Thermomechanical depolymerization of dextran

Native, high-molecular weight dextran was subjected to ultrasonication at 20 kHz and 1.5 MHz, jet-cooking with high pressure steam and twin-screw extrusion under a variety of conditions. The extent of depolymerization was measured by size-exclusion chromatography and viscometry. All methods reduced the molecular weight and solution viscosity of dextran. The greatest degree of depolymerization occurred with 20 kHz ultrasonication. With extrusion, increasing amounts of specific mechanical energy input resulted in greater degrees of depolymerization. Each of these methods has advantages and drawbacks for the production of reduced-molecular weight dextrans. Sonication was more effective at depolymerizing dextran, but is currently too expensive to be amenable to large-scale manufacture. Extrusion is relatively inexpensive and scalable, but produces some undesirable dark-colored side products. Jet cooking is inexpensive and scalable, and does not produce the colored side products, but requires dissolution of the sample in water, followed by drying. Considering all of these factors, jet-cooking may show the most promise for production of low-viscosity dextran fractions. (C) 1999 Elsevier Science Ltd. All rights reserved.