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.

Studies with ring-labeled [UC]BHA (2-(l,l-dimethylethyl)-4-methoxyphenol), ring-labeled [14C]TBHQ (2-(1,1-dimethylethyl)-1,4-benzenediol), and [7-14C]BHT (2,6-bis(l,l-dimethylethyl)-4-methylphenol) were undertaken to determine the fate of these compounds and the associated decomposition products in deep-fat frying and cookie baking. After the equivalent of 12 batches of french-fried potatoes was fried, over 80% of the 14C initially added as ring-labeled BHA was retained by the lard. BHT was more volatile. All three antioxidants underwent extensive decomposition in deep-fat frying. Three conceivable phenolic oxidation products-2-(l,l-dimethylethyl)-2,5-cyclohexadiene-l,4-dione, 2,6-bis(l,l-dimethylethyl)-2,5-cyclohexadiene-l,4-dione, and 3,3'-bis(l,l-dimethylethyl)-5,5'-dimethoxy-l,T-biphenyl-2,2'-diol-were not found in the heated lard. High-performance liquid chromatographic analysis demonstrated that, in cookie baking, BHA and BHT are retained by the cookie as intact antioxidants, in contrast to TBHQ, which undergoes 28% decomposition.

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Singlet oxygen produced by photochemical sensitizers may play an important role in the oxidation of lipids in foods. Therefore, we studied the singlet oxygen oxidation of lipids and the scavenging ability of antioxidants. Singlet oxygen was generated using the photosensitizer rose bengal. The oxidation products of lipids and antioxidants were separated by high‐performance liquid chromatography and monitored using post‐column chemiluminescence and/or iodometric detection. The competitive reaction rates of various antioxidants and lipids were studied to elucidate the roles played by antioxidants in the prevention of food oxidation by singlet oxygen.