The cis, cis-Linoleic Acid Content of Heated Oils

Abstract

Lipoxidase was used to measure die cis-methylene-interrupted, polyenoic acids in heated corn oil, rapeseed oil and soybean oil. The loss of these polyenoic acids was small during the first 4 hours of heating at 180°C, but increased at 212°C and with longer heating times. The total proportion of such acids which disappeared was unrelated to the total amount originally present in the oil. Absorbance at 440mμ by the oils also increased with temperature and time of heating, except that soybean oil appeared the same at 180 and 212°C. The frying of 6 successive batches of potatoes in corn oil was associated with less than a 7% decrease of cis, cis-linoleic acid in this oil. Corn oil in “brownies” was more susceptible to thermal oxidation than in a cake containing more moisture and baked at a lower temperature. Generally, there was good retention of cis-methylene-interrupted, polyenoic acids under these moderate conditions of food processing.