Effect of Heating Temperature and Time on the Volatile Oxidative Decomposition of Linolenate

Abstract

Ethyl linolenate, was thermally oxidized at 7OoC, 180°C, 250°C in a closed system in the presence of atmospheric oxygen. On the basis of the peroxide curve obtained at each of the three temperat u m , three heating times weIe chosen for the analysis of the volatile decomposition products. These products were identified by gas chromatography-mass spectrometry. The qualitative pattern of the volatile decomposition products was the same for all treatments. Nine of the products were consistent with compounds predicted from cleavage of the conjugated linolenate hydroperoxides, with the C9 0x0-ester and theC8 ethyl ester produced in the largest amounts. Other predicted products were not detected and were hypothesized to undergo further degradations. Although the major effect of temperature was found to be a quantitative one, it was difficult to relate the amounts of oxidation products directly to a temperaturedependent preferential hydroperoxide scission.

Volatile components from trilinolenin heated in air1

“…In Table I, data from the Lomanno and Nawar study on the 180 C oxidation of ethyl linolenate in air (15) show they had reported many of the same major volatiles that we noted in this study. Of interest is the mutual observation of 2-(2-pentenyl) furan from oxidized linolenic acid.…”

“…1) was identified in this and other studies involving oxidation of lipids containing linolenic acid (3,11,14,24). However, Gaddis et al (3) and Lomanno et al (15) found little or no 2,4,7-decatrienal from oxidized methyl linolenate. The amount (1.5%) we and other investigators observed is not reflective of the large relative quantity of the 9-OOH formed (23%).…”

“…Products AI and B~ are nonvolatile and would not be observed. However, when methyl and ethyl linolenates are oxidized, the A] fragment (octanoate) and Bl fragment (9-oxo-nonanoate) are the most abundant volatiles observed (11,15). Fragment As, 2,4,7-decatrienal (peaks 72 and 75 in Fig.…”

“…Hoffmann (13) also used the DNPH methodology to isolate volatiles from SBO heated at 120 C. He observed 3hexenal and 2,4-hepta-and octadienals and concluded that the precursor of these compounds was Ln. The most detailed study on oxidation of Ln at elevated temperatures was reported by Lomanno and Nawar (15). They subjected ethyl linolenate to temperatures of 70, 180 and 250 C 1Presented at the 73rd annual AOCS meeting, Toronto, 1982. in air and isolated and identified a number of volatile compounds containing different functional groups.…”

Effect of temperature on the antioxidant activity of phenolic acids

“…This phenomenon can be explained by higher decomposition of hydroperoxides before the end of the induction period at higher temperatures (Lomanno & Navar 1982), forming highly reactive alkoxyl and hydroxyl radicals (Frankel 1980) (more reactive than peroxyl radicals (Becker et al 2004;Choe & Min 2009) which can react with phenolic acids without an impact on the length of the induction periods (Frankel 1996). Further increases in temperature would probably also restrain the reactivity of phenolic acids against alkoxyl and hydroxyl radicals (or increase the relative reactivity of fatty acids) to favour the reactions of fatty acids with all present free radicals, resulting in the protection of phenolic acids by unsaturated fatty acids, as was observed for tocopherols (Verleyen et al 2002).…”