Comparative study of the nonvolatile products in irradiated and thermally oxidized unsaturated fatty acids

Oleic acid, ethyl oleate, trioleyl glycerol, linolenic acid and ethyl linolenate were either heated at 1800C for 1 hour in the presence of air or irradiated under vacuum at 250 kGy. The nonvolatile product analysis showed that: 1) the volatiles amounted to less than 3% while the nonvolatiles represented more than 23%; 2) diene and/or triene conjugation occurred to a substantially greater extent in the case of heating; 3) TLC analysis showed that the heated samples produced more classes of compounds, many of which were highly polar in nature. Irradiated samples produced simpler decomposition products and also of lower polarity; 4) the acidic compounds produced in irradiated esters were the parent acids from cleavage the alkyl-oxygen bond. The heated esters, produced short chain monobasic and dibasic acids from further oxidation of the initial allylic hydroperoxides; 5) the irradiated samples showed a lesser content of dimeric and polymeric decomposition products than that of the heated samples. In the case of irradiated trioleyl glycerol, the intramolecular dimerization is a major source of formation of dimeric compounds; and 6) the nonpolar dehydrodimers were formed in both the heated and irradiated samples (except ethyl linolenate) which had the structure of carbn-carbon crosslinking between two allylic monomers