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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Table 5 Advantages of Lipase Modification of <strong>Lipids</strong> in Organic Solvents<br />

Increased solubility of nonpolar lipid substrates in organic solvents such as hexane <strong>and</strong><br />

isooctane.<br />

Shift of thermodynamic equilibria to the right in favor of synthesis over hydrolysis.<br />

Reduction in water-dependent side reactions, since very little water is required by lipases in<br />

synthetic reactions.<br />

Enzyme recovery is made possible by simple filtration of the powdered or immobilized<br />

lipase.<br />

If immobilization is desired, adsorption onto nonporous surfaces (e.g., glass beads) is<br />

satisfactory; enzymes are unable to desorb from these surfaces in nonaqueous media.<br />

Ease of recovery of products from low boiling point solvents.<br />

Enhanced thermal stability of enzymes in organic solvents.<br />

Elimination of microbial contamination.<br />

Potential of enzymes to be used directly within a chemical process.<br />

Immobilized enzyme can be reused several times.<br />

Source Modified from Ref. 61.<br />

d. Strategies for the Enzymatic Production of Structured <strong>Lipids</strong>. Various<br />

methods can be used for lipase-catalyzed production of SLs (4). The method of<br />

choice depends to a large extent on the type of substrates available <strong>and</strong> the products<br />

desired.<br />

Direct esterification. Direct esterification can be used for the preparation of SLs<br />

by reacting free fatty acids with glycerol. The major problem is that the water molecules<br />

formed as a result of the esterification reaction must be removed as they are<br />

formed to prevent them from hydrolyzing back the product, leading to low product<br />

yield. Direct esterification, rarely used in SL synthesis, is presented in equation form<br />

as follows:<br />

lipase<br />

Glycerol � MCFA � LCFA ⎯→ SL � water<br />

where MCFA = medium chain fatty acid, LCFA = long chain fatty acid, <strong>and</strong> SL =<br />

structured lipid moieties.<br />

Transesterification–acidolysis. Acidolysis is a type of transesterification reaction<br />

involving the exchange of acyl groups or radicals between an ester <strong>and</strong> a free<br />

acid:<br />

lipase<br />

MCT � LCFA ⎯→ SL � MCFA<br />

lipase<br />

LCT � MCFA ⎯→ SL � LCFA<br />

where MCT = medium chain triacylglycerol <strong>and</strong> LCT = long chain triacylglycerol.<br />

Figure 8 shows an example of acidolysis reaction (62), in this case between<br />

caprylic acid <strong>and</strong> triolein. Shimada et al. (63) used acidolysis reaction catalyzed by<br />

immobilized Rhizopus delemar lipase to synthesize an SL containing 22:6n-3 (DHA)<br />

<strong>and</strong> caprylic acids. Product isolation is easy after acidolysis. Free fatty acids are<br />

removed by distillation or by other appropriate techniques.<br />

Transesterification–ester interchange. This reaction involves the exchange of<br />

acyl groups between one ester <strong>and</strong> another ester:<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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