Improving quality of Poria cocos using infrared radiation combined with air impingement drying

Poria cocos has a long history of medicinal use in China. It is a kind of edible and pharmaceutical mushroom. Drying process usually affects the chemical and physical properties of the extracts of Traditional Chinese Medicine (TCM). Quality control remains a big issue, affecting herbs, formulations, and even the practice of TCM. Poria cocos generally takes almost 7 days to be dried by traditional natural drying and is sensitive to microbial spoilage. Poria cocos blocks (15 mm × 15 mm × 15 mm) are also easily broken at the traditional hot air drying, such as oven drying. A promising solution to the problem is to take advantage of innovative process techniques including alternative drying methods in the pharmaceutical processing. In this work, poria cocos was dried by medium and short infrared wave drying combined with air impingement drying. Dincer's model was also applied to the drying process and the lag factor (G), drying coefficient (S), Biot number (Bi), moisture effective diffusivity velocity (Deff), mass transfer coefficient (k) were analyzed. The Deff was also calculated based on Weibull function and Fick's second law, and there was difference among them. Combined with the GB-4857.5 T-1992 Droping Test Method and Pharmacopoeia of People's Republic of China, the broken rate and the extractum of poria cocos under different drying conditions were tested. The main results were as follows: 1) Compared with air impingement drying, drying time was shortened by infrared radiation combined with air impingement drying technology, and It could reduce the broken rate by 18% and improve the extractum mass fraction by 1%; the drying process also occurred in the falling rate period; at the range of the testing parameters, the drying rate increased with the increase of temperature and wind speed, but there was not direct correlation between broken rate, extractum content and drying conditions. 2) The G values of different drying methods were between 1.0136 and 1.0202, steady around 1. Drying coefficient was related to material drying speed; the higher temperature and wind speed, the faster drying ratio and drying coefficient was also larger. 3) The range of combined drying technology's Biot number was 0.0826-0.0982, lower than 0.1, which indicted the drying process was mainly influenced by external resistances. The range of mass transfer coefficient was 1.0319×10-6-1.8003×10-6 m/s. 4) The Deff calculated by Fick's law, Weibull function and Dincer's model showed a certain regularity, and all of them increased with the increase of temperature and wind speed. Fick's law and Weibull function didn't have relation with external resistances; and Fick's law didn't require drying curve in "exponential form", but only was applied in the falling rate drying process. Weibull function and Dincer's model had a broader application, but they needed drying curve must be exponential fitting. In summary, infrared radiation combined with air impingement drying technology can improve the quality of poria cocos. The results provide a reference for the application of Dincer's model on poria cocos drying, and help people to analyze drying process and gain the best drying method.