Oleuropein is a

glycosylated Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not ...

seco-

iridoid Iridoids are a type of monoterpenoids in the general form of cyclopentanopyran, found in a wide variety of plants and some animals. They are biosynthetically derived from 8-oxogeranial. Iridoids are typically found in plants as glycosides, mo ...

, a type of phenolic bitter compound found in green

olive The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ' ...

skin, flesh, seeds, and leaves. The term oleuropein is derived from the botanical name of the olive tree, ''Olea europaea''. Because of its

bitter taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...

, oleuropein must be completely removed or decomposed to make olives edible. During processing of bitter and inedible green olives for consumption as table olives, oleuropein is removed from olives via a number of methods, including by immersion in lye.

Chemical treatment

Oleuropein is a derivative of

elenolic acid Elenolic acid is a component of olive oil, olive infusion and olive leaf extract. It can be considered as a marker for maturation of olives. Oleuropein, a chemical compound found in olive leaf from the olive tree, together with other closely r ...

linked to the orthodiphenol

hydroxytyrosol Hydroxytyrosol is an organic compound with the formula . Classified as a phenylethanoid, i.e. a relative of phenethyl alcohol, Its derivatives are found in a variety of natural sources, notably olive oils and wines. The compound is colorless soli ...

by an ester bond and to a molecule of

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

by a

glycosidic bond A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group ...

. When olives are immersed in a lye solution, the alkaline conditions lead to hydrolysis of the ester bond. The basic conditions also significantly increases the

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

of these derivatives, facilitating their release into the lye solution. The high pH accelerates the oxidation of the phenolics, leading to blackness, as during their normal ripening, if the solution is oxygenated by air injection (alkaline oxidation of olives is also called the ''California process''). The lye solution is replaced several times until the bitter taste has dissipated. An alternative process uses

amberlite Amberlite is the tradename of a range of ion-exchange resin An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of smal ...

macroporous

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on nat ...

s to trap the oleuropein directly from the solution, reducing waste water while capturing the extracted molecules. Enzymatic hydrolysis during the maturation of olives is also an important process for the decomposition of oleuropein and elimination of its bitter taste.

Green olive blackening

Green olives may be treated industrially with

ferrous gluconate Iron(II) gluconate, or ferrous gluconate, is a black compound often used as an iron supplement. It is the iron(II) salt of gluconic acid. It is marketed under brand names such as ''Fergon'', ''Ferralet'' and ''Simron''. Uses Medical Ferrous gluc ...

(0.4 wt. %) to change their color to black.

Gluconate Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH2(CHOH)4COOH. It is one of the 16 stereoisomers of 2,3,4,5,6-pentahydroxyhexanoic acid. In aqueous solution at neutral pH, gluconic acid fo ...

, an edible oxidation product of glucose, is used as non-toxic reactant to maintain Fe²⁺ in solution. When in contact with polyphenols, the ferrous ions form a black complex, giving the final color of the treated olives. Black olives treated with iron(II) gluconate are also depleted in

, as iron salts are

catalysts Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

for its oxidation.

Research

Oleuropein has been proposed as a

proteasome Proteasomes are protein complexes which degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are part of a major mechanism by whi ...

activator.

References

{{Authority control Phenylethanoids Phenol antioxidants Anti-inflammatory agents GPER agonists Phenol glucosides Phytoestrogens Olives Olive oil Phytochemicals

Chemical treatment

Green olive blackening

Research

See also

References