Food Chemistry

224 3 Lipids

(3.98)

Such compounds are undesirable in deep-fried oil
or fat since they permanently diminish the fla-
voring characteristics of the oil or fat and, be-
cause of their HO-groups, behave like surface-
active agents, i. e. they foam.
Disregarding the odor or taste deficiencies devel-
oped in a fat or oil heated for a prolonged pe-
riod of time, the oil is considered spoiled when
its petroleum ether-insoluble oxidized fatty acids
reach a level≥1% (or≥ 0 .7% at the decreased
smokepoint temperature of≤ 170 ◦C). The fats or
oils differ in their heat stability (Table 3.46). The
stability is increased by hydrogenation of the dou-
ble bonds.

3.7.5 Radiolysis

Alkyl and acyloxy radicals are formed during ra-
diolysis of acyl lipids. These will further react to
form volatile compounds. The formation of alka-
nes and alkenes, that lack one or two C-atoms,
from the original acyl residue are of interest for
the detection of irradiation (Fig. 3.39).
The proposed indicators for the irradiation of
meat are the hydrocarbons 14:1, 15:0, 16:1,
16:2, 17:0 and 17:1 which are formed during
radiolysis of palmitic, oleic and stearic acid. It
was demonstrated that their concentrations in fat
increased depending on the radiation dose, e. g.,
in chicken meat (Fig. 3.40).
Alkyl cyclobutanones are another group of com-
pounds which can be used as indicators of irradi-

Table 3.46.Relative stability of various fats and oils on

deep-frying (RSDF)

Oil/fat RSDF Oil/fat RSDF

Sunflower 1.0 Coconut 2. 4

Rapeseed 1.0 Edible beef tallow 2. 4

Soya 1 .0 Soya oil,

Peanut 1. 2 hydrogenated 2. 3

Palm 1 .5 Peanut oil,

Lard 2. 0 hydrogenated 4. 4

Butter fat 2. 3

ation. They are produced from triacylglycerides

(cf. Formula 3.99), but are not formed on heat-

ing, e. g., meat, or by microorganisms. On the ir-

radiation of chicken meat with a dose of 1 kGy,

0 .72 μ g of 2-dodecyl cyclobutanone per g of lipid

were detected. The indicator is stable because this

value fell by only 15% in 18 days.

Fig. 3.39.Formation of alkanes and 1-alkenes during

radiolysis of saturated triacyl glycerols