hydroxytyrosol, 3,4-dihydroxyphenolethanol (3,4-DHPEA) (Gutiérrez-Rosales
et al. 2003). On the other hand, the pungent note in olive oil has been mainly
attributed to the dialdehydic form of decarboxymethylelenolic acid linked to tyrosol,
oleoocanthal, the dialdehydic form of decarboxymethyl ligstroside aglycone
(p-HPEA-EDA) (Andrewes et al. 2003). These authors reported that the
deacetoxy-ligstrosideaglycone has strong burning pungent sensation, while
oleuropein aglycone has slightly weaker pungent notes, and tyrosol shows astringent
but not pungent mouth feelings. On the contrary, the bitterness has been attributed to
the aldehydic form of oleuropein aglycone (Mateos et al. 2004).
Several types of phenolic compounds are found in the olive fruits, including
anthocyanins (cyanidin glucosides); flavonols (mainly quercetin-3-rutinoside); flavones (luteolin and apigenin glucosides); phenolic acids (hydroxybenzoic,
hydroxycinnamic, others); phenolic alcohols (tyrosol, hydroxytyrosol,
3,4-dihydroxyphenylglycol); secoiridoids (oleuropein, demethyloleuropein,
ligstroside, nuzhenide); verbascoside, a hydroxycinnamic acid derivative; and
lignans and oleoside-11-methylester (Boskou 2006, 2015). The secoiridoid compounds found in the olive drupe, ligstroside or oleuropein glucoside, undergo
degradation, in particular spontaneous hydrolysis, and therefore the phenolic compounds found in the resulting olive oils show a different profile. The phenolic
fraction of olive oil is constituted by several dozens of molecules, commonly
classified into phenolic acids, phenolic alcohols, secoiridoids, flavonoids and
lignans. A wide range of total phenolic compounds has been described for
EVOOs, from approximately 100 mg kg
À1 up to almost 1000 mg kg
À1 (Kotsiou
and Tasioula-Margari 2016; Caporaso et al. 2015a, b). A scheme reporting the
structure of several phenolic compounds found in olive oil is shown in Fig. 9.1.
Oleuropein is easily degraded into simpler phenolic compounds during olive oil
extraction and storage of the product. In particular, hydrolysis due to the enzyme
β-glucosidase takes place at the molecular bond between the sugar β-glucopyranose
and the remaining molecule, giving the oleuropein aglycone. Similarly, an aglycone
originates from ligstroside, another compound with bitter-pungent character. A
second hydrolysis leads to the formation of hydroxytyrosol, which has been reported
to exert strong antioxidant capacity. In VOOs, the main phenolic compounds are the
dialdehydic forms of elenolic acid linked to tyrosol (p-HPEA-EDA) and
hydroxytyrosol (3,4-DHPEA-EDA), and ligstroside aglycons, with more limited
concentrations of phenolic acids. Tyrosol, hydroxytyrosol and their secoiridoid
derivatives are the most abundant compounds, reaching up to 90% of the total
phenolic content.
Generally, olive oil phenolic compounds with the hydroxylic groups in ortho
position show higher antioxidant capacity; thus, compounds such as
3,4-dihydroxyphenylethanol-elenolic acid and 3,4-dihydroxyphenylethanol-elenolic
acid dialdehyde are the molecules with the highest expected antioxidant activity in
virgin olive oils.
9 Olive (Olea europaea)
221
et al. 2003). On the other hand, the pungent note in olive oil has been mainly
attributed to the dialdehydic form of decarboxymethylelenolic acid linked to tyrosol,
oleoocanthal, the dialdehydic form of decarboxymethyl ligstroside aglycone
(p-HPEA-EDA) (Andrewes et al. 2003). These authors reported that the
deacetoxy-ligstrosideaglycone has strong burning pungent sensation, while
oleuropein aglycone has slightly weaker pungent notes, and tyrosol shows astringent
but not pungent mouth feelings. On the contrary, the bitterness has been attributed to
the aldehydic form of oleuropein aglycone (Mateos et al. 2004).
Several types of phenolic compounds are found in the olive fruits, including
anthocyanins (cyanidin glucosides); flavonols (mainly quercetin-3-rutinoside); flavones (luteolin and apigenin glucosides); phenolic acids (hydroxybenzoic,
hydroxycinnamic, others); phenolic alcohols (tyrosol, hydroxytyrosol,
3,4-dihydroxyphenylglycol); secoiridoids (oleuropein, demethyloleuropein,
ligstroside, nuzhenide); verbascoside, a hydroxycinnamic acid derivative; and
lignans and oleoside-11-methylester (Boskou 2006, 2015). The secoiridoid compounds found in the olive drupe, ligstroside or oleuropein glucoside, undergo
degradation, in particular spontaneous hydrolysis, and therefore the phenolic compounds found in the resulting olive oils show a different profile. The phenolic
fraction of olive oil is constituted by several dozens of molecules, commonly
classified into phenolic acids, phenolic alcohols, secoiridoids, flavonoids and
lignans. A wide range of total phenolic compounds has been described for
EVOOs, from approximately 100 mg kg
À1 up to almost 1000 mg kg
À1 (Kotsiou
and Tasioula-Margari 2016; Caporaso et al. 2015a, b). A scheme reporting the
structure of several phenolic compounds found in olive oil is shown in Fig. 9.1.
Oleuropein is easily degraded into simpler phenolic compounds during olive oil
extraction and storage of the product. In particular, hydrolysis due to the enzyme
β-glucosidase takes place at the molecular bond between the sugar β-glucopyranose
and the remaining molecule, giving the oleuropein aglycone. Similarly, an aglycone
originates from ligstroside, another compound with bitter-pungent character. A
second hydrolysis leads to the formation of hydroxytyrosol, which has been reported
to exert strong antioxidant capacity. In VOOs, the main phenolic compounds are the
dialdehydic forms of elenolic acid linked to tyrosol (p-HPEA-EDA) and
hydroxytyrosol (3,4-DHPEA-EDA), and ligstroside aglycons, with more limited
concentrations of phenolic acids. Tyrosol, hydroxytyrosol and their secoiridoid
derivatives are the most abundant compounds, reaching up to 90% of the total
phenolic content.
Generally, olive oil phenolic compounds with the hydroxylic groups in ortho
position show higher antioxidant capacity; thus, compounds such as
3,4-dihydroxyphenylethanol-elenolic acid and 3,4-dihydroxyphenylethanol-elenolic
acid dialdehyde are the molecules with the highest expected antioxidant activity in
virgin olive oils.
9 Olive (Olea europaea)
221