Food Chemistry

3.7 Changes in Acyl Lipids of Food 223

Fig. 3.38. Autoxidation of saturated fatty acids.
Hypothetical reactions involved in formation of volatile
aldehydes

3.7.4.2 Polymerization

Under deep frying conditions, the isolenic
fatty acids are isomerized into conjugated
fatty acids which in turn interact by a 1,4-
cycloaddition, yielding so-called Diels–Alder
adducts (cf. Reaction 3.96).

(3.96)

The side chains of the resultant tetra-substituted

cyclohexene derivatives are shortened by oxi-

dation to oxo, hydroxy or carboxyl groups.

In addition, the cyclohexene ring is readily

dehydrogenated to an aromatic ring, hence com-

pounds related to benzoic acid can be formed.

The fatty acid or triacylglycerol radicals formed

by H-abstraction in the absence of oxygen can

dimerize and then form a ring structure:

(3.97)

On the other hand, polymers with ether and

peroxide linkages are formed in the presence of

oxygen. They also may contain hydroxy, oxo or

epoxy groups. The following structures, among

others, have been identified: