The reaction between triacylglycerols catalyzed by nonspecific lipases proceeds
toward randomization provided that the nonspecific lipases have equal specificity
towards the three positions of the glycerol backbone, and have equal preference
towards different fatty acids. The products are, therefore, randomized at the reaction
equilibrium. The triacylglycerol profiles of the products can be calculated from their
fatty acid composition according to the rule of randomization (Sonntag, 1982). If the
enzymaticrandomization is performed between two triacylglycerols: LLL and
MMM, the reaction will result in eight triacylglycerols or isomers. The reaction
is illustrated in Figure 2. Three isomers of LLM (sn-LML,sn-LLM and sn-
MLL) or LMM (sn-LMM,sn-MML, andsn-MLM) each are usually combined
into one species. Therefore, the four species of the products under different substrate
molar ratios (SRm, between LLL and MMM) can be calculated theoretically accord-
ing to the following equations:
LLLðmol%Þ¼
100
ðSRmþ 1 Þ
3 ð^1 Þ
LLMðmol%Þ¼
300 SRm
ðSRmþ 1 Þ
3 ð^2 Þ
LMMðmol%Þ¼
300 ðSRmÞ
2
ðSRmþ 1 Þ
3 ð^3 Þ
MMMðmol%Þ¼
300 ðSRmÞ
3
ðSRmþ 1 Þ
3 ð^4 Þ
Chemical ester – ester exchange proceeds according to the random theory with little
exception in practice, if the reaction is successfully conducted and completed. How-
ever, enzymatic ester – ester exchange depends very much on whether the assump-
tion of absolute nonspecificity is held on the lipase in question. Some lipases may
have slight preferences towards certain fatty acids, or the lipase may not be abso-
lutely nonspecific to the three positions. Therefore, the calculation from these equa-
tions can be used only as a guideline for the experimental design and reaction control.
The ester – ester exchange between triacylglycerols withregiospecific lipaseswill
produce similar species to that catalyzed by nonspecific lipases. However, the con-
tent of each species in the products might be different from nonspecific lipases be-
cause the reaction catalyzed by regiospecific lipases proceeds in a different way in
which fatty acids in thesn-2 position do not exchange with other fatty acids, but
remain in the same place. Studies have shown that this was virtually true in practice
with regiospecific (Rhizomucor miehei) and nonspecific (Candida antarctica) li-
pases in a reaction between cottonseed oil and coconut oil (Mohamed et al., 1993).
11.2 Lipase-catalyzed interesterification: compositional profiles 193
