Biological properties of essential oils and volatiles: Sources of variability

Abstract

Essential oils are a specific type of extracts that result either from hydro-, steam- or dry-distillation from any part of a duly identified botanical species, or by a mechanical process without heating, called expression, from the epicarp of Citrus fruit species. Any other type of extraction may provide a more, or less, volatiles-rich extract, but it is not an essential oil. Essential oils, per se, do not exist in the plant, since they result from a specific extraction procedure. In the plant there is a wide array of metabolites, only some of which will be extracted in the form of an essential oil, with variable composition even if just considering that they can either be obtained by distillation or expression. Man has used for long, both volatiles and essential oils, for a wide range of purposes in the pharmaceutical, food, beverage, cosmetic and perfumery industries, among others. The described biological activities of volatiles and essential oils are wide, but the results are not always congruent. Awareness of the factors that may influence the essential oil chemical variability and ultimately its biological activity, efficacy and safety, are thus very important. These comprise, a) the knowledge on the difference between plant volatiles and essential oils, b) the avoidance of botanical misidentification, c) getting information on plant parts chemical composition variability, the existence of chemotypes and essential oil components enantiomers, and also f) exploring different biological activity assay conditions, which was reviewed in this present work.