Conversion of allylic hydroxy oleate to conjugated linoleic acid and methoxy oleate by acid‐catalyzed methylation procedures

Abstract

Conjugated linoleic acid (CLA), a term describing a group of conjugated octadecadienoic acids that are both naturally occurring and formed during food processing, is the subject of considerable current research because of the recently reported antioxidant and anticarcinogenic prope~ ties of these compounds. Allylic hydroxy oleates (AHOs}, secondary products of lipid autoxidation, have also been found in foods. By means of high-performance liquid chromatography with ultraviolet detection, gas chromatography/mass spectrometry and gas chromatography/matrix isolation/Fourier transform infrared spectroscopy, we dete~ mined that currently used acid-catalyzed methylation procedures convert AHOs to CLA and other products that potentially yield high values in determination of CLA in foods. A mixture of AHOs, containing mainly (8-and ll-)hydroxy-9-octadecadecenoates, was synthesized and tested by methylation procedures with the following catalysts: BF 3, HCI, NaOMe and tetramethylguanidine. Both the BF 3 and the HCI procedures converted AHOs to CLA. The base-catalyzed procedures did not convert AHOs to CLA.

Conjugated linolenic acid (CLnA), conjugated linoleic acid (CLA) and other biohydrogenation intermediates in plasma and milk fat of cows fed raw or extruded linseed

“…The FA methyl esters were converted into 2-alkenyl-4,4-dimethyloxazoline (DMOX) derivatives according to Yurawecz et al (1994). Briefly, 100 ml of 2-amino-2-methyl-1-propanol were added to the fatty-acid methyl ester (FAME).…”

Derivatization of fatty acids and its application for conjugated linoleic acid studies in ruminant meat lipids

“…As with other acid-catalysed methylations, allylic methoxy derivatives are formed. 57,61,62 Lowering the methylation temperature can decrease CLA isomerization, but these milder conditions may not be sufficient to methylate all lipids. 38,60,63 …”

Analytical methods for determination of trans fatty acid content in food

“…For instance, free fatty acids (FFA) and sphingomyelins cannot be transesterified with alkaline catalysts and the amide bond of sphingomyelins requires high-temperature conditions for an extended period in the acidic phase to be disrupted. These conditions are not suitable for some other FA, especially for CLA since conjugated FA are converted to di-trans isomers or to methoxy derivatives in high temperatures, particularly when acid catalysts are present [8][9][10][11][12][13][14][15]. Short FAME present in milk fats are highly volatile and water soluble, however; so it is essential to use a methylation procedure that does not have a stage involving evaporation or an aqueous wash. Several procedures that seem to be convenient and quantitative for obtaining shortchain FAME from milk fat lipids have been reported [16][17][18].…”