Details of the investigation into the quality of 15 ginkgo leaf dietary supplements by the Sydney, Australia-based Network Nutrition-IMCD (summarized in the previous Botanical Adulterants Monitor) have now been published. The results from this evaluation of commercial mono-herbal formulations containing Ginkgo biloba leaf extracts, sourced from stores in Europe can be requested from the company (networknutrition@imcd.com.au) according to a press-release from May 7, 2018.¹ The investigation included the determination of total flavonol glycosides, limits of quercetin and rutin, limits of ginkgolic acids, detection and quantification of genistein, and the kaempferol/quercetin and isorhamnetin/quercetin ratios. Only one of the 15 commercial ginkgo leaf dietary supplements passed all these tests, while each of the 14 other products failed two or more assays.

Particular emphasis is given on a discussion about the usefulness of genistein as a marker compound for ginkgo leaf extract adulteration. According to the press release, “Majority of scientific literature indicates this isoflavone does not occur naturally in Ginkgo leaf and as such, has for some time been touted as an effective marker for detecting adulteration with Sophora japonica. Few research articles suggest genistein occurs naturally in Ginkgo leaf. To give clarity to this controversy, the investigation expands the current available science by identifying and assaying compounds documented as specific to Sophora and not present in Ginkgo leaf.”

Comment: While this investigation found considerable differences in the genistein concentrations among the various ginkgo products, the question if this isoflavone naturally occurs in the ginkgo leaves remains unanswered. Hopefully, the expansion of the research project will deliver a definitive answer on the presence of this compound in ginkgo. One of the outcomes of this research is the recognition that the United States Pharmacopeia staff has made considerable efforts to keep up with new ways to detect adulterated ginkgo extracts, and that adhering to the USP monographs provides an effective means to detect adulteration. However, the addition of a limit test for genistein is suggested by the authors.

Reference

1. Ginkgo biloba Market Report [press release]. Bella Vista, NSW, Australia; Network Nutrition-IMCD; May 7,2018.