Study of chemical changes produced in virgin olive oils with different phenolic contents during an accelerated storage treatment.

Chemical changes produced in an extra virgin olive oil sample in the presence (EVOO) and absence (EVOOP) of its phenolic fraction during an accelerated storage treatment at 60 degrees C up to 7 weeks were studied. Modifications in phenol content, as well as changes in several quality parameters (free acidity, peroxide value, UV absorbance, fatty acid composition, oxidative stability index, and tocopherol content) were also evaluated under the same storage conditions and compared to those of the same sample deprived of phenolic compounds. When the phenolic extract of the EVOO was studied, a decrease of the antioxidants first present in the sample and an increase of the oxidized products were observed. In addition, oxidation seemed to produce the transformation of such phenolic compounds as secoiridoids and the appearance of oxidized forms of them. These latter compounds could be used as molecular markers of the lack of extra virgin olive oil freshness.