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.The work was supported through the projects UIDB/50006/2020 and UIDB/00690/2020, funded by FCT/MCTES (Fundação para a Ciˆencia e Tecnologia and Minist´erio da Ciˆencia, Tecnologia e Ensino Superior) through national funds. L. Grazina thanks FCT and ESF (European Social Fund) through POCH (Programa Operacional Capital Humano) for her PhD grant SFRH/BD/132462/2017. J. Costa thanks FCT for funding through program DL 57/2016 – Norma transitória (SFRH/BPD/102404/2014).