Oxidative stability of virgin olive oils
An investigation was carried out on virgin olive oils of the Gentile (Larino), Gentile (Colletorto), Coratina, and Leccino varieties, harvested at different times, to assess their oxidation stability. The olive oils were analyzed by means of peroxide, K232′ and K270 values at 1, 6, 12, and 18 mon of storage in green bottles, in the dark, at temperatures ranging from a mean of 6°C in winter to 12°C in summer. A subsample was also oven-tested at 75°C and then analyzed on a weekly basis using the same oxidative parameters. The less ripe the olives (harvested in the same area during 1 mon), the more resistant the olive oils were to forced oxidation. The amount of total phenols in the oils was found to be directly related, even if to a low degree, to the oleuropein content in the olives and inversely related, to the same degree, to (3,4-dihydroxyphenyl)ethanol. The latter is a derivative of oleuropein; (3,4-dihydroxyphenyl)ethanol content increases as the olives ripen, but it is very low in fresh virgin olive oils, owing to the hydrophilic nature of the phenolic alcohol, which goes mainly into the waste-water during processing. Among the varieties considered, Coratina oils showed the highest resistance to forced oxidation because of their high total phenol content.
(3,4-Dihydroxyphenyl)ethanol K232′ K232′ K270′ oleuropein olive variety peroxide value phenolic compounds thermal oxidation virgin olive oil