Kinetics of change in the concentration of lipid hydroperoxides (LOOH) and carbonyl compounds (LCO) were simultaneously investigated during peroxidation of purified and unpurified sunflower oils at 60 °C. The oils exhibited two distinct peroxidation steps, comprising four alternate initiation and propagation phases, before attaining the typical termination phase. Significantly higher and lower rates of the LOOH formation and decomposition in the second than in the first step, respectively, were attributed to the dominant peroxidation of linoleic acid in the first step, and the remarkably added peroxidation of oleic acid in the second step. On the basis of the kinetics of change in the concentration of LCO, the first peroxidation step was considered to be the crucial one after which commercial sunflower oils should be discarded from sensory and toxicological standpoints.

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