Abstract SCHIRACK, ANDRIANA VAIS. The Effect of Microwave ...

hexanal are intensified to the high ppm range, while positive olfactory attributes
become imperceptible as heterocycles and thio-derivatives disappear at high
oxidation levels. Low molecular weight aldehydes such as pentanal, hexanal,
heptanal, octanal, and nonanal can also create a cardboard or oxidative rancid flavor
(Warner et al., 1996). St. Angelo et al. (1984) found that when the presence of
hexanal, hexanol and pentane exceeded concentrations of 2-3 ppm in GC
chromatograms, the peanuts were judged as rancid by the sensory panel.
Because off-flavors caused by oxidation have been closely correlated to the
differences in lipid profiles in peanuts, researchers have isolated the peanut oil in
flavor experiments. Chung et al. (1993) studied the differences in the headspace
volatile production from peanut oil heated under a broad range of temperatures from
50-200 °C simulating mild frying, deep-frying, and near-pyrrolysis conditions, and
they identified hydrocarbons as the most abundant class, followed by aldehydes.
During heating, free fatty acids were formed from the hydrolysis of triacylglycerols,
and these were transformed to γ-hydroxy fatty acids by oxidative attack of hydroxy
radicals, followed by transformation to lactones by cyclization. These lactones may
be responsible for the formation of fruitlike aromas in the peanuts, as γ-octalactone
and γ-nonalactone were found in the peanut oil. Formation of fatty and rancid off-
flavors in peanut oil during heating was attributed to the formation of carbonyl
compounds. These low molecular weight carbonyls could be isolated only by
derivatization to thiazolidine compounds (Chung et al., 1993).
Lipid oxidation reactions are strongly influenced by storage conditions, and as
a result, off-flavors can develop during this time. In a study by Warner et al. (1996),
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