Optimization of extraction based on the thin-layer chromatographic fingerprints of common thyme

The main goal of this study was to establish the optimum accelerated solvent extraction (ASE) conditions for the isolation of the total phenolics contained in common thyme (Thymus vulgaris L.) based on the results of TLC. Additionally, two different extraction methods, i.e., Soxhlet extraction and ASE, were compared in terms of their relative performance. Binary methanol-water mixtures in different volume proportions were used as the extraction solvents. Thirteen experiments utilizing different methanol concentrations and different extraction temperatures were designed using response surface methodology. Additionally, the temperature dependence of rosmarinic and caffeic acid extraction yields was analyzed by applying HPLC. Finally, the optimum working conditions established within the framework of the assumed central composite experimental design were determined to be 27% methanol at 130°C. It was found that the extraction carried out by ASE provided higher total phenolic yields than that done in the Soxhlet apparatus. The final aim of this study was a comparison of the six different Thymus species in terms of their total phenolic content and their TLC fingerprints. It was found that the phenolic content of four species, T. pulegioides, T. kosteleckyanus, T. citriodorus, and T. marschallianus, differs from the phenolic content of T. vulgaris and T. serpyllum.