A simple HPLC method for detecting adulteration of ginkgo extracts with flavonol aglycones

Ginkgo leaf contains more than 45 flavone glycosides, most of which are based on the aglycones quercetin, kaempferol and isorhamnetin [1]. Adulteration with rutin, quercetin and other plant extracts has been reported [2,3]. USP and EP/BP monographs for ginkgo extract stipulate 22–27% flavonoids, but pharmacopoeial methods cannot effectively detect adulteration with aglycones, because calculation of glycoside content is based on the aglycone content after acid hydrolysis.

We developed a modification to the pharmacopoeial methods that enables quantification of both glycosides and free aglycones and applied it to 5 leaf samples and 8 retail ginkgo products. Free flavonol aglycones were not present in leaf samples or in two products. Most products largely met their label claim for flavonol glycoside content and relative aglycone content by USP (Identification Test B), but our method revealed high levels of free quercetin and kaempferol in three products, suggestive of adulteration. The presence of free aglycones in these products meant that the pharmacopoeial methods for calculating flavonol glycosides overestimated the glycoside content by up to 40%. We suggest the USP and EP/BP monographs for ginkgo extract be modified to increase their ability to detect adulteration with flavonol aglycones.

References: 1. Lin, L.-Z. et al. (2008) J Food Agric Chem 56:6671–9. 2. Franz, C. et al. (2011) Food Funct 2:720–30. 3. Liu, C. et al. (2005) Analyst 130:325–9.