Stabilization of soybean oil with heated quercetin and 5-caffeoylquinic acid in the presence of ferric ion

The effect of heated quercetin (400 mg/kg of oil) or 5-caffeoylquinic acid (5-CQA) and the presence of ferric ion (2.2 mg/kg of oil) on the stability of soya oil oxidized in an oxidative stability index (OSI) instrument was i nvestigated. After heating the phenolic at 100 degrees C or 150 degrees C, the OSI values of treated oils were not significantly (p < 0.001) different , whereas, at 200 degrees C, the values decreased significantly with additi on of quercetin, but not with 5-CQA. However, the antioxidative activity of quercetin remained significantly greater than that of 5-CQA. The antioxida tive potency of quercetin was reduced significantly by addition of ferric p almitate (FP), but that of 5-CQA was not. Reaction between the ortho-dihydr oxy groups of the quercetin and ferric ion may reduce the number of hydroxy ls available to react with free radicals. Chelating action of 5-CQA might b e provided by ortho-dihydroxy grouping of the quinic acid moiety.