Olive (Olea europaea L.) oil, one of the oldest known vegetable
oil, derives essentially from the mesocarp of olive tree fruits. In
particular, the virgin olive oil is extracted only mechanically and it
is not subjected to refining treatment so that virgin olive oil is
unique among vegetable oils. Olive fruits, and the oils obtained
from them, have been studied for many years from analytical point
of view because of their commercial value and of their potential
health benefits [38,43]. One of the principal aspect concerning the
olive oil quality is the acidity which in turn exerts a great influence
on the olive oil stability [11]. Extra virgin olive oil, as indicated in
the European Community Regulation 1513/2001 [10], needs to
contain less than 0.8% of total free fatty acids (FFAs, expressed as
oleic acid). In damaged olives, before processing and/or during
transformation, enzymes may be responsible for the increment in
FFAs level. In fact, it is known that the quality of virgin olive oils and
the amount of FFAs that they contain depend from the characteristics
of olives and from the extraction procedures utilized. The
hydrolysis of the olive oil triglycerides may begin when the fruits
are still on the tree as endogenous lipases seem to be active when
the fruit ripens [20]. Furthermore, hydrolytic enzymes are released
during fruit milling and be active during the malaxation phase, so
that the malaxation step performed for long time at high temperatures
gives a higher recovery in oil but a lower quality.