Radiolysis of Fatty Acid Esters in n-Hexane Solution

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This investigation was undertaken as a basic experiment to discuss the radiolysis of lipids in food irradiation. Many experiments have been made on the effect of ionizing radiation on fatty acids, natural fats or oils, and foods which contain much fat or oil. Following analyses of those irradiated samples were various according to the purpose. In this paper, methyl esters of fatty acids-methyl stearate (C18:0), methyl oleate (C18:1), methyl linoleate (C18:2), methyl linolenate(C18:3), methyl arachidate (C20:0) and methyl arachidonate (C20:4) were irradiated in n-hexane solution in attempt to obtain larger changes by lower dose. On radiolysis of n-hexane which would be expected to take place, repoTts by Dewhurst, Hardwick, Windmer and his coworkers, Shida and his coworkers and Kimura and his coworkers were referred. Prior to experiment methyl esters of fatty acids were purified by recrystallization or urea complex method or bromination. The hemical purities of these esters assayed by GLC analyses were 94-99%. Each solution was sealed in glass ampule and rradiated with 60Co-γ ray at room temperature. Conditions of γ-irradiation and items of analysis were shown in Table 1. Analyses employed in this examination were GLC, IRspectrometry and determination of IV. In GLC analysis, solution was injected directly after cutting the ampule. Conditions for GLC analysis were shown in Table 2. Preparations for IRspectrometry and IV determination were the oils obtained by vacuum evapolation in N2gas stream. IR-spectra were examined with KBr pellets. IV determinations were carried by Wijs method. Two gas chromatograms were shown in Fig. 1 and 2. Methyl stearate was the most stable and methyl linoleate was the most labile. In the gas chromatogram of methyl linoleate appeared unidentified peak (peak 1). Decreasing curves of methyl esters in n-hexane solution with the increase of dose were shown in Fig. 3. Remains of esters presented by peak area and remaining ratios at 7.1 Mrad irradiation were shown in Table 3 and Fig. 4. There were some generalizations in IRspectra of irradiated and unirradiated-esters. In high dose level, the bands at 1670 cm-1were decreasing and the bands at 970 cm-1were more intensive (Fig. 5). The bands around 1670 cm-1were due to the double bond system of carbon and those at 970 cm-1the trans configuration. These observations were indicative of the occurrence of any changes at double bond system and of isomerization from cis to trans configuration by γ-irradiation. IV of four esters were shown in Table 4. The values of methyl stearate were unchanged and nearly zero at any dose. Those of unsaturated esters were diverse and showed no equal tendencies. However, these observations were not well understood, they agreed with the results of Bancher reported that IV of irradiated oleic acid and linoleic acid varied irregular with increase of dose.
日本食品照射研究協議会の論文

Radiolysis of Fatty Acid Esters in n-Hexane Solution

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日本食品照射研究協議会 | 論文

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