NMR-based metabolomics for frauds detection and quality control of oregano samples

In this work 1H NMR metabolomics has been employed for quality control of oregano samples. NMR data and morphological analysis (MA) were combined by PCA, obtaining a model able to individuate non-marketable samples, and to distinguish between the two marketable oregano species (Origanum vulgare and O. onites) on the basis of their metabolomic profile. Through this approach distinctive biomarkers of the two species were found, namely apigenin and p-cymene for O. onites, and salvianolic acid B for O. vulgare. Furthermore, the percentage of the samples' impurity (evaluated by MA) and the metabolomic profiles were correlated by OPLS models, which showed that, in addition to the species-specific biomarkers, thymol and rosmarinic acid (common to both marketable species) strongly correlate to oregano degree of purity. Cistus was one of the most frequent contaminants, thus, a further OPLS model, able to detect the degree of cistus contamination in oregano samples, was also built.