Effect of acidic hydrolysis on RAW264.7 macrophage cells stimulation and antioxidant properties of galactofucan from plant Azolla filiculoides

Polysaccharides are one of biomacromolecules that, in addition to their peculiar physicochemical properties, possess promising biological capabilities depending on chemical structure. The objective of the present study was to evaluate the effect of molecular weight of galactofucan polysaccharides from freshwater plant Azolla filiculoides on its ability to stimulate RAW264.7 macrophage cells and inhibition of oxidation reactions. Galactofucan polysaccharide was extracted by distilled water at 65°C for 2 hours and recovered using 70% ethanol. Polysaccharide hydrolysis was performed using 0.01N HCl at 100°C for 5, 10 and 15 minutes. Crude and hydrolyzed polysaccharides were mainly composed of neutral sugars (67.46-68.02%), lower amounts of uronic acids (4.48-4.53%) and ranged in the molecular weight of 99.4-783.0 × 103 g/ mol. Crude and hydrolyzed polysaccharides were non-toxic and hydrolysis 15 resulted in the greatest stimulation of proinflammatory response in RAW264.7 macrophage cells releasing a considerable amount of nitric oxide (55.6 μmol) into culture medium. Hydrolysis 15 led to the highest DPPH radical scavenging (65.2%) and Fe3+ reducing power (0.5 Abs). Overall, the present findings indicated that galactofucan polysaccharides have the ability to boost immune system and inhibit oxidation reactions and that molecular weight reduction to specific levels could improve the biological activities.