Effect of microwave vacuum drying on the drying characteristics,color, microstructure,and antioxidant activity of green coffee beans

To explore the moisture and components change law of Peucedani Radix slices during microwave vacuum drying, and effectively improve the drying efficiency and slice quality of Peucedani Radix slices, by carring out drying characteristics analysis and simulation of Peucedani Radix Slices during microwave vacuum drying. Microwave vacuum drying experiments of Peucedani Radix slices under different drying conditions (microwave power density, vacuum degree and slice thickness) were carried out. The changes of moisture ratio and drying rate during drying process were studied. The contents of three coumarin ingredients (praeruptorin A, praeruptorin B and praeruptorin E) in dried Peucedani Radix slices were determined by HPLC. Weibull function was used to simulate and analyze the moisture ratio curve during drying process. Microwave vacuum drying process of Peucedani Radix slices has three stages: acceleration, constant speed and deceleration. Compared with vacuum degree and slice thickness, increasing microwave power density could shorten drying time and improve drying efficiency more effectively. In the range of experimental parameters, the optimum drying conditions were as follows: microwave power density was 3.0 W·g^–1, vacuum degree was 800 Pa, and slice thickness was 2 mm. The changes of all drying conditions had no significant effect on the content of coumarins in dried Peucedani Radix slices. The results of Weibull function simulation and analysis showed that the scale parameters under different drying conditions ranged from 17.43 to 45.38, and the smaller the value, the shorter the drying time. The shape parameters ranged from 1.41 to 1.77 and were all greater than 1, indicating that the drying process was controlled by internal and external water diffusion.The research work not only provides important theoretical basis and technical support for the process improvement and quality control of microwave vacuum drying process of Peucedani Radix slices, but also provides important reference for the standardization of Peucedani Radix slices drying and the formation of quality characteristics.