[Research progress on percolation extraction process of traditional Chinese medicines]

Percolation extraction is a conventional extraction method used in the processing of traditional Chinese medicines. After medicinal material powder is placed in a percolation tank, the extraction solvent is continuously added, and percolation extract is collected simultaneously. The percolation equipment is simple. The percolation operation is easy. It is applicable to a wide range of medicinal materials. Components that are unstable under thermal conditions can be effectively extracted. However, there are also disadvantages, such as high solvent consumption, long extraction time, and high energy consumption in subsequent concentration processes. This article mainly reviews the research progress on the common equipment types, affecting factors, parameter optimization methods, and process monitoring. According to analysis on literatures, solvent composition, impregnation time, percolation speed, and solvent consumption are considered as the important factors of percolation processes. At present, near-infrared spectroscopy is widely used in the monitoring of percolation process, and partial least square is a commonly used quantitative modeling method. According to the concept of "Quality by Design", in-depth investigation of the percolation process mechanism and development of process control methods are future development trends. Therefore, process modeling, process optimization and process monitoring shall be improved. The mechanism models and the empirical models of column chromatography can be used as references to construct the percolation process models. The effect of the quality changes of medicinal materials shall be taken into account when optimizing the percolation process parameters. More simple and easy methods shall be developed to monitor the percolation process status and key properties of percolation extracts.