2009_Book_FoodChemistry

224 3 Lipids
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
(3.98)
Such compounds are undesirable in deep-fried oil
or fat since they permanently diminish the flavoring
characteristics of the oil or fat and, because
of their HO-groups, behave like surfaceactive
agents, i. e. they foam.
Disregarding the odor or taste deficiencies developed
in a fat or oil heated for a prolonged period
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 double
bonds.
ation. They are produced from triacylglycerides
(cf. Formula 3.99), but are not formed on heating,
e. g., meat, or by microorganisms. On the irradiation
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.
3.7.5 Radiolysis
Alkyl and acyloxy radicals are formed during radiolysis
of acyl lipids. These will further react to
form volatile compounds. The formation of alkanes
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 compounds
which can be used as indicators of irradi-
Fig. 3.39. Formation of alkanes and 1-alkenes during
radiolysis of saturated triacyl glycerols