Rheology and characterization of sulfated agarans from the edible epiphytic red alga, Vertebrata lanosa (truffle seaweed)

Abstract

The effect of different cations (K+, Ca2+ and Ba2+) on the gel forming properties of sulfated polysaccharides isolated from the red epiphytic alga, Vertebrata lanosa, using a successive cold (25 °C) and hot (95 °C) alkaline extraction process is presented. The elucidation of their monomeric composition using a two-step reductive hydrolysis and structural analyses (1D and 2D NMR) revealed d-galactose (G) linked to 3,6-anhydro-l-galactose (LA) and also sulfated 3,6-anhydro-l-galactose (L6S) as the major monomers with some amounts of glucose, β-d-xylose, 6-O-methyl-d-galactose (G6M), 2-O-methyl-l-anhydrogalactose (LA2M) and l-arabinofuranose. This composition implied the presence of both diads of agaran types, funoran and porphyran in polysaccharides from Vertebrata lanosa. Similar to funorans, their gelation, was highly influenced in the presence of Ba2+ ions compared to other tested salts. 0.2 M of BaCl2 in the hot extracted fractions recorded storage modulus (Gʹ) to up to ∼80 Pa and increased complex viscosity to 16,000 mPa s compared to the <5 Pa storage modulus from pristine solutions with no added salts. Sulfate amount contained within these fractions ranged up to ∼30% with less than 1 % (gallic acid equivalent, GAE) total phenolic compounds. Some of these fraction, nonetheless, have shown good α-amylase and reactive oxygen species (ROS) inhibition activities thus suggesting a nutraceutical potential of hydrocolloids from this algal species.