Ginkgo Adulteration, Part 2:
Analysis of 20 Batches of Powdered Ginkgo Extract from One Supplier Shows
Inconsistent Quality
Reviewed: Yang J, Wang AQ, Li XJ, Fan X, Yin
SS, Lan K. A chemical profiling strategy for semi-quantitative analysis of
flavonoids in ginkgo extracts. J Pharm Biomed Anal.
2016;123:147-154.
Keywords: Ginkgo biloba, ginkgo leaf extract, adulteration, fingerprint, HPLC-UV
Another approach
for the evaluation of ginkgo leaf extracts is the semi-quantitative
determination of the major ginkgo leaf flavonols and flavonol glycosides. In
this paper, a calibration curve was created by correlating peak areas and molar
concentrations of four standard compounds, i.e., rutin, quercetin, isorhamnetin,
and kaempferol. This standard curve was used to quantify the 17 major peaks in
the high-performance liquid chromatography (HPLC) trace at a wavelength of 254
nm. Using molecular weight data obtained from mass spectrometric experiments,
the molar concentration of each of these compounds was then converted into amounts
expressed as percentage of dry extract.
This approach was
applied to the semi-quantitative analysis of flavonoids in 20 batches of
powdered ginkgo extract purchased from a company in Xuzhou, China. Statistical evaluation of the
extracts allowed a clear distinction of the majority of samples into two
clusters. However, three extracts did not align with either of these two
clusters. One sample had lower amounts of flavonoids overall, while the other two
samples had unusually high amounts of free aglycones (quercetin, kaempferol,
and isorhamnetin). In addition, one of these samples contained 4.0% of
genistein, suggesting adulteration with Styphnolobium japonicum
(syn. Sophora japonica, Fabaceae).
Comment: The paper provides an insight into
the batch consistency provided by one particular supplier. The reasons for the separation
of the majority of samples into two main clusters are not explained, but the
data suggest that one cluster has higher amounts of ginkgo flavonoids (ca. 30%)
compared to the other cluster (ca. 20%). Of the three remaining samples, one
was obviously adulterated with S. japonicum,
another had unusually low flavonoid content (13.9%), and one sample had high
free aglycone levels of 1.4% quercetin, 1.0% kaempferol, and 0.6% isorhamnetin.
Interestingly, genistein 7-O-glucoside and genistein, two marker compounds indicative
of adulteration with S. japonicum,
co-eluted with isorhamnetin-3-O-glucoside and
apigenin using the HPLC conditions outlined in the paper. In addition, apigenin
and genistein have the same molecular weight, and therefore could possibly be mistaken
for one another if compound identification was based on retention time and mass
spectrometric data. However, the striking difference of apigenin and genistein in
the UV spectra makes it easy to distinguish between these two compounds (Figure
1).