Handbook of Functional Lipids

may benefit from being cooked at slightly lower temperatures to avoid elevating refining
losses. The temperature of the flakes is raised to 110 to 132.2

C (230 to 270

F) in the

lower kettles. The seeds are cooked for up to 120 min. Overcooking lowers the nutri-
tional quality of the meal and can darken both the oil and meal. Poor-quality seeds with
high levels of FFAs cannot be cooked for as long a period as high-quality seeds because
of darkening. Darker oil requires additional refining to achieve a certain bleachable
color. For soybeans, this heat treatment is often done prior to flaking process.

5.2.1.6 Expanding

Sometimes low shear extruders called expanders are used. This equipment has the
capability to process both low- and high-oil content materials. The meats are fed
into an extruder after dehulling, flaking, and cooking and are heated as they are
conveyed by a screw press through the extruder barrel. The meats are under consid-
erable shear, pressure, and temperature when they reach the exit of the extruder. The
change in pressure as the material leaves the extruder causes it to expand and most
of the oil cells are ruptured, releasing the oil, which is rapidly reabsorbed to the
porous “collets” or pellets. The expanded collets produced are then cooled and
extracted with solvent. Because of the excellent efficiency of expanders, almost all
cottonseed in the United States is direct solvent extracted from the expanded collets.
Large amounts of soybean are also expanded and direct solvent extracted.

5.2.2 O

XTRACTION

5.2.2.1 Mechanical Extraction

Olive oil is still routinely obtained from olives by using a low-temperature hydraulic
press process, referred to as “cold press.” This is done to minimize the heat-related
degradation to olive oil. Palm fruit and some cottonseed are extracted with an expeller
or screw press; both are continuous processes. To achieve a higher yield of oil, often
a higher heat treatment of the cottonseed flakes is carried out prior to expelling. This
process can extract up to 90% of the available oil from the cottonseed kernels and
leaves about 3 to 5% residual oil in the pressed cake. The cake is ground or palletized
as feed protein ingredients for the livestock.

5.2.2.2 Prepress Solvent Extraction

In this process, the oil-bearing material is first mildly pressed mechanically by means
of a continuous screw press operation to reduce the oil by half to two thirds of its
original level, before solvent extraction to remove the remaining oil in the prepressed
cake. Pressing followed by solvent extraction is more commonly used when high-
oil-content materials (e.g., canola/rapeseed, sunflower seed, flaxseed, corn germ,
and cottonseed) are processed. This process reduces the amount of oil to be extracted
by solvent and, therefore, requires a smaller extractor and less solvent than a direct
solvent extraction facility of the same throughput.

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