Review Microencapsulation of essential oils with biodegradable polymeric carriers for cosmetic applications Isabel M. Martins a,⇑ , Maria F. Barreiro b , Manuel Coelho c , Alírio E. Rodrigues a a LSRE – Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE/LCM, Department of Chemical Engineering, Faculty of Engineering of University of Porto, Rua Dr Roberto Frias, 4200-465 Porto, Portugal b LSRE – Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE/LCM, Polytechnic Institute of Bragança, Campus Santa Apolónia Ap 1134, 5301-857 Bragança, Portugal c LEPAE – Laboratory for Process, Environmental and Energy Engineering, Department of Chemical Engineering, Faculty of Engineering of University of Porto, Rua Dr Roberto Frias, 4200-465 Porto, Portugal highlights  Microencapsulation has numerous industrial applications.  The choice of the appropriate technique depends on several factors.  Coacervation is one of the preferable techniques to encapsulate essential oils.  Microencapsulation efficiency depends on several variables.  The release profile of essential oils can be explained by a diffusion mechanism. article info Article history: Received 5 November 2013 Received in revised form 3 February 2014 Accepted 6 February 2014 Available online 17 February 2014 Keywords: Microencapsulation Coacervation Essential oils Encapsulation efficiency Release abstract Microencapsulation provides an important tool for cosmetic and/or pharmaceutical industry, enabling protection and controlled release of several active agents. The encapsulation of essential oils in core–shell or matrix particles has been investigated for various reasons, e.g., protection from oxidative decomposi- tion and evaporation, odor masking or merely to act as support to ensure controlled release. A large num- ber of microencapsulation methods have been developed in order to be adapted to different types of active agents and shell materials, generating particles with a variable range of sizes, shell thicknesses and permeability, providing a tool to modulate the release rate of the active principle. With this work, an overview regarding properties and applications of essential oils and biodegradable polymers in the cosmetic field, focusing the use of polylactide as the base material to encapsulate thyme oil, as well as of microencapsulation processes with a particular emphasis on the coacervation, will be presented. Ó 2014 Elsevier B.V. All rights reserved. Contents 1. Introduction ......................................................................................................... 192 2. Efficient microencapsulation methodologies ............................................................................... 192 2.1. Microencapsulation methods ...................................................................................... 192 2.2. Encapsulation efficiency .......................................................................................... 194 2.3. Encapsulation materials .......................................................................................... 195 3. Microencapsulation of essential oils ...................................................................................... 195 4. Microencapsulation and controlled release ................................................................................ 195 4.1. Microcapsules morphology and release mechanisms ................................................................... 195 4.2. Diffusion characteristics of poly(lactic acid) microcapsules .............................................................. 197 http://dx.doi.org/10.1016/j.cej.2014.02.024 1385-8947/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +351 220 413 658; fax: +351 225 081 674. E-mail address: isa@fe.up.pt (I.M. Martins). Chemical Engineering Journal 245 (2014) 191–200 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej