A high performance size‐exclusion chromatographic method for evaluating heated oils

High performance size‐exclusion chromatography (HPSEC) was used to measure compounds with high‐molecular weight (MW) formed during the heating of oil. Formation of the high‐MW compounds is believed to be a reliable indicator of heat abuse in oils. The HPSEC method employs two µ‐spherogel size‐exclusion columns (500 and 1000 Å) in a series to separate the high‐MW compounds which are detected at a wave‐length of 234 nm by using a variable wavelength detector. The method was examined in the following study. Two sources of soybean oil were heated under laboratory conditions at 182 ± 2 C for eight 7‐hr days. Samples were taken periodically and tested by using HPSEC. Oil samples from two commercial deep‐fat frying operations were similarly tested. In all cases, size, number and apparent MW of the compounds formed increased with increasing frying time. The HPSEC procedure was compared with a method involving separation of polar and nonpolar components in a used frying fat by means of column chromatography on silica gel.