Discrimination of Shirazi thyme from thymus species and antioxidant activity prediction using chemometrics and FT-IR spectroscopy

Local names are not reliable sources for identification of plants, because they differ significantly from one region to another. Apart from confusing nomenclature, the similar appearance and fragrance of Shirazi thyme and Thymus species cause misidentification. In order to prevent the adverse events in relation to the use of improper herbal products, easy-to-use quality control (QC) methodology was developed to classify these culinary plants. Fourier transform infrared (FT-IR) fingerprinting technique was applied for classification of these plants on the basis of their biochemical compositions. Powerful PLS-DA classification model with classification accuracy of 100% was obtained. For the first time in the present study, it was revealed that Shirazi thyme samples have higher antioxidant activity [average IC 50 of 37.03 (µg/ml)] compared to different Thymus species [average IC 50 of 148.35 (µg/ml)]. FT-IR fingerprint profiles were also used to construct a predictive model for antioxidant activity of the plants based on a reliable PLSR model. The developed PLSR model revealed that IR wavenumbers of 1000–1200, 1700, and 3200–3500 cm −1 are important for antioxidant activity prediction of the analyzed plants. The applied approach has the potential for being used in QC programs not only for fraud mitigation and detection, but also for estimation of antioxidant activity of the culinary plants.