Ginkgo Adulteration, Part 1: Publication Suggests Many Ginkgo Supplements Are of Low Quality
Reviewed: Booker A, Frommenwiler D, Reich E, Horsfield S, Heinrich M. Adulteration and poor quality of Ginkgo biloba supplements. J Herb Med. 2016;6(2):79-87.
Keywords: Ginkgo biloba, ginkgo leaf extract, adulteration, fingerprint, HPTLC, 1H NMR
This publication, resulting from a collaboration between the University College London and instrument manufacturer CAMAG, details adulteration of commercial products labeled to contain Ginkgo biloba(Ginkgoaceae) extracts sold in the United Kingdom. The authors purchased 35 ginkgo food supplements in the London area or from the Internet, and compared the high-performance thin-layer chromatography (HPTLC) fingerprints and proton nuclear magnetic resonance (1H NMR) patterns between 6 and 8 ppm to authentic ginkgo obtained from the National Institute of Standards and Technology (NIST). HPTLC fingerprints were evaluated visually, while 1H NMR data were subjected to statistical examination by principal component analysis (PCA).
Visual inspection of the HPTLC chromatograms indicated that only two (less than 6%) out of the 35 samples corresponded to the NIST reference material. Four samples (11%) were predominantly composed of rutin, while one sample contained only a blue band, which – based on subsequent NMR analysis – was found to be a derivative of 5-hydroxytryptophan. A majority of the samples – 26 (74%) out of 35 – contained a strong yellow band indicative of large amounts of quercetin. Most of these samples had a fingerprint consistent with ginkgo leaf, but with variable intensity of the bands that correspond to the flavonol glycosides. According to the HPTLC results, six samples (17%) contained no or only small amounts of ginkgo terpene lactones. 1H NMR results confirmed the large variability in the composition of the ginkgo food supplements, with the majority of products scattered in a cluster between the ginkgo reference material and pure rutin.
Comment: The results of this study are in agreement with recent data on widespread issues with ginkgo authenticity and quality, some of which were summarized in our recent review article in HerbalGram.1 A particular problem is the occurrence of large amounts of free flavonols, especially quercetin. In crude leaves, and in the most widely clinically tested ginkgo extract (EGb 761®, manufactured by Dr. Willmar Schwabe GmbH & Co. KG; Karlsruhe, Germany), these flavonols occur only in trace amounts. Wohlmuth et al. found less than 0.05% of free quercetin in authentic unhydrolyzed ginkgo extracts, and up to 2.48-7.42% in adulterated materials.2 Ma et al. analyzed 15 powdered ginkgo leaf extracts and 14 ginkgo dietary supplements for the contents of rutin, quercetin, kaempferol, and isorhamnetin prior to hydrolysis. The quercetin concentrations were between 0 and 5.76% in powdered extracts, and between 0.26 and 6.37% in finished ginkgo products.3 It is not clear what an acceptable limit for free aglycones such as quercetin and kaempferol should be. Wohlmuth et al.2 suggested that the concentrations of quercetin, kaempferol, and isorhamnetin should be limited to a maximum of 0.5%. A quercetin limit of ≤ 0.5% prior to hydrolysis has been incorporated in the most recent monograph for powdered ginkgo extract in the United States Pharmacopeia.4
1. Gafner S. Ginkgo extract adulteration in the global market: a brief review. HerbalGram. 2016;(109):58-59.
2. Wohlmuth H, Savage K, Dowell A, Mouatt P. Adulteration of Ginkgo biloba products and a simple method to improve its detection. Phytomedicine. 2014;21(6):912-918.
3. Ma YC, Mani A, Cai Y, et al. An effective identification and quantification method for Ginkgo biloba flavonol glycosides with targeted evaluation of adulterated products. Phytomedicine. 2016;23(4):377-387.
4. United States Pharmacopeial Convention. Powdered Ginkgo Extract. In: United States Pharmacopeia and National Formulary (USP 39–NF 34). Rockville, MD: United States Pharmacopeial Convention; 2016.