Pure trilinolein and mixtures of trilinolein‐tristearin, trilinolein‐triolein, and trilinolein‐triolein‐tristearin were heated to 192 C in air. Volatiles were collected, separated, and identified by gas chromatography‐mass spectrometry. Major volatiles observed from each heated sample produced compounds unique to the autoxidation‐decomposition of the trilinolein component and included: pentane, acrolein, pentanal, 1‐pentanol, hexanal, 2‐ and/or 3‐hexenal, 2‐heptenal, 2‐octenal, 2,4‐decadienal, and 4,5‐epoxydec‐2‐enal. When samples containing both trilinolein and triolein were heated, volatiles were produced that could be ascribed to each triglyceride. However, heated mixtures containing tristearin produced no observable volatiles that could be related to the oxidized saturated triglyceride. Minor volatiles identified from the heated trilinolein and its mixtures included; aliphatic acids, saturated and unsaturated aldehydes, primary and secondary alcohols, gamma lactones, furans, hydrocarbons, and methyl ketones.

The gas chromatography‐mass spectrometry (GC‐MS) method developed in the preceding papers was extended to the analysis of autoxidation products of methyl linolenate. Four isomeric hydroxy allylic trienes with a conjugated diene system were identified after reduction of the linolenate hydroperoxides. All eight geometrictrans,cis‐ andtrans, trans‐conjugated diene isomers of these hydroxy allylic compounds were identified and partially separated by GC of the trimethylsilyl (TMS) ether derivatives. The proportion found of 9‐ and 16‐hydroperoxides was significantly higher (75–81%) than the 12‐ and 13‐hydroperoxides (18–25%). The tendency of the 12‐ and 13‐hydroperoxides to form cyclic peroxides, cyclic peroxidehydroperoxides, and prostaglandin‐like endoperoxides was supported by indirect evidence for the presence of 9,10,12‐ and 13,15,16‐trihydroxyoctadecanoate in hydrogenated derivatives of the highly oxygenated products. The quantitative GC‐MS method was used to determine the relative contribution of linolenate, linoleate, and oleate in mixtures to the formation of hydroperoxides.

AND SUMMARYIn a continuing study to identify volatile odor constituents and their precursors from heated soybean oil, the following model triglycerides were heated to 192 C in air for I0 min: (a) pure triolein, (b) a mixture of triolein (25%)-tristearin, and (c) a randomly esterified triglyceride composed of oleic (25%) and stearic acids. Each model system produced the same major compounds which were identified as heptane, octane, heptanal, octanal, nonanal, 2-decenal, and 2-undecenal. These seven compounds apparently are unique to the oxidation of the oleate fatty acid in each triglyceride sample. Minor volatile compounds from oxidized triolein included saturated and unsaturated aldehydes and n-hydrocarbons and saturated primary alcohols, methyl ketones, gamma lactones, and monobasic acids. Incorporation of stearic acid in the triglycerides noticeably increased the amounts of saturated minor compounds and the range of their carbon chain lengths. Decomposition products characteristic of the oxidation of stearate were apparent among decomposition products associated with the oxidation of oleate.

Linoleate hydroperoxides from autoxidation of methyl linoleate and from lipoxidase oxidation of linoleic acid are compared. Data indicate an equal amount of methyl 9- and 13-hydroperoxyoctadecadienoate produced by autoxidation of methyl linoleate, and the exclusive formation of 13-hydroperoxyoctadeca-9,11-dienoic acid from the incubation of lipoxidase with linoleic acid. As a result of these findings, a specific mechanism for the reaction of lipoxidase with linoleic acid is postulated.