Effect of α-tocopherol on the volatile thermal decomposition products of methyl linoleate hydroperoxides |
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Authors: | E N Frankel H W Gardner |
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Affiliation: | (1) Northern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 61604 Peoria, IL |
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Abstract: | α-Tocopherol and 1,4-cyclohexadiene were tested for their effect on the thermal decomposition of methyl linoleate hydroperoxide
isomers. The volatiles generated by thermolysis in the injector port of a gas chromatograph at 180°C were analyzed by capillary
gas chromatography. In the presence of either α-tocopherol or 1,4-cyclohexadiene, which are effective donors of hydrogen by
radical abstraction, volatile formation decreased in all tests, and significant shifts were observed in the relative distribution
of products in certain hydroperoxide samples. When an isomeric mixture of methyl linoleate hydroperoxides (cis, trans andtrans, trans 9- and 13-hydroperoxides) was decomposed by heat, the presence of α-tocopherol and 1,4-cyclohexadiene caused the relative
amounts of pentane and methyl octanoate to decrease and hexanal and methyl 9-oxononanoate to increase. A similar effect of
α-tocopherol was observed on the distribution of volatiles formed from a mixture of thetrans,trans 9- and 13-hydroperoxides. This effect of α-tocopherol was, however, insignificant with purecis,trans 13-hydroperoxide of methyl linoleate. The decrease in total volatiles with the hydrogen donor compounds, α-tocopherol and
1,4-cyclohexadiene, indicates a suppression of homolytic β-scission of the hydroperoxides, resulting in a change in relative
distribution of volatiles. The increase in hexanal and methyl 9-oxononanoate at the expense of pentane and methyl octanoate
in the presence of hydrogen donor compounds supports the presence of a heat-catalyzed heterolytic cleavage (also known as
Hock cleavage), which seems to mainly affect thetrans,trans isomers of linoleate hydroperoxides. |
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