Integrated evaluation of Algerian Rosmarinus officinalis essential oils: Chemical composition and antioxidant, antibacterial, and anti-inflammatory activities

Rosmarinus officinalis L. is a Mediterranean aromatic plant widely known for its pharmacological potential, particularly antimicrobial, antioxidant, and anti-inflammatory effects attributed to its essential oils (EOs) rich in oxygenated monoterpenes. This study investigated the physicochemical properties, chemical composition, and biological activities of rosemary EOs collected from two Algerian regions. Hydrodistillation yielded an average essential oil content of 0.78%. The oils met international quality standards, showing a pH close to neutrality (~ 6.5), a relative density ranging from 0.98 to 0.92, and an acid index between 1.0 and 1.9 (p < 0.001). GC–MS analysis revealed a composition dominated by 1,8-cineole (up to 18.53%) and camphor (~ 12%), with other key constituents such as borneol, camphene, and limonene. Phytochemical quantification showed the presence of polyphenols (~ 0.42 mg GAE/g), flavonoids (~ 0.22 mg QE/g, p < 0.01), and tannins (~ 0.11 mg CE/g, p < 0.05), which contribute to the oil’s strong bioactivity. The essential oils demonstrated remarkable antioxidant activity, reaching nearly 98% DPPH radical inhibition at 100 μg/mL (p > 0.05), and significant antibacterial effects against Staphylococcus aureus and Klebsiella pneumoniae (p < 0.05). Anti-inflammatory assays confirmed a dose-dependent inhibition of protein denaturation and erythrocyte hemolysis, with IC₅₀ values comparable to aspirin (~ 18–21 μg/mL). These statistically supported results highlight the therapeutic, cosmetic, and food-industry potential of Algerian rosemary essential oils. Moreover, they suggest that environmental and geographical factors influence the biosynthesis of bioactive compounds, enhancing the pharmacological diversity and industrial value of this natural resource.