Front Matter

tion, the glycerolysis reaction continues to form predominantly monoglycerides

(McNeill and Berger, 1993; McNeill et al., 1991).

With regard to the biocatalysts applied for directed glycerolysis, the highest yields

were obtained using non-specific lipases fromPseudomonassp. orChromobacter-

ium viscosum(Rosu et al., 1997, Bornscheuer et al., 1994; McNeill et al., 1991).

An alternative approach for 1,3-diglyceride synthesis is the esterification of free

fatty acids and glycerol. Here the use of a 1,3-specific lipase, e.g., fromRhizomucor

miehei(Rosu et al., 1999; Kim and Rhee, 1991) orRhizopus arrhizus(Millqvist

Fureby et al.,1996; Weiss, 1990) can effectively be exploited.

Experimental data show that diglyceride yields between 60 % and 85 % have been

obtained using both fatty acids and ethyl esters as acyl donor. Higher yields (>90 %)

were even obtained applying continuous removal of water, e.g., under vacuum (Rosu

et al., 1999), or again temperature programming (Weiss, 1990; Millqvist Fureby et

al.,1996).

Similar to the production of 1,2-diglycerides described above, the low reaction

temperature (15–40 8 C) applied in these processes is important to control acyl mi-

gration. At higher temperatures, racemization of mono- and diglycerides will lead to

acylation of the 2-position and subsequent production of triglycerides by esterifica-

tion, especially when applying vacuum (Ergan et al., 1990; McNeill et al., 1996; Diks

and Lee, 1999).

It should be noted that directed glycerolysis as well as directed esterification are

preferably carried out using free lipases. Due to solidification of the reaction mixture

the rate of mass transfer is severely limited, and depending on the actual enzyme

input applied, this may result in reaction times of several days. Moreover, because

of process economics recovery of the free enzyme in an active form is often required.

This is generally rather difficult, but immobilization of the enzyme on a finely dis-

persed carrier can solve this issue. Good recovery ofPseudomonassp. orChromo-

bacterium viscosumlipase on CaCO 3 was obtained by filtration of the biocatalyst,

having dissolved the entire reaction mixture in acetone (Rosu et al., 1997).

The esterification of diglycerides to triglycerides, as mentioned above, can also be

avoided by using a mono- and diacylglycerol specific lipase, e.g., fromPenicillium

camembertii(Yamaguchi and Mase, 1991),Penicillium cyclopiumM1 (Okumura et

al., 1980) orFusariumsp. (Mase et al., 1995). These lipases strongly discriminate

against triglycerides, and hence partial glycerides will accumulate during synthesis

from fatty acids and glycerol.

Starting with a glycerol/oleic acid weight ratio of 4 : 1, approximately 60 % con-

version was thus obtained after 5 days of incubation, yielding 60 % diglycerides and

40 % monoglycerides (Yamaguchi and Mase, 1991). This work also showed that

selectivity of the lipase for either monoglyceride or diglyceride synthesis could

be controlled by the water activity applied during synthesis. The higher the aw,

the higher the rate of diglyceride production, especially for a water activity>0.05.

14 1 The Exploitation of Lipase Selectivities for the Production of Acylglycerols