Page 421 - Biosystems Engineering

398 Cha pte r F o u r tee n

Hydroxytyrosol is the olive phenol most studied because it is
characterized by major bioantioxidant activity. In ripe olives, it is
–1
present in quantities ranging from 1.0 and 2.9 g per 100 g of dry mat-
ter (Amiot et al. 1986; Romero et al. 2002).
–1
In the virgin olive oil, total phenol ranged from 50 to 500 mg kg of
oil; the final content is the result of several factors including cultivar
and quality of the olives, degree of maturation, climate, time and con-
dition of olive storage, and oil-extraction system (Montedoro and Garo-
falo 1984; Solinas 1987; Bruni et al. 1994; Caponio et al. 1999). Actually,
only one or two of the total phenols present in olives are found in virgin
oil because the majority of them remain in the wastewaters and in the
pomace (Rodis et al. 2002; Di Giovacchino et al. 1993).
During the first phase of the olive oil–extraction process, during
the initial grinding and the thermomixing of the olive paste, chemical
and enzymatic reactions are carried out that degrade at least 80 percent
of the olive’s complex polyphenols. In the three-phase system, it is
estimated that the major part of olive polyphenols, especially
hydroxytyrosol, relocate themselves in the wastewater (Niaounakis
and Halvadakis, 2004). Hydroxytyrosol is very abundant in olive mill
wastewaters in the free form or as a component of oleuropein, demeth-
yloleuropein, verbascoside, and hydroxytyrosol-4-β-D-glucoside
(Vásquez et al. 1987; Gutfinger 1998; Servili et al. 1999b; Capasso et al.
1999; Visioli and Galli 1999).
On the contrary, in virgin olive oil, simple phenols are lower than
complex phenols; principal simple phenols are hydroxytyrosol, tyro-
sol and caffeic acid, p-coumaric, syringic and vanillic acids (Monte-
doro et al. 1992a; Montedoro et al. 1992b; Limiroli et al. 1995).
When virgin oil is inedible, the refining process is necessary
where almost all phenols are destroyed (Tiscornia et al. 1982). For the
loss of natural antioxidants, refined olive oil is of lower quality than
extra virgin olive oil.

14.4 Antioxidant and Nutraceutical Properties
In the best storage conditions, virgin olive oil has a protracted shelf
life, up to almost 2 years. Accordingly, olive oil’s higher stability has
been attributed to its phenolic content (De Leonardis and Macciola
1998; Psomiadou and Tsimidou 2002).
It was repeatedly found that among olive polyphenols, o-diphenols,
especially hydroxytyrosol and caffeic acid, are the most effective
substances (Papadopoulos and Boskou 1991; Tsimidou et al. 1992;
Baldioli et al. 1996). However, the monophenol tyrosol and its deriva-
tives and p-hydroxybenzoic, o-coumaric, and p-coumaric acids have
insufficient or no antioxidant effect (Litridou et al. 1997).
Hydroxytyrosol is a good antioxidant that is more effective than
tocopherol, butylated hydroxytoluene (BHT), and other synthetic anti-
oxidants permitted for use in foods (De Leonardis and Macciola 2008).