Oxidation of a functional, CLA-rich oil: determination of volatile and non-volatile compounds

• Published in: European food research & technology Vol. 242; no. 11; pp. 1993 - 2000
• Main Authors: Márquez-Ruiz, Gloria, Holgado, Francisca, Ruiz-Méndez, Mª Victoria, Velasco, Joaquín, García-Martínez, Mª Carmen
• Format: Journal Article
• Language: English; German
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.10.2016; Springer Nature B.V
• Subjects: Agriculture; Analytical Chemistry; Biotechnology; Chemistry; Chemistry and Materials Science; Fatty acids; Food; Food Science; Forestry; Original Paper; Oxidation; Polymers; Safflower oil; Sensors; CLA; Oxidation; Polymers; Volatiles
• ISSN: 1438-2377; 1438-2385
• DOI: 10.1007/s00217-016-2698-9

The objective of this work was to monitor and compare formation of non-volatile and volatile oxidation compounds in a conjugated linoleic acid (CLA)-rich oil, Tonalin ® oil (TO) and a linoleic acid (LA)-rich oil, safflower oil (SO) at 40 °C in the dark. In the TO, formation of hydroperoxides was negligible and the first and major compounds formed were polymerization products. When tocopherols were exhausted, the SO showed 152 meq O 2 /kg oil and 3 % polymers, values which are consistent with the expected progress of oxidation in unsaturated oils under these conditions, while the TO showed only 19 meq O 2 /kg oil of peroxide value and as much as 15 % polymers. In relation to the composition of volatile compounds, that found in the SO was close to that expected from the cleavage of the alkoxyl radicals formed from the LA-derived hydroperoxides, where hexanal is the main compound. However, the composition of volatile compounds of the TO was characterized by the occurrence of heptanal and t -2-nonenal, which were absent in the SO. An alternative route of formation for these distinct volatile oxidation compounds in TO could be scission of dioxoethanes coming from 1,2 cycloadditions of CLA with oxygen. Overall, the results obtained in this study, both on non-volatile and on volatile compounds, support that oxidation kinetics of CLA-rich oils differ substantially from that expected according to the hydroperoxide theory. Oxidation of CLA seems to proceed preferentially by the addition of the peroxyl radical to a double bond during propagation reactions, thus supporting the formation of oligomeric peroxides from the early events of lipid degradation.