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Handbook of Functional Lipids

(380 to 500

F), and reaction time (30 to 90 min). Most hydrogenation processes are

carried out in a batch operation. Since the hydrogenation process is not entirely
selective, several side reactions can also occur during the process, which create both
geometric and positional isomers. Naturally occurring double bonds in the liquid oil
are normally in the cis form, where the hydrogen atoms are on the same sides of the
double bonds. Instead of saturating the double bond, the hydrogenation process can
create a new double bond with the two hydrogen atoms on the opposite side of the
double bond, which is the trans isomer. The formation of the trans double bonds is
often accompanied with a migration of the double bonds from their naturally occurring
positions. These are positional isomers. All three events occur simultaneously during
the hydrogenation reaction but the degree of hydrogenation can be controlled in a
repeatable manner. A series of hydrogenated oils with various melting profiles can be
generated and serve as the base stocks. These hydrogenated base fats will then be used
to formulate or blend into the final margarine, baking shortening, stable frying short-
ening, and the like. Hydrogenation and blending have many advantages in meeting
the market demands: they are flexible, easy to manage, and cost effective. During the
last 50 to 60 years, hydrogenation and blending gradually have replaced most of the
traditional applications where animal fats were used.

The formation of trans fats by the hydrogenation process has become an important

health-related issue. As a result, the U.S. Food and Drug Administration (FDA) pub-
lished a final rule in 2003, which starting on January 1, 2006, requires manufacturers
to list trans fats on the nutrition facts panel on food packaging and some dietary
supplements sold at retail (see section 5.4.3.2). This regulation has caused the vegetable
oil producing and extracting industries to reformulate many products. Instead of par-
tially hydrogenating soy oil, some manufacturers are totally hydrogenating some soy
oil and adding that to unhydrogenated soy oil to get the desired consistency and
functionality. Other methods are being considered to lower or eliminate trans fats in
human edible products.

5.3.5.2 Esterification and Interesterification

The esterification reaction between hydroxyl-rich moieties (glycerol, propylene glycol,
polypropylene glycol, and sucrose) and fats or fatty acids are frequently applied to
produce food emulsifiers, such as monoglycerides, propylene glycol monoglycerides,
polyglycol esters, and sucrose esters. The interchange of fatty acids between two
different fats and oils is called interesterification. Both esterification and interesterifi-
cation reactions are commonly catalyzed by sodium methoxide. Interesterification can
also be carried out using lipase. Chemically catalyzed interesterification is not selective
like lipase interesterification; therefore, it is sometime called randomization or random
rearrangement. Even though randomization is a mature technology, randomized inter-
esterification was never popular due to the cost, limited choices of base fat, difficulties
in carrying out the process, and product quality control. Therefore, lipase interesteri-
fication is favored by the industry as the means to produce various base fats for
formulation and blending. Recently, nutritional concerns about trans fatty acids generated
during the hydrogenation process have prompted scientists to reactivate the interest-
erification technology as the means to deliver functional fats.

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