Control of viscosity in starch and polysaccharide solutions with ultrasound after gelatinization

Application of power ultrasound has immense potential for a wide variety of processes in the food industry which include sterilization, emulsification, extraction, crystallization, degassing, filtration, drying, and more. Controlling the viscosity of starch (polysaccharide) solutions is one of the most promising processes to be developed. Power ultrasound can effectively decrease the viscosity of starch solutions after gelatinization. At the high starch concentrations (20-30%), starch gel can be liquidized by sonication. The viscosity of the starch solution of moderate concentration (5-10%) can be reduced about two orders of magnitude to 100 mPa s by the ultrasonic irradiation for 30 min. The treated solution can be efficiently powdered by a spray-dryer after the sonication. The effectiveness of the ultrasonic process has been evaluated by measuring the changes in viscosity. Granule disintegration was determined using a method which measures the swelling power of starch. Change in molecular weight of the starch was monitored by gel permeation chromatography and a static light scattering method. The depolymerization process of the starch has been also monitored by NMR spectroscopy. The elucidated merits of the ultrasonic process are: 1) the process does not require any chemicals and additives; 2) the process can be simple and rapid, which means that the process is cost effective; and 3) the process will not induce large changes in the chemical structure and in particular, the properties of starches. The ultrasonic process has been confirmed to be applicable for many kinds of starches (corn, potato, tapioca, and sweet potato) and polysaccharides. (C) 2007 Elsevier Ltd. All rights reserved.