Relation between the molecular structure of some polysaccharides and original properties in sol and gel states

This paper concerns the properties of a few natural polysaccharides investigated in our laboratory. We also present the different techniques used in our group for a long time and their advantages to characterize polysaccharides. In a first part, the behavior of galactomannans with different chemical structures is discussed; the distribution of galactose units along the mannan backbone is very important. Then, xanthan is developed as one of the best thickening polymers due to its high intrinsic stiffness related to the helical conformation stabilized in the presence of excess salt. Gellan under native or deacylated structure is described to demonstrate the role of substituents on the physical properties in solution and especially on the sol–gel transition. The last part concerns the cooperative interaction between xanthan and galactomannan giving in specific conditions two different gels with a gel–sol melting transition around 25°C and 50–60°C, respectively, depending on the galactomannan microstructure.