Impact of the Extraction Method on the Chemical Composition and Antioxidant Potency of <i>Rosmarinus officinalis</i> L. Extracts

<i>Rosmarinus officinalis</i> L. is a dietary source that produces polyphenols as secondary metabolites. These natural compounds with potent antioxidant abilities are increasingly recommended as a supplement to inhibit oxidative stress. In the current work, we evaluated the impact of the extraction method on the chemical composition of <i>R. officinalis</i> extract, especially on the content of carnosic (CA) and rosmarinic (RA) acids using UPLC-MS-DAD as well as on their antioxidant potency. Four extracts of Tunisian rosemary were obtained from non-conventional extraction techniques:ultrasound-assisted extraction (UAE),supercritical extraction (SFE) and UAE and SFE combined ((UAE-SFE(I), UAE-SFE(II)). The UAE exhibited the best total phenolic compounds (i.e., 85.27 mg GAEg⁻¹), the highest content of CAand RA and the strongest antioxidant abilities (i.e., IC₅₀ = 0.13 mg/mL and EC₅₀ = 0.93 mg/mL for DPPH scavenging test and iron reducing power ability assay). The evaluation of antioxidant activity of UAE inhuman skin fibroblast (HS-68) cell line was carried out after the induction of oxidative stress. The results determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed a strong protective effect against H₂O₂oxidative stress induction in cells pretreated with UAE. The obtained results allow us to give new insight about the effect of the extraction method on the chemical composition and biological activities of the extract and the importance of the choice of the most appropriate processing technique to prepare rosemary extract with a high antioxidant potency and protective effect against oxidative stress.