The lipases from porcine pancreas andR. mieheiselectively cleave the VLCMFA,
esterified almost exclusively at thesn-1,3-positions of the triacylglycerols (Mukher-
jee and Kiewitt, 1986), and consequently, the VLCMFA are extensively enriched in
the fatty acid fraction, whereas the C 18 -fatty acids, esterified predominantly at thesn-
2 position, are enriched in the mono- and diacylglycerols (Figure 5) (Mukherjee and
Kiewitt, 1996a).
Thesn-1,3-regioselectivity of theR. mieheilipase has also been utilized for the
enrichment of VLCMFA from high-erucic oils via selective transesterification of the
triacylglycerols with alkyl acetates or selective alcoholysis of the triacylglycerols
withn-butanol.
Transesterification of triacylglycerols of high-erucic mustard oil with ethyl, pro-
pyl and butyl acetate, catalyzed by the lipase fromR. miehei, yields alkyl esters
(ethyl, propyl and butyl, respectively) of fatty acids and a mixture of acetylacylgly-
cerols (e.g., monoacetyldiacyl- + diacetylmonoacylglycerols) as well as acylglycer-
ols (tri- + di + monoacylglycerols) (Mukherjee and Kiewitt, 1996a). Regioselective
transesterification of the triacylglycerols at thesn-1,3 positions leads to enrichment
of the VLCMFA in the alkyl ester fractions and decrease in the level of these fatty
acids in acetylacylglycerols and acylglycerols; concomitantly, the level of the C18
fatty acids is increased in the acetylacylglycerols and acylglycerols, and decreased in
the alkyl ester fractions (Mukherjee and Kiewitt, 1996a).
Similarly, alcoholysis of high-erucic mustard oil withn-butanol, catalyzed byR.
mieheilipase, yields butyl esters and mixtures of acylglycerols (mono- + di- + tria-
cylglycerols) and minor proportions of fatty acids (Mukherjee and Kiewitt, 1996a).
The VLCMFA, esterified at thesn-1,3 positions of the triacylglycerols, are selec-
tively transesterified, resulting in enrichment of these fatty acids in the butyl ester
fraction and decrease of their level in the acylglycerols (Figure 6). Simultaneously,
the C 18 fatty acids are enriched in the acylglycerols.
Transesterification of triacylglycerols with alkyl acetates orn-butanol is nearly as
effective for the enrichment of VLCMFA in the alkyl ester fraction as selective
hydrolysis of triacylglycerols for the enrichment of VLCMFA in the fatty acids
or acylglycerols (Mukherjee and Kiewitt, 1996a). The ultimate choice of a process
for the enrichment of VLCMFA depends on selectivity, cost and reusability of the
2.2 Fractionation of fatty acids and other lipids by lipase-catalyzed reactions 37
Figure 5. Scheme of kinetic resolution for the enrichment of erucic (ERUC) acid via lipase-catalyzed
regioselective hydrolysis of triacylglycerols.