Germination of wheat grains from uneven microwave heating in an industrial microwave dryer

Manickavasagan, A., Jayas, D.S. and White, N.D.G. 2007. Germination of wheat grains from uneven microwave heating in an industrial microwave dryer . Canadian Biosystems Engineering/Le genie des biosystemes au Canada 49 : 3.23-3.27. Hot spots, produced on products due to the non-uniform heating pattern of microwaves, may be one of the important factors for the quality degradation of products during microwave treatment. In this study, the germination percentage of wheat samples collected from hot-spot and normal heating zones after microwave treatment was determined. Canadian hard red spring wheat samples (50 g in each experiment) at four moisture levels (12, 15, 18, and 21% wet basis) were subjected to microwave treatment at five power levels (100, 200, 300, 400, and 500 W) and two exposure times (28 and 56 s) in a laboratory scale, continuous type, industrial microwave dryer (2450 MHz). After microwave treatment, the samples were collected from the hot-spot and normal heating zones by viewing the live thermal images on the monitor of the data-acquisition computer of a thermal-imaging system. At all moisture and power levels, germination percentages were significantly (�=0.05) lower for samples collected from hot spots than those from the normal heating zone. At 500 W for 28 s exposure, the germination percentage became zero in the hot-spot zones, whereas it was 4 to 33% in the normal heating zone. The germination percentage was near zero at 300 W for the samples collected from the hot spot, when the exposure time was increased to 56 s and the initial moisture content was 18 and 21%. At 400 and 500 W power and 56 s exposure, the germination percentage was almost zero for samples collected from both normal and hot-spot regions. Keywords : germination percentage, hot spot, microwave drying, thermal imaging.