Hydrotropic Extraction of Carnosic Acid from Rosemary with Short-Chain Alkyl Polyethylene Glycol Ethers

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 CiEj 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 CiEj (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 angstrom(3)), (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 C4Ej compared to ethanol.