Bioactivity of sulfated polysaccharides from the edible red seaweed Mastocarpus stellatus

Abstract

Carrageenans are typical sulfated-galactans from red seaweeds. Their main biological properties as antioxidants and anticoagulants were studied in vitro in Mastocarpus stellatus. On sequential extraction with cold-water (F1), hot-water (F2), acid (F3) and alkali (F4), four soluble polysaccharide fractions plus an insoluble cellulose residue (F5) were obtained. Composition was assessed by gas-liquid chromatography, ion chromatography and Fourier Transform Infrared (FTIR-ATR) spectroscopy. Multifunctional antioxidant capacity was assayed by FRAP- reducing power, ABTS- and photochemiluminiscence (PCL)- radical scavenging methods. Heparin-like anticoagulant capacity was studied by intrinsic-APTT and extrinsic-PT pathways. Recovery of F1-F4 yielded almost 60%, which main components were: neutral sugar (21.2-34.7 g/100 g), sulfate (0.6-3.9 g/100 g), protein (0.1-3.4 g/100 g) and uronic acid (0.9-2.7 g/100 g). Galactose (70.2-95.2 mol/100 g) was the predominant sugar in F1-F4 and sulfate their main inorganic anion (75-80% of total). F1-F3 contained the bulk of carrageenans. Degree of sulfation ranged from 0.22 (F1) to 0.03 (F3), respectively. Typical absorption bands of kappa-/iota-carrageenans at 930, 845 and 805 cm-1 assigned respectively to 3,6-anhydro-galactose, galactose-4-sulfate and 3,6-anhydro-galactose-2-sulfate appeared in FTIR spectra. Upon extraction with acid and alkali polymerization degree decreased significantly meanwhile iota- versus kappa-carrageenan increased. The highest FRAP-reducing power (44.9 μmol Trolox equivalents/g) and ABTS-radical scavenging ability was shown for cold-water soluble F1. Regarding anti-coagulant capacity, again F1 showed the best values (28 mg heparin equivalents/g), suggesting that its higher sulfate content associated to its high MW might exert a positive effect. Sulfate played a determinant role as antioxidant and anticoagulant, but a high MW was also relevant for the anticoagulant capacity of M. stellatus carrageenans. © 2014 Published by Elsevier Ltd.