Implications of microwave drying using 915 MHz frequency on rice physicochemical properties

Abstract

Background and objectivesHigh moisture content (MC) rough rice was dried using an industrial microwave (MW) operated at a frequency of 915 MHz, and the impacts of the drying on the rice physicochemical properties were investigated. The treatments were performed at MW power levels 5, 10, and 15 kW, treatment durations 4, 6, and 8 min and for rice at initial MC of 24% (w.b.) and bed thicknesses 5, 10, and 15 cm. Near infrared spectroscopy and a rapid visco‐analyzer were used to assess the milled rice protein content, surface lipid content (SLC), total color difference (TCD), and rice peak and final viscosities.FindingsThe effect of increasing MW specific energy was statistically significant for all of the responses studied. Increasing MW specific energy resulted in an increase in measured rice SLC, protein content, and final and peak viscosities. Responses increased to a maximum then decreased at specific energies over 800 kJ/kg‐grain. The opposite profile was true for TCD. The TCD decreased as a result of increasing MW specific energy to a trough at 533.33 kJ/kg‐grain then increased at specific energies over 600 kJ/kg‐grain. The effect of varying rice bed thicknesses was not statistically significant.ConclusionsIt is vital to select appropriate MW specific energy to maintain the rice physicochemical properties.Significance and noveltyUsing MW heating with a frequency at 915 MHz provides new avenues to scale up the MW heating technology for rice drying; this may allow rapid, one‐pass rice drying while maintaining important quality characteristics.