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Buriti fruit [194], carrot [195-198], cloudberry [199], hiprose fruit [174], olive husks [200], tomato [201-207] are the main fruits and vegetables studied (Table 3.8). Lyco-pene is the dominant carotenoid (85% to 90% of total carotenoids) in the tomato extract [207], whereas β-carotene (60% to 80%) is the major one in carrot extract.

Squalene, tocopherol, and sterols are the main bioactive components found in olives.

TaBlE 3.7 Fatty acid Composition of Cereal Oils raw Material

Fatty acid Contenta C14:0C16:0C16:1C18:0C18:1C18:2C18:3C20:0C20:1ref. Amaranth—12.32–17.94—2.71–4.6623.85–32.8843.66–47.48—0.38–1.54—180 Oat0.1–0.213.6–15.7—1.4–1.638.3–43.739.1–42.21.0–1.5—0.8–0.9181 Rice bran—16.5–17.9—1.1–1.438.8–41.437.8–40.41.5–1.70.3–0.60.4–0.6183 Wheat germ—18.09–18.950.22–0.240.49–0.7313.69–16.5257.1–58.996.46–8.51——188 Palmitic acid (C16:0), Palmitoleic acid (C16:1), Stearic acid (C18:0), Oleic acid (C18:1), Linoleic acid (C18:2), Linolenic acid (C18:3), Arachidic acid (C20:0), Eicosenoic acid (C20:1). a Units not indicated.

Drying of samples prior to extraction is necessary, as carrots and tomatoes contain 80% to 95% moisture. Grinding is also needed to achieve small particle size. Olive pomace and husk are by-products of olive oil production. To further recover the valu-able bioactive compounds by SC-CO2 extraction, pretreatment of such by-products the conventional fruit and vegetable processing industry is necessary.

a) Particle size: During extraction of freeze-dried carrots, a higher extrac-tion yield was obtained with smaller carrot particles [196, 198]. The total carotenoid yield increased from 1109.9 to 1369.6 and 1503.8 μg/g dry carrot when the particle size was decreased from 1–2 mm to 0.5–1 mm and 0.25–0.5 mm, respectively [198].

b) Moisture: Moisture had different effects on the carotenoids yield. The α- and β-carotene yields increased with decreasing level of moisture in the feed material, while the lutein yield decreased [198]. The lutein yield decreased from 55.3 to 29.9, 19.3 and 13.0 μg/g dry carrot with a decrease in moisture from 84.6 to 48.3, 17.5 and 0.8%, while the α- and β-carotene yields increased from 184.1 to 323.0, 442.3 and 599.0 μg/g, and from 354.2 to 547.8, 668.3 and 891.7 μg/g dry carrot, respectively [198]. On the other hand, only trace amounts of lycopene were extracted when the tomato feed material contained 50% to 60% moisture [207]. This can be explained by the fact that water can act as a cosolvent for the extraction of relatively polar compounds, like lutein, whereas the presence of water is not favorable for the relatively nonpolar lycopene and carotenes.

3.3.4.1.2 Extraction Parameters

a) Temperature and pressure: Lycopene extraction yield increased with pressure from 33.5 MPa to 45 MPa at a constant temperature of 66°C and increased with temperature from 45°C to 66°C at a constant pressure of 45 MPa [207], because SC-CO₂ density increases with pressure at constant temperature and solubility increases with temperature above the crossover pressure. Temperature greatly affects the extraction rate at pressures above the cross-over pressure. Using tomato skin [202], the extraction rate and yield were greatly increased at 110°C, resulting in 96% lycopene recovery in 40 min and 100% recovery in 50 min. However, only about 20% and 30% recovery were achieved in 80 min at 60°C and 85°C, respectively.

Pressure also affected the composition of the extracts as the recovery of trans-lycopene increased and that of cis-lycopene decreased with CO2 density [205]. Therefore, the fractionation of trans-lycopene is possible when optimum CO2 density is chosen as the lycopene isomers have differ-ent solubilities in SC-CO2.

b) Flow rate: Total carotenoids yield increased with flow rate [198], ranging from 934.8 to 1332.3 µg/g and 1973.6 µg/g dry carrot at CO2 flow rates of 0.5, 1, and 2 L/min (measured at STP), respectively. However, the lycopene

TaBlE 3.8 Extraction of Compounds from Fruits and vegetables using SC-CO2 raw MaterialFeed (g) Sample preparation Bioactive Compound

Extraction Conditions recoverya (%)ref.particle Size (mm)H2O (%)T (°C)p (Mpa)Flow rateTime (min)Cosolvent Buriti fruitn.i.n.i.11Carotenoids, tocopherols40, 5520, 3018.6, 25.8 g/minn.i.None7.8 c194 Carrot20.5–10.8α-,β-Carotene, lutein40, 5012–331.2 L/min480Nonen.i.195 n.i.0.26, 0.47, 1.12n.i.Carotenoids40, 50, 607.8–29.4n.i.n.i.1, 3, 5% EtOH+n.i.196 2000n.i.n.i.carotenes, phenolics, phytosterols, linolenic acid

45–5035–38n.i.120–180Nonen.i.197 20.25–0.5, 0.5–1, 1–20.8, 17.5, 48.7, 84.6α-,β-carotene, lutein40, 55, 7027.6, 41.3, 55.10.5, 1, 2 L/min2400, 2.5, 5% canola oil+0.2c198 Cloudberry42n.i.n.i.Unsaturated oil, β-carotene, tocopherols

