**2. Supercritical fluid technology**

Supercritical Fluid Technology (SFT) has received growing interest as a green technology, with extraction being the main application in the food industry. Fluids become supercritical by increasing pressure and temperature above the critical point. Supercritical fluids have liquid-like solvent power and gas-like diffusivity. These physical properties make them ideal clean solvents for extraction of lipids.

Carbon dioxide (CO2) is the most widely used supercritical fluid due to a lack of toxicity and flammability, low cost, wide availability, tunable solvent properties, and moderate critical temperature and pressure (31.1°C and 7.38 MPa) (Black, 1996). Because of the relatively low viscosity, high molecular diffusivity and low surface tension of the system, mass transfer is improved in supercritical CO2 (SC-CO2) in comparison to liquid organic solvents (Oliveira & Oliveira, 2000). Moreover, separation of CO2 from the product can easily be achieved by reduction of pressure, because the products do not dissolve in CO2 at atmospheric pressure.

Another unique property of supercritical fluids is their selectivity. The density of a supercritical fluid is higher than that of a gas, making them better solvents. Extraction selectivity of supercritical fluids can be changed altering density which is done by adjusting

Potential Applications of Green Technologies in Olive Oil Industry 295

SC-CO2 extraction of olive husk oil is superior compared to conventional hexane extraction because the oil is also deacidifed and deodorised during the extraction process, and the resulting extract is free of residual solvent (Esquível & Bernardo-Gil, 1993). Esquivel and Bernardo-Gil (1993) extracted olive husk oil using SC-CO2 under pressures of 12 to 18 MPa

Crude olive oil contains free fatty acids (FFA) and other impurities which must be removed, yielding a triacylglycerol (TAG) rich fraction. A high FFA content decreases the oxidative stability of the oil and leads to rancidity. A reduction in FFA content in virgin olive oil

Supercritical fluid extraction has been proposed as an alternative technology for deacidification of oils and has been used for deacidification of olive pomace oil, an important by-product of olive oil industry. Crude olive pomace oil is often very acidic, darkly colored and highly oxidized. Intensive refining is thus required to make it suitable for human consumption. Neutralization is currently applied, but there are drawbacks to this process. Product yield is very low and neutralization increases the cost per unit. Therefore, it is necessary to reduce the FFA content before refining (Fadiloglu et al., 2003). Supercritical deacidification is actually a selective supercritical fluid extraction process. During the process, FFAs preferentially extracted with minimum neutral oil (TAGs, tocopherols, phytosterols) loss (Vázquez et al., 2009). A schematic diagram of a supercritical fluid extraction system for deacidification of oils is shown in Fig. 2. The oil is fed to the extraction column by a pump. The extraction column consists of two sections: an enriching (above of the oil feeding point) section, and a stripping section (below the oil feeding point). Raffinate is first separated from the extract and sent to the stripping section. Then, in the stripping section, the extract is separated from raffinate and transported to the enriching section. Extract rich in minor lipid compounds and CO2 is separated in the separator. A specified amount of the extract is transferred to the top of the column as reflux (Brunner, 2009). CO2 can be purified and recycled

Deacidification of different oil sources using supercritical fluids have been performed at laboratory scale by several researchers. Turkay et al. (1996) achieved a selective and quantitative (90%) FFA extraction for deacidification of high acidic black cumin seed oil using SC-CO2 at relatively low pressure (15 MPa) and relatively high (60 °C) temperature. Ooi et al. (1996) decreased the FFA content of palm oil to 0.1% in a continuous SC-CO2

Brunetti et al. (1989) obtained deacidification of high acidic olive oil with SC-CO2 at pressures of 20 and 30 MPa, and temperatures of 40 and 60 °C. They reported that the selectivity for FFAs was highest at 20 MPa and 60 °C. Bondioli et al. (1992) studied the supercritical fluid deacidication of olive oil in the pressure range of 9–15 MPa and 40–50 °C. The acidity was reduced from 6.3% to values less than 1% at 40 °C and 13 MPa. In another application, Vázquez et al. (2009) used SC-CO2 as an extraction solvent to remove FFAs from cold-pressed olive oil in a packed column. The acidity was reduced from 4 to

results in an increase in commercial value (Vázquez et al., 2009).

into the system. Raffinate is collected at the bottom of the column.

and temperatures of 35 to 45 °C.

**2.2 Deacidification** 

extractor.

1.43% at 25 MPa and 40 °C.

pressure and temperature. Selectivity can also be changed by the addition of a co-solvent such as ethanol, methanol, hexane, acetone, chloroform and water to increase or decrease the polarity. Ethanol is the most preferred co-solvent because it is non-toxic and meets green technology criteria (GRAS status) (Dunford, 2004).

SC-CO2 processing adds value because products obtained may be considered as natural. Although SFT is used for extraction of plants and vegetables of different sources (Table 1), applications in the olive oil industry have been limited. SFT can be used in olive oil processing for extraction and deacidification, as well as separation, purification or concentration of minor components.


Table 1. Supercritical fluid extraction of different plants and vegetables.

#### **2.1 Extraction**

SC-CO2 has been used to replace hexane in the olive oil industry and meets the growing demand for natural products (Temelli, 2009). The most common applications are extraction of total lipids from olive husk or minor lipid components from olive oil. Extraction of high value minor components without degradation led industry and researchers to focus on SC-CO2 extraction. Fig. 1 represents a typical lab scale SC-CO2 system used for extraction of lipids.

Fig. 1. Schematic diagram of a lab scale SC-CO2 extraction system: 1, CO2 tank; 2,4,10, shutoff valves; 3, pressure gauge; 5, filter; 6, compressor; 7, back pressure regulator; 8, extraction vessel; 9, thermocouple; 11, micrometering valve; 12; sample collector; 13, oil and moisture trap; 14, flowmeter; 15, gas meter.
