Lethal effects and mechanism of infrared radiation on Sitophilus zeamais and Tribolium castaneum in rough rice

The objective of this study was to investigate the characteristics of adult Sitophilus zeamais and Tribolium castaneum, and the 21.1% dry base (d.b.) MC of rough rice by ATR-FTIR spectra, and determine the theoretical optimum infrared (IR) heating temperature of the tested samples. In laboratory experiments, a ceramic IR drying device was used to heat infested rough rice to research the mortality of Sitophilus zeamais and Tribolium castaneum, the drying characteristics of rough rice, and milling quality. The theoretical calculation optimum temperature of IR heating was 300 ˚C according to the results of FTIR spectra. In addition, the effects of the different IR radiation intensities and heated rough rice temperatures on mortality of insects, moisture removal, and milling quality were determined in this text. A high insect mortality, heating rate and corresponding high moisture removal were achieved by using IR heating. After heating, tempering process significantly increased insect mortality when the heated tempered rice temperature was less than 55 ˚C, and improve moisture removal and milling quality of rough rice during nature air cooling. When the rice heated under the IR radiation intensity of 2780 W/m2 for 110 s, the rice temperature reached 60.2˚ ± 0.5˚C, 100% mortality of S. zeamais and T. castaneum, and 3.97 percentage points of moisture removal during the heating period after tempering and natural cooling. In addition, the high rice milling quality can be achieved after tempering treatment. Therefore, it can be concluded that the optimum conditions of simultaneous disinfestation and drying were 60 ˚C rice temperature under the IR radiation intensity of 2780 W/m2, followed by tempering and natural cooling.