Effect of season on the composition of bioactive polysaccharides from the brown seaweed Saccharina longicruris.

The structural features of laminarans and galactofucans extracted from the brown seaweed Saccharina longicruris were determined for four harvest periods (M05, A05, N05 and J06). Crude laminarans were purified and crude galactofucans were fractionated using DEAE Sepharose anion exchange chromatography with increasing levels of NaCl (0.5, 1 and 2 M). The results showed differences in terms of their monosaccharide compositions. Purified laminaran contained a high proportion of D-glucose, between 45.1% and 69.1%, with a higher amount in M05 and A05, while the amount of D-mannitol remained constant (less than 1.7%). Crude galactofucans from M05, A05, and N05 contained 19.9-21.5% of sulphates, where J06 had only 14.3%. The 2 M fractionated galactofucans contained a higher proportion of sulphate groups, from 27.1% to 36.9%, for each harvest period, while the 1 M fraction contained 9.2% to 15.9% of sulphates. An important variation in the amount of L-fucose and D-galactose was observed for crude and fractionated galactofucans. In M05, a higher content of L-fucose was observed for crude galactofucans compared to that observed for D-galactose (21.5% vs. 11.1%), whereas the opposite was found for A05 (18.5% vs. 36.6%), N05 (20.9% vs. 36.8%), and J06 (12.8% vs. 19.6%). Also, the 0.5 and 2 M fractions were similar to the crude galactofucans. A05, N05, and J06 contained lower amounts of L-fucose than D-galactose, while the M05 fractions showed the opposite behaviour. However, the 1 M fraction showed a higher amount of L-fucose than D-galactose for each harvest period. The next step will be to study the biological activity of the fractions and to attempt to relate this activity to the structure of the galactofucan and laminaran fractions.