Keywords: Adulteration, flavonoids, Ginkgo biloba, HPLC-MS/MS, HPLC-UV/Vis, quality control, terpene lactones

In one of the largest investigations into the quality of ginkgo (Ginkgo biloba, Ginkgoaceae) dietary supplements to date, more than 50 commercial ginkgo product samples from markets in Europe were analyzed for their contents of flavonol aglycones (after hydrolysis) and terpene lactones. Approximately 80% of the analyzed samples were found to have quality issues. These quality issues were illustrated by the authors using a subset of 11 samples labeled to contain ginkgo leaf extract (n = 8) or powdered ginkgo leaf (n = 3).

Flavonol aglycones were quantified in ginkgo extract using high-performance liquid chromatography with ultraviolet/visible detection (HPLC-UV/Vis), before and after hydrolysis, while terpene lactones were measured by HPLC with tandem mass spectrometric detection. Based on the analytical data, a number of deviations from authentic ginkgo were observed. Three ginkgo extracts contained negligible amounts of terpene lactones (0.03–0.85%), and one sample of powdered leaf did not contain measurable quantities of these lactones. Four extracts contained unusually high concentrations of flavonol aglycones (expected to be less than 0.1%) prior to hydrolysis, with up to 3.34% quercetin, 2.11% kaempferol, and 0.79% isorhamnetin. One dietary supplement labeled to contain ginkgo extract was made with powdered leaf, and one powdered ginkgo leaf product was found to contain substantial amounts of an unidentified plant material after microscopic analysis. Overall, two products were found to be of high quality, two products contained only trace amounts of ginkgo extract, one product marketed as ginkgo extract contained powdered ginkgo leaf, and the remaining six were deemed to be adulterated.

Comment: While the approach using specifications listed in the European Pharmacopoeia¹ without actually using pharmacopeial test methods to measure them may be questioned, the paper provides more evidence of widespread quality issues with ginkgo dietary supplements. While the addition of flavonol aglycones from extraneous sources has been the subject of many papers focusing on ginkgo authenticity,² the sale of ginkgo extracts without appreciable amounts of flavonoids and diterpenes (i.e., one extract containing only 0.49% flavonoids and 0.03% terpene lactones respectively, compared to the 24% flavonoids and 6% terpene lactones found in most standardized extracts) or the sale of powdered leaf as leaf extract has rarely been documented before. It is up to the industry members who either sell ginkgo extract or who purchase it to use in finished consumer products to ensure that future investigations into ginkgo dietary supplements will show a much improved picture of the quality and authenticity.

References

1. Ginkgo leaf. European Pharmacopoeia 9. Strasbourg, France: Council of Europe;2017: 01/2011:1828.
2. Gafner S. Adulteration of Ginkgo biloba leaf extract. Austin, TX: ABC-AHP-NCNPR Botanical Adulterants Prevention Program. 2017;1-8.