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CH06 THE ROLE OF OXYGEN AND WATER IN THE EXTRA-VIRGIN OLIVE OIL PROCESS HO O
O
HO
O OCH3
Moderately soluble in water
HO
OH
O
O
R
R = OH, oleuropein R = H, ligstroside
O HO
Enzymatic hydrolysis of glycosidic bond
O
HO Insoluble in water
OCH3 O
O
R
O R = OH, oleuropein aglycone
HO
Hydrolysis of the ester bond
R
O
HO
Soluble in water
OCH3
OH O
HO HO R = OH, hydroxytyrosol
O
Elenoic acid
Figure 6.2 A simplified picture of the transformation of phenolic compounds in the extra-virgin olive oil process.
of elenoic acid esterified with a β-pyranose molecule on one side and tyrosol (in the case of ligstroside) or hydroxytyrosol (in the case of oleuropein) on the other side. Oleorupein and ligstroside are moderately soluble in water and almost insoluble in oil. Therefore, their concentration in oil is always very low (a few mg/kg). Oleuropein and ligstroside are found in the olive fruit but also in a very high amount in the olive leaves. They confer resistance to disease and insect infestation. They are present in relatively high concentrations in olive mill wastewater, with a significant antimicrobial and phytotoxic effect, which makes waste disposal more difficult. An endogenous β-glucosidase causes the formation of oleuropein and ligstroside aglycones; they are esters of elenoic acid with tyrosol or hydroxytyrosol. The second molecule in Figure 6.2 represents oleuropein aglycone.