Formation of Conjugated Polyenes, Malondialdehyde and Methylglyoxal in French Fries Produced with Four Different Types of Oils

Résumé

Lipid peroxidation products in French fries are a potential risk factor for non-communicable diseases. Malondialdehyde and methylglyoxal are among the most pathophysiologically-relevant lipid peroxidation products, but are generally not regarded as major products of the oxidation of linoleic acid- or monounsaturated fatty acid (MUFA)-rich oils, because mechanisms of their formation from such fatty acids are poorly understood. This study aimed to determine the formation of malondialdehyde and methylglyoxal, as well as conjugated dienes and conjugated trienes (precursors of secondary products including aldehydes) in French fries fried with four oils having different fatty acid composition. Conjugated dienes and trienes (CDs and CTs, respectively) were determined spectrophotometrically, malondialdehyde by the thiobarbituric acid test, and methylglyoxal by high performance liquid chromatography (HPLC). CT formation occurred to the same extent in sunflower and canola oils although the former lacked fatty acids with at least three double bonds, signifying desaturation of fatty acids during lipid peroxidation. More malondialdehyde was formed in sunflower oil containing more linoleic acid than canola oil with higher α-linolenic acid (18:3, n-3) content, indicating the importance of linoleic acid as a malondialdehyde precursor. Olive oil generated more malondialdehyde, methylglyoxal, CD and CT than palm olein, which is attributable to greater monounsaturated fatty acid content in the former. Mechanisms are proposed for the formation of CDs, CTs, malondialdehyde and methylglyoxal from MUFA and linoleic acid. Thus, MUFA- and linoleic acid-rich oils are relevant as sources of the two dialdehydes in fried foods. CDs and CTs can be considered as appropriate for monitoring lipid peroxidation even in MUFA- or linoleic acid-rich oils. Furthermore, formation of CDs through fatty acid desaturation helps to explain the formation of some 'unexpected' lipid oxidation products.

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