The influence of hybrid drying (microwave-convective) on drying kinetics and quality of white mushrooms

In this study, white mushrooms were dried in a laboratory scale hybrid dryer. The effects of microwave power (100 and 200 W) combined with convection, at two different air temperatures of 30 and 50 degrees C, on the total drying time, drying rate, effective diffusion coefficient, specific energy consumption and several quality indicators were studied. The drying data were approximated with few thin-layer drying models that originated from the Newton's law of cooling, Fick's second law of diffusion, and the empirical ones. Results showed that microwave-assisted convective drying was characterized by considerably shorter drying time, higher drying rate, increased moisture diffusivity, and is more energy efficient as compared to conventional drying. Based on the statistical analysis, it was found that the Page and Weibull models were the most valid in approximation of the experimental drying curves. The quality assessment indicated that all samples dried by hybrid methods became discolored and shrunk. However, the highest polyphenol content was observed for the mushrooms dried with microwave power of 200 W at 30 degrees C. Retention of polyphenol content was in this case at the level of 83%. Water activity from both drying techniques was below 0.5, therefore microbiologically stable dry products were obtained.