Degradation of fatty acids and tocopherols to form tocopheryl quinone as risk factor during microwave heating, pan‐frying and deep‐fat frying

Abstract

We investigated degradation of tocopherols to form tocopheryl quinones (TQ) and cytotoxic γ‐tocopheryl quinone in oils and French fries during microwave heating, pan‐frying and deep‐fat frying. We proved that the microwave oven caused rapid increase of oil temperature, with the consequence of two to three times greater degradation of fatty acids and tocopherols than pan‐frying and deep‐fat frying. Pan‐frying with sunflower oil caused three‐time greater formation of fatty acids polymers, compare with rapeseed oil. The gentlest one was deep‐fat frying, which caused two times slower formation of fatty acid hydroperoxides and tocopheryl quinones in 900 g of oil. We found that not only the quantity but also the type of oil had critical effect on the formation of cytotoxic γ‐tocopheryl quinone. During 50 min of pan‐frying in rapeseed oil, 22 mg/kg of γ‐tocopheryl quinones was formed, of which 5–7 mg/kg penetrated into the homemade French fries. While the deep‐fat frying technique generated only 6 mg/kg of γ‐tocopheryl quinones in rapeseed oil. The rapid microwave heating caused formation of 8 mg/kg of γ‐tocopheryl quinones within 10 min. The emergence of γ‐tocopheryl quinones during culinary preparation of food has not yet been explored.Practical applications: Although an extensive research have been conducted in the area of microwave heating of foods, this is the first report about formation of cytotoxic γ‐tocopheryl quinone in microwave‐heated rapeseed oil. Formation of this reactive compound was also confirmed during frying process. The most γ‐tocopheryl quinone was formed during pan‐frying and subsequently entered into fried food. It was observed that the amount of oil used for frying has a major impact on slowing formation of cytotoxic γ‐tocopheryl quinone and other tocopherols and fatty acids degradation product.Formation of health‐promoting α‐tocopheryl quinone and cytotoxic γ‐tocopheryl quinone during pan‐frying.