Solvent structure and gelation of polysaccharides in concentrated solutions of simple sugars

Simple sugars added at high concentration strongly influence the gelation properties of polysaccharides. Starch, K-carrageenan, gellan and low-methoxy and high-methoxy pectins have been extensively studied. With concentrations of sugar of up to about 40% gels typically become firmer (higher storage modulus, G') and the gelation temperature (T-g) increases. Sugars appear to stabilise the junction zones in the gel network and these effects are strongly dependent on the chemical structure of the added sugar, as well as its concentration. The geometric requirements of the hydrogen bonds made by water molecules impart considerable structure to the water surrounding solutes such as simple sugars. The effects of different sugars on G' and T-g can be correlated with physical parameters that are related to the effect of the sugar on the structure of the surrounding water molecules. Recent computer simulation studies of aqueous sugar solutions, using the molecular dynamics approach, have revealed more details of the solution structure than was previously accessible from spectroscopic and thermodynamic studies. This leads to a better understanding of how simple sugars stabilise the junction zones in polysaccharide gel networks and leads to some unifying principles that might be helpful in practical applications.