spectroscopy were 0.43 and 0.55 for SVHV and 0.36 and 0.58 for SVLV samples, respectively, these values typically being within 0.28–0.77 and 0.07–0.41, respectively. Therefore, the alginate samples from S. vulgare are much richer in mannuronic block structures than those from other Sargassum species. Values of Mw for alginate samples were also calculated using intrinsic viscosity data. The Mw value for SVLV (1.94 × 105 g/mol) was lower than that for SVHV (3.3 × 105 g/mol). Newtonian behavior was observed for a solution concentration as high as 0.7% for SVLV, while for SVHV the solutions behaved as a Newtonian fluid up to 0.5%. The optimal conditions for obtaining the alginates from S. vulgare were 60 °C and 5 h extraction. Under these conditions, a more viscous alginate in higher yield was extracted from the seaweed biomass.

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