Drying kinetics of onion (Allium cepa L.) slices with convective and microwave drying

Abstract

Onion slices were dried using two different drying techniques, convective and microwave drying. Convective drying treatments were carried out at different temperatures (50, 60 and 70 °C). Three different microwave output powers 328, 447 and 557 W were used in microwave drying. In convective drying, effective moisture diffusivity was estimated to be between 3.49 × 10−8 and 9.44 × 10−8 m2 s−1 within the temperature range studied. The effect of temperature on the diffusivity was described by the Arrhenius equation with an activation energy of 45.60 kJ mol−1. At increasing microwave power values, the effective moisture diffusivity values ranged from 2.59 × 10−7 and 5.08 × 10−8 m2 s−1. The activation energy for microwave drying of samples was calculated using an exponential expression based on Arrhenius equation. Among of the models proposed, Page’s model gave a better fit for all drying conditions used.