Food Lipids: Chemistry, Nutrition, and Biotechnology

techniques have been used to assess rancidity of fats and oils [55]. Significant correlations
existed between the amount of pentane produced and the number of rancid
descriptions of stored vegetable oils [56]. Correlation of headspace pentane concentrations
and sensory scores of stored freeze-dried pork samples was reported by
Coxon [8].
Another secondary change that occurs during autoxidation of biological systems
is the formation of fluorescent products from the reaction of MA with amino
compounds such as proteins and nucleotides [57]. This method has been used to
determine the extent of lipid oxidation in biological tissues. It has been established
that fluorescent compounds with a general structure of 1-amino-3-iminopropane may
develop through the reaction of an amino group with carbonyl compounds, mainly
MA [58–60] (Fig. 8).
Kikugawa and Beppu [61] reported that the development of fluorescence depends
not only on the formation of condensation products between malonaldehyde
and free amino groups, but also on the nature of the substituents of the latter compounds.
Different excitation and emission maxima were observed for different condensation
products. Advantages of the fluorescence method as a means of measuring
lipid oxidation have been reported by Dillard and Tappel [58]. This method can
detect fluorescent compounds at concentrations as low as parts per billion levels and
is found to be 10–100 times more sensitive than the TBA assay.
III. MEASUREMENT OF FRYING FAT DETERIORATION
Deep frying is a popular method for food preparation, especially in fast food restaurants.
Although vegetable oils are used primarily as a heat exchange medium for
cooking, when used for deep frying, they contribute to the quality of fired products.
In the process of deep fat frying, a complex series of chemical reactions take place.
These reactions are characterized by a decrease in the total unsaturation content of
the fat with a concurrent increase in the amount of free fatty acids, cyclic fatty acids
Figure 8 Production of fluorescent chromophores from the reaction of lipid oxidation products
and amines.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.