## 3 Extractions Processes
### RA Extraction
[80] compared pressurized liquid extraction (PLE), using water and ethanol as solvents, supercritical fluid extraction (SFE), using neat CO\({}_{2}\) and supercritical CO\({}_{2}\) modified with ethanol, water extraction and particle formation on-line (WEPO). InWEPO, a first dynamic subcritical water extraction (SWE) is followed by extract drying under hot N2 (70 \({}^{\circ}\)C) with supercritical CO2 assisted nebulization. The second step allows the precipitation of the extracts, which forms particles with variable diameter, depending on the drying conditions. Compared to single step SWE, with WEPO the extraction yield was lower (but still higher respect to SFA), probably because of the absence of an equilibration step, but it is compensated by the elimination of any lyophilization procedure. Comparing the three techniques, PLE using water was able to maximize both the extraction yield and the antioxidant activity. A systematic work published in 2020 [81] discussed the extraction efficiency of RA from _Lamiaceae_ herbs (lemon balm, peppermint, oregano, rosemary, sage, and thyme) using various extraction techniques (macceration with stirring, HRE and MAE) and extraction conditions (solvent acidity, solvent type, extraction time and temperature). The authors found that solvent acidity was the parameter which most significantly affected the recovery of RA, regardless the extraction technology. In most of the works found in the literature, a One Variable at a Time (OVAT) methodology was used to optimize RA extraction. This approach, however, does not consider the interactions among extraction parameters and does not assure the maximization of the extraction yield. In 2017, [PERSON] et al. [82] compared, for the treatment of _Melissa officinalis_, HRE, MAE and UAE performances through response surface analysis. A circumscribed central composite design of three variables (time, temperature, and ethanol-water proportion) with five levels was used to maximize three response values (mg RA/g plant DW, mg RA/g extracted residue, and g extracted residue/g plant DW), and optimal variable conditions were found for each extraction technology. UAE emerged as the most efficient method, apparently in contrast with previous studies, which revealed a higher yield for MAE but obtained with water as extraction solvent and under conditions not properly optimized. The studies discussed so far made use of dry rosemary leaves, eventually cryogenically grinded. [PERSON] and co-workers [83] studied, together with the role of the extraction process, the influence of different pre-treatments (de-oiling, de-oiling and milling) for RA recovery with pure water from rosemary. Plant pre-treatments are aimed at maximizing the extraction efficiency and at overcoming inner mass transfer limitations by reducing particle size and by breaking cell membranes, to facilitate the access of the solvent. With both pre-treatments, water extraction showed significantly better yields than extraction with ethanol, regardless of the chosen extraction technique (conventional, MAE and UAE). By DPPH assay, the authors found also that in aqueous systems, RA shows an antioxidant activity superior, with respect to lipid environments.