EFFECT OF MICROWAVE-RADIATION ON PHYSICOCHEMICAL PROPERTIES AND STRUCTURE OF POTATO AND TAPIOCA STARCHES

The time-temperature profiles of selected starch-water systems subject ed to microwave processing were established and the effect of microwav e radiation on the physico-chemical properties and structure of potato and tapioca starches was studied. The experimental starch samples wer e examined by the Brabender rheological method, light microscopy, scan ning electron microscopy and X-ray diffractometry. Microwave radiation was evidenced to affect the temperature and moisture contents of the experimental starches, with a strong correlation between the moisture content and the rate of temperature rise. An isothermal transformation was revealed with the samples of moisture contents over 20%, causing a rise in the gelatinisation temperature of the starch and a drop in i ts solubility in water. The most pronounced change was observed in the case of potato starch: its crystal structure changed from type B to t ype A. The tapioca starch underwent similar but less marked changes. ( C) 1998 Published by Elsevier Science Ltd. All rights reserved.