‘A significant contribution to the quality assurance of ginkgo products’: Scientists present simple method to test for adulterants

According to a paper published in Phytomedicine​​, ​simple modification of the existing United States Pharmacopeia – National Formulary (USP-NF) test for flavonol aglycones could solve the problem of identifying adulterants in commercial ginkgo extracts.

The researchers also found “compelling evidence”​ of adulteration with flavonol aglycones in three out of eight ginkgo leaf retail products purchased in Australia and Denmark. Of particular interest was the presence of genistein, an isoflavone that does not occur naturally in Ginkgo biloba.

The Australian method supports a method developed by Ethical Naturals, Inc. (ENI)​, which used HPLC analysis with an altered wavelength to optimize for genistein.

The need for vigilance​

“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,”​ explained the researchers, led by Hans Wohlmuth.

“Pharmacopoeial monographs for botanical raw materials and dose forms, such as those in the [United States Pharmacopeia – National Formulary (USP-NF) and the British and European Pharmacopoeias], play an essential role in assuring the quality of such products. Here we have demonstrated that the tests currently pre-scribed in these monographs do not provide for the detection of adulteration of ginkgo extracts and products with free flavonol aglycones.​

“As a solution to this specific problem, we have proposed a simple modification of the USP-NF test for Content of Flavonol Glycosides that allows for the accurate estimation of these compounds, thus avoiding the overestimation that will result from the presence of free flavonol aglycones (likely of extraneous origin) when applying the current test. ​

“We believe that the proposed test, along with the setting of a maximum acceptable level for free flavonol aglycones and testing for the presence of genistein (an extraneous compound) would make a significant contribution to the quality assurance of ginkgo leaf extracts and products.”​

Widespread adulteration?​

Ginkgo biloba is one of the herbal industry’s big players, with data from the ABC Herb Market Report for 2011 (using SPINS data for the sale of single ingredient Ginkgo extracts) putting the US Ginkgo market at an estimated $18.4 million ($4.1 million in the natural health foods channel, and $14.3 million in the food drug and mass market channel). The global market is reported to be worth $1 billion.

It is estimated that 50 kg of dried ginkgo leaf is required to make one kg of extract, and the extract is expensive and complex to manufacture. Since costs are so high, there have been numerous reports of adulteration of ginkgo extracts dating back decades. The most common form of adulteration has been the use of quercetin and rutin to artificially enhance the flavonol glycoside content.

Ginkgo extracts are typically standardized to contain a minimum of 24% flavonol glycosides, 6% terpene lactones, and less than 5ppm ginkgolic acids.

According to NutraIngredients-USA’s in-depth article last year​, ginkgo adulteration is ‘widespread’, and becoming more sophisticated.

While many in the industry are now aware of the rutin issue, a study by Amitabh Chandra from Amway Corp. et al​. in the Journal of Functional Foods​ (2011, Vol. 3, pp. 107-114), highlighted the relatively new practice of using extracts from Sophora japonica​ fruit (Japanese pagoda tree).

While the new Australian study did indeed identify the adulterant, they did propose that Sophora japonica​ was a candidate, and since the adulterated ginkgo products contained genistein, quercetin and kaempferol in free aglycone form, the researchers said that Sophora japonica​ extracts would have undergone processing leading to the hydrolysis of the flavonoid glycosides.

Setting levels​

Wohlmuth and his co-workers have proposed a simple modification of the USP-NF test for flavonol glycosides content to allow for the accurate estimation of these compounds, and suggested a suitable maximum level for free flavonol aglycones be set for ginkgo leaf extract of 0.5% w/w.

“Such a limit would further contribute to the quality assurance of ginkgo extracts, including limiting adulteration with flavonol aglycones from extraneous sources.”​

USP revises its monograph​

The United States Pharmacopeial Convention (USP) contacted NutraIngredients-USA to explain that it proposed a revision to its Powdered Gingko Extract ​monograph to include ginkgo authentication procedures similar to those described by Wohlmuth et al.​ The USP monograph was posted for public comment from July 1, 2013 to September 30, 2013 on USP’s Pharmacopeial Forum (http://www.usp.org/usp-nf/pharmacopeial-forum​) and contains provisions for analysis of flavonol aglycones without prior hydrolysis, said Nandakumara Sarma, PhD, director of dietary supplements at USP.

"The same three products identified as adulterated by Wohlmuth ​et al would fail the ​Specific Test: Limit of Rutin and Quercetin under USP’s revised ​Powdered Ginkgo Extract monograph," ​explained Dr Sarma. "Use of the full USP gingko monograph enables the detection of adulteration and provides analytical procedures for establishing the identity, purity, strength, composition as well as limits on contaminants.Further, the analytical methodology proposed in the revised USP ginkgo monograph addresses adulteration with both rutin and quercetin, while the Wohlmuth ​et al. study only targets the latter.​

"The recent proposed revision of the ​Powdered Gingko Extract monograph is an illustration of USP’s commitment to updating public standards to help fight the ever increasing tide of adulteration.  We invite the research community to contribute their valuable ideas and practical efforts to helping USP maintain the dietary supplement marketplace adulteration-free,​" added Dr Sarma. 

Source: Phytomedicine​​
Published online ahead of print, 22 February 2014, doi: 10.1016/j.phymed.2014.01.010
“Adulteration of Ginkgo biloba products and a simple method to improve its detection”​
Authors: H. Wohlmuth, K. Savage, A. Dowell, P. Mouatt