Aldehydes from oxidized lipids can react with 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals in isooctane systems

Oxidized lipids can decrease the absorbance of 2,2-diphenyl-1- picrylhydrazyl (DPPH) in isooctane. However, the compounds responsible for the decrease in DPPH absorbance are still not known. Major factors and possible compounds decreasing the DPPH absorbance during lipid oxidation were identified using linoleic and oleic acid model systems. Changes in the hydroperoxides and conjugated dienoic acid value in thermally oxidized linoleic acid were not highly correlated with those of DPPH absorbance under air-tight and nitrogen flushing conditions. Radical scavenging compounds from oxidized oleic acid were tentatively identified as mixtures of aldehydes, alcohols, and acids. Aldehydes from oxidized fatty acids including pentanal, t-2-heptenal and t-2-nonenal can react with DPPH, whereas most alcohols and hydrocarbons did not show DPPH scavenging activity. Aldehydes rather than conjugated dienes and hydroperoxides may be the radical scavenging compounds from oxidized lipids. The results of this study will help to understand better the changes in oxidation products during lipid oxidation.