Decrease in essential fatty acid content of edible fats during the frying process.

Degradation of sunflower oil, rapeseed oil, and lard during the frying operation was investigated by studying the loss of essential fatty acids compared to the accumulation of decomposition products. Linoleic and/or linolenic acid concentration was measured by GLC, and for detecting decomposition products determination of polymer content by GPC was chosen. Twelve laboratory experiments with different heating or frying conditions were run aimed at modelling practice and studying the effects of certain factors. The results indicated that loss of essential fatty acids being a parallel process to the accumulation of breakdown products is suitable both for detecting the decrease in nutritive value and for quality assessment of used frying fats. It was also found that the rate of deterioration is considerably affected by the nature of fat and the frying parameters. Study of the relationship between polymer content and the decrease in essential fatty acid concentration (using data from 110 samples) showed that high, linear correlation depending on the nature of fat can be found. Correlation coefficients and equations of regression lines were calculated.