(715d) Rheological Study of Polysaccharides in Aqueous/Salt Solutions Subjected to Ultrasound Fields

Xanthan and locust bean gums, which behave as typical polyelectrolytes and non-polyelectrolytes respectively, are broadly used in the food processing industry as thickeners and stabilizers. In order to efficiently collect and recycle these gums from food processing wastes, it is often desirable that their molecular weights should be reduced to a lower value and be confined to a narrow range. Thus, ultrasonic fields were investigated as a potential degradation technique for polysaccharides in aqueous solution. Gum solutions were sonicated at 20^oC for 2 min, 5 min, 10 min, 30 min, 60 min, and 120 min. Ubbelohde capillary viscometry was used to evaluate the solution’s viscosity; and the intrinsic viscosity, molecular weights, and changes in chain conformation were accessed by the Huggins, Kraemer, Mark-Houwink, and power-law equations. It was found that ultrasound can efficiently degrade the polysaccharides, and that the conformation of molecular chains may behave as rod-like at low molecular weight instead of a random-coil configuration at high molecular weight. The effects of salt on the ultrasonic degradation of polysaccharides in aqueous solution were also studied. Results indicate that the ability of the salts to influence the rheology of sonicated polysaccharide solutions may follow the Hofmeister series, which is used to describe the influence of salts on proteins, and that the effect of anions is more significant than that of cations. To better understand the influence of salts to the ultrasonic degradation of polysaccharides, the salting-in behavior salts and salting-out behavior salts, which were classified on the base of Hofmeister series, were studied respectively. The gums were pre-mixed with 0.1 M, 0.01 M, 10^-3 M, and 10^-4 M salts in aqueous solutions, and then sonicated for different times. It was found that the salts can effectively influence the ultrasonic degradation rate of xanthan gum more so than that of locust bean gum, suggesting that the polyelectrolyte’s degradation rate is easier to be tuned compared to that of non-polyelectrolyte in aqueous salt solution.