Deterpenation of Citrus Essential Oils Using Glycerol-Based Deep Eutectic Solvents

Abstract

Citrus essential oils are complex hydrocarbon mixtures mainly composed of terpenes and terpenoids and are widely used as raw materials in food, pharmaceutical, and fine chemical industries. However, essential oil deterpenation (i.e., separation of terpenes and terpenoids) is required to preserve the quality of the final product for practical applications. Currently, there is a need to find efficient and environmentally friendly solvents to replace the harmful volatile organic compounds that are conventionally used as extraction solvents. Therefore, alternative solvents with more benign and environmentally friendly characteristics are crucial to develop sustainable citrus essential oil deterpenation processes. In this work, biorenewable deep eutectic solvents (DES) composed of glycerol (Gly) and choline chloride (ChCl) are evaluated as sustainable solvents for citrus essential oil deterpenation, using model mixtures and real citrus crude orange essential oils (COEO). The liquid–liquid extraction process for essential oil deterpenation using DES was performed at 298.15 K and 101.3 kPa, and the solvent performance was evaluated in terms of the experimental solute distribution coefficients and selectivity values, which were compared against those predicted using the conductor-like screening model for real solvents (COSMO-RS). The effect of solvent composition (i.e., hydrogen bond acceptor/donor ratio) and the addition of water (pure DES vs diluted DES) were also explored. Overall results indicate the feasibility of using DES as extraction solvents for citrus essential oil deterpenation, with pure ChCl:Gly 1:2 providing the highest extraction yield, while the addition of water decreased the distribution coefficient but increased the selectivity of the process.

Ionic liquids as entrainers for terpenes fractionation and other relevant separation problems

“…For [C 4 mim][OAc], encouraging experimental selectivities were found for terpene/linalool mixtures, being the highest found for R(+)limonene/linalool (S ij ∞ = 30.29). This particular mixture represents the majority of the components present in Citrus essential oils profiles [20,22,75], and the removal of R(+)-limonene improves the oil stability [21]. The high selectivity value found for the R(+)-limonene/linalool mixture along with the reasonable capacity of linalool (1.26) at 403.15 K suggest that [C 4 mim][OAc] is a potential option in the deterpenation of citrus essential oils, in accordance with the study of Lago et al [38].…”

“…Terpenoids are the main responsible for the aroma and antioxidant properties of EOs, while terpenes contribute little to the aroma, being easily oxidized and producing off-flavors that deteriorate the quality of the of EOs [20,21]. The removal of terpenes from the oxygenated rich part, process known as deterpenation, is crucial to improve the stability, solubility and storage requirements of commercial EOs [22,23].…”

“…Traditionally, this technique is performed using conventional volatile organic solvents, such as methanol, hexane, acetone, ethyl acetate and petroleum ether derivatives [20]. However, alternative neoteric solvents such as hydroalcoholic solvents [25][26][27][28][29][30][31], deep eutectic solvents [22,32], or ionic liquids [33][34][35][36][37][38] are being studied as potential replacements, aiming at better separation performances.…”

Deep Eutectic Solvents for the Extraction of Bioactive Compounds from Natural Sources and Agricultural By-Products

“…An exhaustive revision of the literature shows that, apart from vegetables, plants, fruits or agricultural by-products, other natural matrices have also served as source of valuable compounds and as occur with previous sources, the use of NADESs as extraction solvents has been also carried out. In this sense, oils obtained from citric, cereals, olives, and palm [40][41][42][43][44][45][46] have been the products most widely evaluated using DESs, although flour [47], eggs [48] and milk [49] as well as nonagricultural by-products [10,50] have been also investigated. As can be seen in Table 3, the studies were focused on the search of different and varied types of molecules including phenolic compounds [40][41][42]46], flavonoids [40,43], terpenoids [10,42,44], proteins [48], lignans [45] or minerals [50].…”

“…[47] In this kind of application, again ChCl was the preferred HBA combined with alcohols, organic acids, sugars or urea [40,41,[43][44][45][46]50] although other quaternary ammonium salts combined with alcohols [42,47,48], lactic acid combined with glucose [49] or terpenes (menthol) together with myristic acid [10] have been also applied. In all cases, natural components were used, thus the application of NADESs has been the choice in the studies developed so far in this area.…”