Impact of specific energy input of a 915 MHz microwave dryer on quality, functional, and physicochemical properties of different rice cultivars

Background and objectives The 915 MHz industrial microwave has a great penetration depth relative to the 2.45 GHz microwave and holds the potential to achieve one-pass drying of deeper rice beds within a short drying duration. The objective of this research is to determine the effect of microwave specific energy on the quality, functional, and physicochemical properties of different rice cultivars. Two rice cultivars were used: a medium grain cultivar (Titan) and a long grain hybrid cultivar (XL753) from two different locations (Burdette and Carlisle). Rice samples at harvest moisture content of 20% wet basis were dried using the 915 MHz industrial microwave at specific energies ranging from 360 to 720 kJ per kg of initial wet grain mass (kJ.[kg-grain](-1)). Rice physicochemical and functional properties were analyzed. Findings Results indicate that specific energy had a significant effect (p-value < 0.0001) on moisture removal and head rice yield. On average, increasing specific energy (drying duration 3-4 min, power 4-6 kW) resulted in increased moisture points removed from 2.5% to 7.3% and 3.7% to 7.5% for long grain hybrids and medium grain cultivars, respectively, while head rice yield decreased. Setback and final viscosities increased while peak viscosity decreased with increasing specific energies. Kernel surface lipid and protein content slightly decreased with increasing specific energies, although specific energy did not have a significant effect on these responses. Resistant starch content decreased with increasing specific energy for hybrid rice. Water and oil absorption capacities varied at different specific energies. The most desirable specific energy for moisture removal that maintains rice quality characteristics (relative to control samples) was 525 kJ.[kg-grain](-1). Conclusions The 915 MHz industrial microwave has the potential to achieve one-pass drying of rice. A study of the best specific energy for drying different cultivars of rice using this technology is essential to meet the diverse industrial needs for rice drying. Significance and novelty This study provides science-based information on the properties of different rice cultivars dried using the 915 MHz microwave and selection of desirable microwave parameters for rice drying. The technology has a great potential to transform the rice drying industry by decreasing rice drying duration, improving milling yield, and energy efficiency.