Supercritical CO₂ Extraction of Waste Citrus Seeds: Chemical Composition, Nutritional and Biological Properties of Edible Fixed Oils

Abstract

Seeds of Citrus plants (Rutaceae), an major agro‐industrial waste, are a potential source of valuable by‐products. The chemical composition, the antioxidant profile, and the biological/nutritional properties of fixed oils (SFE oils) obtained by supercritical CO2 extraction (at 300 bar and 40 °C) from seeds of mandarin (Citrus reticulata), lemon (Citrus limon), and grapefruit (Citrus paradisi), discarded by a local agro‐alimentary industry are studied. The yields and compositions of SFE oils are compared to oils obtained by n‐hexane extraction of Citrus seeds in a Soxhlet apparatus (SoxE oils). Linoleic (35–42%), oleic (22–28%), palmitic (21–25%), α‐linolenic (4–10%), and stearic (4–7%) are the main oil fatty acids, while monolinolein and dilinolein derivatives represent the main triacylglycerols in SFE oils, determined by GC‐FID and HPLC‐DAD/ELSD techniques. Citrus SFE oils show lower yields than SoxE oils but similar chemical profiles. Principal components analysis applied to fatty acid and triacylglycerol data indicates that the oils from different seeds are tightly clustered. Moreover, SFE oils show radical scavenging activities (ABTS assays), an inhibitory effect on the growth of murine B16F10 melanoma cells and on the mushroom tyrosinase activity. Citrus SFE oils and de‐coated seeds are also evaluated for their attractant effect on the Mediterranean fruit fly Ceratitis capitata by behavioral assays. The results qualify Citrus SFE oils as a potential natural, environmentally‐friendly, resource for food/pharmaceutical applications. Practical Applications: The environmentally‐friendly supercritical CO2 extraction of waste lemon, mandarin, and grapefruit seeds gives edible fixed oils a richness in essential fatty acids, suitable for human nutrition and the preparation of nutraceuticals and pharmaceuticals. Edible fixed oils obtained from lemon, mandarin, and grapefruit seeds by SFE‐CO2 extraction show high levels of essential fatty acids, antioxidant, anticancer, and antityrosinase activity.

The Second Life of Citrus Fruit Waste: A Valuable Source of Bioactive Compounds

“…In this regard, different sustainable and green methodologies for the effective reuse of waste have been recently developed. Protocols for the recovery of valuable compounds include different steps: (i) extraction (i.e., enzyme-assisted, ultrasound-assisted, microwave-assisted, supercritical fluid, pressurized liquid extractions); (ii) separation and purification (via filtration and chromatographic techniques); (iii) identification and characterization (through NMR, mass spectroscopy or chromatography); (iv) toxicological screening both in vitro and in vivo [ 26 , 46 , 64 , 72 ]. Alternatively, conversion of CF waste into biofuels can be performed through thermochemical and biochemical processes such as pyrolysis, thermolysis, gasification, combustion [ 19 ].…”

“…Seeds are isolated during the juice extraction, and are a useful source of oil, proteins, limonoids and phenolic compounds, in particular, the flavonoids eriocitrin and hesperidin [ 46 ].…”

“…Recently, EOs from lemon, mandarin and grapefruit seeds discarded by an agro-alimentary industry were studied to evaluate their nutritional and biological properties. Noteworthy, even if to a different extent, all three oils possess antioxidant, antifungal and antitumor properties, inhibitory effect on the mushroom tyrosinase activity, as well as and antiproliferative effect on murine B16F10 melanoma cells [ 46 ]. EOs isolated from lemon leaves, rich in limonene, citronellal and citronellol, possess antibacterial activity against Gram-negative ( Salmonella typhimurium , P. aeruginosa and E. coli ) and Gram-positive bacterial strains ( Staphylococcus epidermidis and two S. aureus strains), as well as insecticidal potential [ 109 , 110 ].…”

Comparative evaluation of the composition of vegetable essential and fixed oils obtained by supercritical extraction and conventional techniques: a chemometric approach

“…Fatty acids profiles of C. paradisi , C. reticulata , C. lemon seed oils (FO 1–3), parsley seed oil (FO 4) and wheat germ oil (FO 5), obtained by SFE‐CO 2 , were in line with those reported by other authors for the same vegetable matrices extracted with different techniques, as indicated in our previous papers (Piras et al ., 2009; Rosa et al ., 2019; Piras et al ., 2020; and citations therein). In this manuscript, by a comparative chemometric approach, we evidenced that FO 1–7 obtained by SFE‐CO 2 generally showed FA profiles similar to FO obtained by conventional hexane extraction.…”

“…Solvent extraction (with n ‐hexane or petroleum ether) in a Soxhlet apparatus represents the most used process of extracting oils from vegetable matrices, achieving almost complete recovery of FO (Yeddes et al ., 2012; Satriana et al ., 2019). Nevertheless, owing to the significant disadvantages of this technique (volatile compounds loss, residues of toxic substances and oxidation of fatty acids induced by high temperature), novel and greener methods are actually used for FO extraction such as microwaves, ultrasound‐assisted extraction and the supercritical fluid extraction (Yeddes et al ., 2012; Rosa et al ., 2019; Satriana et al ., 2019).…”