tina sui
(Tina Sui)
#1
Immobilization of lipases provides some benefits; i.e. increased stability, ease of
recovery and re-use of the enzyme, thereby reducing the production cost.Rhizomu-
cor miehei, Candida antarcticaandPseudomonassp. lipases are available commer-
cially in immobilized forms. Chandler et al. (1998) prepared immobilized lipase
using macroporous polypropylene particles and Shimada et al. (1996a,b; 1999) im-
mobilizedRhizopus delemarlipase onto porous ceramic particles for their studies on
enzymatic sTAG production. The author’s group reported the effective immobiliza-
tion of fungal and bacterial lipases on fine CaCO 3 powder (Rosu et al., 1997;
1998a,b). CaCO 3 powder is used commercially as a food additive, so it is a very
cheap and safe material. The enzymes were effectively immobilized by physical
adsorption, which is an easy method of immobilization. Due to tight adsorption,
leakage of the enzymes was negligible in neat liquid organic substrate, which re-
sulted in the product being perfectly free from contamination with the protein.
The immobilized lipases were reusable on many occasions (Rosu et al., 1997).
9.3.2 Solvent-free systems
Since the emergence of ‘nonaqueous enzymology’, it has been recognized (though
not explicitly) that all enzymatic reactions in organic media have been classified into
two systems: solvent systems and solvent-free systems. In the former system, the
substrate(s), is dissolved in an inert liquid organic solvent. The solvent does not
participate in the reaction in any respects, but provides an environment in which
the dissolved substrate(s) is consumed by the enzymatic action. By contrast, in
the latter system, no organic compounds (except enzyme or immobilized en-
zyme) other than the substrate(s) exist in a bioreactor. In other words, the bioreactor
is occupied with substrate(s) only. In some cases, the reaction system is composed of
two or more substrates, one of which exists in a large excess (much higher than the
stoichiometric molar ratio). In such a case, the excess substrate also works as bulk
solvent for the second substrate. This case is sometimes called ‘reaction-in-neat’.
Solvent-free systems have a number of merits over solvent systems if they work
successfully, including very high volumetric productivity, avoidance of enzyme in-
activation by the solvent, and preference for safety in food industry. The solvent-free
system also offers a better factory environment, without the need for explosion-free
equipment, and the absence of the solvent is highly desirable for the health of work-
ers engaged in bioprocessing. One possible disadvantage of using the solvent-free
system, even if it is feasible, may be longer reaction times as compared to the solvent
counterpart, and the enzyme may be inactivated due to the longer duration of the
reaction. It should be noted, however, that a longer reaction time is quite reasonable
if one considers the fact that in the solvent-free system greater absolute amounts of
substrate(s) exist in the bioreactor volume than in the solvent system. Volumetric
productivity [(kg product formed)(liter of reactor volume)–1h–1] of the sol-
vent-free system may be higher than that of the solvent system if they are compared
on the basis of the same volume of the reaction mixture and the same amount of the
enzyme used. The solvent-free system can be implemented not only in a monophasic
system, but also in a biphasic system, as exemplified by the author’s group (Rosu et
160 9 Lipase-Catalyzed Synthesis of Structured Triacylglycerols
