FWD 2 Botanical Adulterants Monitor: FT-NIR Combined with Chemometric Analysis as a Means to Distinguish Powdered Goldenseal Root from its Adulterants


FT-NIR Combined with Chemometric Analysis as a Means to Distinguish Powdered Goldenseal Root from its Adulterants

Reviewed: Liu Y, Finley J, Betz JM, Brown PN. FT-NIR characterization with chemometric analyses to differentiate goldenseal from common adulterants. Fitoterapia. 2018;127:81-88.

Keywords: adulteration, Berberis aquifolium, coptis, Coptis chinensis, FT-NIR, goldenseal, Hydrastis canadensis, Oregon grape, Rumex crispus, Xanthorhiza simplicissima, yellow dock, yellow root

The roots of goldenseal (Hydrastis canadensis, Ranunculaceae) are an important medicinal ingredient in North American herbal medicine and elsewhere. Practitioners appreciate the root as a stand-alone ingredient because of its antimicrobial activities, but it is also frequently combined with echinacea (Echinacea spp., Asteraceae) and other botanicals in dietary supplements to support healthy immune function.

Adulteration of goldenseal has been reported on a number of occasions, and is thought to be due to the availability of materials that also contain berberine, or similar benzylisoquinoline alkaloids at a considerably lower price, thus providing an incentive for economically-motivated fraud.1 Most often, analytical laboratories use chromatographic methods, e.g., high-performance liquid chromatography (HPLC) combined with ultraviolet/visible spectrophotometry (UV/Vis) to measure the goldenseal alkaloids.2-5 Using Fourier-transform near-infrared (FT-NIR) spectroscopy, a faster and less costly approach was evaluated for its ability to differentiate powdered crude goldenseal from its known adulterants, and to determine the level at which these adulterants could be detected.

The main goal of the project was to determine which statistical assays would represent the best choice for the evaluation of the FT-NIR spectra. The authors compared partial least square (PLS) regression analysis alone and with preprocessing methods (external parameter orthogonalisation [EPO] and generalized least squares weighting [GLSW]), soft independent modelling with class analogy (SIMCA) alone and with preprocessing methods (EPO, GLSW, and extended multiplicative scatter correction [EMSC]), and moving window – principal component analysis (MW-PCA) without preprocessing of the data.

Only MW-PCA and SIMCA combined with EMSC provided satisfactory results in distinguishing among the five species included in the analysis. The model was then tested at theoretical adulteration levels of 2%-95%. It was able to easily detect yellow root (Xanthorhiza simplicissima, Ranunculaceae), Oregon grape (Berberis aquifolium, Berberidaceae) root, and coptis (Coptis chinensis, Ranunculaceae) root adulteration in goldenseal at levels of 10% and above. For yellow dock (Rumex crispus, Polygonaceae), SIMCA-EMSC was only able to detect the adulteration at 15-20%. Using the MW-PCA model, FT-NIR was able to detect coptis adulteration levels as low as 2%, and yellow dock and Oregon grape adulteration between 15% and 20%. Baseline drift issues were observed in yellow root, leading to much higher detection limits (15%-50%).

Comment: The results provide evidence that FT-NIR in combination with an optimized chemometric model allows the detection of four common goldenseal adulterants in cases where materials are purchased in whole, cut, or powdered root form at levels generally between 5-20%. The low costs and quick sample turnaround will be appealing features for using this method in quality control laboratories. Another advantage is the possibility of making computer-generated spectra of hypothetical sample mixtures, eliminating the need to weigh out and homogeneously mix goldenseal and adulterants at specific levels (i.e., 1.5 grams of adulterant in 8.5 grams of goldenseal to make a sample containing 15% adulterant). As is often the case with statistical models requiring a large number of samples, one of the bottlenecks is the availability of authenticated plant material, especially of the alleged adulterants. As such, the inclusion of only one sample of yellow dock in this project is not ideal. In addition, many manufacturers may need to detect adulterants at levels below what FT-NIR was able to provide as the 5% limit of detection exceeds the proscribed 2% foreign organic matter limit established by most pharmacopoeias.

Interestingly, yellow dock was one of the more difficult ingredients to distinguish from goldenseal despite the absence of alkaloids and the presence of anthraquinones such as aloin, emodin, and physcion.6,7 Most previously-reported chromatographic methods have relied on the evaluation of alkaloids other than those in goldenseal, such as palmatine and jatrorrhizine, which is an easy way to detect adulteration with coptis, yellow root, or Oregon grape, and is suggested as another appropriate way to determine the authenticity of goldenseal root and root extracts.2-5

References

  1. Tims M. Adulteration of Hydrastis canadensis root and rhizome – Botanical Adulterants Prevention Bulletin. Austin, TX: ABC-AHP-NCNPR Botanical Adulterants Prevention Program. 2016;1-6.
  2. Avula B, Wang YH, Khan IA. Quantitative determination of alkaloids from the roots of Hydrastis canadensis L. and dietary supplements using ultra-performance liquid chromatography with UV detection. J AOAC Int. 2012;95(5):1398-1405.
  3. Weber HA, Zart, MK, Hodges AE, White KD, Barnes SM, Moody LA, Clark AP, Harris RK, Overstreet JD, Smith CS. Method validation for determination of alkaloid content in goldenseal root powder. 2002; J AOAC Int. 86:476.
  4. Kamath S, Skeels M, Pai A. Significant differences in alkaloid content of Coptis chinensis (Huanglian), from its related American species. Chinese Medicine. 2009;4:17.
  5. Upton R, Graff A, Swisher D. Goldenseal root, Hydrastis canadensis L.: Standards of Analysis, Quality Control, and Therapeutics. Santa Cruz, CA: American Herbal Pharmacopoeia; 2001.
  6. Jeelani SM, Farooq U, Gupta AP, Lattoo SK. Phytochemical evaluation of major bioactive compounds in different cytotypes of five species of Rumex L. Ind Crop Prod. 2017;109:897-904.
  7. Wegiera M, Smolarz HD, Wianowska D, Dawidowicz AL. Anthracene derivatives in some species of Rumex L. genus. Acta Soc Bot Pol. 2007;76(2):103-108.