Palm and soybean oils were used in experiments of frying of potatoes in 1 L, household electric deep fryers with a surface-to-volume ratio of 0,3 cm-1. The oils were heated for five hours every day for five consecutive days at a temperature of 183.1 ± 1.7 °C. the evaluation of oil degradation was followed by the increase of polymer contents and changes in fatty acid composition. After 25 hours, the loss of fatty acids were 15.0 and 62.2% for oleic and linoleic acid, respectively in palm oil and 6.5, 24.9 e 39.7% for oleic, linoleic, and linolenic acid, respectively in soybean oil. The content of polymers ranged from 0.4 to 23.7% and from 0.5 to 30.7% for palm and soybean oils, respectively. Linear association between the loss of total unsaturated fatty acids and polymers formation presented high correlation coefficients (0.9951 and 0.9740 for palm and soybean oils, respectively. The results obtained clearly indicate that the higher the degree of fatty acid unsaturation, the higher its degradation, and also that the quantitative determination of polymers would be a very useful analysis to evaluate the oil degradation.
fatty acids; frying oils; palm oil; polymers; soybean oil
