High-Quality Essential Oils Extracted by an Eco-Friendly Process from Different Citrus Fruits and Fruit Regions

Essential oils (EOs) were extracted from three types of citrus fruits (orange, lemon, and grapefruit) grown in Sicily and harvested in December or early January, considered to be the best picking season. Different fruit parts were used as sources for EO isolation: outer skin (exocarp), peel (exo- and mesocarp), and waste (exo-, meso-, and endocarp). The extraction was performed by a solvent-free microwave extraction (SFME) process. Very high yields were obtained, in comparison to other industrial methods (0.4% vs 0.05-0.25%). Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to assess the distribution of the main constituents of the EOs. A number of compounds were identified in the EOs, with limonene being the major constituent (50-80%) in most cases. Orange oils proved to be richer in beta-myrcene, whereas lemon oils have gamma-terpinene and higher contents of beta-pinene. Lemon provides more valuable EOs, with higher amounts of oxygenated compounds, although orange and grapefruit oils are richer in citral isomers. Generally, EOs extracted from the exocarp contain higher amounts of oxygenated monoterpenes, whereas those extracted from the exo-/mesocarp are richer in flavone and furanocoumarin derivatives.