New research by a University of Minnesota professor and a graduate student shows that when highly unsaturated vegetable oils are heated at frying temperature (365 F) for extended periodsor even for half an houra highly toxic compound, HNE (4-hydroxy-trans-2-nonenal) forms in the oil.

A. Saari Csallany, professor of food chemistry and nutritional biochemistry at U. of Minn. said HNE is a well known, highly toxic compound that is easily absorbed from the diet.

The toxicity arises because the compound is highly reactive with proteins, nucleic acidsDNA and RNAand other biomolecules.

HNE is formed from the oxidation of linoleic acid, and reports have related it to several diseases, including atherosclerosis, stroke, Parkinsons, Alzheimers, Huntingtons and liver diseases.

Nutritionists regard vegetable oils such as soybean, sunflower and corn as heart-healthy because of their high levels of linoleic acid, a polyunsaturated fatty acid.

HNE is incorporated into fried food in the same concentration as it forms in the heated oil.

Csallanys work underscores the risk of repeated heating, or reusing, highly unsaturated oils for frying because HNE accumulates with each heating cycle. In future studies, Csallany and her colleagues plan to determine how long polyunsaturated oil must be heated at lower temperatures in order to form HNE and its related compounds.