Development of a SCAR marker for the identification of Olea europaea L.: a newly detected adulterant in commercial Mediterranean oregano

A recent pharmacognostic survey on the European food market highlighted a previously unreported adulteration of Mediterranean oregano. Dried crushed leaves, silvery grey in colour but devoid of glandular hairs and with unequivocal xerophytic adaptations were copiously spotted (20–30% w/w) in a number of commercial samples. Microscopical investigations narrowed the range of suspect candidates to Olea europaea L. and a method based on Sequence-Characterised Amplified Regions markers (SCARs) was developed from Random Amplified Polymorphic DNA markers (RAPDs) specific for O. europaea, in order to authenticate the contaminant and set up a fast, sensitive, reliable and low-cost screening of dried commercial Mediterranean oregano samples. The method enabled the unequivocal detection of low amounts (up to 1%) of olive leaves in both artificial and commercial batches, allowing the preemptive rejection of suspect samples and reducing the number of samples to be subjected to more careful pharmacognostic analyses. The relatively short dimension of the amplicons is suitable for the analysis of potentially degraded DNA obtained from dried and processed commercial plant material and given their specificity the method may be enforceable also in case of forensic disputes even in case of finely ground material.