Sulfated fucans are among the most widely studied of all the sulfated polysaccharides of plant origin that exhibit biological activities in mammalian systems. In this report fucoidans from some Vietnamese Sargassum species such as S. polycystum, S. oligocystum, S. mcclurei, S. swartzii and denticaprum were extracted and fractionated on a DEAE-Sephadex A-25 column.On the basis of chemical and spectral analyses, the fucoidan fractions obtained were found to be the sulfated fucogalactans containing sulfate ester groups and uronic acid, and composed essentially of fucose and galactose, as well as a minor amount of other sugars. The polysaccharide fractions were tested for anticancer activity. The primarily obtained results showed that all fucoidan fractions isolated from S. swartzii demonstrate bioactivity effects against cancer cells, while fraction F5 with a highest sulfate content exhibits the strongest antiinvasion activity. This indicates that sulfate content plays an important role in the anticancer activity of the brown algal fucoidans.A laboratory scale pilot for fucoidan production from Vietnamese brown seaweeds has been set with a capacity of 500 g of crude fucoidan per day.

Polysaccharides extracted from six red seaweed species growing in Vietnam have been studied. Characterisation of their structure by chemical and spectroscopic methods showed that all of them have a basic repeating structure of alternating 3-linked -D-galactopyranosyl and 4-linked 3,6-anhydro -L-galactopyranosyl units with substituted methyl ether groups.The native agar offers only weak gelling abilities owing to the 4-linked -L-galactopyranosyl -6-sulfate as its precursor. Conversion of this unit into the corresponding 3,6-anhydride by treating with hot alkali generally led to gel strength increasing.The agars from G. fisheri and G. firma are poorly substituted, while those from G.asiatica, G.tenustipitata and G. heteroclada are partly methylated on position 6 of the 3-linked -Dgalactose. Agar from Gelidiella acerosa is partlly methylated on both positions 6 and 2 of the 4-linked 3,6-anhydro -L-galactose.The alkali-modified agars have been obtained in acceptable quantities with gel strength of 300-932 g/cm 2 . The obtained results showed that all the six algal species are suitable as raw material for commercial agar production and worthy of further cultivation.