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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 13 Triacylglycerol products from the transesterification of two triacylglycerols, 1,3dipalmitoyl-2-oleoyl<br />

glycerol <strong>and</strong> 1,3-distearoyl-2-oleoyl glycerol, using either a nonspecific<br />

lipase or chemical esterification.<br />

acid composition of positions 1 <strong>and</strong> 3 can be changed to meet the targeted structural<br />

requirements while retaining the nutritionally beneficial essential fatty acids in position<br />

2. Using r<strong>and</strong>om chemical interesterification, retention <strong>and</strong> improvement in<br />

beneficial fatty acid content cannot be accomplished due to the complete r<strong>and</strong>omization<br />

of the fatty acids in the triacylglycerols (59).<br />

3. Stereospecificity<br />

In triacylglycerols, the sn-1 <strong>and</strong> sn-3 positions are sterically distinct. Very few lipases<br />

differentiate between the two primary esters at the sn-1 <strong>and</strong> sn-3 positions, but when<br />

they do, the lipases possess stereospecificity. In reactions where the lipase is stereospecific,<br />

positions 1 <strong>and</strong> 3 are hydrolyzed at different rates. Stereospecificity is<br />

determined by the source of the lipase <strong>and</strong> the acyl groups, <strong>and</strong> can also depend on<br />

the lipid density at the interface, where an increase in substrate concentration can<br />

decrease specificity due to steric hindrance. Differences in chain length can also<br />

affect the specificity of the lipase (12). Lipase from Pseudomonas species <strong>and</strong> porcine<br />

pancreatic lipase have shown stereoselectivity when certain acyl groups are hydrolyzed<br />

(60).<br />

4. Fatty Acid Specificity<br />

Many lipases are specific toward particular fatty acid substrates. Most lipases from<br />

microbial sources show little fatty acid specificity, with the exception of lipase from<br />

Geotrichum c<strong>and</strong>idum, which is specific toward long chain fatty acids containing<br />

cis-9 double bonds (9). Lipases can also demonstrate fatty acid chain length specificity,<br />

with some being specific toward long chain fatty acids <strong>and</strong> others being specific<br />

toward medium chain <strong>and</strong> short chain fatty acids. For example, porcine pan-<br />

Figure 14 Transesterification products of 1,3-dipalmitoyl-2-oleoyl-glycerol <strong>and</strong> 1,3-distearoyl-2-oleoyl-glycerol<br />

using a 1,3-specific lipase.<br />

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

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