Evidence for Adulteration of Turmeric Extracts with Synthetic Curcumin

Details of the investigation into the authenticity of 14 turmeric (Curcuma longa, Zingiberaceae) dietary supplements randomly purchased on the internet were presented by Len Monheit, Executive Director of the Global Curcumin Association (GCA), during a webinar on December 3, 2020.¹ The commercial samples were analyzed for curcuminoid contents according to the HPLC-UV method for turmeric extracts described in the United States Pharmacopeia² and for contents in non-biobased curcumin by ¹⁴C isotope mass spectrometry.

In the initial investigation in 2018, out of the 13 turmeric supplements that were evaluated, six contained non-biobased (petroleum-based) curcumin, and four had less than 50% of the declared content in curcuminoids. The results were promptly communicated to the manufacturers, and in 2020, GCA retested the same and one additional turmeric supplement, bringing the total to 14 samples. In the second round of testing, five turmeric products contained non-biobased curcumin, and four products had only a fraction (between 0.8 – 2.7%) of the declared curcuminoid amount. A fifth product contained 62.2% of the claimed curcuminoids, but all the other products complied with the standardization claim. Interestingly, four of the five products that had synthetic curcumin complied with the declared amount of curcuminoids. The fifth product with non-biobased curcumin was the one with 62.2% of the labeled curcuminoid content.

Comment: This investigation represents a good example of the usefulness of stable isotope measurements. Isotope mass spectrometry has not been widely used to assess the authenticity of herbal ingredients. However, it represents one of the few analytical techniques that can directly measure the presence of synthetic molecules using petroleum-based starting materials. Conventional methods, such as HPLC-UV/Vis, or HPTLC can only infer presence of synthetic molecules, e.g., based on unusual constituent ratios (e.g., the ratio of curcumin to demethoxycurcumin and bis-demethoxycurcumin). The determination of characteristic byproducts — if present — of a particular chemical synthesis generally needs more sophisticated instrumentation that enables structure elucidation, such as a combination of a mass spectrometer and nuclear magnetic resonance (NMR) instrument. While the use of synthetic substances in most cases does not represent a health risk to the consumer, it is misleading to label a product as a plant extract when it contains petroleum-based synthetic constituents. As such, the use of ¹⁴C isotope mass spectrometry represents a useful tool to detect the fraudulent addition of undeclared synthetic curcumin to turmeric extracts.  

References

1. Monheit L. Curcumin stewardship challenges & opportunities. Presented at: Stewarding Responsible Growth by Protecting the Integrity of the Curcumin Category. Webinar; December 3, 2020.
2. US Pharmacopeia, Powdered Turmeric Extract. USP 42-NF 37. Rockville, MD: United States Pharmacopeial Convention; 2019:5258.