Optimization of Hot Air-microwave Combined Drying Process of Shiitakes by Response Surface Method

Hot air-microwave combined drying process was used to dry shiitakes in the current study. Effects of switching point (dry basis moisture contents 2.00~5.00 g/g), hot air temperature (50.0~70.0℃) and microwave power density (6.67~33.33 W/g) on the drying characteristics and quality of shiitakes were investigated. Single factor experiments combined with Box-Behnken design was used to optimize the process parameters of hot air-microwave drying process. Effects of dry process on total drying time, and quality of final products (color, shrinkage, polysaccharide retention) were analyzed. Results showed that the optimal parameters for this combined drying process for shiitakes were:Dry basis moisture content at switching point 4.20 g/g, hot air temperature 60.60℃ and microwave power density 30.00 W/g, and the corresponding drying time was 178.33 min (the hot air was dried for 170 min and the microwave was dried for 8.33 min), total color difference was 11.21, shrinkage was 65.28%, lentinan retention was 66.98%, and the overall score was 0.145. This study suggested that the hot air-microwave combination could be an effective drying method to obtain dehydrated shiitakes with high quality.