Reduction of oil bitterness by heating of olive (Olea europaea) fruits

Olives (Olea europaea) of the Manzanilla and Verdial varieties, harvested at the green mature stage of ripening, were heated at 30, 40, 45, and 50 degreesC during 24 h and at 40 degreesC during 24, 48, and 72 h, respectively. Just after treatments, oils were physically extracted from the olives. Olive heating promotes a reduction of oil bitterness in direct relationship to the time and temperature used. Fruit heating at less than or equal to 40 degreesC during 24 h did not produce significant changes of acidity, UV absorption, peroxide index, panel test score, or oxidative stability of the obtained oils. Both longer treatments at 40 degreesC and heating at > 40 degreesC yielded oils with less oxidative stability. Oils obtained from olives heated at greater than or equal to 40 degreesC showed higher concentrations of chlorophylls and carotenes. For each olive variety, a good correlation between oil bitterness and content of hydroxytyrosol secoiridoid derivatives was found.