The total free radical scavenger capacity (RSC) of 57 edible oils from different sources
was studied: olive (24 brands of oils), sunflower (6), safflower (2), rapeseed (3),
soybean (3), linseed (2), corn (3), hazelnut (2), walnut (2), sesame (2), almond (2),
mixture of oils for salad (2), "dietetic" oil (2), and peanut (2). Olive oils were
also studied according to their geographical origins (France, Greece, Italy, Morocco,
Spain, and Turkey). RSC was determined spectrophotometrically by measuring the disappearance
of the radical 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(*)) at 515 nm. The disappearance
of the radical followed a double-exponential equation in the presence of oils and
oil fractions, which suggested the presence of two (fast and slow) groups of antioxidants.
RSC was studied for the methanol-soluble phase ("methanolic fraction", MF) of the
oil, the fraction nonsoluble in methanol ("lipidic fraction", LF), and the nonfractionated
oil ("total oil"; TF = MF + LF). Only olive, linseed, rapeseed, safflower, sesame,
and walnut oils showed significant RSC in the MF due to the presence of phenolic compounds.
No significant differences were found in the RSC of olive oils from different geographical
origins. Upon heating at 180 degrees C the apparent constant for the disappearance
of RSC (k(T)) and the half-life (t1/2) of RSC for MF, LF, and TF were calculated.
The second-order rate constants (k2) for the antiradical activity of some phenolic
compounds present in oils are also reported.