Rheological characterization of mixed biopolymer gel systems

Rheological properties of two mixed biopolymer gel systems, xanthan-carob (X/C) and surimi-starch (S/St), were studied to investigate polysaccharide/polysaccharide (P/P) and protein/polysaccharide (Pr/P) interactions, respectively. These systems can also be categorized as thermo-reversible and thermoirreversible gelling systems, depending upon their thermorheological behavior before, during, and after gelation.; Small amplitude oscillatory shear (SAOS) tests, such as frequency sweep and temperature sweep, were used to characterize the rheological properties before, during, and after gelation. Because the biopolymer gels are thermally unstable, the effect of temperature on rheological behavior at each stage was also studied in the 10 to 80°C range.; A non-isothermal kinetic model was used to determine the activation energy (Ea) for gelation. The Ea was used to characterize the contribution of individual components of the mixture to the overall rheological behavior of the system during gelation. The Ea of both mixed gels showed a dependence on the mixing ratio of components. The Ea of X/C and S/St decreased with increase of xanthan and fish muscle protein concentration, respectively. The thermoreversible X/C gels showed thermal hysteresis. The melting behavior was strongly dependent on the concentration. The monomeric friction coefficient of the X/C mixture determined from frequency sweep tests was nearly independent of concentration. The concentration dependence of equilibrium modulus of the X/C mixed gel followed the power-law relation, however the power exponents varied with concentration. The exponent value obtained for the gel system with low total biopolymer concentration (n = 3.38) was higher than that obtained for the system with high total biopolymer concentration (n = 2.12). Steady shear viscosity of S/St mixture before gelation was estimated based on the Cox-Merz relation. The problems of steady shear viscosity measurements of surimi paste were partially overcome by measuring the dynamic viscosity by SAOS tests and applying the Cox-Merz rule. However, this procedure was not applicable for the surimi-starch mixture.