Since solvents of petroleum origin are now strictly regulated worldwide, there is a growing demand for using greener, bio-based and renewable solvents for extraction, purification and formulation of natural and food products. The ideal alternative solvents are non-volatile organic compounds (VOCs) that have high dissolving power and flash point, together with low toxicity and less environmental impact. They should be obtained from renewable resources at a reasonable price and be easy to recycle. Based on the principles of Green Chemistry and Green Engineering, vegetable oils could become an ideal alternative solvent to extract compounds for purification, enrichment, or even pollution remediation. This review presents an overview of vegetable oils as solvents enriched with various bioactive compounds from natural resources, as well as the relationship between dissolving power of non-polar and polar bioactive components with the function of fatty acids and/or lipid classes in vegetable oils, and other minor components. A focus on simulation of solvent-solute interactions and a discussion of polar paradox theory propose a mechanism explaining the phenomena of dissolving polar and non-polar bioactive components in vegetable oils as green solvents with variable polarity.

The present study was designed to evaluate five green solvents, i.e. 2-methyltetrahydrofuran (2-MeTHF), dimethyl carbonate (DMC), cyclopentyl methyl ether (CPME), isopropyl alcohol (IPA) and ethyl acetate, for the substitution of n-hexane in the extraction of carotenoids from carrots. Initially, solvent selection was made through the theoretical physicochemical solvent properties and solubility results obtained using two simulation programs, Hansen Solubility Parameters (HSPs) and Conductor-like Screening Model for Realistic Solvation (COSMO-RS) which use a statistical thermodynamics approach based on the result of quantum chemical calculation, for comprehension of the dissolving mechanism. On the basis of the HSPs analysis, non-polar or slightly polar solvents were the most suitable solvents for extraction of carotenoids. COSMO-RS analysis showed a higher probability of solubility for all the carotenoids from carrot in CPME, 2-MeTHF and ethyl acetate compared with n-hexane. The experimental results using a conventional solid–liquid extraction by maceration showed that the best green solvents were CPME, 2-MeTHF and ethyl acetate in accordance with the predictive results from COSMO-RS. The highest carotenoid content (78.4 mg 100 g⁻¹ DM) was observed in CPME where 66% was represented by β-carotene and 34% was α-carotene. These results support the potential of CPME and 2-MeTHF as alternative green solvents for extraction of carotenoids.

The objective of this study was to transform limonene as an agro-chemical platform for the production of a wide range of added-value compounds for pharmaceutical, cosmetic and food ingredients. This molecule was also evaluated as an alternative solvent for the extraction of several bioactive compounds compared to n -hexane. Limonene was extracted from the essential oils of orange peels through a solvent-free microwave extraction technique. Limonene was successfully transformed into products with industrial interest by catalytic oxidation using three different iron catalysts. The ability of limonene to be used as an alternative solvent was performed using two simulation tools, Hansen solubility parameters (HSPs) and the Conductor-like Screening Model for Real Solvents (COSMO-RS), and via experimentation. The results indicated that limonene could be a promising green solvent and synthon for petroleum substitution in the extraction or synthesis of bioactive compounds.

Cadmium (Cd) is a non-physiological heavy metal that can be harmful at low concentrations. Increasing anthropogenic activities are incrementing the risk of accumulation of this heavy metal in different organs and tissues of the body. In the case of pregnant women, the threat is more serious due to the implications affecting not only their own health but also fetal development as well. Metallothioneins (MTs), small cysteine-rich proteins, are involved in zinc (Zn) and copper homeostasis in mammals but can, however, also bind with Cd if present. The accumulation of Cd in maternal tissues (e.g. placenta, maternal blood, and mammary glands) induces the synthesis of MTs, preferably MT2, in an attempt to sequester the metal to avoid toxicity. The formed Cd–MT complexes will avoid the Cd transport from the placenta to the fetus and end up accumulating in the maternal kidneys. At the same time, high concentrations of MTs will increase the formation of Zn–MT complexes, therefore decreasing the amount of Zn ions available to be transported to the fetus by means of Zn transporters such as ZnT2, ZIP14 and DMT1. Although MTs cannot transport Cd from the mother to the fetus, the divalent DMT1 transporter is suggested to carry the metal to the fetus. As a consequence, the low levels of Zn(II) in the fetus, together with the presence of Cd(II) coming from the mother either via the placenta and cord blood or via breast milk induce changes in the fetal development including fetal growth retardation, and low weight or height of the newborn. Likewise, the concentrations of Cd(II) in the newborn can cause alterations such as cognitive disabilities. In summary, the presence of Cd(II) in the maternal tissues will induce MT synthesis in an attempt to detoxify these tissues and reduce the possible toxicity of Cd in fetal and newborn tissues.

The ability to be used as an alternative solvent of a cis-rich pinane (cis/trans: 7/3), which was obtained for the first time at the multigram scale through an environmentally friendly catalytic hydrogenation of α/β-pinenes or turpentine oil under neat conditions over a Pd/C catalyst, was investigated and compared to n-hexane for the extraction of several bioactive compounds. Experimental evaluation as well as a simulation of the cis-rich pinane extraction capacity have been undertaken. The predictive approach was performed using the simulation software COSMO-RS (conductor like screening model for realistic solvents), which uses a statistical thermodynamics approach based on the result of quantum chemical calculation, for the understanding of dissolving mechanism. COSMO-RS simulation showed that the bio-based solvent is a good solvent to solubilize carotenoids, oil from rapeseed and aromas from caraway seeds. The experimental results indicated that the highest carotenoid yield was obtained with the cis-rich pinane with 95.4% of the maximum carotenoid content in carrots while n-hexane was only able to extract 78.1% of them. With respect to the extraction of oil from rapeseeds, both solvents showed similar extraction yields and no differences were observed in the fatty acid profiles. In relation to the aromas, the characterization of the essential oil extracted by the two solvents showed a similar composition, where carvone (64%) was the main component followed by limonene (34%). No selectivity of the solvents was observed for any of the two major compounds. The results indicate that the bio-based solvent could be a promising solvent for n-hexane substitution.

The search for economic and sustainable sources of polyunsaturated fatty acids (PUFAs) within the framework of the circular economy is encouraged by their proven beneficial effects on health. The extraction of monkfish liver oil (MLO) for the synthesis of omega-3 ethyl esters was performed to evaluate two blending systems and four green solvents in this work. Moreover, the potential solubility of the MLO in green solvents was studied using the predictive simulation software COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS). The production of ethyl esters was performed by one or two-step reactions. Novozym 435, two resting cells (Aspergillus flavus and Rhizopus oryzae) obtained in our laboratory and a mix of them were used as biocatalysts in a solvent-free system. The yields for Novozym 435, R. oryzae and A. flavus in the one-step esterification were 63, 61 and 46%, respectively. The hydrolysis step in the two-step reaction led to 83, 88 and 93% of free fatty acids (FFA) for Novozym 435, R. oryzae and A. flavus, respectively. However, Novozym 435 showed the highest yield in the esterification step (85%), followed by R. oryzae (65%) and A. flavus (41%). Moreover, selectivity of polyunsaturated fatty acids of R. oryzae lipase was evidenced as it slightly esterified docosahexaenoic acid (DHA) in all the esterification reactions tested.