DNA Authentication of Raw Herbal Drugs for Industrial Quality Assurance

Many plant-based medicines are still prepared from plants collected from the wild, requiring routine testing to ensure their correct identity. Quality control of wild-harvested plant materials has typically involved morphological and chemical analysis, but both approaches have their limitations. DNA-based authentication assays could complement these techniques and are currently under development for incorporation into industrial quality assurance procedures for a number of commercial products. A general strategy for the design of a robust DNA authentication assay for routine testing has been established. Specimens of the commercial plant species and its potential adulterants are collected and a DNA barcode sequence library created. PCR primers are designed to informative sequence strings that can be used to distinguish a target species from others in the dataset. Primers designed to generate short amplicons can be optimized for multiplex PCR, quantitative PCR and high resolution melt curve (HRM) assays.

Rhodiola rosea is a one such target for DNA test development. Raw material for R. rosea containing products still derives mainly from collection in the wild, with almost a dozen closely related species growing in the same habitat. Positive identification of the correct plant species is not obvious and misidentifications or even adulterations are common. Although rosavines are considered to be characteristic constituents of R. rosea, there is some doubt about their use as chemical markers. Informative sequence differences between the DNA barcodes of different Rhodiola species have been used to design a specific qPCR assay. This allows the quantitation of the target species DNA, but cannot detect unknown adulterant species. Conversely, an HRM assay can detect unknown species in mixed samples, but only at relatively high levels of contamination. Lessons learned from these and other examples will be discussed.