Effects of different pretreatment methods on quality and drying characteristics of Poria cocos after harvest

In order to optimize the drying process and to make the quality of Poria cocos under control, in this study, the traditionally sweated, steamed, and directly peeled and cut Poria cocos (without pretreatments) were evaluated through quality and drying kinetics to examine the relevance between pretreatments and the quality of Poria cocos and drying. Results showed that: 1) pretreatments played a dominant role in the quality control of Poria cocos. ① By comparing the mass fraction of water-soluble polysaccharides, Poria cocos after traditional sweating were 1.5 times higher than those without pretreatment and 1.7 times higher than those after steaming. The mass fraction of water-soluble polysaccharides of Poria cocos after steaming was significantly lower than that of those without pretreatment. ② The mass fraction of triterpenes of Poria cocos after traditional sweating was significantly lower than that of those after other two pretreatments. No statistical difference was found between steaming and no pretreatment. By controlling the sweating time and sweating temperature to maintain the mass fraction of tritrpenes. ③ Because of the material migration and accumulation during traditional sweating, Poria cocos after traditional sweating were whiter with better lustre compared with those after steaming (turned yellow and red). 2) Pretreatments is the key factor to affect the drying process. Compared with those with no pretreatment, Poria cocos after traditional sweating and steaming has a different the structure of material (hardness and porosity) and chemical composition (content), which made Bi significantly increased (indicating the increase of heat resistance within the material during the drying process). The shape parameter β was significantly reduced in the range of 0.3-1 (indicating that the drying process was always controlled by the internal water diffusion). The effective water diffusivity and mass transfer coefficient increased significantly, the drying rate increased and the drying time shortened. The steaming pretreatment is more effective in improving drying rate. The results of the study (the visual results displayed by the test data and he theoretical analysis based on the experimental data,) can further optimize the processing technology of Poria cocos, reduce the risk of quality deterioration, study the mechanism of different pretreatment methods on the quality formation of Poria cocos and the change of drying dynamics, and study the mechanism and work of the sweating of Chinese medicinal materials. It provides experimental reference and basis for promoting standardization of primary processing of Chinese medicinal materials by mechanism.