Determination of Oxidative Stability of Oils and Fats

Abstract

In a new approach to evaluating the oxidative stability of oils and fats, the consumption of oxygen by a sample confined in a reactor of adjustable temperature is monitored with a gas-phase flow injection analysis (FIA) system. Temperature-dependent data are collected in a low-oxygen-content atmosphere. For a variety of samples, log(oxygen consumption) is linearly related to the reciprocal of the absolute temperature (minimum linear r(2) > 0.99). This makes it possible to extrapolate the temperature-dependent data to predict the stability of the samples at other temperatures, e.g., typical ambient storage temperatures at which the direct determination of oxidative stability would be too slow for most samples. The proposed method is instrumentally simple and is easily automated. The sample throughput rate is an order of magnitude faster relative to current alternatives; temperature-dependent stability characterization for a sample (three temperatures, triplicate measurement at each temperature) requires ≤ 2 h. The reproducibility of the results is excellent. For a cottonseed-oil sample studied over 3 days, the slope and intercept of the log(O(2) consumption) vs 1/T linear plot (for all the 45 measurements made) exhibited uncertainties of 2.1% and 2.0% for the slope and the intercept, respectively, with a linear r(2) value of 0.9929. In a high-temperature (160 °C) oxidation experiment with various oils, the oxygen consumption was well-correlated (linear r(2) 0.9692) with the concomitant decrease in iodine absorption number (IAN). In contrast, it was poorly and negatively correlated with an increase in the peroxide value.