Oleuropein is a glycosylated seco-iridoid, a type of phenolic bitter compound found in green olive skin, flesh, seeds, and leaves.

[4] When olives are immersed in a lye solution, the alkaline conditions lead to hydrolysis of the ester bond.

An alternative process uses amberlite macroporous resins to trap the oleuropein directly from the solution, reducing waste water while capturing the extracted molecules.

[9][10] Enzymatic hydrolysis during the maturation of olives is also an important process for the decomposition of oleuropein and elimination of its bitter taste.

When in contact with polyphenols, the ferrous ions form a black complex, giving the final color of the treated olives.