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
References
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.