Extraction of essential oils and cuticular waxes with compressed CO2: Effect of matrix pretreatment

The effect of the pretreatment of the matrix on the CO2 extraction of essen tial oils and cuticular waxes from aromatic herbs was studied. The vegetabl e matrix, oregano bracts, was submitted to different mechanical and physica l treatments prior to extraction with compressed CO2 under standard conditi ons (100 bar, 310 K, and 0.25 kg/h). The rates and yields of extraction of both essential oils and cuticular waxes were evaluated and compared with th ose obtained from an untreated matrix. The losses of essential oils during the pretreatments were estimated. Comminution under atmospheric and cryogen ic conditions and comminution in a closed atmosphere (internal comminution) were the mechanical pretreatments under investigation. The physical disrup tion of essential oils glands by a fast decompression treatment (FD treatme nt) was also tested. The structure of the matrixes and essential oils gland s, before and after CO2 extraction, were observed by scanning electron micr oscopy (SEM). Cryogenic comminution, internal comminution and FD treatment were all found to be effective matrix pretreatments for the extraction of e ssential oils. However, the selective liberation of the essential oils with respect to cuticular waxes obtained by the FD treatment results in a final extract with a higher content of essential oils. Moreover, the essential o ils themselves are believed to be of better quality than those obtained fro m mechanically treated matrixes.