Phytochemical Characterization and Biological Activities of Ethanol Extract from Sideritis stricta via Ultrasound-Assisted Extraction

Due to the growing interest in natural antioxidants and enzyme inhibitors, evaluating the bioactivity profiles of underexplored species is essential. Here, the ultrasound-assisted ethanolic extract from the aerial parts of Sideritis stricta was phytochemically characterized, revealing a polyphenol-rich profile (68.52 mg Gallic Acid Equivalent (GAE)/g extract) dominated by verbascoside (17.267 μg/g) and chlorogenic acid (10.402 μg/g). Minor flavonoid constituents such as apigenin (52.7 μg/g) and kaempferol (18.7 μg/g) were also present. Antioxidant assays indicated moderate reducing power [Cupric Reducing Antioxidant Capacity (CUPRAC), half maximal effective concentration (EC₅₀) = 0.26 mg/mL; Ferric reducing antioxidant power (FRAP), EC₅₀ = 0.18 mg/mL] and radical scavenging capacity [2,2-diphenyl-1-picrylhydrazyl (DPPH), half maximal inhibitory concentration (IC₅₀) = 0.56 mg/mL; 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), IC₅₀ = 0.30 mg/mL] compared to Trolox. However, the ferrous ion chelating ability was relatively low (IC₅₀ = 5.97 mg/mL). Enzyme inhibition assays showed modest inhibitory activity towards tyrosinase (IC₅₀ = 1.21 mg/mL), acetylcholinesterase (IC₅₀ = 1.17 mg/mL), and butyrylcholinesterase (IC₅₀ = 2.51 mg/mL), all substantially weaker than reference inhibitors. The extract displayed moderate α-glucosidase inhibition (IC₅₀ = 1.09 mg/mL), comparable to acarbose, while α-amylase inhibition was limited (IC₅₀ = 3.92 mg/mL). Overall, S. stricta demonstrates promising bioactivity, highlighting its potential for further nutraceutical exploration.