Cyclodextrins-Assisted Extraction for the Recovery of Bioactive Compounds from Rosemary Post-Distillation Residues—In Vitro Antioxidant Activity, Comparisons to Conventional Liquid Extracts

This study investigated the valorization of rosemary (<i>Rosmarinus officinalis</i> L.) post-distillation residues-by-products derived from essential oil production-using cyclodextrins (CDs) as green co-solvents for the efficient extraction of bioactive compounds. This work aimed to explore key extraction parameters, i.e., extraction time, liquid-to-solid ratio, type of CD (β-CD or HP-β-CD), and CD concentration, and assess the antioxidant potential of the resulting extracts. Total phenolic content (TPC), total flavonoid content (TFC), DPPH radical scavenging activity, and ferric reducing antioxidant power (FRAP)assays were performed to evaluate the composition and antioxidant potency of the extracts. Regression analysis identified CD concentration and liquid-to-solid ratio as the most influential factors. Both β-CD and HP-β-CD significantly enhanced polyphenol recovery and antioxidant activity compared to conventional solvents (water, ethanol, methanol), with HP-β-CD showing slightly superior performance. The β-CD-assisted extract exhibited up to four-fold higher DPPH radical scavenging capacity than ethanol-based extracts. Among the extracts, the activity to scavenge superoxide and peroxyl (AAPH) radicals notably varied depending on the type of solvent. The findings demonstrated that rosemary post-distillation residues can be valorized to produce extracts rich in bioactive compounds suitable for food, cosmetic, and pharmaceutical applications. CD-assisted extraction offers an efficient, low-cost, and environmentally friendly approach to achieve this. As a continuation of this work, future studies should include LCA, thermodynamic, and techno-economic analyses to confirm the reduced environmental impact and operational costs indicated by the green metrics.