When polyunsaturated fats like omega-6 fatty acids (found in soybean or corn oils) are subjected to elevated temperatures, they can generate various types of aldehydes. The breakdown of these fats primarily involves thermal oxidation.
Types of Aldehydes Formed
a. Hexanal
Formed from the oxidation of linoleic acid.
b. Trans-2-alkenal Aldehydes
Example: 2-alkenal such as 2-hexenal.
c. Malondialdehyde (MDA)
A product of lipid peroxidation of polyunsaturated fatty acids.
d. Aldehydes from Longer Fatty Acids
Example: Decanal or dodecanal, generated from longer-chain fatty acids.
Mechanisms Involved
The formation of aldehydes from polyunsaturated omega-6 fats through thermal oxidation can be explained using the following mechanisms
Initiation
Free Radical Formation: High temperatures lead to the formation of free radicals from the polyunsaturated fatty acids. The double bonds in these fatty acids are particularly susceptible to radical attack.
Propagation
Reaction with Oxygen: The free radicals react with molecular oxygen (O₂) to form peroxy radicals.
Peroxide Formation: The peroxy radicals can further react with the fatty acids, generating hydroperoxides.
Decomposition of Hydroperoxides: Hydroperoxides can break down into various aldehydes and other volatile compounds.
Termination
Combination of Free Radicals: Free radicals can terminate by combining with each other, leading to stable products that include aldehydes.
Conclusion
The breakdown of polyunsaturated omega-6 fats like those found in soybean and corn oils at elevated temperatures leads to the formation of various aldehydes such as hexanal, malondialdehyde, and others. The primary mechanisms involved are free radical formation, oxidation, and decomposition of hydroperoxides, which collectively contribute to the development of these aldehydes during thermal treatment.
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