Phenolic characterization, antioxidant properties, and brine shrimp toxicity of different aerial part extracts of Thymbra capitata Cav. (Lamiaceae) wild from Sicily (Italy)

Thymbra capitata (Lamiaceae) is a Mediterranean plant used in folk medicine and in the pharmaceutical, cosmetic, and food industries. This work was designed to establish a suitable method to obtain phenolic-rich extracts from the aerial parts of T. capitata growing wild in Sicily (Italy). For this purpose, extractions with 70% ethanol at room temperature (Tc-1) and at 50 °C in an ultrasonic bath (Tc-2), Soxhlet with 96% ethanol (Tc-3), and decoction (Tc-4) were performed. The antioxidant properties were investigated by in vitro methods. Tc-2 extract showed the best activity, displaying strong radical scavenging properties in the DPPH test (IC50 = 0.227 ± 0.001 mg/mL), moderate reducing power (ASE/mL = 4.630 ± 0.098), and good Fe2+ chelating ability (IC50 = 0.653 ± 0.012 mg/mL). Furthermore, the protective effect against lipopolysaccharide (LPS)-induced oxidative stress was evaluated on the human microglia clone 3 (HMC3) cell line, resulting Tc-3 extract the most active. Phenolic compounds were determined spectrophotometrically and characterized by HPLC-PDA/ESI-MS. The highest phenolic content was found in Tc-3 extract, followed by Tc-2 (141.344 ± 0.644 and 117.092 ± 0.224 mgGAE/g extract). Notably, the Artemia salina lethality bioassay showed lack of toxicity for Tc-2, as well as for Tc-4; contrarily, Tc-1 and Tc-3 extracts showed low and medium toxicity, respectively.