Monthly changes in the content and monosaccharide composition of fucoidan from Undaria pinnatifida (Laminariales, Phaeophyta)

Crude fucoidan was extracted from the brown alga Undaria pinnatifida collected monthly from April to last July in Peter the Great Bay (Japan Sea, Russia). The amount of crude fucoidan rose markedly from April to June-July (from 3.2 to 16.0% dry weight) as the plant matures. An analysis of the monosaccharide composition of the fucoidan extracted showed that the alga synthesized polysaccharides with various structures which were dependent on the algae age. In juvenile plants collected in April-May, this was represented by sulfated manno-galactofucan containing up to 19-28 mol% of mannose and about 20 mol% of galactose, whereas in matured plants collected in June-July, the polysaccharide was represented by a sulfated galactofucan containing more than 38 mol% galactose. It is postulated that the production of sori causes a subsequent effect on fucoidan synthesis and leads to an enhanced of crude fucoidan content and an increased molar concentration of galactose. Crude fucoidan content in sporophylls increased 5 times, and galactose content in this polysaccharide rose s1.6 times with sori formation. The structural characteristics of the fucoidan extracted from sporophylls of Undaria collected in July were also studied. The fractionation of crude fucoidan on DEAE-Sephadex A-25 gave two fractions, F1 and F2 in equal quantities. F1 was characterized as manno-galactofucan sulfate and F2 was galactofucan sulfate. The molecular weights of both fractions were in a range of 30-80 kDa. Analysis of fucoidan structure using ESI-FTICR mass spectrometry showed the presence of mixed oligosaccharides consisting of fucose and galactose. Presumably, the polysaccharide molecules contain blocks built up of successively linked residues of fucose and galactose. These blocks are built from two to five or more residues of monosaccharides. According to IR-spectroscopy data, the main portion of sulfates is located at C2; in addition, sulfate esters are also present at C4 on the fucose and C3 and C6 of the galactose units.