The antioxidant activity of capsaicin, as compared to BHT and melatonin, was determined by the direct measurement of lipid hydroperoxides formed upon linoleic acid autoxidation initiated by AIBN. The formation of four isomeric lipid hydroperoxides was detected after reverse-phase HPLC separation. Data from three detectors, UV absorption, glassy carbon electrode electrochemical detection, and postcolumn chemiluminescence using luminol, were compared. Capsaicin was more effective than melatonin in suppressing the formation of lipid hydroperoxides but not as effective as BHT. The formation of capsaicin and BHT dimers was observed during oxidation, and the dimers were characterized using APCI MS(n).
To investigate the effects of heating conditions on the decomposi‐tion of linoleates, samples of linoleic acid and its esters were heated at 70 C, 180 C and 250 C for different periods of time and their decomposition products analyzed by gas chromatography and mass spectrometry. Qualitatively, the polar decomposition products were basically the same. However at the higher temperature and longer heating time the nonpolar decomposition products contained a large number of cyclic hydrocarbons which could not be detected with the milder heat treatments. A series of alkyl ethers, not previously reported, was identified in samples heated at 250 C for 5 hr. Quanti‐tatively, hexanal and aldehyde esters were found in significantly greater amounts in the samples heated at a lower temperature, whereas the reverse was true fort, t‐2,4‐decadienal.
When linoleic acid or its esters were heated in the presence of valine a number of interaction products were formed. The major product was 2-pentylpyridine which is thought to be produced by the reaction of 2,4-decadienal with ammonia. Also formed were two secondary amides, isobutyloctanamide and isobutyllinoleylamidc. Additional interaction products found include alkylpyridines and alkylpyrroles. The formation of these compounds is similar to the formation of 2-pentylpyridine. They can result by reaction of an aldehyde with an anainc or ammonia to form a Schiff base intermediate, followed by cyclization and rearrangement to form either the pyridinc ring or the pyrrole ring. In addition, a branched nitrilc compound was produced. This compound is considered to bc formed by cleavage of the pyridinc ring in 2 pcnrylpyridine. CH 2 I C-Oi /CH3 N-CH 2 "CH \CH 3 CIt 5" CH 2" CH Q i I N --CH., -./ CH 3-CH 2-CH 2 CH 3 Schiff bose intermediote J o "CH3CH2" ~OH /CH 3 CH % FIG. 3. Formation of the tertiary amide.
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