Oleuropein hydrolysis in natural green olives: Importance of the endogenous enzymes

• Endogenous enzymes hydrolyse oleuropein, a bitter compound of olives.
• The enzymatic hydrolysis of oleuropein is rapid during the first months.
• Chemical hydrolysis of oleuropein is slow over the common range of pH of natural olives.
• A high concentration of HyEDA and hydroxytyrosol are found in natural green olives.

The bitter taste of olives is mainly caused by the phenolic compound named oleuropein and the mechanism of its hydrolysis during the processing of natural green olives was studied. First, a rapid chemical hydrolysis of oleuropein takes place at a high temperature of 40 °C and at a low pH value of 2.8, but the chemical hydrolysis of the bitter compound is slow at the common range of pH for these olives (3.8–4.2). However, decarboxymethyl elenolic acid linked to hydroxytyrosol and hydroxytyrosol have been found in a high concentration during the elaboration of natural green olives. When olives were heated at 90 °C for 10 min before brining, these compounds are not formed. Hence, the debittering process in natural green olives is due to the activity of β-glucosidase and esterase during the first months of storage and then a slow chemical hydrolysis of oleuropein happens throughout storage time.