Influence of microwave parameters and water activity on radical generation in rice starch

•We study the response of rice starch radicals in microwave electromagnetic field.•We reveal three different components of radical in the treated rice starch samples.•Microwave power level and water content could influence the amount of radicals.•We validate the effect of microwave on chemical bonds of rice starch radicals. Radical generation in rice starch under microwave treatment as well as the related chemical bond changes were investigated by electron paramagnetic resonance (EPR) and Raman spectroscopy. Samples with water activity of 0.4 and 0.7 have been treated and analyzed. It was found that microwave power level and water content could influence the amount of radicals along with the radical components and their contribution. Raman spectra showed corresponding changes in vibrational features of chemical bonds. During storage the signal intensity started to drop after a short period of increase. Rice starch radicals were relatively stable and could exist a long time in room temperature. Through signal simulation, 3 main components were separated from the original spectra and the evolving process was investigated. The main component was the radical located on C1 position in the glucose ring.