Tracing Styphnolobium japonicum (syn: Sophora japonica) as a potential adulterant of ginkgo-containing foods by real-time PCR

The rising demand for ginkgo-containing products and their high economic value make them desirable targets for adulteration, particularly by the partial substitution with other plant species. Styphnolobium japonicum (plant rich in flavonol glycosides) is known as a potential adulterant of ginkgo-based foods. Therefore, this work aimed at developing a species-specific real-time polymerase chain reaction (qPCR) method for the identification/quantification of S. japonicum as an adulterant of ginkgo-containing products. The method used the EvaGreen dye, targeting the internal transcribed spacer 2 (ITS2) region of S. japonicum, providing acceptable performance parameters and a sensitivity down to 0.02 pg of DNA. Moreover, a qPCR assay was established using binary mixtures of S. japonicum in G. biloba, covering the dynamic range of 50-0.05% (w/w) of added adulterant. After trueness evaluation with blind samples, the approach was applied to 21 commercial herbal infusions, from which one was positive to S. japonicum, but below the limit of quantification (0.05 %), suggesting its inadvertent contamination rather than adulteration. To the best of our knowledge, for the first time, a specific method was proposed to quantify potential adulterations of G. biloba products with S. japonicum, providing an accurate and cost-effective tool to authenticate ginkgo-containing herbal foods.

Automated summary

A specific method using real-time polymerase chain reaction (qPCR) was developed to identify/quantify Styphnolobium japonicum as an adulterant in ginkgo-containing products. The method showed acceptable performance parameters with a sensitivity down to 0.02 pg of DNA. It was applied to commercial herbal infusions, revealing one sample tested positive for S. japonicum but below the quantification limit, suggesting inadvertent contamination rather than intentional adulteration.