Relationship between chemical and physical indexes and column and HPSE chromatography methods for evaluating frying oil.

Standard chemical and physical indexes, such as color index, acid value, and K270 were compared with the polar content and the specific thermoxidative and hydrolytic compounds originated during 75 potato fryings with sunflower oil. The color index, acid value, K270 and total polar content showed a significant increase (p < 0.05) after the first 30 fryings, followed by a tendency of the last three indexes to reach a near-steady state. Triglyceride polymers and triglyceride dimers showed a significant increase (p < 0.05) after 30 fryings, while the oxidized triglycerides were not increased significantly after 30 fryings. The amount of diglycerides and free fatty acids related to hydrolytic alteration did not change significantly throughout the frying operations. The significant correlations between acid value and total polar content, triglyceride dimers, triglycerides polymers and oxidized triglycerides, or between color index and polar content and triglyceride polymers or between K270 and triglyceride polymers indicate that these simple and standard methods can be applied and they are as useful as more specific methods of evaluation in the monitoring of frying operations, provided that initial values of all of these indexes are available.