Effect of sugar type on rheological properties of high-methoxly pectin gels

The effect of different sugars (sucrose, glucose, fructose, and sorbitol) at a concentration 60% on rheological properties of high-methoxly pectin gel (1% w/w) was investigated in steady and dynamic shear. The mixtures of pectin with sugars at 20 C are highly shear thinning fluids (n=0.37-0.44) with large magnitudes of Casson yield stresses (26.7-45.4 Pa). Consistency index (K), apparent viscosity (eta(a, 100)), and Casson yield stresses (sigma(oc)) increased in the following order: sucrose > glucose > sorbitol > fructose. Magnitudes of storage modulus (G) were much higher than those of loss modulus (G") over the entire range of frequencies (omega) with the high dependence on omega. All pectin-sugar mixture samples exhibited the rheological behavior similar to weak gel. In the order of increasing G' values in pectin-sugar mixtures, sugars were ranked as: sorbitol > sucrose > glucose > fructose. Cox-Merz rule was not to applicable to pectin-sugar mixtures.