Selection of methylation procedures for quantitation of short-chain glycerol-bound compounds formed during thermoxidation.

Five methylation procedures, including base- and acid-catalyzed methods, were tested in thermoxidized methyl linoleate and trilinolein, in order to quantitate major oxidation short-chain glycerol-bound compounds by gas chromatography. Results indicated that transmethylations using KOH in methanol or CH3ONa-CH3OH in tert.-butylmethyl ether were the most appropriate methods, given the excellent reproducibility and practically complete recovery obtained for the compounds of interest, mainly short-chain fatty acids and aldehydic acids. Also, formation of acids from aldehydes during thermoxidation as well as modifications of aldehydic functions under acidic conditions, such as conversion to acetals, were checked using dodecanal as model aldehyde.