Formation mechanisms of reactive carbonyl species from fatty acids in dry-cured fish during storage in the presence of free radicals

This study aimed to better understand the changes of fatty acids in dry-cured fish during storage, and to analyze the reactive carbonyl species (RCS) formation mechanism primarily from the standpoint of oxygen-derived free radical reactions interactions. Oleic acid and linoleic acid were the predominant unsaturated fatty acids in dry-cured fish. The content of unsaturated fatty acids in dry-cured fish increased over time at 4°C, while decreased at 25°C. Singlet oxygen, superoxide anion and hydroxyl-alkyl radical levels increased with time, and more free radicals were yielded in the samples held at 25°C. Redundancy analysis revealed that hydroxyl-alkyl radicals had the greatest influence on the oxidation of lipids. Hydroxyl-alkyl radicals and singlet oxygen levels were positively correlated with 4-hydroxy-2-nonenal (HNE), malondialdehyde (MDA), peroxide value and acid value levels, but adversely to 4-hydroxy-2-hexenal (HHE) and fatty acids levels. Moreover, HNE and MDA were both inversely linked with fatty acids contents. It is possible that the intermediates of lipid oxidation undergo oxidation, cleavage and other reactions due to free radical activity, resulting in the generation of aldehyde precursors. These findings help us further characterize the lipid oxidation and RCS formation mechanism in dry-cured fish during storage.