Moisture diffusion modelling and effect of microwave vacuum drying on drying kinetics and quality of yam

Microwave vacuum drying (MVD) is a rapid drying method, which can achieve a good balance between drying rate and quality. In the present work, the effects of MVD processes on the quality, drying kinetics, and moisture diffusion of yam (Dioscorea opposita L.) were investigated. Results indicated that the loss of moisture in the MVD of yam slices mainly occurred in the stage with a constant and decreasing speed. When the moisture content of the dry base was decreased to about 1.3 g/g (dry basis, D.B.), it began to enter the deceleration phase. The effective moisture diffusivity (Deff) and mass transfer coefficient (km) increased following the power, loading amount at one time, and vacuum (pressure drop). The established equation of these parameters described well this variation law. Furthermore, a neural network model was established to predict the change in moisture content in the drying process, and the law of moisture diffusion was described. In terms of quality, the contribution ranked from high to low was loading, power, and pressure. Increasing the microwave power, loading, and maintaining a high vacuum degree could reduce energy consumption and ensure quality, thus improving the economic feasibility of microwave vacuum in the drying process.