GC-Derived Volatile Profiling of Commercial Thyme and Oregano Labeled Products and Evaluation of Portable NIR Screening

Commercial aromatic herbs sold under the names thyme and oregano may encompass heterogeneous plant materials, making chemical-profile screening important even when botanical identity is unknown. This study characterized 110 commercial products marketed in Türkiye and evaluated whether portable near-infrared (NIR) spectroscopy could predict chemical-profile classes derived independently from GC-FID/MS data. Commercial labels were recorded but were not treated as verified species identities. Essential oils were measured in technical duplicate for 23 volatile compounds; replicate means were subjected to compositional data treatment, principal component analysis and Ward clustering. Two clusters were selected by the silhouette criterion (0.485), and cluster stability under technical-replicate resampling was high (median adjusted Rand index, 0.907). Cluster 1 (n = 17) was relatively enriched in sabinene, caryophyllene, carvacrol and delta-3-carene, whereas Cluster 2 (n = 93) showed higher myrcene, p-cymene, alpha-pinene and beta-pinene. Two NIR spectra were collected per sample. To prevent replicate leakage, spectra were averaged before repeated nested cross-validation; a grouped-replicate analysis was also performed. A majority-class baseline achieved 84.55% accuracy but only 0.500 balanced accuracy. The best primary model, shrinkage linear discriminant analysis, yielded a mean accuracy of 0.689, a balanced accuracy of 0.565, a macro-F1 of 0.530 and a Matthews correlation coefficient of 0.103. The grouped-replicate sensitivity analysis gave a balanced accuracy of 0.592. Thus, GC-FID/MS revealed a stable chemical-profile structure, but portable NIR did not reliably recover the minority chemical class. NIR may support exploratory triage after broader calibration, but the present data do not support stand-alone botanical authentication or definitive chemical-class assignment.