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'' ("European olive"), is a species of Subtropics, subtropical evergreen tree in the Family (biology), family Oleaceae. Originating in Anatolia, Asia Minor, it is abundant throughout the Mediterranean ...

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 and

astringency An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin '' adstringere'', which means "to bind fast". Astringency, the dry, puckering or numbing mouthfeel caused by th ...

, 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 Lye is the common name of various alkaline solutions, including soda lye (a solution of sodium hydroxide) and potash lye (a solution of potassium hydroxide). Lyes are used as cleaning products, as ingredients in soapmaking, and in various other c ...

Chemical treatment

Oleuropein is a derivative of

elenolic acid Elenolic acid is a component of olive oil and olive leaf extract. It can be considered as a marker for maturation of olives. It is a subunit of oleuropein, a bitter chemical compound found in olives and the leaves of the olive tree, alongside c ...

linked to the orthodiphenol

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

by an ester bond and to a molecule of

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

by a

glycosidic bond A glycosidic bond or glycosidic linkage is a type of ether 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 o ...

. 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 chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form su ...

of these derivatives, facilitating their release into the

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 macroporous

resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

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, 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 increase in reaction rate, rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst ...

for its oxidation.

Research

Oleuropein has been proposed as a

proteasome Proteasomes are essential protein complexes responsible for the degradation of proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are found inside all e ...

activator.

References

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

Chemical treatment

Green olive blackening

Research

See also

References