Polysaccharides of red alga Gracilaria intermedia: structure, antioxidant activity and rheological behavior

A sulfated polysaccharide fraction from the red alga Gracilaria intermedia (PLS) was obtained by papain digestion (60 degrees C,30 min). The extract was subjected to colorimetry and turbidimetry analysis, Fourier transform infrared (FTIR) spectroscopy, H-1, C-13 and D-2 H-1 COSY nuclear magnetic resonance (NMR) and gas chromatography/mass spectrometry analysis. Antioxidant activity tests were performed (chelation of ferrous ion, total antioxidant capacity, and scavenging of DPPH radicals); significant activity of the extract indicated that these polysaccharides may be used as non-synthetic antioxidants. The rheological behavior of aqueous polysaccharide solutions was studied at 25 +/- 1 degrees C using steady-shear and dynamic oscillatory measurements. All the solutions analyzed showed pseudoplastic behavior and potential to act as a thickening agent, as proved through a preliminary comparison with a commercial product used for this application.