Microwave drying of sprouted little millet and assessment of their kinetic and physiochemical properties

Abstract

In the present study, little millets were germinated at 30 °C with a relative humidity of 90% for 72 h. The sprouted little millets were dried in a power-controlled microwave (MW) system at a temperature of 50 °C at various power levels of 450, 750, and 1050 W. The "Page kinetic model" was found to be the best fit at various power levels. At MW-750 W and MW-1050 W, the rate constant (k) increased by 3.83–6.33 times as compared to MW-450 W. The activation energy for the germinated microwave-dried little millet was found to be 13.13 W/g. Similarly, the antioxidant activity increased by 34.54% at a power level of 1050 W as compared to the native flour (ungerminated). With the increase in the microwave power for drying, the total phenolic content (TPC) and total flavonoid content (TFC) were increased and found to be 364 (mg GAE/100 g) and 214.8 (mg CE/100 g), respectively, at a microwave power level of 1050 W. The TPC and TFC of MW-450 were increased to 15.6% and 2.3%, respectively, as compared to raw millet. However, at MW-1050, the TPC increased to 23.2%, and the TFC rose to 6.5%, compared to raw millet. The percentage crystallinity and enthalpy of melting from differential scanning calorimetry (DSC) were found to be the lowest at 12.18% and 107.7 J/g, respectively, at MW-1050. The present study showed that the application of microwaves enhanced the nutritional properties.