Front Matter

It should be noted here that thePenicilliumsp. lipase referred to above, is a dif-

ferent lipase from the ‘triglyceride-specific’ lipase described above for 1,2-diglycer-

ide production. Several strains ofPenicilliumspp. are known to produce both types

of lipases, i.e., one selective for, and the other selective against triglyceride hydro-

lysis and synthesis (Gulomova et al., 1996).

By combining the selectivity of the biocatalyst with adjustment of the reaction

conditions, and especially the reaction temperature, much better monoglyceride

yields were obtained. Using the partial glyceride-specific lipase fromPenicillium

cyclopiumat 40 8 C, up to 90 % (w/w) degree of conversion towards monoglycerides

was achieved, even when using palmitic acid (Weiss, 1990). This result is quite

remarkable, considering the fact that both the fatty acid substrate and the monogly-

ceride product are essentially solid at reaction temperature. Under these conditions,

dissolution of the fatty acid becomes the rate-limiting step, and hence the process

takes 10–15 days to complete. However, crystallization of the monoglycerides is

promoted, resulting in very high yield of near-pure product. Clearly, the particle

size and initial mixing are very important in starting the reaction and obtaining a

high yield (Weiss, 1991). Patatin could presumably be used in a similar process.

The selectivity of theP. cyclopiumlipase for mono- or diglyceride formation

during directed esterification could be changed in a similar way as described earlier

for theP. camembertiilipase. Increasing the water content in the glycerol from 5 %

(w/w) up to 20 % (w/w), the product composition changed from monoglycerides to

near-pure diglycerides (Weiss, 1990).

Temperature control, as applied above, also appeared crucial during the directed

glycerolysis of triglycerides. Using the nonspecific lipases fromPseudomonas fluor-

escenssp. orChromobacterium viscosum(Rosu et al., 1999; McNeill and Berger,

1993; McNeill et al., 1991), high-yield monoglyceride synthesis was obtained, sim-

ply by controlling the reaction temperature below a certain upper limit – referred to

as the ‘critical temperature’ (McNeill et al., 1991). It was shown that this ‘critical

temperature’ was dependent on the saturation level and the type of triglyceride sub-

strate involved. Monoglyceride yields between 70 % (w/w) and 90 % (w/w) were

reported, predominantly consisting of the 1-isomer (Bornscheuer et al., 1994;

Rosu et al., 1997).

As discussed earlier, recovery of the lipase during directed glycerolysis is rather

difficult. Applying solvent-based systems, this problem can easily be solved using

other means of directing synthesis towards monoglyceride production. In these cases

the reaction mixture is circulated over an enzyme reactor and a separator vessel,

removing the monoglycerides from the product mixture by selective adsorption

(Padt et al., 1990), crystallization (Berger and Schneider, 1993) or extraction (Ste-

venson et al., 1992). As the removal system is monoglyceride selective a conven-

tional non-selective lipase can be applied.

18 1 The Exploitation of Lipase Selectivities for the Production of Acylglycerols