Quality assessment of used frying fats: A comparison of four methods

The level of petroleum ether insoluble oxidized fatty acids in used frying fats is one of the recommended criteria for assessing their quality in Germany; however, the method of determination is time consuming and inaccurate. Gel permeation chromatography (GPC) allows the determination of dimeric and oligomeric triglycerides in a heated fat irrespective of the presence of oxidized material. An indication of the total amount of polar and oxidized compounds can be obtained by liquid chromatography (LC) on a silica gel column in connection with a moving-wire detector. A comparatively simple and quick method is the separation of polar and unpolar components in a used frying fat by means of column chromatography (CC) on silica gel. Over a large number of investigations, a good correlation was seen between the results obtained with GPC, LC, and CC and the amount of petroleum ether insoluble oxidized fatty acids isolated from used frying fats. Limits of the analytical data obtained by the new methods are proposed which indicate deterioration of used frying fats.