40, 609, 10, 12, 15, 30n.i.n.iNonen.i.199 Hiprose fruitn.i.0.36n.i.Tocopherols, carotenoids35251–1.5 L/minn.i.None100174 Olive husksn.i.0.4n.i.Unsaturated oil (oleic acid)35–5710.4–18n.i.n.i.Nonen.i.200 continued

TaBlE 3.8 (continued) Extraction of Bioactive Compounds from Fruits and vegetables using SC-CO2 raw MaterialFeed (g)Sample preparationBioactive CompoundExtraction Conditionsrecover (%)particle Size (mm)H2O (%)T (°C)p (Mpa)Flow rateTime (min)Cosolvent Tomato0.50.05–0.25n.i.Phytoene, phytofluene, ξ-carotene, β-carotene, lycopene

40, 50, 608–264 × 10–3 L/min30Nonen.i. 0.3n.i.n.i.Lycopene60, 85, 11040.51.5 × 10–3 L/min50Acetone, MeOH, EtOH, hexane, dichloromethane, water++

100 n.i.n.i.n.i.Lycopene45–8035–38n.i.120–180None55 3n.i.n.i.Lycopene, tocopherols32–8613.8–48.32.5 × 10–3 L/minn.i.None61 0.5n.i.n.i.Lycopene408–284 × 10–3 L/minn.i.Nonen.i. 20n.i.n.i.Lycopene4032n.i.n.i.Nonen.i. 30001n.i.Lycopene45–7033.5–45133.3–333.3 g/min120–4801–20% hazelnut oil++60 T: temperature, P: pressure, n.i.: not indicated. a Recovery (g extract/g oil in feed material × 100), bsuperficial velocity, cyield (g/100 g feed material), +cosolvent added to sample before extraction at the level (%, indicated, ++cosolvent added to sample before extraction at the level (%, w/w) indicated.

yield decreased as flow rate was increased from 2.5 to 15 mL/min (measured time of CO2 in the extractor and therefore the CO2 leaving the extractor not being saturated with oil. A low flow rate (1.8 g/min) produced a smaller amount of squalene but at a higher concentration, whereas a high flow rate (5.4 g/min) produced a higher amount of squalene at a lower concentration in the extract [209].

c) Use of cosolvent: Acetone, ethanol, methanol, hexane, dichloromethane, and water have been compared as cosolvents in SC-CO2 by mixing the cosolvent with the sample prior to extraction [202] and it was shown that all cosolvents tested except water increased lycopene recovery. In fact, water showed a negative effect, decreasing lycopene recovery to 2%.

Ethanol increased recovery but decreased extraction rate. All the other cosolvents studied not only increased the lycopene yield but also improved the extraction rate to varying degrees [202]. The use of vegetable oils as a cosolvent for the recovery of carotenoids from vegetables was recently developed [198, 203, 207]. For example, hazelnut oil was chosen by Vasapollo et al. [207] because of its low acidity, which can prevent the degradation of lycopene during extraction. Lycopene yield increased with hazelnut oil addition as a cosolvent, but the extract was more diluted at higher amounts of oil [207]. For the extraction without cosolvent addi-tion, the lycopene recovery was practically maintained below 10%

from 2 to 5 hours extraction time, while in the presence of hazelnut oil, the lycopene recovery increased to about 20% in 5 hours and 30% in 8 hours. Sun and Temelli [198] added canola oil in a continuous manner into SC-CO2 for the recovery of carotenoids from carrot. The extraction yield with SC-CO₂ without canola oil addition for α-carotene was 137 to 330.4 μg/g and β-carotene was 171.7 to 386.6 μg/g feed material at dif-ferent temperatures and pressures, while the yields more than double to 288.0–846.7 μg/g and 333.8–900.0 μg/g feed for α- and β-carotene, respectively, upon addition of canola oil. The major advantage of using vegetable oils as cosolvents is the elimination of organic solvent addi-tion, which needs to be removed later, and the fact that the oil enriched in bioactives can be used as is in a variety of product applications.

3.3.4.2 Characterization of products Extracted by SC-CO2

3.3.4.2.1 Chemical Composition

Fatty acid composition of oils extracted from various fruits and vegetables is shown in Table 3.9. Trilinolein (LLL) is the main triglyceride present in carrot oil followed

by LLP, LLO, POL, and OOP [197]. Linoleic acid is the main fatty acid, followed by palmitic acid in both carrot and tomato oils [197, 204]. The fatty acid composition of tomato extract obtained by SC-CO₂ was similar to that of chloroform extract. But the extracts obtained by SC-CO2 at different temperature and pressure conditions had different fatty acid compositions, which were due to the differences in the solubili-ties of linoleic and palmitic acids at different conditions [204].

3.3.4.2.2 Other Quality Attributes

The yellow-orange color of carrot oil was mainly contributed by the carotenes, which are fat-soluble pigments [197].

3.3.4.3 Comparison with Conventional Methods

Carrot oil extracted by SC-CO₂ had higher carotenes (1,850 mg/kg) than that of com-mercial carrot oil (170 mg/kg) [197]. It also had a high sterol content (30.2 mg/kg), which was 17-fold higher than that in commercial carrot oil (1.7 mg/kg). The squalene concentration of olive oil in the SC-CO2 extract was 10 times higher than that obtained with solvent extraction. However, this enrichment was accompanied by a drop in the overall extracted squalene quantities [209]. SC-CO2 extraction pro-duced superior olive husk oil in terms of oil acidity, PV, and phosphorus content [208]; therefore, a simpler refining process would be required.