Investigation of the composition and quality of commercial medicinal oil samples sold in herbal shops in Aksaray province

This study aimed to determine the chemical composition and quality characteristics of several commercial essential and fixed oils sold in herbal stores in Aksaray Province, Türkiye. The research sought to evaluate the compositional variability and compliance of these oils with pharmacopeial standards and to identify possible issues related to adulteration, quality differences, and consumer safety. The essential oil group included thyme (Origanum spp.), lavender (Lavandula spp.), and peppermint (Mentha spp.), while the fixed oil group comprised rose (Rosa damascena Mill.), flaxseed (Linum usitatissimum L.), sesame (Sesamum indicum L.), black cumin (Nigella sativa L.), and St. John's wort (Hypericum perforatum L.) oils. Gas chromatography (GC-MS and GC-FID) analyses were performed to identify the major components. In essential oils, carvacrol, thymol, linalool, linalyl acetate, menthol, and menthone were identified as the dominant compounds, whereas in fixed oils, oleic, linoleic, and α-linolenic acids were predominant. The high phenolic content (carvacrol and thymol) in thyme oil, balanced menthol–menthone ratios in peppermint oil, and linalool–linalyl acetate equilibrium in lavender oil were found to be key determinants of quality. Among fixed oils, flaxseed oil exhibited a high α-linolenic acid content (42–54%), sesame oil was rich in sesamin and sesamol, black cumin oil contained thymoquinone as its principal bioactive, and St. John's wort oil showed an oleic–linoleic acid profile typical of macerated products. The findings revealed considerable compositional variations among brands, attributed to multiple factors including genetic and ecological differences in plant material, harvest time, extraction methods, and storage conditions. Some samples did not fully meet pharmacopeial quality standards, with certain volatile components such as menthofuran and linalool detected in atypical proportions. This research represents one of the first comprehensive studies on the compositional diversity and quality assessment of commercial medicinal oils in Aksaray. The results provide valuable insights for consumer protection and quality control within the herbal oil market, emphasizing the necessity of product standardization and traceability. These findings will contribute to future regulations, quality assurance protocols, and scientific studies in the field of medicinal and aromatic plant-derived oils.