Microwave absorption capacity of rice flour. Impact of the radiation on rice flour microstructure, thermal and viscometric properties

The microwave radiation thermal treatment of rice flour was studied and its impact on physical and structural characteristic in relation to the initial moisture content (IMC) (20% and 30%) was evaluated. To explain the fundamentals of observed changes the microwave radiation absorption capacity of flour as well as temperature and moisture change during the treatment were evaluated. The flour particle morphological structure as well as crystallinity/amorphous region ratio changed after the treatment. The flour thermal properties also altered revealing IMC significant impact on the gelatinization temperature, that raised up to 3 °C, and the amylopectin retrogradation extent that increased up to a 7% in the most intense microwave-treated flours with respect to the native flour. Lower peak, setback and breakdown viscosities - that decreased with respect to the native flour up to 42%, 34% and 86% respectively-and higher pasting temperatures -that increased up to 10 ºC- were also observed. An exceptional microwave irradiation efficiency resulting in rice flour physical changes in significantly shorter times, 4-8 min, than conventional heat-moisture treatment processes was concluded.