Effect of Food Components on Changes in Frying Oil
Jan Pokorný* and Zuzana Réblová
Institute of Chemical Technology, Department of Food Chemistry and Analysis, Technická 5, CZ-166 28 Prague 6, Czech Republic
Received October 5, 1998
Accepted February 15, 1999
deep fat frying, flavour formation, fried food influence, frying oil quality, oxidation
Frying oil is oxidized by air oxygen and degradation takes place due to high temperature, but its changes are influenced by fried food, too. The most important reaction is the formation of steam by contact of hot oil with water present in fried food. Steam hydrolyses triacylglycerols of frying oil. Fried food absorbs a part of frying oil, but the absorption may be inhibited by batter, especially covered by a layer of polysaccharides. In case of fatty foods, fat is released from fried food into frying oil. Proteins inhibit oxidation reactions, with formation of lipid- -protein complexes, but excessive temperatures may cause formation of heterocyclic mutagens, mainly isoquinolines and isoquinoxalines. The oxidation of frying oil is inhibited by various other components of fried food, such as tocopherols, carotenoids, phenolics or certain sterols, mainly avenasterols. On the contrary, heavy metals, chlorophylls and other prooxidants are released into oil, enhancing its oxidation. Fried food contributes to the formation of flavour substances, such as pyrazines, pyrroles or sulphides, which modify the typical fried flavour.
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