Microwave popping characteristics of paddy as affected by sample placement and geometry and process optimization

Uniformity and magnitude of heating in a domestic microwave oven are attributed to both sample and oven factors. The present study investigated the effect of sample and oven parameters: sample size in terms of thickness (2.09-10.45 mm), spread areas (32.18-58.11 cm2) of different volumes of vessels (250-600 mL) and positions on turntable (0-10 cm) on popping characteristics (popping percentage, expansion ratio, beginning of popping, threshold energy) of paddy (Heera variety) using a domestic microwave oven. The maximum value of popping percentage and expansion ratio was obtained when the sample was placed at 6 cm away from the center of the turntable. Smaller spread area with minimum thickness gave good popping characteristics. A D-optimal experimental design was used to develop models for the popping characteristics. Analysis of variance showed that a second-order polynomial model suitably fitted the experimental data. Optimum popping conditions were found to be single layer grain mass in 250 mL container with popping percentage of 75.90%, expansion ratio of 6.03, beginning of popping at 15.86 s and threshold energy of 15.93 kJ. Validation experiment was conducted with one sample t-test (p < 0.05) at the derived optimum conditions.