Front Matter

1.4 Monoglycerides

1.4.1 Introduction

Monoglycerides are widely applied as emulsifiers or surfactants in the food, cos-

metics and pharmaceutical industries (Boyle, 1997). They have excellent emulsify-

ing properties, have low odor and taste, are biodegradable, and are generally recog-

nized as safe (GRAS).

Conventional production involves high-temperature glycerolysis (180–220 8 C)

using an inorganic catalyst. The result is a crude mixture of mono- and diglycerides

(roughly equal amounts) and some unreacted triglycerides (overall conversion

90 %). Further separation is generally carried out by molecular distillation yield-

ing high-purity monoglycerides (>90 %).

Due to the high temperature applied during glycerolysis, decomposition and oxi-

dation reactions take place which often result in a dark-colored, burnt-flavor product.

Obviously this requires extensive purification during further downstream proces-

sing. Because of the ambient reaction temperature applied, biocatalysis can poten-

tially yield a higher quality product with lower energy consumption in a more ‘nat-

ural’ type process. Various lipase-catalyzed routes are discussed below, and major

data from these processes have been summarized in Table 5.

1.4.2 2-Monoglycerides

From the point of view of yield, synthesis of monoglycerides from glycerol and free

fatty acids would clearly be the most attractive route. However, lipases with a high

selectivity for the 2-position on the glycerol backbone in esterification do not exist,

and hence triglycerides are the necessary starting material to produce 2-monogly-

cerides by lipase-catalyzed synthesis.

Direct hydrolysis using the 1,3-regiospecific porcine pancreatic lipase has been

reported as a means to produce 2-monoglycerides (Plou et al., 1996) in a solvent-free

system. It was shown that hydrolysis of triolein at 40 8 C, using Celite-immobilized

lipase, resulted in a product mixture with a maximum monoglyceride content of

68 % (w/w), predominantly being the 2-position isomer. It should be noted that

the product composition is controlled by kinetic resolution, and hence enzyme input

and incubation time are rather important.

It was shown that immobilization of the lipase significantly changed its selectivity

towards monoglycerides. As discussed above, use of the free lipase predominantly

gave diglycerides during the early stages of the reaction, whereas monoglycerides

were the main product when using the immobilized enzyme.

A considerable monoglycerides yield was also reported for hydrolysis of palm oil

in an AOT/isooctane microemulsion system (Holmberg and Osterberg, 1988). Cat-

alyzed byRhizopus delemarlipase at 35 8 C, an 80 % degree of conversion was ob-

tained (on a molar basis) towards monoglycerides. Due to the low reaction tempera-

ture and high water activity in the apolar solvent, acyl migration takes place only

slowly; thus mainly the 2-position isomer will be obtained. Similar results were

1.4 Monoglycerides 15