Effect of the Different Pre-Treatments Thermal, Pulse, Chemical and Mechanical on the External Mass Transfer Coefficient Changes, Moisture Diffusion Coefficient and Activation Energy

Analysis of internal and external mass transfer coefficient can be a useful means to control the drying process of food and agricultural products better. Accordingly, in this study, the effects of different treatments (thermal pretreatment by blanching, pulsed pretreatment with microwave radiation, mechanical pretreatment by ultrasound waves, and chemical pretreatment by osmotic dehydration) on the internal mass transfer coefficients (effective moisture coefficient), external mass transfer coefficients and activation energy were investigated. Experiments included three temperatures (45, 55 and 65 °C) and various pretreatments including thermal blanching with hot water (at 70, 80 and 90 °C), microwave pulses (90, 180 and 360 W), chemical osmosis (at 30, 50 and 70% concentrations), and mechanical ultrasound (at 15, 30 and 45 min intervals). The results showed that microwave and osmotic pretreatments had the largest and smallest effects on internal and external mass transfers compared with the control treatment. The highest internal (36.21×10-10 m2/s) and external (3.49×10-6 kgwater/m2s) mass transfer values observed under 360 W microwave pretreatment with the drying temperature of 65 °C, whereas the lowest internal (7.61×10-10 m2/s) and external (3.49×10-6 kgwater/m2s) values were observed in the control treatment at the drying temperature of 45 °C. The activation energy also ranged from 18.52 to 32.04 kJ/mol under various pretreatments and temperatures.