Oxidative stability and minor constituents of virgin olive oil and cold-pressed rapeseed oil

The oxidative stability and minor constituents of three cold-pressed low erucic acid rapeseed oils and three virgin olive oils were compared. The rapeseed oils were more easily oxidized, in part due to their higher contents of polyunsaturated fatty acids. The rapeseed oils were rich in gamma-tocopherol and had low initial peroxide values (PVs), but their hydrophilic phenol content was low, only 3-4 ppm. Olive oils contained a-tocopherol and 40-100 times more hydrophilic, phenols compared to the rapeseed oils. The initial PVs of fresh olive oils were much higher than those of rapeseed oils. Lutein and P-carotene were present in all oils but chlorophylls (pheophytin a) only in the olive oils. The phenolic extract from the olive oils protected both bulk and emulsified methyl linoleate (MeLo) from oxidation at the 100 ppm level. The extracts obtained from the rapeseed oils had either moderate or no antioxidative effect in MeLo. Testing of the extracts for their 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity yielded similar results. We conclude that phenolic compounds contribute significantly to the oxidative stability of cold-pressed oils.