Optimization of microwave-assisted extraction recovery of bioactive compounds from Origanum glandulosum and Thymus fontanesii

Microwave-assisted extraction (MAE) was used for the recovery of bioactive compounds of two Lamiaceae species: Origanum glandulosum and Thymus fontanesii. MAE was combined with response surface methodology (RSM) to optimize the effect of concentration of ethanol (%EtOH), temperature and extraction time on the total phenolic content (TPC), the extraction yield and the antioxidant capacity from the aerial parts of O. glandulosum and T. fontanesii. The total phenolic content was determined using the Folin-Ciocalteu reagent, while the antioxidant capacity was evaluated using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radicals. Optimum conditions obtained for O. glandulosum MAE extracts were 0% ethanol, 42 degrees C and 2 min of extraction time, which give individual response values of 23.29 +/- 0.38%, 311.36 +/- 6.09 mg GAE/g extract, 5.54 +/- 0.42 mu g/mL and 3.61 +/- 0.14 mmol Trolox/g extract for yield, TPC, DPPH (EC50) and trolox equivalent antioxidant activity (TEAC) assay, respectively. Whereas, the optimum conditions obtained for T. fontanesii MAE extracts were 50% ethanol, 150 degrees C, and 9.5 min. These latter give individual response values of 26.81 +/- 0.30%, 227.63 +/- 31.87 mg GAE/g extract, 8.58 +/- 1.75 mu g/mL, 3.92 +/- 0.61 mmol Trolox/g extract for yield, TPC, DPPH (EC50) and TEAC assay, respectively. The main phenolic compounds identified in O. glandulosum and T. fontanesii optimized MAE extracts, using the HPLC-DADESI-MS/MS method were gallocatechin and rosmarinic acid, respectively.