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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 14 Effect of interesterification on butterfat triacylglycerols: �, native butterfat;<br />

●, r<strong>and</strong>omized butterfat. (Adapted from Ref. 34.)<br />

A. Shortening<br />

Chemical interesterification has been successfully used for decades to improve the<br />

physical properties of lard. Ordinary lard has a grainy appearance, a poor creaming<br />

capacity, <strong>and</strong> a limited plastic range, which is not improved by plasticizing in a<br />

scraped-surface heat exchanger [43,47]. Addition of a hard stock plus plasticizing<br />

helps in these respects, but the product develops an undesirable graininess during<br />

storage [83]. Chemical interesterification halves the solid fat content of the lard at<br />

20�C, improves the plastic range of the fat considerably, <strong>and</strong> prevents the development<br />

of graininess, which is due to the large proportion (64%) of palmitic acid at<br />

the sn-2 position [83,84]. This improvement in plasticity <strong>and</strong> stability is due to<br />

alterations in the polymorphic behavior, with interesterified lard crystallizing in a ��-<br />

2 form, characteristic of hydrogenated vegetable oil shortenings [83].<br />

Chemically, the ��3-tending disaturated OPS (1-oleoyl-2-palmitoyl-3-stearoylglycerol)<br />

(large crystals responsible for lard graininess) are exchanged for a mixture<br />

of disaturated triacylglycerols, with a lower melting point <strong>and</strong> greater intersolubility;<br />

the sn-2 palmitic acid concentration drops from 64% to 24% promoting �� behavior<br />

[83]. A detectable morphological change that accompanies these chemical changes<br />

is an increase in the relative proportion of small fat crystals [85].<br />

Duterte [86] mentioned that the crystalline modifications were observed prior<br />

to the theoretical completion of r<strong>and</strong>omization. Production of fine crystals extends<br />

lard’s plastic range <strong>and</strong> gives it a smooth appearance [47]. R<strong>and</strong>om interesterification<br />

helps to resolve the graininess problem, yet the limited plastic range problem is not<br />

fully resolved. The S2U triacylglycerols in r<strong>and</strong>omized lard give little plasticity at<br />

higher temperature. Directed interesterification resolves the plastic range problem<br />

[56].<br />

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

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