Effects Of Microwave On Rice Starch

Effects of microwave at 2450 MHz on starch-water system with different moisturecontent were studied in this paper and to guide application of microwave in starch-foodprocess. The main results were as follows:1. Under microwave irradiation, dielectric relaxation represented in starch-watersystem and resulted in temperature increase. Microwave treatment could changemolecular structure, including molecular weight decrease and crystal structure change,and could improve amylose dissolvability as well as amylopectin dispersion. Thetemperature increase of microwave was more quickly than conduction heating. Comparedwith conduction heating, the water binding capacity and digestibility of starch treated bymicrowave increased but swelling properties decreased, both gelation and sol was moredense. Microwave treatment could result in granule rupture and became lesssmooth-faced. Parameters of microwave heating could influemced the effects ofmicrowave, and the lager the power or longer the treating time was, the effects ofmicrowave were more obvious.2. Effects of microwave were different when the moisture content of starch-watersystem was various. The higher the moisture content was, the more quickly thetemperature increase was, and heating rate of microwave was fatser than conductionexcept that under low power with excessive water. Along with moisture contne increasing,the blue value and enzyme digestibility increased, the crystal diffraction became weaker,the original teperature of bound water vaporization decreased and the enthalpy change ofbound water vaporization increased. So we could conferred that increase of moisturecontent could accelerate the crystal collapse, improve the polarity groups orientation,enhance the amylose dissolvability, amyiopectin dispersion water binding capacity as wellas digestibility.3. Dielectric relaxation represented variously in starch-water system with differentmoisture content when the microwave was canceled. Along with storage, the digestibilitydecreased. When with low moisture content, the X-diffraction of starch granule treated bymicrowave shew more weak peak, the original teperature of bound water vaporizationdecreased and the enthalpy change of bound water vaporization increased, blue value andswelling properties climbed up, the molecular structure, morphology andphiscal-chemical properties was closer to those of starch untreated along with storage.When with limited or excessive water, the X-diffraction ofgelation or sol made by microwave enhanced, the original teperature and the enthalpy change of bound watervaporization increased along with storage. So we could conferred that the digestibility ofstarch-warer system decreased and the water binding capacity of starch with low moisturecontent fell along with storage. With limitted or excessive water, new crystal created instarch-water system, the polarity groups orientation and amylose dissolvability fell downalong with storage, but the water binding capacity was enhanced.