Chemistry of fried food flavors

To better understand flavor development in frying oils that contain high levels of oleic or linoleic acids, triolein and trilinolein were heated to 190degreesC and the odor significance of volatile compounds was evaluated by purge and trap-gas chromatography-mass spectrometry-olfactometry. Predominant odors of triolein heated 1, 3 and 6 h at 190degreesC were fruity and plastic with other negative odors of acrid, grassy, mushroom and fishy. Predominant volatile compounds with negative odors detected in triolein (in order of decreasing ppm) were nonanal (fruity), octanal (fruity), heptanal (fruity), (E)-2-decenal (plastic), and (E)-2-undecenal (plastic). Predominant compounds that produced negative odors in heated trilinolein included hexanal (grassy), 2-pentyl furan (fruity), and pentanal (grassy). The amounts of volatile compounds produced and intensity levels of the negative odors were significantly lower in trilinolein than in triolein. The components (E,E)-2,4-decadienal, (E,Z/ Z,E)-2,4-decadienal, (E,E)-2,4-nonadienal, (E)-2-octenal, (E)-2-heptenal, and (E,E)-2, 4-octadienal produced deep fried odor at moderate-strong intensities in heated trilinolein. However, unexpected aldehydes, namely -(E,E)-2,4-decadienal, (E,E)-2,4-nonadienal, (E,E)-2,4-undecadienal, and (E)-2-octenal, were detected in triolein heated 6 hr and produced deep fried odor at weak to moderate intensities. (E,E)-2,4-decadienal, the predominant aldehyde producing a deep fried odor, was present in trilinolein at 632 ppm but at only 14 ppm in triolein. This information helps explain sources of deep fried flavor characteristic of high linoleic frying oils but which is only at low intensity levels in high oleic oils. The odors produced from triolein also help explain the plastic, fruity odors and flavors characteristic of high oleic frying oils.