Study on the Microwave Vacuum Drying Characteristics and Drying Kinetic Model of Lycium barbarum Extract

In order to investigate the microwave vacuum drying characteristics of Lycium barbarum extract, the prediction model of drying kinetics of the relationship between its moisture ratio and drying time was established by investigating the influence rule of microwave power density and the initial relative density of the extract on the temperature, dry basis moisture content and water loss rate of the extract, and the model was validated. The experimental results showed that the microwave vacuum drying process of Lycium barbarum extract could be divided into two stages: The extract was transformed from a fluid state to a semi-fluid state (stage I) and from a semi-fluid state to a dry paste state (stage II). The higher the microwave power density and the initial relative density, the rising trend of the temperature of the extract seemed more obvious. The faster the water content of the dry base decreased, the greater the change in the rate of water loss, and the shorter the drying time required. By fitting six commonly used empirical models for thin-layer drying, among which the Wang model R² was between 0.98878~0.99902, X ² and SSE were less than 0.0017 and 0.00849, which were the smallest values among the six models. And after verification, the predicted values of the model were basically fitted with the experimental values, which could better predict the moisture of Lycium barbarum extract during microwave vacuum drying change rule.