Influence of the uronic acid composition on the gastroprotective activity of alginates from three different genus of Tunisian brown algae

•Sodium alginates were extracted and purified from three Mediterranean brown algae.•Physico-chemical characterization and uronic acid composition of the extracted polysaccharides were performed.•The influence of the M/G ratio of alginates on their anti-ulcerogenic effects was investigated.

Alginates from three genus of Tunisian brown algae were isolated and characterized by size exclusion chromatography and Solid-state NMR spectroscopy. Alginate from Padina pavonica (APP) had the highest molecular weight (Mw) with 147,000 g/mol while it was 85,000 g/mol for alginate from Cystoseira compressa (ACC) and 58,000 g/mol for alginate from Dictyopteris membranaceae (ADM). The mannuronate (M) to guluronate (G) ratios were estimated from spectral deconvolution of the 13C CP/MAS spectra and the results has shown that all the extracts are mannuronic acid-rich alginates with M/G ratio increased in the order ADM - ACC - APP. An interesting gastroprotective effect was observed for the extracts; ADM and ACC exhibited the highest inhibition of gastric lesions, at 50 mg/kg, with 83.41% and 75.39% respectively. Otherwise, it has been shown that the gastroprotective effect of alginates depends mainly on their uronic acid composition.