PRECURSORS OF ALK-2,4-DIENALS IN AUTOXIDIZED LARD

Evidence suggested that the low proportions of C 10 alk-2,4-dienal found in mildly autoxidized linoleate or lard was basically due to a selective scission mechanism of the 13 and 9 conjugated linoleate hydroperoxide isomers. Spontaneous scission tended to be at the carbon linkage between a double bond and the hydroperoxide group. Thus the 13 hydroperoxide isomer produced the typically predominant amounts of hexanal. The 9 hydroperoxide isomer formed little C 10 dienal and scission between the 9 and 10 carbons possibly led to some C 9 alk-2-enal. Earlier studies of free aldehyde formation by autoxidized oleate, linoleate, linolenate and arachidonate support such a scission mechanism. Autoxidized linoleate was decomposed by dilute acid to C 6 alkanal, some C 9 enal and no dienal. Under different stress, such as heat, alkaline conditions and Cu ++, large proportions of C 10 dienals were formed. This appeared due to a shift in the point of scission to the saturated side of the hydroperoxide group. © 1969 AOCS Press.