09.12.2012 Views

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

Food Lipids: Chemistry, Nutrition, and Biotechnology

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

(Fig. 9), foaming, color, viscosity, <strong>and</strong> formation of polar matter <strong>and</strong> polymeric<br />

compounds. As these reactions proceed, the functional, sensory, <strong>and</strong> nutritional quality<br />

of frying fats change <strong>and</strong> may reach a point where high-quality foods can no<br />

longer be prepared. Therefore, it is essential to determine when the frying fat is no<br />

longer usable.<br />

Quality evaluation of frying fats may be carried out in many ways. The first<br />

attempt to define a deteriorated frying fat was made by the German Society for Fat<br />

Research in 1973. It recommended that ‘‘a used frying fat is deteriorated if, without<br />

doubt, its odor <strong>and</strong> taste were unacceptable; or if in case of doubtful sensory assessment,<br />

the concentration of petroleum ether–insoluble oxidized fatty acids in it<br />

was 0.7% or higher <strong>and</strong> its smoke point was lower than 170�C; or if the concentration<br />

of petroleum ether–insoluble oxidized fatty acids was 1.0% or higher.’’ Although<br />

sensory evaluation of foods is the most important quality assessment, taste evaluations<br />

are not practical for routine quality control. It is always preferred to have a<br />

quantitative method for which rejection point could be established by sensory means.<br />

Peroxide values provide an indication of frying fat quality if they are used in a very<br />

specific way. However, peroxides generally decompose at about 150�C <strong>and</strong> hence at<br />

frying temperatures (usually 180–190�C) no accumulation of peroxides occurs. Free<br />

fatty acids from frying fats can be determined by direct titration with a st<strong>and</strong>ardized<br />

base in ethanol. Fritsch [62] has shown that in most deep fat frying operations the<br />

amount of free fatty acids produced by hydrolysis is too small to affect the quality<br />

Figure 9 Structures of cyclic fatty acids formed during frying.<br />

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!