Profiling of Lavandula angustifolia Mill. Essential Oils: GC-MS and Chemometric Insights Under Variable pH and Drying Conditions

In this study, essential oils of Lavandula angustifolia cultivated in Muğla province, Türkiye, were obtained by hydrodistillation after drying the plant material under various conditions and durations. Distillations were conducted at three pH values (5.8, 7.0, and 8.0) to investigate the influence of pH on oil composition. A total of 33 essential oil samples were produced under different drying and pH conditions and analyzed by gas chromatography–mass spectrometry (GC-MS). The tyrosinase inhibitory activity of the essential oils was also evaluated to explore their potential dermatological applications. GC-MS analysis identified 41 compounds, with linalool (23.93–53.79%), linalyl acetate (0.05–37.32%), borneol (1.91–19.01%), α-terpineol (0.88–18.40%), and D-camphor (1.15–16.13%) as the predominant constituents. Monoterpenes and monoterpenoids were the main chemical classes observed across all samples. The relative percentages of the 16 most abundant compounds were subjected to chemometric analysis using Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) to reveal patterns related to drying and pH conditions. Among all samples, the oil labeled 2.LU-B, obtained from sun-dried material after 1 day under basic conditions, showed the closest compliance with European Pharmacopoeia standards; however, three compounds-3-octanone (trace), D-camphor (5.20%), and α-terpineol (2.52%)-slightly exceeded the specified limits. Overall, the findings demonstrate that both drying method and distillation pH significantly affect the chemical profile of L. angustifolia essential oils, providing useful information for standardization and targeted production for pharmaceutical, cosmetic, or aromatherapeutic applications.