Optimization of Process Parameters for Microwave Vacuum Drying of Apple Slices Using Response Surface Method

A combination of microwave and vacuum methods was applied for drying apple slices. Predictive regression models were developed by using an orthogonal rotatable central composite design. The influences of various variables and their interactions on response variables were analyzed using a response surface method, and tridimensional response surfaces were plotted. The optimal conditions were determined to be 12.0W/g microwave power, 0.089MPa vacuum level, and 0.692kg/kg db initial moisture content. A separate validation experiment was conducted at the derived optimum conditions to verify the prediction and adequacy of the models. Close agreement between experimental and predicted values was obtained. Microwave vacuum-dried product exhibited a more prominent honeycomb network structure compared with that of the hot air-dried product.