Developments on gelling algal galactans, their structure and physico-chemistry

The wide uses of the algal galactans agar, agarose and carrageenans arebased on their unique properties to form strong gels in aqueous solutions. These gels result from peculiar regular chemical structures, specific orderedmolecular conformations and aggregations. In recent years, newmethodologies and instruments have provided a more accurate view of therelationships between the chemical structure and the gelling characteristicsof these complex hybrid and heterogeneous polysaccharides. Methanolysisand reductive acid hydrolysis procedures coupled to differentchromatographic separations allowing the quantitative determination of allthe constituent sugars including the acid labile 3,6-anhydyrogalactose areparticularly emphasised. Means of determining sugar linkages, substitutionsand sequences using chemical, enzymatic and spectroscopic methods arealso presented. Developments in multi- and low-angle laser-light diffusiondetectors coupled to high performance size exclusion chromatography nowrender the determination of molecular weight and molecular weightdistribution of these galactans more accessible. Such techniques also yieldnew information on the aggregate formation of these sulphatedpolysaccharides. These and other data question the existence of thegenerally assumed intertwined double helical conformations of thesegalactans during gel formation.