Solvent Extraction to Obtain Edible Oil Products

115

done in a chilled room held at 42

F (5.6

C) with the oil in deep, narrow, rectangular

tanks. After 2 to 3 d, the solid portion of the oil will grow to desired crystal size,
which is separated by a filtration step.

5.3.4 D

EODORIZATION

Deodorization, which removes the volatile compounds along with residual FFAs, is
a critical step in ensuring the purity of any vegetable oil and improves flavor, odor,
color, and oxidative stability. Many of the volatile compounds removed are formed
by the auto-oxidation of fat, which produces aldehydes, ketones, alcohols, and
hydrocarbons that are associated with undesirable rancid flavors and odors. The
process also is effective in removing any remaining residues of pesticides or pesticide
metabolites that may be in the oil.

Deodorization, which can be conducted as a batch operation in smaller plants

or as a continuous or semicontinuous process in larger deodorizing facilities, consists
of a steam distillation process in which the oil is heated to 230

C (446

F) under a

vacuum of 2 to 10 mmHg. Steam is sparged through the oil to carry away the volatiles
and provide agitation. The odor and flavor compounds, which are more volatile than
the triglycerides, are preferentially removed. After deodorization and during the
cooling stage, 0.005 to 0.01% citric acid is generally added to chelate trace metals,
which can promote oxidation. Deodorized oils preferably are stored in an inert
atmosphere of nitrogen to prevent oxidation. Tocopherols and sterols are also par-
tially removed in the deodorization process. Tocopherols can be recovered from the
deodorizer distillate in a separate operation.

The deodorization process is usually carried out as the last step prior to packaging

or bulk shipping. If the oil is to be further processed, as described in the following
section, the oil is normally processed through bleaching, the further processing step or
steps (e.g., hydrogenation, esterification, fractionation, and formulation) are performed,
and then the product is deodorized as the final step.

5.3.5 F

URTHER

ROCESSES

ATS

AND

ILS

RBD oils are the largest and still growing segment in the U.S. fats and oils market.
Fats and oils used for other major applications, such as shortenings for frying and
baking, margarines, high-stability oil, and food emulsifiers, require additional pro-
cessing steps to achieve the desired functional characteristics. In this section, only
hydrogenation and blending, esterification and interesterification, and fractionation
are briefly described [37].

5.3.5.1 Hydrogenation and Blending

The primary objective of hydrogenation is to modify the melting properties of oils.
This is accomplished by converting a certain number of the unsaturated double bonds
in the liquid oil to saturated bonds by reaction with hydrogen using a metal catalyst.
Nickel is the most frequently used catalyst for this process. The targeted melting profile
or solid content of the end product is controlled by the concentration of catalyst
(0.01 to 1%), amount of hydrogen (hydrogen pressure 10 to 60 psig), temperature

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