Effect of conformation and molecular weight of co-solute on the mechanical properties of gellan gum gels

The mechanical properties of 0.5% gellan systems in the presence of a range of commonly used co-solutes, from monomeric sugars (glucose and fructose) and disaccharides (sucrose and maltose), to starch hydrolysates (corn syrups and maltodextrins), have been studied up to 60% w/w addition. Their effects are discussed in terms of co-solute concentration, conformation, configuration and M-w. Addition of co-solute generally resulted in a lowering of the calcium required for maximum network strength accompanied by at least a three-fold decrease in the maximum measured Young's modulus from 0 to 60% and an increase in the yield strain at the maximum modulus. This argues for limited aggregation of the polymer chains, which create a more flexible network in the high solids environment. At 60% solids, gel modulus decreases in the order: fructose > glucose > sucrose, which reflects a reduced level of aggregation due to different ring conformation and molecular weight of the co-solute. The network firmness recovered partially in the presence of maltose, which has a smaller hydration layer than sucrose, with the greater number of available water molecules facilitating more stable gellan structures. The recovery of Young's modulus continued with corn syrup and maltodextrin, which was rationalised on the basis of partial phase separation between gellan chains and the polymeric fractions of the starch hydrolysates. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.