Determination of oxidative stability of lipids in solid samples
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A gas-phase flow injection analysis (FIA) method for the direct determination of the oxidative stability of solid fat/oil samples is described. Samples are confined with a low level of oxygen in a reactor of adjustable temperature. The oxygen consumption by the sample is automatically monitored after a preset period. The temperature-dependent data exhibit Arrhenius behavior. Normally, it is difficult to directly determine the stability at ambient temperatures because of inordinately long time requirements. The close correspondence to Arrhenius behavior makes it possible to use the results obtained at higher temperature to calculate the stability of samples at lower temperature conditions, such as at ambient storage temperature. The effects of sample size, sample particle size, sample fat content and the reproducibility of the method over time were studied using synthetic and bone meal samples. The oxygen consumption was found to be linearly dependent on the amount of sample taken, inversely dependent on the particle diameter, and independent of the exact lipid content, given some minimum lipid content. The results exhibited high day-to-day reproducibility. The gasphase FIA system developed in this work is easy to operate. Compared with the currently used method, the sample throughput rate is much faster (2–3h for complete multitemperature characterization of a sample) and the sample requirement is much lower (∼1 g). Furthermore, it eliminates the need to extract and recover the fat from the sample for further processing as is required by the other methods commonly used to measure oxidative stability.
Key WordsActive oxygen oil/fat oxidation oxidative stability oxidative stability index
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