Elsevier

Phytomedicine

Volume 21, Issue 6, 15 May 2014, Pages 912-918
Phytomedicine

Adulteration of Ginkgo biloba products and a simple method to improve its detection

https://doi.org/10.1016/j.phymed.2014.01.010Get rights and content

Abstract

Extracts of ginkgo (Ginkgo biloba) leaf are widely available worldwide in herbal medicinal products, dietary supplements, botanicals and complementary medicines, and several pharmacopoeias contain monographs for ginkgo leaf, leaf extract and finished products. Being a high-value botanical commodity, ginkgo extracts may be the subject of economically motivated adulteration. We analysed eight ginkgo leaf retail products purchased in Australia and Denmark and found compelling evidence of adulteration with flavonol aglycones in three of these. The same three products also contained genistein, an isoflavone that does not occur in ginkgo leaf.

Although the United States Pharmacopeia – National Formulary (USP-NF) and the British and European Pharmacopoeias stipulate a required range for flavonol glycosides in ginkgo extract, the prescribed assays quantify flavonol aglycones. This means that these pharmacopoeial methods are not capable of detecting adulteration of ginkgo extract with free flavonol aglycones.

We propose a simple modification of the USP-NF method that addresses this problem: by assaying for flavonol aglycones pre and post hydrolysis the content of flavonol glycosides can be accurately estimated via a simple calculation. We also recommend a maximum limit be set for free flavonol aglycones in ginkgo extract.

Introduction

Extracts of ginkgo (Ginkgo biloba L.) leaf are sold worldwide as the active ingredient of numerous dietary supplements, botanicals, herbal medicinal products and complementary medicines. Indeed, ginkgo is currently one of the most widely sold medicinal plants, and the global market for ginkgo has been estimated at more than US$700 million (Euromonitor International Ltd., 2009). In the United States, the most recent (2012) data show the retail market for ginkgo products to be worth US$30 million (Lindstrom et al., 2013).

Ginkgo is also one of the most intensely studied medicinal plants, with more than 3000 scientific papers published on the topic between 2001 and 2009 alone (van Beek and Montoro, 2009). Ginkgo leaf extracts are recommended for a range of conditions, including cerebral insufficiency, vertigo and tinnitus of vascular origin, and peripheral arterial disease (Blumenthal, 2003, Bone and Mills, 2013).

The pharmacologically active compounds in ginkgo leaf are considered to be flavonol glycosides (quercetin, kaempferol and isorhamnetin being the principal aglycones) and terpene lactones (bilobalide and ginkgolides). Most ginkgo leaf extracts on the market are produced by selective, multi-step extraction processes involving organic solvents and carry quantitative claims concerning their content of flavonol glycosides and terpene lactones. Accordingly, most ginkgo leaf extracts are more high-tech and high-cost than typical botanical extracts.

Botanical raw materials including extracts present special challenges in terms of quality control and assurance due to their chemical complexity and inherent natural variability. The most fundamental aspects of quality assurance for such materials are to ensure the correct morphological part(s) from the right botanical taxon is used, and that the material is not adulterated with other botanical or extraneous material. Adulteration, either accidental or intentional and economically motivated, is a well-known issue for botanicals, and one that potentially can jeopardise not only the quality but also the safety of the finished product (Khan, 2006, Walker and Applequist, 2012). The potential safety issues associated with adulterated or sub-standard ginkgo extracts have been highlighted by recent toxicology and carcinogenicity studies using such inferior materials, while other studies using pharmaceutical quality ginkgo extract have found it to be safe (Koch et al., 2013, Krenn et al., 2013).

Pharmacopoeial monographs play an important role in the quality assurance of botanicals and herbal medicinal products (Vlietinck et al., 2009). Monographs for ginkgo raw materials (leaf and extract) can be found in various pharmacopoeias, including the United States Pharmacopoeia-National Formulary (USP-NF) (United States Pharmacopeial Convention, 2013), the European Pharmacopoeia (EP) and the British Pharmacopoeia (BP) (British Pharmacopoeia Commission, 2012). The USP-NF monograph for Powdered Ginkgo Extract and the BP/EP monograph for Refined and Quantified Ginkgo Dry Extract specify a flavonoid content of 22–27%, calculated as flavonol/flavone glycosides and a maximum content of 5 ppm for ginkgolic acids (putative allergens). In addition, specifications are provided for the terpene lactones, bilobalide and ginkgolide A, B and C, but the ranges for these differ between the USP-NF and the BP/EP. The USP-NF also provides monographs for Ginkgo Tablets and Ginkgo Capsules.

Here we report on ginkgo retail products found to be adulterated with free flavonol aglycones and also containing the isoflavone genistein, which is not native to ginkgo. We demonstrate that current pharmacopoeial methods are inadequate for the detection of this type of adulteration, and we propose a simple modification of the USP-NF method that addresses this problem.

Section snippets

Plant materials and botanicals

Five samples of dried Ginkgo biloba leaf were obtained from commercial suppliers. These leaf samples came from ginkgo cultivated in China (3), New Zealand (1) and Australia (1). They were authenticated by an experienced pharmacognosist (H.W.), and voucher materials were deposited in the Medicinal Plant Herbarium (PHARM) at Southern Cross University.

Eight retail products containing Ginkgo biloba as the sole active ingredient were purchased in Australia (6) and Denmark (2). Four of these were

Results

The content of quercetin, kaempferol and isorhamnetin in unhydrolysed and hydrolysed extracts of five ginkgo leaf samples, four tablet samples and four capsule samples is shown in Table 1. None of the unhydrolysed leaf samples contained detectable levels of any of these flavonol aglycones. The quercetin content in the hydrolysed leaf samples varied almost five-fold (range 0.87–4.30‰ w/w), the kaempferol content more than three-fold (range 1.35–4.29‰) and the isorhamnetin content 1.6-fold (range

Discussion

Ginkgo extract is used in numerous dietary supplements, botanicals, herbal medicinal products and complementary medicines around the world. Being a high-value botanical commodity, ginkgo extract is a target for economically motivated adulteration, and suspected adulteration with the flavonols quercetin and kaempferol, the flavonol glycoside rutin (quercetin 3-rutinoside) or with other plant extracts containing flavonols has been reported (Chandra et al., 2011, Harnly et al., 2012, He and

Conclusions

The need for ongoing vigilance in relation to the quality of herbal medicinal products and botanicals has been highlighted by our finding that three out of eight ginkgo retail products tested showed clear evidence of adulteration. Pharmacopoeial monographs for botanical raw materials and dose forms, such as those in the USP-NF, EP and BP, play an essential role in assuring the quality of such products. Here we have demonstrated that the tests currently prescribed in these monographs do not

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