HerbalEGram: Volume 12, Issue 12, December 2015

Ginkgo biloba (Ginkgoaceae) leaf extract (GBE) is one of the most popular and well-researched herbal preparations Worldwide, ginkgo is accepted as a formal medicine for enhancing mental acuity, a use supported by dozens of clinical trials based on a few proprietary extracts manufactured in Europe. Unfortunately, in the past decade, growing evidence of the production and sale of sub-standard and adulterated ginkgo extracts in the international supply chain, much of it reportedly coming from China, has emerged.

In 2003, an investigation into the quality of nine commercial ginkgo extracts from suppliers in Europe, Asia, and North America found one sample with an unusually high content of rutin, a flavonol glycoside that occurs in many plant species (including ginkgo), and one sample with almost no ginkgo terpene lactones (e.g., the ginkgolides A and B, and bilobalide, which are exclusively found in ginkgo), and no ginkgo flavonols. The authors suggested that pure rutin was added to one sample to increase the content in total flavonol glycosides.¹ Similarly, four out of 14 commercial ginkgo products sourced in the Edmonton (Alberta, Canada) area were likely adulterated with pure flavonols (the glycoside rutin, and the non-glycosylated [aglycones] quercetin, kaempferol and isorhamnetin).²

A comparison of HPLC (high-performance liquid chromatography) fingerprints of ginkgo extracts from 19 different sources published in 2006 suggested that three products were adulterated with added rutin.³ In 2008, the adulteration issue was raised again by Dr. Hermann Kurth of the German extract manufacturing company Finzelberg in a conference presentation.⁴ In the presentation, rutin (allegedly sourced from buckwheat [Fagopyrum esculentum, Polygonaceae] or Japanese sophora [Sophora japonica syn. Styphnolobium japonicum, Fabaceae]) and kaempferol were found as adulterants of ginkgo extracts. 

In 2010, a report about ginkgo food supplements purchased and analyzed in Europe indicated the existence of adulterated ginkgo extracts.⁵ The adulteration of ginkgo extracts with pure flavonoids, or flavonoid-rich extracts also was detailed in 2011. In that study, Chandra et al. reported that chromatographic profiles of three products (out of eight products analyzed) labeled to contain ginkgo extracts closely resembled those of commercial extracts obtained from Japanese sophora.⁶ A Japanese study published in 2012 detailed the analysis of 22 commercial products (16 ginkgo products from Japan and 6 from Germany and France). The authors found three products with unusually high amounts of quercetin, and suspected that the quercetin was an “artificial additive,” or that the ginkgo was manufactured using a special process.⁷ In May 2013, the California company Ethical Naturals, Inc. issued a revised report on ginkgo adulteration, titled “Ginkgo Adulteration & Identification w/Fructus sophorae (Sophora japonica),” which describes an HPLC-UV method using genistein as a marker compound to detect adulteration of ginkgo extracts with extracts from the fruit of Japanese sophora.⁸

Adulteration with rutin of commercial ginkgo products purchased in the Turkish market was reported by Demirezer in 2014.⁹ Also in 2014, Australian researchers published a relatively simple method to detect adulteration of ginkgo extract in commercial dietary supplement products.¹⁰ By using the HPLC conditions of the United States Pharmacopeia before and after hydrolysis, the authors discovered admixtures of the flavonols quercetin and kaempferol in three of the eight commercial samples that were analyzed. The three adulterated samples also contained genistein, an isoflavone that has not been found in ginkgo leaves, but is characteristic of some plants in the pea family (Fabaceae), including in the genus Sophora, which was previously implicated in analyses, thereby demonstrating adulteration of ginkgo extracts. The authors hypothesized that the genistein could come from extracts of the fruit of Japanese sophora. They noted that current pharmacopeial methods are not sufficient to detect ginkgo adulteration and proposed to analyze the samples not only after hydrolysis, as currently required, but also without hydrolysis, as a way to more readily detect adulterations with pure quercetin, kaempferol, and isorhamnetin.

