There is a widespread perception that DNA testing is infallible when it comes to identifying organisms. The unquestioning acceptance of the New York Attorney General’s flawed DNA testing of herbal supplements is a testament to this perception.

There are a number of factors that can impact the accuracy of DNA testing. The specific laboratory, the particular methods used, and the individual scientists all play an important role in the accuracy and validity of DNA test results.

The capabilities and limitations of DNA testing are detailed in a recent whitepaper commissioned by the American Herbal Products Association (AHPA), the Consumer Healthcare Products Association (CHPA), the Council for Responsible Nutrition (CRN) and the United Natural Products Alliance (UNPA). The following are some highlights from that whitepaper.

Pitfalls Must Be Avoided
DNA can be found nearly everywhere, not only in test sabut also on surfaces in the laboratory, microscopic organisms living in water, pollen grains and fungal spores in dust, and even on pens, desks and notebooks. Strict quality control and contamination elimination procedures must be followed in order to avoid errors. When contamination has been detected, specific criteria for re-testing must be followed to ensure accurate results.

Testing Plant DNA is More Difficult
The term “DNA barcoding” was first introduced as a method to identify animal species and it has been particularly useful for distinguishing tissue obtained from distinct species. The method underlying plant DNA barcoding—sequencing of genes for identification—is not debated. DNA barcoding of plant materials has also been used to identify major plant groups such as grasses and pine trees.

However, the controversy is whether a single or standard set of a few genes is enough to differentiate between species. Because most genes are identical from plant to plant, it is difficult to identify the few regions of the plant genome that vary enough to confirm identity. DNA from a plant’s gene region that is identical across many species is not useful for identification and will provide ambiguous results. Numerous genes must be tested to identify the gene(s) that uniquely occur in one species, but not other plant species.

Plant species that have a broad geographic distribution may show inconsistent genes, even if they are considered the same species taxonomically and chemically. Therefore, it is critical to understand the acceptable variation within the species, so that test samples are not falsely rejected. To do this, multiple reference sequences must be obtained from across the morphological, chemical and geographical diversity within each species.

Dynamic lineages of closely related species, like Echinacea for example, are also difficult to distinguish using DNA because of widespread hybridization. It is critical to locate the genes that contain the appropriate level of variation to allow for differentiation of species. This often requires extensive research into the evolutionary history and biology of the plant.

Testing Supplement DNA is Even More Difficult
For botanical identification, DNA barcoding is mostly limited to raw materials. Because of the relatively new application of DNA barcoding to finished supplements, there is a general lack of understanding of its limitations.

When it is not practical to obtain whole or powdered plants, the use of multiple methods on processed materials is necessary to increase the accuracy of identity and quality testing. DNA barcoding is not capable of identifying the chemical constituents or plant parts, nor is it able to quantify the amount of plant material used in the product. Therefore, the use of additional methods (e.g., microscopic and chemical) is necessary to control the overall quality of a botanical dietary supplement and to verify label claims by identifying chemicals of interest, confirming the plant part, and/or ensuring the potency of the product.

Typically most, if not all, of the material containing cells (with the DNA) is removed or damaged when the phytochemicals are extracted. Any remaining DNA is generally low in quality and concentration. Original, long DNA strands are usually fragmented into short pieces, leaving a lack of relatively long gene regions required for accurate DNA testing of botanicals.

Despite several reports indicating the successful use of DNA barcode methods on botanical extracts, the results tend to be erroneous, likely due to cross-contamination by other materials either in manufacturing or in the laboratory conducting testing.

Because most botanical dietary supplement ingredients are in powder form, it increases the risk of contamination with airborne particles that may have DNA present.

Methods of “specific DNA authentication” have been used successfully in some botanical extracts, oils and tinctures, but the methods are not publically available (through peer-reviewed publications) for most commercially used species. Thus, independently developed and validated methods for these materials are necessary to assure accurate results.

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Maged Sharaf, PhD
American Herbal Products Association (AHPA)

Maged Sharaf, PhD, is the chief science officer of the American Herbal Products Association (AHPA), the national trade association with a focus primarily on herbs and herbal products. AHPA’s membership represents U.S. and international growers, processors, manufacturers, marketers and institutes specializing in botanicals and herbal products. Before AHPA, Dr. Sharaf was the director, Foods, Dietary Supplements and Herbal Medicines at the United States Pharmacopeial Convention (USP). Before USP he was pharmacy associate professor and has preceding experience conducting bioanalytical assay development and validation, and human bioequivalence studies in support of the pharmaceutical industry; and quality control and manufacturing of pharmaceutical dosage forms. He can be reached at 301-588-1171; E-mail: [email protected]; Website: www.ahpa.org.