Oleuropein

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Oleuropein
Oleuropein.png
Names
IUPAC name
(4S,5E,6S)-4-{2-[2-(3,4-dihydroxyphenyl)ethoxy]-2-oxoethyl}-5-ethylidene-6-{[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)-2-tetrahydropyranyl]oxy}-4H-pyran-3-carboxylic acid methyl ester
Other names
2-(3,4-Dihydroxyphenyl)ethyl [(2S,3E,4S)-3-ethylidene-2-(β-D-glucopyranosyloxy)-5-(methoxycarbonyl)-3,4-dihydro-2H-pyran-4-yl]acetate
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.046.466
Properties
C25H32O13
Molar mass 540.51 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Oleuropein is a glycosylated seco-iridoid, a type of phenolic bitter compound found in green olives, olive leaves, and argan oil.[1][2] Oleuropein is the ester of the elenolic acid and hydroxytyrosol. During processing of bitter and inedible green olives for human consumption as table olives, oleuropein is removed from olives by immersion in lye.[3][4]

Chemical treatment[edit]

Alkaline conditions favor the elimination of oleuropein from the tissues of fresh fruits immersed in a lye solution. Different mechanisms are simultaneously at work. First, at high pH (>  10), in a 3 wt. % NaOH solution, more than half of the phenolic groups (pKa ≈ 10) present in the molecule are deprotonated and become dissociated. The ionised phenolate groups increase the solubility of the molecule in the tissue of the olives. The oleuropein can then freely diffuse out of the fruits and is leached in the lye solution. At the same time, under alkaline conditions, the oleuropein molecule is also hydrolysed into non-bitter degradation products. And finally, at high pH, as phenols and polyphenols, the molecule is sensitive to oxidation and can degrade faster, while olives turn black as during their normal ripening, if the solution is oxygenated by air injection (alkaline oxidation of olives also called Californian process).[5][6] The NaOH solution is replaced several times by a fresh one until the bitter taste has completely disappeared. A newly developed process uses an Amberlite macroporous resins to trap the oleuropein molecule directly from the solution. The advantage is to reduce waste water while valorising the molecule.[7][8]

Green olive blackening[edit]

Sometimes, green olives are industrially treated with ferrous gluconate (0.4 wt. %)[5] to change their color into black.[9] Gluconate, an edible oxidation product of glucose, is used as non-toxic complexant to maintain Fe2+ into solution. When in contact with polyphenols, the ferrous ions form a black complex modifying the color of the treated olives.[7][8][5] Black olives treated with iron(II) gluconate are also depleted in hydroxytyrosol, as iron salts are catalysts for its oxidation.[10]

See also[edit]

References[edit]

  1. ^ Z. Charrouf and D. Guillaume (2007). "Phenols and polyphenols from Argania spinosa". American Journal of Food Technology. 2 (7): 679–683. doi:10.3923/ajft.2007.679.683.CS1 maint: Uses authors parameter (link)
  2. ^ Rupp R. (1 July 2016). "The bitter truth about olives". National Geographic. Retrieved 24 June 2019.
  3. ^ "How olives are made". California Olive Committee. 2017. Retrieved 5 August 2017.
  4. ^ Colmagro S., Collins G., and Sedgley M. "Processing technology of the table olive" (PDF). Retrieved 25 June 2019.CS1 maint: Uses authors parameter (link)
  5. ^ a b c El-Makhzangy, Attya; Ramadan-Hassanien, Mohamed Fawzy; Sulieman, Abdel-Rahman Mohamed (2008). "Darkening of brined olives by rapid alkaline oxidation". Journal of Food Processing and Preservation. 32 (4): 586–599. doi:10.1111/j.1745-4549.2008.00198.x. ISSN 0145-8892.
  6. ^ Ziena, H.M.S.; Youssef, M.M.; Aman, M.E. (1997). "Quality attributes of black olives as affected by different darkening methods". Food Chemistry. 60 (4): 501–508. doi:10.1016/S0308-8146(96)00354-8. ISSN 0308-8146.
  7. ^ a b "A 'greener' way to take the bitterness out of olives". phys.org. Retrieved 23 June 2019.
  8. ^ a b Johnson, Rebecca; Mitchell, Alyson E. (2019). "Use of Amberlite macroporous resins to reduce bitterness in whole olives for improved processing sustainability". Journal of Agricultural and Food Chemistry. 67 (5): 1546–1553. doi:10.1021/acs.jafc.8b06014. ISSN 0021-8561.
  9. ^ Kumral, A.; Basoglu, F. (2008). "Darkening methods used in olive processing". Acta Horticulturae (791): 665–668. doi:10.17660/ActaHortic.2008.791.101. ISSN 0567-7572.
  10. ^ Vincenzo Marsilio; Cristina Campestre; Barbara Lanza (July 2001). "Phenolic compounds change during California-style ripe olive processing". Food Chemistry. 74 (1): 55–60. doi:10.1016/S0308-8146(00)00338-1.