Enzyme Technology
Interesterification of lipids
There
is no opportunity or established need to build up polymers or oligomers using
lipases or esterases yet it is possible and commercially advantageous to use
these enzymes as transferases in transesterifications (carboxyl group exchange
between esters), acidolyses (carboxyl group exchange between esters and
carboxylic acids) and alcoholyses (alcohol exchange between esters and
alcohols). Certain triglycerides, cocoa butter being the outstanding example,
have high value because of their physical properties and comparative rarity.
There is a commercial pull, therefore, to fund routes to the production of high
value triglycerides from more plentiful, cheaper raw materials. This may be done
using lipases (e.g., ex.Rhizopus or ex. Mucor Miehei) acting as transacylases.
[7.18]
This acidolysis reaction may be used for
increasing the value of rapeseed oil by exchanging linoleic acid for linolenic
acid residues and increasing the value of palm oil and sunflower oil by
increasing their content of oleic acid residues. Cocoa butter is a relatively
expensive fat, used in confectionery, because of its sharp melting point between
room temperature and body temperature; chocolate literally melts in the mouth.
This is due to the fairly small variation in the structure of the constituent
triglycerides; 80% have palmitic acid or stearic acid in the 1 and 3 positions
with oleic acid in the central 2 position. For the production of cocoa butter
substitute from palm oil, a process which increases the value of the product
three-fold, the acidolysis utilises stearic acid (i.e., R4 is C17H35) in hexane containing just sufficient water to
activate the lipase. Olive oil may be similarly improved by exchanging its
1,3-oleic acid residues for palmityl groups. The products may be recovered by
recrystallisation from aqueous acetone. Such reactions may also be used for the
resolution of racemic mixtures of carboxylic acids or alcohols, the lipase
generally being specific for only one out of a pair of optical isomers.
The
secret of success has been the selection of lipases with the correct specificity
and the selection of reaction conditions that favour transacylation rather than
hydrolysis. Because the hydrolytic activity of industrial lipases is 10 - 15
times the transacylation activity, it is advantageous to minimise the water
content of the reaction system and use the aqueous/organic biphasic systems
described earlier.An example of lipase being used in an alcoholysis reaction is
the biphasic production of isoamyl acetate, a natural aroma.
lipase
CH3CH2OCOCH3 + (CH3)2CHCH2CH2OH
(CH3)2CHCH2CH2OCOCH3 + CH3CH2OH
[7.19]
Ethyl acetate + isoamylalcohol
isoamyl acetate +
ethanol
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This page was established in 2004 and last updated by Martin
Chaplin on
6 August, 2014
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