Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 123

that needs to be included in process optimization studies. Several studies have reported the
presence of significant interactions among extraction time, enzyme concentration and water
to solid ratio (Xie et al ., 2011 ; Zhang et al ., 2007). The optimum combination of these
factors needs to be investigated by employing an appropriate experimental design such as
factorial design or response surface methodology (RSM) in order to achieve the maximum
oil extraction yield.
Microemulsion-based aqueous extraction of oilseeds by using surfactants has also been
examined (Ugolini et al ., 2008 ; Naksuk et al ., 2009 ; Do and Sabatini, 2010 ). The role of the
surfactant in oil extraction is to lower interfacial tension between the aqueous solvent and
the oil vegetable seeds. As a result, oil can be extracted from the seeds. Application of this
technology to oil extraction from oilseeds is still at research phase. The main disadvantages
of the surfactant-based oil extraction techniques include: (1) production of wet meal, (2)
requirement for small particle size that might cause significant problems in large oilseed
production operations, (3) high energy cost for solvent removal and (4) in some cases
presence of surfactant in water or oil phase might not be desirable or acceptable.
4.3.5 Supercritical fluid technology
Supercritical fluids (SCF) have been studied as alternative solvents to conventional hexane
for oilseed extraction. The fundamentals of SCF technology and its utilization for oilseed
processing have been reviewed elsewhere (Dunford et al ., 2003 ; Dunford, 1995 ; King and
List, 1996 ; McHugh and Krukonis, 1994 ; Stahl et al ., 1980 ; Stahl et al ., 1987). Supercritical
carbon dioxide (SC-CO 2 ), which refers to CO 2 above its critical pressure (7.3MPa) and
temperature (31°C), has been the preferred solvent for the edible applications of SCF.
However, nitrous oxide and some organic compounds, such as ethane, propane and butane, as
well as halogenated hydrocarbons, such as chlorotrifluoromethane, have also been employed
as SCF for extraction of natural materials. The advantage of SC-CO 2 is the easy removal of
solvent from the extract. When pressure is released, CO 2 returns to the gas phase and oil
precipitates out of the CO 2 -oil mixture, then CO 2 is recycled to the system. Hence, CO 2
release from the system is not an environmental issue. Density and selectivity of SCF can be
regulated by adjusting pressure and temperature of the system. This property makes the
selective extraction of desired compounds from a complex matrix possible by using SCF.
Oil extraction with SCF was first reported in patent literature in the 1950s (Dickinson,
1947 ; Palmer and Fanwood, 1950 ). Processes for the SC-CO 2 extraction of copra, sunflower
seeds, soybeans and groundnuts were patented later (Vitzthum and Hubert, 1971; Zosel,
1964). Some of the oil and oilseeds successfully extracted with SC-CO 2 are soybean
(Stahl et al ., 1983 ; Friedrich, 1984 ; Snyder et al ., 1984 ), jojoba oil (Stahl et al ., 1983 ;
Friedrich et al ., 1998), cottonseed and corn (Friedrich and Pryde, 1984), sunflower and
rapeseed (Stahl et al ., 1984 ), palm (Kalra et al ., 1987 ), evening primrose (Favati et al ., 1991 )
and canola (Dunford, 1995 ; Dunford and Temelli, 1996 , 1997 ; Fattori et al ., 1988 ). The
SC-CO 2 technique has not been widely used because of the high costs of high-pressure
equipment and high-pressure processing. A study carried out with soybeans demonstrated
that a substantial reduction in the operating costs could be obtained by optimization of heat
transfer and recovery systems. In such a case the operating cost of oil extraction with SC-CO 2
could be in the same range as conventional hexane extraction (Reverchon and Osséo, 1994).
In gas-assisted mechanical expression, liquid CO 2 is introduced into the screw press
under high pressure. This process takes advantage of the high solubility of dense CO 2 in oil
to enhance the extraction yield. Oilseed cell structure swells and eventually ruptures