Characterization of Phenolic Constituents and Antioxidant Capacity of Rosemary Extracts Produced via Different Extraction Methods

This study details a comparative evaluation of Rosmarinus officinalis L. extracts obtained through different extraction techniques—namely, supercritical CO2 (SC-CO2) extraction, water-Soxhlet extraction, ethanol-Soxhlet extraction, ethanol tincture preparation, oil-based tincture preparation, and hydrodistillation—with the aim of determining their phenolic composition and antioxidant potential. Rosemary samples from Durrës, Albania, were collected in January and May of 2025. Phenolic profiling was performed using LC-MS analysis, enabling the quantification of major bioactive compounds including caffeic acid, hesperidin, rosmarinic acid, luteolin, apigenin, carnosol, and carnosic acid. Antioxidant activity was assessed through three complementary assays—ABTS radical cation decolorization, DPPH radical scavenging, and FRAP reducing power—each calibrated using Trolox equivalents. The results reveal that SC-CO2 extraction produced extracts with the highest levels of lipophilic diterpenes—especially carnosic acid (414.4 ± 44.3 mg/g extract in the May preparation) and carnosol—along with significant amounts of phenolic acids and flavonoids. The SC-CO2 extracts exhibited the strongest antioxidant activity across all assays, with ABTS, DPPH, and FRAP values higher than those of the other extracts. Soxhlet extraction with water yielded intermediate phenolic levels and antioxidant activity, particularly enriching rosmarinic acid and selected flavonoids, whereas ethanol-Soxhlet, ethanol tincture, and oil-based tincture preparations showed lower phenolic concentrations and minimal antioxidant performance. Hydrodistillates contained only trace amounts of phenolics and showed negligible antioxidant capacity. Differences between January and May preparations were dependent on the extraction procedure and did not follow a uniform seasonal pattern. Higher values were observed with material collected in May for some preparations, particularly SC-CO2 extracts, whereas water-Soxhlet and ethanol tincture preparations showed higher values for several parameters with that collected in January. Under the conditions evaluated in this study, the SC-CO2 extracts showed the highest contents of carnosic acid and carnosol, as well as the highest antioxidant capacity on an extract mass basis.