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).