9 Lipase-Catalyzed Synthesis of Structured
Triacylglycerols Containing Polyunsaturated
Fatty Acids: Monitoring the Reaction and
Increasing the Yield
Tsuneo Yamane
9.1 Introduction
Structured triacylglycerols (sTAGs) are in the broadest sense defined as any triacyl-
glycerols (TAGs) that have been restructured to change positions of fatty acids (FAs)
and modified to change the FA compositions from the native state (Akoh, 1995).
Natural edible fats and oils are simply mixtures of a number of TAGs that are dif-
ferent in terms of both FA species and their distribution along the glycerol backbone.
In contrast to natural edible lipids, sTAGs are TAGs modified either chemically or
enzymatically in either the type of FA or the position of the FAs. In a less broad sense,
sTAGs are structured lipids (SLs) containing mixtures of either short-chain fatty
acids, or medium-chain fatty acids (MCFA), or both, and long-chain fatty acids,
in the same glycerol molecule. A number of studies have been carried out for
the synthesis of sTAGs having (medium chain)-(long chain)-(medium chain)-type
FAs (Christophe, 1998). These SLs are claimed to provide fewer metabolizable cal-
ories per gram than do traditional fats and oils, and to be efficient food sources for
patients with pancreatic insufficiency and other forms of malabsorption. Cocoa-but-
ter substitute, which consists predominantly of stearoyl-oleoyl-stearoylglycerol
(SOS) or more generally saturated fatty acid-unsaturated fatty acid-saturated fatty
acid type TAG (SUS), and ‘Betapol’ manufactured by Unilever, which has the struc-
ture of oleoyl-palmitoyl-oleoylglycerol (OPO), are included in this category of
sTAGs.
In recent years, the concept of sTAGs has been extended to such that sTAGs are
designer TAGs with desired fatty acids in terms of their structures and positions as
‘nutraceuticals, functional food, or pharmaceuticals’ to target the optimal nutrition,
better metabolic conditions, and specific diseases. Along this trend, in the strictest
sense, the term sTAG is given to a TAG with a particular FA at a specific position of
glycerol hydroxyl moieties. The strictest definition of sTAG is applied in this review
article, and is led to its classification shown in Table 1 (Iwasaki and Yamane, 2000),
i.e. sTAG is either monoacid sTAG, diacid sTAG, or triacid sTAG. Note that in Table
1, FAs are shown in the order of their positions located atsn-1,sn-2 orsn-3 of the
glycerol backbone. Thus AAB is not identical to BAA, but they are enantiomers.
AAB (or BAA) type diacid sTAGs and all triacid sTAGs are identical to chiral
TAGs (Villeneuve et al., 1994). This nomenclature is applied throughout this review.
sTAGs containing polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic
acid (EPA), docosahexaenoic acid (DHA) or arachidonic acid (AA), have become of
Enzymes in Lipid Modification.Edited by Uwe T. Bornscheuer
Copyright2000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. ISBN: 3-527-30176-3
