Microwave and hot air drying of cashew nut: Drying kinetics and quality aspects

The objective of this research was to study effect of one-stage drying with constant drying temperature and two-stages drying using combined microwave and hot air on drying kinetic, some physical qualities of cashew nut and to evaluate specific energy consumption for cashew nut kernel. The microwave irradiative power ranging of 308 to 546 W and inlet drying temperatures of 70 to 80°C at the constant flow rate of 0.79 m/s were used for this work. The initial moisture content of cashew nut was in range between 10 and 11% dry-basis and final moisture content of dried cashew nut was 0.06±0.02% dry-basis. For determination of drying kinetic of cashew nut, the experimental data of evolution for moisture content among the one-stage and two-stages drying was formulated in various empirical drying models while the effective diffusion coefficient was evaluated by the Fick´s law of diffusion. The best fitting of simulated drying models was determined by the highest determination of coefficient value (r²) and the lowest root mean square error (RMSE). For physical qualities of dried cashew nut with drying conditions mentioned above as yellowness value (Hunter b value), percentage of shrinkage, peeling acceptance, sensory evaluation (Hedonic scale) and finally, the specific energy consumption in each drying condition were comparative studied. The results showed that at microwave power 546 W and hot air temperature of 75.7°C gave all acceptable qualities for the market, especially on peeling acceptability. In addition, the specific energy consumption for drying with microwave of 346 W at 75.7°C was relatively low compare to each others.