The effect of pan frying on thermooxidative stability of refined rapeseed oil and professional blend.

The pan fryings of frozen pre-fried French fries in refined rapeseed oil (RO) and professional blend (PB) were of 8 h duration. Initially, while fresh, and after every 1 h of frying, the oils were analyzed for acid and anisidine values, colour, refractive index, fatty acid composition (by GC), polar fraction content and composition (by high pressure size exclusion chromatography). Additionally the fat content and fatty acid composition of French fries were determined. Hydrolytic and oxidative changes in the frying media varied with oil composition and increased with frying time. The pace of oxidation in RO was three times higher than in PB. The loss of polyunsaturated fatty acids (sum of C18:2 and C18:3) after 8 h of frying was 7 % in PB and 20 % in RO. The polar fraction content was two times lower in PB, but did not exceed 25 % in either of the frying media. The predominant fraction in RO was oxidized triacylglycerols, while in PB - diacylglycerols. During frying the proportions of triacylglycerol polymers and dimers increased in both oils, reaching 32 % in RO and 23 % in PB.