Degradation of (1→3)(1→6)-α-D-dextran by ultrasound: Molecular weight, viscosity and kinetics.

The (1→3)(1→6)-α-D-dextran (alternating dextran) produced by Leuconostoc citreum SK24.002 is a novel functional exopolysaccharide, and its low molecular weight derivatives have potential applications in the food, pharmaceutical, and chemical industries. In this work, we used sonication, a green polysaccharide disruption method, to study the degradation process of this dextran by changing the intensity and duration of the sonication treatment and the concentration of the dextran solution. The molecular weight and viscosity of the dextran products were measured with a high-performance size exclusion column chromatography-multi-angle laser light scattering-refractive index system and by rheometry, respectively. The degradation efficiency of dextran was directly affected by the duration and intensity of the ultrasonic treatment and the concentration of the dextran solution. The polydispersity index fluctuated as the duration of the sonication treatment increased. The combination of a high intensity (672 W/cm) and long (120 min) sonication treatment and a low solution concentration (3 g dextran/100 mL) was most effective for reducing the apparent and complex viscosities of dextran. The storage modulus of dextran was always slightly larger than its loss modulus, indicating that it formed a gel-like structure. The second-order kinetic model (1/Mw - 1/Mw = kt) was the best fit to explain the degradation dynamics of dextran by sonication at intensities of 168 W/cm-834 W/cm and with dextran solution concentrations of 1 g/100 mL - 7 g/100 mL. Our findings show that sonication is an effective way to reduce the molecular weight of alternating dextran.