Similar findings were reported in a study by Avula et al.¹¹ Eight botanically authenticated ginkgo leaf samples were analyzed by HPTLC and UHPLC-UV/MS. Additionally, samples of authenticated ginkgo fruit (n=3), stem (n=2), seed (n=2), and one National Institute of Standards and Technology (NIST)-certified leaf extract were analyzed. Also included in the study were authenticated Japanese sophora fruit (n=3) and flower (n=2) samples. The HPTLC and UHPLC-UV/MS methods were then used to evaluate the authenticity of three bulk ginkgo leaf raw materials, two bulk ginkgo extracts, and 25 commercial dietary supplements labeled to contain G. biloba extract. The dietary supplements were purchased online from retailers in the United States.

Isoflavones were not detected in any of the authentic ginkgo materials, including leaf, fruit, seed, and stem. However, genistein was present in both Japanese sophora fruit and flower. The fruit of Japanese sophora also contained a number of flavonoids that are absent in ginkgo (e.g., kaempferol-3-O-sophoroside, genistein-4'-O-glucoside, and genistein-4'-O-neohesperidoside [sophorabioside]). Most of the characteristic ginkgo terpene lactones (i.e., ginkgolide A, ginkgolide B, ginkgolide C, ginkgolide J, bilobalide) were present in all of the analyzed ginkgo samples, including the commercial dietary supplements. However, 11 out of the 25 tested supplements contained flavonol glycosides that are typically found in S. japonica fruit. Eight supplements contained genistein, plus quercetin, kaempferol, and isorhamnetin levels inconsistent with authentic ginkgo leaf, suggesting adulteration with Japanese sophora flower or an unknown adulterant. Overall, 19 out of 25 (76%) commercial ginkgo dietary supplements were found to be adulterated.

The ABC-AHP-NCNPR Botanical Adulterants Program — an international consortium of nonprofit research and standards-setting organizations, independent analytical laboratories, industry trade associations and industry companies, professional research organizations, and other interested parties — is currently developing a Botanical Adulterants Bulletin on ginkgo extract adulteration.

—Stefan Gafner, PhD

References

1. Duff Sloley B, Tawfik SR, Scherban KA, Tam YK. Quality control analysis for ginkgo extracts require analysis of intact flavonol glycosides. J Food Drug Anal. 2003;11(2):102-107.
   
   
2. Liu C, Mandal R, Li XF. Detection of fortification of ginkgo products using nanoelectrospray ionization mass spectroscopy. Analyst. 2005;130:325-329.
   
   
3. Xie P, Chen S, Liang Y-Z, Wang X, Tian R, Upton R. Chromatographic fingerprint analysis--a rational approach for quality assessment of traditional Chinese herbal medicine. J Chromatogr A. 2006;1112(1-2):171-180.
   
   
4. Kurth H. Extract Adulteration – Recognizing the fact and fakes. Presentation at agency meeting of the Martin Bauer Group. Sinzig, Germany, Sept. 2008.
   
   
5. Tawab M, Krzywon M, Schubert-Zsilavecz M. Dietary supplements with Ginkgo under the microscope [in German]. Pharm Ztg. 2010;20:62-67.
   
   
6. Chandra A, Li Y, Rana J, et al. Qualitative categorization of supplement grade Ginkgo biloba extracts for authenticity, J Funct Food. 2011;3(2):107-114.
   
   
7. Kakigi Y, Hakamatsuka T, Icho T, Goda Y, Mochizuki N. Comprehensive analysis of flavonols in Ginkgo biloba products by ultra-high-performance liquid chromatography coupled with ultra-violet detection and time-of-flight mass spectrometry. Biosci Biotechnol Biochem. 2012;76(5):1003-1007.
   
   
8. Ethical Naturals, Inc. PhytoReport #5: Ginkgo Adulteration & Identification w/Fructus sophorae (Sophora japonica). San Anselmo, CA. Ethical Naturals, Inc., May, 2013.
   
   
9. Demirezer LÖ, Büyükkaya A, Uçaktürk E, Kuruüzüm-Uz A, Güvenalp Z, Palaska E. Adulteration determining of pharmaceutical forms of Ginkgo biloba extracts from different international manufacturers. Rec Nat Prod. 2014;8(4):394-400.
   
   
10. 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.
    
    
11. Avula B, Sagi S, Gafner S, et al. Identification of Ginkgo biloba supplements adulteration using high performance thin layer chromatography and ultra high performance liquid chromatography-diode array detector-quadrupole time of flight-mass spectrometry. Anal Bioanal Chem. 2015;407(25):7733-7746.