Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 29 Specificity constants in the esterification of mixtures of myristic acid (reference
standard) and individual fatty acids with n-butanol in hexane using papaya latex as biocatalyst.
(From Ref. 256.)
� was calculated from the substrate concentrations Ac1X0 and Ac2X0 at time zero
as follows:
� = Log[Ac1X0/Ac1X]/Log[Ac2X0/Ac2X]
From the competitive factor specificity constant was calculated as 1/� with reference
to the specificity constant of myristic acid taken as 1.00. The higher the specificity
constant of a fatty acid the greater is the specificity of the biocatalyst for that particular
fatty acid. The data presented in Fig. 29 show that the fatty acids having a
cis-4, cis-6, or a cis-8 double bond are poor substrates in esterification reactions as
compared to those having a cis-5 or cis-9 double bonds or fatty acids having hydroxy,
epoxy, or cyclopentenyl groups.
The above substrate specificities have been utilized for the enrichment of definite
fatty acids or their derivatives from mixtures via kinetic resolution (257,258),
e.g., by selective hydrolysis as shown in Scheme 3 and the following examples.
Despite relatively high prices of lipase preparations, lipase-catalyzed hydrolysis
could be economically attractive for the preparation of specific products of high
commercial value, such as polyunsaturated (�3) fatty acid concentrates via selective
hydrolysis of marine oils, catalyzed by fatty acid–specific lipases that enable the
enrichment of docosahexaenoic 22:6 �3 and eicosapentaenoic 20:5 �3 acids in the
unhydrolyzed acylglycerols, as outlined in Fig. 30 (257,259–263). Such polyunsaturated
fatty acids which are interesting as dietetic products (264) cannot be obtained
by conventional steam splitting without substantial decomposition.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.