Food Lipids: Chemistry, Nutrition, and Biotechnology

B. Phospholipases
Figure 38 shows the reactions catalyzed by phospholipases (see also Chapter 26).
Phospholipases A1 and A2 hydrolyze the acyl moieties from the sn-1 and sn-2 positions,
respectively, of glycerophospholipids, such as diacylglycerophosphocholines.
Phospholipase C cleaves the polar head groups, such as phosphocholine or phosphoethanolamine
residues, esterified at the sn-3 position of these phospholipids yielding
diacylglycerols. Phospholipase D cleaves the bases or alcohols, such as choline
or ethanolamine, from these phospholipids yielding phosphatidic acids. Under certain
conditions, such as in the presence of less polar organic solvents at low water content,
most of the above reactions can be reversed to modify the composition of the acyl
moieties or the head groups of the phospholipids.
Phospholipids, such as commercial ‘‘soya lecithin’’ or ‘‘egg lecithin,’’ are
widely used for their emulsifying and other functional properties in food, cosmetic,
and pharmaceutical products. The composition of phospholipids can be altered to
modify their properties by chemical reactions (288) or enzymatic reactions catalyzed
by phospholipases (95,118,289).
1. Phospholipids Modified by Phospholipases A1 and A2 and
Triacylglycerol Lipases
The following examples show the various possibilities of modifying the composition
of acyl moieties of phospholipids by interesterification reactions catalyzed by phospholipase
A1, phospholipase A2, or triacylglycerol lipase. Such modified phospholipids
may find interesting biomedical applications.
Selective hydrolysis of diacylglycerophospholipids, catalyzed by phospholipase
A2 or A1, yields 1-acyl- or 2-acyllysoglycerophospholipids, respectively (118) (Fig.
38). Phospholipases A1 and A2 as well as regiospecific or nonregiospecific triacylglycerol
lipases have been found to cleave the fatty acids from the sn-1 and/or sn-2
positions of diacylglycerophospholipids to yield sn-1- or sn-2-lysoglycerophospholipids
with interesting functional properties (290–295). Studies on hydrolysis of soybean
phospholipids have revealed that fungal triacylglycerol lipase preparations that
also contain phospholipase A1 and A2 activities as well as lysophospholipase activity
are more efficient in the cleavage of fatty acids than fungal and mammalian enzyme
preparations that have only phospholipase A1 and/or A2 activities (296). Moreover,
fungal preparations of both triacylglycerol lipases as well as phospholipase A1 cleave
in the course of time the fatty acids esterified at both sn-1 and sn-2 positions of
diacylglycerophospholipids yielding completely deacylated products, e.g., glycerylphosphorylcholine
(296). However, phospholipase A2 preparations of fungal as well
as mammalian pancreatic origin yield primarily sn-1-acyllysophospholipid by selective
partial deacylation at the sn-2 position (296).
Esterification of sn-1-acyllysoglycerophosphocholines with eicosapentaenoic
acid and docosahexaenoic acid, catalyzed by porcine pancreatic phospholipase A2 in
a microemulsion system containing small amounts of water, has been carried out to
prepare diacylglycerophosphocholines containing well over 30% �3 polyunsaturated
fatty acids (�3 polyunsaturated fatty acids, PUFAs) as outlined in Fig. 39 (297).
Transesterification of phosphatidylcholine with ethyl eicosapentaenoate, catalyzed by
porcine pancreatic phospholipase A2 in the presence of toluene, has led to about 14%
incorporation of eicosapentaenoyl moieties into phosphatidylcholine (298).
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.