6.2 Partial glycerides
Mixtures of long-chain monoglycerides and other partial glycerides of varying com-
position and constitution are widely employed as non-ionic surfactants (emulsifiers)
in the processing of foods and related applications (Sonntag, 1982a; Porter, 1991; Lie
Ken Jie et al., 1997; Gunstone, 1999). They also serve as starting materials for the
preparation of numerous conjugates, e.g. with citric, lactic, tartaric and acetic acid
(Aebi et al., 1978).
Isomeric mixtures of such ‘monoglycerides’ are classically produced by alcoho-
lysis of the corresponding triacylglycerols with two equivalents of glycerol in the
presence of metal catalysts at temperatures of 210–240 8 C (Lauridsen, 1976; Sonn-
tag, 1982b) (Figure 3). The resulting mixtures contain only ca. 50–60 % of the de-
sired monoglycerides as isomeric mixtures together with isomeric diglycerides, tri-
glycerides and free fatty acids.
Due to the high temperatures employed, these materials are usually colored and
not free of odor. ‘Monoglycerides’ of higher chemical (not isomeric!) purity (>
90 %) can only be obtained by cost- and energy-intensive molecular distillation
of these crude mixtures.
6.3 Biotechnological routes to mono- and diglycerides
Enzymes catalyze a wide variety of organic reactions under mild conditions and
frequently in a highly chemo-, regio- and stereoselective manner (Schmid and Ver-
ger, 1998; Bornscheuer and Kazlauskas, 1999; Gunstone, 1999). This is particularly
true for numerous lipases which are available from a wide variety of commercial
sources. Consequently, the use of biocatalysts for the preparation of partial glycer-
6.3 Biotechnological routes to mono- and diglycerides 101
Figure 2. Surface-active compounds via enzymatic acyl transfer.