Heating Vegetable Oil to Frying Temps Forms Toxic Compound

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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 periods?or even for half an hour?a 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 acids?DNA and RNA?and other biomolecules.

HNE is formed from the oxidation of linoleic acid, and reports have related it to several diseases, including atherosclerosis, stroke, Parkinson's, Alzheimer's, Huntington's 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.

Csallany's 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.

John Hart is the editor of Pathogen Alert, a daily blog that tracks deadly pathogens around the globe. Visit the site at

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