Studies of the changes in edible fats during heating and frying

For detecting the changes in edible fats during the frying operation and for quality assessment of used frying fats 5 relatively simple methods were proposed: determination of polymer content by gel permeation chromatography, measurement of total polar artefacts by TLC followed by densitometry or by adsorption column chromatography, determination of decrease in essential fatty acid concentration and photometric measurement of absorbance at 232 nm. Using the above methods degradation of sunflower oil, rapeseed oil and lard was investigated by running 12 laboratory experiments with different heating or frying conditions. The results showed that both the composition of fat and the frying parameters greatly influence the rate of deterioration. Study of relationships between values obtained by different methods (using data from 110 samples) indicated that high, linear correlations depending on the nature of fat can be found. Correlation coefficients and equations of regression lines were calculated.