Combined Microwave and Hot Air Drying of Sapota (Acharas zapota L.) Slices: Analysis of Quality and Mass Transfer Parameters

This effects of combined microwave and hot air on drying of sapota (Acharas zapota L.) slices were studied. The slices were dried from the initial moisture level of 75-78 % (w.b.) to a final moisture content of ~10 % (w.b.). Process parameters such as drying time, moisture diffusivity, specific energy consumption and quality attributes of dried sapota slices were evaluated. Drying time at the power level of 2 W.g-1 reduced up to 14 to 21 times compared to only hot air drying. Dincer and Dost model was used to estimate Biot number and mass transfer coefficient which ranged from 0.29 to 1.23, and 0.23×10-7 m.s-1 to 8.81×10-7 m.s-1, respectively. Specific energy consumption was reduced by 12 to 17 times during combination drying (2 W.g-1, 50-70 °C) compared to only hot air drying (50-70 °C). Process modelling results indicated that Midilli model was best fitted describing the drying kinetics of sapota slices during combination drying. Optimization for better quality dried sapota slices suggested slice thickness of 5 mm using combination of microwave (1.5 W.g-1) and hot air drying (60 °C).