Comprehensive analysis of Hyssopus officinalis L. essential oils: chemotype characterization, bioactivity assessment, and quality control implications

Hyssopus officinalis L. (Lamiaceae) essential oil (EO), known for its complex chemical composition and various chemotypes, has been extensively studied for its pharmacological properties [1]. This complexity enhances its value in traditional and modern medicine, aromatherapy, pharmaceuticals, and as a natural preservative. This research analysed 20 samples of commercial EOs obtained from the aerial parts of Hyssopus officinalis subsp. officinalis (var. decumbens has been considered a synonym since 2022), provided and certified by producers or retailers based in Italy, Spain, France, and Bulgaria. The chemical characterisation, performed by GC-MS-FID and by 1H NMR-based metabolomics supported by further 2D NMR experiments, revealed two primary chemotypes characterised by eucalyptol and pinocamphones (cis- and trans-) and a third linalool chemotype. The pinocamphones chemotype can be further divided into two groups, one of which is characterised by a high content of β-phellandrene. The evaluation of the biological properties of the EOs was focused on checking the antifungal activity against two dermatophytes (Trichophyton menthagrophytes, CBS 120356, and T. violaceum, CBS 459.61) and the antioxidant potential (DPPH test). The chemotype containing pinocamphones and a high concentration of beta-phellandrene exhibited the highest antioxidant activity (IC50 = 3.24 μl/ml). The same subgroup also exhibited the most significant antifungal activity, with an interesting growth inhibition of T. mentagrophytes (28%) and T. violaceum (15%). The eucalyptol chemotype, however, exhibited negligible antifungal activity, except for one sample that showed 55% growth inhibition of T. mentagrophytes growth, distinguished by its high aromatic or olefinic compound concentration. The supervised and unsupervised multivariate data analysis overviews the global phytochemical and biological results. This work underscores the need for detailed quality control procedures on commercial essential oils, especially when the plant of interest expresses extremely diversified chemotypes with different bioactivities and organoleptic properties. In this context, the predictive OPLS-DA model provided in this work offers a valuable tool for EOs quality control.