Food Lipids: Chemistry, Nutrition, and Biotechnology

Cast et al. [55] demonstrated the regioselectivity of chemical interesterification
in the presence of phase transfer catalysts (tetraalkyl ammonium bromides), with
trilaurin (LaLaLa) and methyl palmitate in the presence of sodium methoxide. Under
normal conditions, interesterification resulted in 17.7% LaLaP and 82.3% unreacted
LaLaLa. Using tetrahexyl ammonium bromide, 11.9% LaLaP, 6.2% LaPP, and 81.2%
LaLaLa were obtained. Seven quaternary ammonium salts were tested for their effect
on the reaction: tetraethyl, tetrapropyl, tetrabutyl, tetrapentyl, tetrahexyl, and tetraheptyl
ammonium bromides. The amount of LaLaOH diacylglycerol increased as the
chain length increased up to tetrahexyl ammonium bromide (Fig. 8). The amounts
of LaPOH and PPOH diacylglycerol species increased up to tetraheptyl ammonium
bromide. Reactions were performed for 48 hours, with a fivefold increase in the
amount of LaPOH diacylglycerols compared to the amount after 1 hour of reaction.
Most importantly, following lipase hydrolysis and subsequent 2-monoacylglycerol
isolation, it was discovered that the reaction between trilaurin and methyl palmitate
in the presence of tetrapentyl ammonium bromide contained 49% lauric acid
and 51% palmitic acid, which represents an enrichment factor for the 2-position of
1.51 times. Hence, under these conditions, chemical interesterification was not a
random process.
E. Directed Interesterification
If the interesterification reaction is carried out at temperatures below the melting
point of the highest melting component (most likely a trisaturated triacylglycerol
species), the end result will be a mixture enriched in this component. This was first
reported by Eckey [35] who, for the interesterification of lard, discovered that certain
Figure 8 Composition of diacylglycerol content versus phase transfer catalyst chain length
for sodium methoxide–catalyzed interesterification of trilaurin and methyl palmitate in the
presence of seven quaternary ammonium salts. PPOH (�); LaPOH (●); LaLaOH (▫). (Adapted
from Ref. 55.)
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.