1H NMR based metabolic profiling of the processing effect on Rehmanniae Radix

The roots of Rehmannia glutinosa Libosch, Rehmanniae Radix, also known as Dihuang in China, are an important herbal drug in Traditional Chinese Medicine (TCM). According to the theory of TCM, the raw and processed Rehmanniae Radix are used quite differently. In this study, the chemical change of Rehmanniae Radix induced by processing is investigated by 1H NMR spectroscopy based fingerprinting coupled with multivariate data analysis. The results indicated that big chemical change had occurred after the processing of Rehmanniae Radix. Due to the high concentration of sugars, liquid–liquid partition approach was used to eliminate the interfering effect from sugars, in which more metabolites could be detected, and phenethylalcohol glycosides were concentrated in the EtOAc fractions, while the iridoid glycoside were enriched in the n-BuOH part. In addition, various statistical methods were used to find the differential metabolites between the groups. The results obtained in this study suggest that more than one extraction and statistical method should be used for comprehensive metabolic profiling of medical plants, which contained various metabolites in different concentrations.