Front Matter

reported for tripalmitin hydrolysis in ethers usingRhizopus arrhizuslipase at 35 8 C,

with over 95 % molar yield of 2-monopalmitin being obtained at a water activity

>0.5 (Millqvist et al., 1994).

Alcoholysis of triglycerides in polar solvents has been described as an alternative

means to hydrolysis for the production of 2-monoglycerides. Better control over acyl

migration is claimed for alcoholysis compared to hydrolysis.

Using ethanol either in pure form (Millqvist Fureby et al., 1997) or dissolved in

ethers (Millqvist et al., 1994; Soumanou et al., 1998), high-purity 2-monoglycerides

(97–99 %) were thus obtained. After purification by crystallization, the molar yield

was between 60 % and 81 %. A high water activity during alcoholysis (aw>0.75)

was found to be essential to suppress acyl migration and to maximize 2-monogly-

ceride production.

1.4.3 1(3)-Monoglycerides

Synthesis of 1(3)-monoglycerides by esterification of fatty acids with glycerol is

rather simple using one of the many 1,3-regiospecific lipases. However, high-purity

monoglyceride can be produced only when minimizing the subsequent esterification

reaction towards diglycerides.

This may easily be achieved by using patatin, an acylhydrolase from potato tubers,

which has an almost absolute specificity towards hydrolysis of monoglycerides

(Macrae et al., 1998; Huang, 1987; Racusen, 1984).

Using the enzyme from the Sante ́variety of potato, it was shown that patatin

displays the same specificity during synthesis (Macrae et al., 1998). In the presence

of a small molar excess of glycerol,>95 % (w/w) pure monoglycerides were pro-

duced, even using a crude protein extract. Although the free enzyme has an optimum

temperature of approximately 50 8 C, at higher temperatures the lipase deactivated

rather quickly, making it difficult to esterify saturated fatty acids longer than myr-

istic acid, which are solid at 50 8 C.

Less selective for monoglycerides, but at least strongly discriminating against

triglyceride formation are the lipases from several strains ofPenicillium.

In particular, the lipase fromPenicillium camembertii(Lipase G) gave appreciable

results in fatty acid esterification. By carefully controlling water activity and sub-

strate ratio, almost 90 % pure monoglycerides were obtained at 76 % degree of con-

version (molar basis) (Yamaguchi and Mase, 1991). The conversion was even in-

creased to 97 % (w/w) by removal of water via molecular sieves. However, under

the conditions applied, a somewhat reduced monoglyceride purity (74 %) was ob-

tained.

Control of the water activity appeared of major importance, as it determined the

maximum conversion as well as the selectivity of theP. camembertiilipase. The

higher the water activity, the lower the selectivity for monoglyceride formation

and hence the higher the diglyceride content in the final product mixture. Despite

the fact that the rate of reaction was significantly reduced below 5 % water in the

glycerol, the highest conversion towards monoglycerides was obtained at a water

content around 2 % (w/w) (aw0.1).

1.4 Monoglycerides 17