Effect of Heat-Assisted and Ultrasound-Assisted Extraction Methods on the Phenolic Profile and Biological Activity of Thymus vulgaris L. Extracts

This study compares the phenolic composition and antioxidant activity of extracts obtained using heat-assisted extraction (HAE) and ultrasound-assisted extraction (UAE), both optimized through response surface methodology (RSM), with the primary goal of maximizing the extraction of bioactive compounds from <i>Thymus vulgaris</i> L. Eight phenolic compounds were identified in the extracts, with rosmarinic acid being the most abundant. Depending on the selected conditions in each optimization, the concentration of this compound varied from 2.04 to 72.6 mg/g of extract for HAE and 0.73 to 73.5 mg/g of extract for UAE. The optimal conditions for each method that yielded the highest rosmarinic acid levels were as follows: for HAE, 27% ethanol at 91 °C for 121 min; and for UAE, 60 min at 500 W using 50% ethanol. The UAE-produced extract demonstrated superior antioxidant performance, particularly in inhibiting the formation of thiobarbituric acid reactive substances and oxidative haemolysis. Additionally, the extracts obtained using both optimized methodologies exhibited cytotoxic activity against five tumor cell lines and showed significant bactericidal and fungicidal effects against six bacterial and fungal strains. Overall, UAE proved more efficient as it enables the production of rosmarinic-acid-enriched extracts in less time, making them suitable as natural ingredients for industrial applications.