Microwave-Conventional Drying Characteristics of Red Pepper: Modeling, Temperature Profile, Diffusivity and Activation Energy

Microwave combined drying is an alternative technique that can be applied to dry foodstuffs, especially fruits and vegetables, due to shorter drying time and higher energy efficiency. In this regard, the effect of hybrid (microwave-conventional) drying conditions on drying kinetics, modeling, temperature profile, moisture and thermal diffusivities and activation energy of red pepper was investigated in a specially designed hybrid domestic oven. Three levels of microwave powers (120, 150, and 180W) and air temperatures (50, 60, and 70°C) were used. Both energy sources were applied simultaneously during the whole drying process. The drying process continued until the moisture content of the red pepper reached 10% on wet basis. Drying time decreased with increasing microwave power and air temperature. Temperature of red pepper slices sharply increased within the first 60 minutes, then reached equilibrium with drying medium and finally increased at the end of the drying process. Nine semi-theoretical models were applied to determine the drying behavior of the samples. Modified Logistic model was determined as the best model because it had the lowest RMSE and χ2 and the highest R2 values. Effective moisture and thermal diffusivity values increased with increasing microwave power and air temperature and ranged from 8.86×10-10 to 4.23×10-9 m2 s-1 and 4.57×10-10 to 1.81×10-9 m2 s-1, respectively. The activation energy of the dried red pepper slices was between 29.30 and 56.61 kJ mol-1. The hybrid drying can be used as an alternative drying method for red pepper drying.