Hydrolates: a review on their volatiles composition, biological properties and potential uses

An hydrolate (also known as hydrosol, floral water, aromatic water, or herbal water)is a distillate which is a product of condensation obtained after an essential oil distillation isolation procedure. Hydrolates are colloidal suspensions composed of a continuous phase, the distilled water, and a dispersed phase, the emulsion of essential oil droplets and water-soluble components, namely oxygen-containing compounds. The movement towards a circular economy, has increased the interest in the essential oil industry co-products, such as hydrolates. Hydrolates composition were mostly studied based on their volatile constituents. Moreover, they showed a diverse range of biological properties, with potential application in food, beverages, cosmetic and pharmaceutical industries, as well as in the agroforest sector. Nevertheless, the information is fragmented and dispersed under the different hydrolates designations. In the present review, the main volatile components of 362 hydrolates obtained from 194 species from 50 families is described, and the information on the corresponding essential oil main components is detailed. Additionally, the methodologies of extraction and analysis are surveyed, as well as hydrolates characteristics and traditional uses. This review also describes the different biological properties attributed to hydrolates and, according with these properties, their potential uses.