Evolution of short‐chain glycerol‐bound compounds during thermoxidation of FAME and monoacid TAG

Methyl heptanoate and octanoate, methyl 8‐oxooctanoate and 9‐oxononanoate, and dimethyl suberate and azelate were quantitated in model systems of FAME, i.e., methyl oleate and linoleate, and monoacid TAG, i.e., triolein and trilinolein, heated at 180°C for 5, 10, and 15h. Polar compounds, ranging from 20.2 to 53.2% in TAG systems, were also quantitated as a reference for the level of degradation of the samples analyzed. Base‐catalyzed techniques were used for methylation as they did not modify the structure of the compounds of interest. The maximum amounts of short‐chain FAME and of aldehydic FAME obtained were of the same order (3–4 mg/g sample in methyl linoleate and trilinolein heated for 15 h). After a second methylation step with diazomethane, amounts of dimethyl suberate and azelate were also quantitated. The total amounts of dimethyl esters in TAG model systems ranged from 1.07 to 3.35 mg/g of heated sample and were similar to those found for total aldehydic FAME (from 1.03 to 3.15 mg/g of heated sample), suggesting that oxidation of the aldehydic acyl group to an acid acyl group was a major reaction.