Advancements in Oil and Oilseed Processing - Food and Industrial Bioproducts and Bioprocessing - page 121

pressing, replacing more capital intensive use of steam-heated dryers and cookers and
associated steam generation equipment. These are high-shear extruders running at screw
speeds of about 600 rpm (Wijeratnea et al ., 2004). The partially defatted meal produced by
E-E, typically with 6-7% residual oil content, is used in livestock rations.
4.3.3 Aqueous extraction
Aqueous extraction (AE) is traditionally used in many developing countries. The process,
called water flotation, has been used for extracting coconut and palm oil. It involves heating
oily material, grinding with or without water and boiling with water to liberate the oil. The
oil which appears on the surface is collected and heated to remove moisture. Oil extraction
yields of around 50% are generally considered to be satisfactory for traditional non-
commercial processes. This process can be used to extract oil as well as high quality proteins.
However, there are certain limitations to the process. Finely ground seeds, which cause
dusting, may lead to an explosion if the processing area is not ventilated well. Other
disadvantages for aqueous oilseed include the need for breaking emulsion (that might form
during the process) to separate oil and water phases and the costs of the treatment of aqueous
effluents and wet meal.
4.3.4 Enzyme and surfactant-aided oil extraction
The objective of enzyme-aided oil extraction is to improve aqueous oil extraction yields.
In general the process involves the following steps: (1) oilseed grinding (wet or dry),
(2) incubation of the feed material with aqueous enzyme solution, (3) separation of liquid
and solid phases by centrifugation or filtration and (4) recovery of oil from liquid phase.
Additional unit operations may be needed depending on the chemical composition of the
specific oil-bearing material. For example, corn germ was hydrotreated to inactivate the
intrinsic lipase and increase the quality of oil prior to the incubation of corn germ with
enzyme (Bocevska et al ., 1993 ; Domínguez et al ., 1994 ; Moreau et al ., 2004 ; Dickey et al .,
2008). Similarly, rapeseed or canola seeds need to be cooked prior to enzyme incubation to
inactivate native enzyme myrosinase, which can produce toxic compounds, such as nitriles
and isothiocyanate, during the extraction process (Rask et al ., 2000 ; Zhang et al ., 2007 ;
Latif et al ., 2008 ).
Unlike in the organic solvent extraction where oil is recovered as free oil, enzymatic
extraction produces oil in three forms: free oil, emulsified oil and oil in skim. The presence
of all three forms of oil during enzymatic extraction of soybean has been reported (Rosenthal
et al ., 2001). Both emulsified and free oil were obtained from corn germ (Moreau et al .,
2004 ), rapeseed (Zhang et al ., 2007) and coconut (Chen Man et al ., 1996 ; Sant'Anna et al .,
2003). Enzymatic extraction of sunflower and Moringa oleifera seeds resulted in only the
emulsified form of oil (Domínguez et al ., 1995 ; Abdulkarim et al ., 2006 ). The forms of oil
obtained from enzymatic extraction depend on the compositions of the seeds as well as the
processing parameters, such as particle size of the comminuted material, liquid to solid
ratio, enzyme concentration, incubation time and mixing rate (Sharma et al ., 2002 ).
The role of enzymes in oil extraction from oilseeds is to hydrolyze the structural
components of plant cells and facilitate the release of oil. Hence, enzyme selection depends
on the composition of the cell wall and membrane that encapsulates oil bodies and the
cytoplasmic network where oil bodies are imbedded in the oilseed. Carbohydrases such as
cellulase, hemicellulase and pectinase and protease are effective in breaking up the cell