Dissecting chemical markers for controlling "Paozhi" method of traditional Chinese medicine with untargeted metabolomics: Vinegar-baked Euphorbia kansui as a case study.

The processing of Traditional Chinese Medicine requires the appropriate parameters, while the specific chemical markers are still absent to obtain the optimized processing. In this study, we used vinegar-baked Euphorbia kansui as a case to dissect the chemical markers for the baking process using untargeted metabolomics. The robust chemical markers were selected based on the three rules, correlation, significant difference, and controllability. All the differential features were categorized based on their mass defects. After the differential analysis, 310 differential compounds were screened out and could be mainly divided into six categories: diacylglycerols and triacylglycerols demonstrated increasing trends with the baking time in the discriminant model, while ingenane-type diterpenes, jatrophane-type diterpenes, fatty acid esters, and fatty acids had decreasing trends. It was unexpected to find that the diterpenes did not correlate with the baking time. Only very few compounds meet the three rules. They were validated with a high-performance liquid chromatography method. Finally, only 13-Hydroxy-9,11-octadecadienoic acid and its isomer 9-Hydroxy-10,12-octadecadienoic acid could be used further to differentiate the commercial vinegar-baked Euphorbia kansui. It would be of interest to evaluate whether these two compounds could be utilized as markers to control more processing methods in future studies.