Oxygenated heterocyclic compounds to differentiate Citrus spp. essential oils through metabolomic strategies

• Characterisation and authentication of citrus species using metabolomic strategies.
• Oxygenated heterocyclic compounds (OHC) patterns of seven citrus species.
• Quantification of 18 compounds using extrapolative dilution approaches.
• Metabolite profiling based on 18 compounds for citrus essential oils.
• Metabolite targeted fingerprinting approaches based on 140 OHC.

This study aimed to characterise and discriminate 44 authenticated commercial samples of citrus essential oils (EO) from seven species (bergamot, lemon, bigarade, orange, mandarin, grapefruit, lime) by analysing the non-volatile oxygenated heterocyclic compounds (OHC) by UHPLC/TOF-HRMS, multivariate data analysis (PCA, PLS-DA) and metabolomic strategies; the OHC fraction includes coumarins, furocoumarins, and polymethoxylated flavonoids. Two different approaches were adopted: (i) targeted profiling based on quantifying 18 furocoumarins and coumarins, some of which are regulated by law, and (ii) targeted fingerprinting based on 140 OHCs reported in citrus essential oils, from which 38 discriminant markers were defined. This approach correctly discriminated the Citrus species; its “sensitivity” to relatively low adulteration rate (10%) was highly satisfactory. The proposed method is complementary to that of analysing the citrus EO volatile part by GC techniques.