Precursors of alk‐2,4‐dienals in autoxidized lard

Abstract

Abstract 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.