Review of Published Data on DNA-Based Botanical Ingredient Authentication Suggests that Adulteration is Common

Reviewed: Ichim MC. The DNA-based authentication of commercial herbal products reveals their globally widespread adulteration. Front Pharmacol. 2019;10:1227.

Keywords: Adulteration, DNA barcoding, metabarcoding, next-generation sequencing

For this review, the author systematically evaluated literature published between 2000-2018 using a number of search terms to find papers describing the use of genetic methods to authenticate botanical ingredients and finished dietary supplement products. Publications had to be peer-reviewed, pertaining to plants used as medicine (as opposed to food use), clearly state the country where the botanical ingredient was purchased, and authenticity was evaluated by the author(s) of the investigation. A total of 206 studies involving 5,957 commercial herbal products sold in 37 countries was included in the analysis.

The majority of the herbal products were from Asian countries, with China (n = 2809), India (n = 752), Taiwan (n = 453), and South Korea (n = 212) having the largest representations. This may reflect an early adoption of DNA-based authentication techniques by academic research groups in these countries. The only non-Asian countries with more than 100 samples analyzed were the United States (n = 465) and Brazil (n = 154).

Using this approach, author Ichim estimated that 27% of the analyzed samples were adulterated. When separated by continent, adulteration was most prevalent in Australia (79% of samples adulterated), followed by South America (67%), Europe (43%), North America (33%), Africa (27%), and Asia (23%). Given the low number of samples in Australia (n = 63) and Africa (n = 119), it is unclear how representative for the trade these percentage numbers are.

Comment: In light of the known shortcomings of DNA-based authentication of herbal ingredients, this attempt to assess the extent of adulteration is unlikely to provide an accurate picture of botanical ingredient and finished product quality. It is not clear how many of the samples were crude raw herbs (whole, cut, or powdered plant) and how many of these were processed ingredients/finished products. Adulteration is more likely to occur with powdered herbs and extracts, since identity determination is more complicated. It is also well-known that DNA barcoding and metabarcoding techniques have a number of limitations with highly processed materials, notably the inability to distinguish among plant parts, the preferential amplification of non-target DNA using Sanger sequencing and the amplification of contaminants present at permissible concentrations (i.e., acceptable levels of foreign organic matter) using next-generation sequencing (NGS).^1-4

Some of these issues have been pointed out by the author, while others have not. The country assignment of plant materials based on the papers is not really straightforward. An example is the paper on licorice characterization using DNA barcoding and ¹H nuclear magnetic resonance (NMR) spectroscopy by Simmler et al.⁵ Having provided some of these samples (S. Gafner), it’s is clear that many were sourced directly in China, and not in the United States as written by the authors.

This is not the first time that results from DNA-based identification of herbal ingredients have been used to invoke a potential danger with contaminants. In this case, the author states that “one pollen grain from another species deposited on the harvested species can potentially lead to false-positives unless it originates from an allergenic or poisonous plant and then the method will became literally a lifesaver.” While pollen can certainly cause allergies, to our knowledge, there is no plant of which a single pollen grain would be poisonous enough to cause death.

References

1. Pawar RS, SM Handy, R Cheng, N Shyong, E Grundel. Assessment of the authenticity of herbal dietary supplements: comparison of chemical and DNA barcoding methods. Planta Medica. 2017;83:921-936. doi: 10.1055/s-0043-107881.
2. Ivanova, NV, Kuzmina ML, Braukmann TWA, Borisenko AV, Zakharov EV. Authentication of herbal supplements using next-generation sequencing. PloS One. 2016;11(12): e0168628. https://doi.org/10.1371/journal.pone.0156426. Accessed November 1, 2019.
3. Parveen I, Gafner S, Techen N, Murch SJ, Khan IA. DNA Barcoding for the identification of botanicals in herbal medicine and dietary supplements: strengths and limitations. Planta Med. 2016;82(14):1225-1235.
4. Heinrich M, Anagnostou S. From pharmacognosia to DNA-based medicinal plant authentication – pharmacognosy through the centuries. Planta Med. 2017;83(14-15):1110-1116.
5. Simmler C, Anderson JR, Gauthier L, Lankin DC, McAlpine JB, Chen SN, Pauli GF. Metabolite profiling and classification of DNA-authenticated licorice botanicals. J Nat Prod. 2015;78(8):2007-2022.