A Phenomenological Model of the Peroxide Value's Rise and Fall During Lipid Oxidation

During isothermal lipid oxidation at relatively high temperatures, the peroxide concentration frequently peaks while at relatively low temperatures it only rises slowly. These are two manifestations of a process where formation and degradation happen simultaneously on different time scales. A phenomenological mathematical model, comprising a decay factor superimposed on an accumulation term can describe these scenarios. Each has a characteristic time constant shortened by raising the temperature and a rate constant that increases with it. The model's mathematical structure and the magnitude of its coefficients depend on the particular system. However, regardless of the chosen expressions, if the degradation characteristic time falls within or just beyond the experiment's duration, a peak peroxide value will be observed whose height and shape will primarily depend on the other model's parameters. If this characteristic time is far outside the time of the experiment , no peak will be recorded. The model need not be unique and no detailed knowledge of the oxidation mechanisms is required for its formulation. Consequently it can be derived directly from experimental peroxide value versus time relationships, without the need to monitor the intermediate reactions by specialized instrumental methods such as DSC. Through the formation term adjustment, the model can also account for the temperature dependent lag in the rise of the peroxide value and/or the appearance of its peak.