Evidence for Adulteration of Ginkgo Leaf Extracts from Europe

Sydney, Australia-based Network Nutrition-IMCD has forwarded the results from an evaluation of finished product market samples (capsules and tablets) of mono-herbal formulations containing Ginkgo biloba leaf extracts, sourced from stores in Europe. Applying the United States Pharmacopeia (USP) monograph HPLC methodology for ginkgo extracts,¹ and the acceptance criteria provided therein, 14 of the 15 samples were found to be either fortified with rutin/quercetin and/or adulterated with Japanese sophora (Sophora japonica, Fabaceae) extracts.

In addition, the researchers quantified the amounts of genistein in the 15 products. Six of the samples contained over 1% genistein (ranging from 1.73% to as high as 9.56%), three samples contained more than 0.1% genistein (0.17% – 0.22%), and the remaining six samples were below 0.1%, with two clean samples in which the isoflavone concentration was below the detection limit (< 0.01%). The researchers note that if a maximum upper limit of 0.14% (a limit based on concentrations of 5 – 27 mg genistein/kg dry ginkgo leaf in the publication by Yao et al.² and a 50:1 concentration factor for the extract) of genistein in commercial ginkgo leaf extracts is accepted, nine of the commercial samples from Europe would have failed. When rutin and quercetin limits set by the USP monograph were considered in addition, only one of the 15 samples passed.

Comment: The data reported by Suresh Govindaraghavan, PhD, Research and Development Manager at Network Nutrition, provide more evidence for the continued, seemingly intentional, adulteration of ginkgo leaf extracts. While some deviations from the flavonoid fingerprint of authentic ginkgo leaf can be expected in extracts due to the manufacturing process, a majority of the tested products are clearly adulterated, supporting the conclusions of the Botanical Adulterants Bulletin on ginkgo leaf extracts. It is disappointing to see that the problems with ginkgo quality persist despite the raised awareness of the issue.

References

1.     Powdered ginkgo extract. USP 39-NF 34. Rockville, MD: United States Pharmacopeial Convention; 2016.

2.     Yao JB, Du X, Jin HH, Fang L, Min H, Qiao HX, Wang RW, Kuchta K. Seasonal variability of genistein and 6-hydroxykynurenic acid contents in Ginkgo biloba leaves from different areas of China. Nat Prod Commun. 2017;12(8):1241-1244.