[Comparison of methods to characterise thermally altered frying fats and oils].

During the process of deep fat frying the fat or oil undergoes several chemical and physical changes. To guarantee an effective quality control for used frying fats simple and rapid methods for the measurement of heat abuse are needed. Therefore several frying oils were heated with and without foodstuff and the change of polar parts, acid number, colour acid number, specific absorption and dielectric properties with prolonged heating time were determined. It could be shown that under usual frying conditions acid number and colour acid number, which are often used in praxis, as well as the specific absorption are not unrestrictedly useful to characterise heated frying fats. It turned out, however, that the determination of the dielectric properties with a foodoil-sensor is a useful tool to investigate heat abuse of frying fats and oils in routine analysis.