Search

Abstract: Essential oils are important in the flavour and cosmetic industries. Recently, microwave energy has been applied in different extraction processes to obtain essential oils with quality and yield similar to those obtained using steam distillation, but using less energy and time. The dielectric properties of any given material are of critical importance when seeking to understand its response to applied electromagnetic waves. Nevertheless, data related to aromatic plants are scarce. This paper addresses the measurement and estimation of dielectric properties of herbal matrices as a part of the study of the fundamental phenomenology behind the extraction of essential oils with microwaves. A cavity perturbation system was used to measure the properties of the plant matrix, and dielectric mixture equations were used later to try to reproduce the results obtained. The dielectric properties of partly dried rosemary, rosemary''s essential oil and oven-dry plant material were measured at temperatures between 20°C and 160°C, and atmospheric pressure, at frequencies of 2450MHz and 910MHz. The results show a strong influence of water content on the dielectric properties. A new predictive approach that uses the results from measurements of dielectric properties from the different constituents to obtain effective mixture dielectric properties is proposed. The predicted values of the dielectric constants were better than those of the loss factors. [Copyright &y& Elsevier]