Authentication of Commercial Licorice Root/Rhizome Samples Used in the UIC/NIH Center for Botanical Dietary Supplements Research: The Importance of Licorice Genotyping

Botanical dietary supplements (BDSs) containing licorice root/rhizome are derived mainly from three Glycyrrhiza (Fabaceae): Glycyrrhiza glabra L., G. inflata Batalin; and/or G. uralensis Fisch. ex DC. Licorice BDSs can consist of whole, chopped-up, or powdered root/rhizome. Due to morphological similarity and natural hybridizations among the three aforementioned species, their authentication using morphological traits is difficult and prone to error. Thus, the goal of this study was to develop a protocol for identifying all commercial BDS licorice root/rhizome samples to species before extensive chemical and biological investigations are undertaken at our Center. We used an established licorice Sanger DNA sequencing protocol and molecular genetic phylogeny to authenticate commercial BDS licorice root/rhizome samples by species. Interestingly, among ten investigated samples, two were found to contradict the species designated by the supplier. Signs of admixture were found in another two of the ten samples, which were auspiciously both bags/vials of chopped-up material. Amplified plant DNA was not detected in all PCR negative reactions. In conclusion, genotyping of source material was found to be crucial to ensuring the reproducibility of further phytochemical and biological studies of licorice BDSs. Proper handling of BDS materials prior to DNA testing is essential, and samples may be mixed by the manufacturer (inadvertent or not) and not labeled as such.