Analytical Methods Comparison of two isolation methods for essential oil from rosemary leaves: Hydrodistillation and microwave hydrodiffusion and gravity Nabil Bousbia a,b , Maryline Abert Vian c, * , Mohamed A. Ferhat b , Emmanuel Petitcolas c , Brahim Y. Meklati b , Farid Chemat c, * a Institut National Agronomique, El Harrach, Alger, Algeria b Centre de Recherche Scientifique et Technique en Analyses Physico-Chimiques (CRAPC), BP 248 Alger RP 16004, Alger, Algeria c Université d’Avignon et des Pays de Vaucluse, UMR A 408 INRA – UAPV, Sécurité et Qualité des Produits d’Origine Végétale, F-84029 Avignon, France article info Article history: Received 7 May 2008 Received in revised form 25 September 2008 Accepted 27 September 2008 Keywords: Microwave Hydrodiffusion Antioxidant Essential oil Rosemary abstract Traditional hydrodistillation (HD) and innovative Microwave Hydrodiffusion and Gravity (MHG) methods have been compared and evaluated for their effectiveness in the isolation of essential oil from fresh Rosmarinus officinalis leaves. The microwave method offers important advantages over traditional alter- natives, namely: shorter isolation times (15 min against 3 h for hydrodistillation), environmental impact (energy cost is fairly higher to perform HD than that required for rapid MHG isolation), cleaner features (as no residue generation and no water or solvent used), increases antimicrobial activities, increases anti- oxidant activity and provides a more valuable essential oil (with high amount of oxygenated com- pounds). It offers also the possibility for a better reproduction of natural aroma of the essential oil from rosemary leaves than the HD essential oil. Moreover, microwave procedure yielded essential oils that could be analysed or used directly without any clean-up, solvent exchange or centrifugation steps. Scanning electron microscopy shows important structural changes for MHG extraction in contrast to those obtained by HD. Electron micrographs show clearly that the cells are broken and damaged during microwave treatment. Finally, the mechanism of Microwave Hydrodiffusion and Gravity is proposed and discussed. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Rosemary (Rosmarinus officinalis L.) is a perennial herb with fra- grant evergreen needle-like leaves. It is native to the Mediterra- nean region and it has been cultivated for a long time. It belongs to the Lamaiaceae family, which comprises up to 200 genera and about 3500 species. The leaves are evergreen, with dense short woolly hairs. Rosemary has been a significant herb since antiquity, although rosemary is more familiar to contemporary Westerners as a kitchen herb used to add a spicy or slightly medicinal flavour to some foods, it was traditionally used as an antiseptic, astringent, and food preservative before the invention of refrigeration. Rose- mary’s antioxidant properties are still used to extend the shelf life of prepared foods (Cuvelier, Richard, & Berest, 1996). Rosemary is also known medicinally for its powerful antioxidant activity (Ibanez et al., 2003), its antibacterial and antimutagenic properties, and as a chemopreventive agent (Oluwatuyi, Kaatz, & Gibbons, 2004). Besides the therapeutical application, the essential oil is widely applied in the cosmetic industry producing various Cologne waters, bathing essences, hair lotions and shampoos and as a com- ponent of disinfectants and insecticides (Boelens, 1985). The essential oil secreted by glandular trichomes is mainly located in leaves. Essential oil can be isolated using a number of isolation methods, e.g. hydrodistillation, steam distillation and organic solvent extraction. Nevertheless, monoterpenes are well known to be vulnerable to chemical changes under steam distilla- tion conditions, and even conventional solvent extraction is likely to involve losses of more volatile compounds during removal of the solvent (Presti et al., 2005). Many of these methods are more- over time-consuming and energy intensive. There are many publi- cations dealing with the extraction of R. officinalis using alternative techniques. Recently, the supercritical fluid extraction of rosemary with CO 2 has been the object of a lot of research (Carvalho, Moura, Rosa, & Meireles, 2005) and has become a valid alternative to the more conventional extraction procedures, mainly because the dissolving power of the extracting medium can be adjusted by reg- ulating the pressure and temperature conditions. However, the technological conditions required for the use of supercritical fluid extraction are onerous and the high cost of producing specific prod- ucts has limited its use. Moreover, in certain cases, the extractive power of supercritical CO 2 , towards specific analytes, is insufficient under conventional conditions (Lucien & Foster, 2000) and 0308-8146/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2008.09.106 * Corresponding authors. E-mail address: maryline.vian@univ-avignon.fr (M. Abert Vian). Food Chemistry 114 (2009) 355–362 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem