Carnosic acid (CA) is a hydrophobic secondary metabolite and the main antioxidant of rosemary. Extractions of CA from whole leaves of rosemary have been performed with aqueous solutions of 12 short-chain alkyl polyethylene glycol ethers, abbreviated as C i E j with i = 4–8 and j = 1–4. Such compounds act as hydrotropes which are known to enhance the solubilization of hydrophobic molecules in water while avoiding the formation of liquid crystals like surfactants. The extractions are compared with those carried out with alcohols, sodium xylene sulfonate (SXS) which is an archetypical ionic hydrotrope, and longer C i E j (i = 10 or 12 and j = 4) which behave as true surfactants. C5E2 and C4E1 are the best candidates and provide 1.21 g/L CA in 21 h and 1.02 g/L in 8 h, respectively. They are more efficient than SXS and alcoholic aqueous solutions. Correlations between the chemical structure and activity have highlighted three requirements for better performances: (i) a small molecular volume V m (<250 Å3), (ii) a log P above 1, and (iii) a linear alkyl chain rather than a branched one. Finally, kinetic study and optical microscopy observations of the leaves after extraction give insight into the mode of action of the C4E j compared to ethanol.

Rosemary (Rosmarinus officinalis L.) is a Mediterranean herb known for its high antioxidant power that has been widely attributed to carnosic acid (CA). Passive extractions of CA have been performed in water by using five commercially available short-chain alkyl polyglycosides (APG) with alkyl chain lengths ranging from 4 to 10 carbon atoms and polar heads composed of pentoses and/or glucoses. APGs are nontoxic amphiphiles with high biodegradability. Their solubilizing capacity for CA has been determined, highlighting heptyl glucoside (C7Glu) as the most efficient one, followed by 2-ethylhexyl glucoside (C6,–2Glu) and isoamyl xyloside (iC5Xyl). However, iC5Xyl exhibited the highest selectivity toward CA solubilization as compared to ursolic acid (UA), a potential coextracted compound of rosemary leaves. In addition, it was found to be the most efficient amphiphile to extract CA from both ground and whole rosemary leaves. To optimize the maceration process and the recovery of the extract, a full factorial design 24 was performed investigating iC5Xyl concentration, temperature, stirring, and extraction time. A high concentration of hydrotrope was found to be the most important condition to optimize the maceration step, while the temperature particularly increases the yield, but in detriment of the CA content in the final dried extract.