Oleuropein Explained

Oleuropein is a glycosylated seco-iridoid, a type of phenolic bitter compound found in green olive skin, flesh, seeds, and leaves.[1] The term oleuropein is derived from the botanical name of the olive tree, Olea europaea.

Because of its bitter taste, 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.[2] [3]

Chemical treatment

Oleuropein is a derivative of elenolic acid linked to the orthodiphenol hydroxytyrosol by an ester bond and to a molecule of glucose by a glycosidic bond.[4] 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 of these derivatives, facilitating their release into the lye solution.[5] [6]

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).[7] [8]

The lye solution is replaced several times until the bitter taste has dissipated. 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.[11]

Green olive blackening

Green olives may be treated industrially with ferrous gluconate (0.4 wt. %) to change their color to black.[12] 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 hydroxytyrosol, as iron salts are catalysts for its oxidation.[13]

Research

Oleuropein has been proposed as a proteasome activator.[14] [15]

See also

Notes and References

  1. Web site: The bitter truth about olives. Rupp R.. 1 July 2016. National Geographic. 24 June 2019. 10 July 2019. https://web.archive.org/web/20190710080202/https://www.nationalgeographic.com/people-and-culture/food/the-plate/2016/07/olives--the-bitter-truth/. dead.
  2. Web site: How olives are made. California Olive Committee. 2017. 5 August 2017. https://web.archive.org/web/20170805183626/http://calolive.org/our-story/how-olives-are-made/. 5 August 2017. dead.
  3. Web site: Colmagro S. . Collins G. . Sedgley M. . Processing technology of the table olive . 25 June 2019 . 9 August 2017 . https://web.archive.org/web/20170809155640/http://ucanr.edu/datastoreFiles/608-760.pdf . live .
  4. Panizzi. L.. Scarpati. M.L.. Oriente. E.G.. 1960. Structure of the bitter glucoside oleuropein. Note II. Gazzetta Chimica Italiana. 90. 1449–1485.
  5. Yuan. Jiao-Jiao. Wang. Cheng-Zhang. Ye. Jian-Zhong. Tao. Ran. Zhang. Yu-Si. Enzymatic hydrolysis of oleuropein from Olea Europea (olive) leaf extract and antioxidant activities. Molecules. 20. 2. 2015. 2903–2921. 1420-3049. 10.3390/molecules20022903. 25679050. 6272143. free.
  6. Ramírez. Eva. Brenes. Manuel. García. Pedro. Medina. Eduardo. Romero. Concepción. Oleuropein hydrolysis in natural green olives: Importance of the endogenous enzymes. Food Chemistry. 206. 2016. 204–209. 0308-8146. 10.1016/j.foodchem.2016.03.061. 27041317. 10261/151764. free. 2019-09-27. 2018-07-23. https://web.archive.org/web/20180723221236/http://digital.csic.es/bitstream/10261/151764/1/Postprint_2016_FoodChem_V206_P204.pdf. live.
  7. El-Makhzangy. Attya. Ramadan-Hassanien. Mohamed Fawzy. Sulieman. Abdel-Rahman Mohamed. Darkening of brined olives by rapid alkaline oxidation. Journal of Food Processing and Preservation. 32. 4. 2008. 586–599. 0145-8892. 10.1111/j.1745-4549.2008.00198.x. free.
  8. Ziena. H.M.S.. Youssef. M.M.. Aman. M.E.. Quality attributes of black olives as affected by different darkening methods. Food Chemistry. 60. 4. 1997. 501–508. 0308-8146. 10.1016/S0308-8146(96)00354-8.
  9. Web site: A 'greener' way to take the bitterness out of olives. phys.org. 23 June 2019. 23 June 2019. https://web.archive.org/web/20190623104729/https://phys.org/news/2019-01-greener-bitterness-olives.html. live.
  10. Johnson. Rebecca. Mitchell. Alyson E.. Use of Amberlite macroporous resins to reduce bitterness in whole olives for improved processing sustainability. Journal of Agricultural and Food Chemistry. 67. 5. 2019. 1546–1553. 0021-8561. 10.1021/acs.jafc.8b06014. 30636418. 58570570. 2021-05-18. 2020-06-26. https://web.archive.org/web/20200626231400/https://escholarship.org/uc/item/2sg8n70x. live.
  11. Restuccia. Cristina. Muccilli. Serena. Palmeri. Rosa. Randazzo. Cinzia L.. Caggia. Cinzia. Spagna. Giovanni. An alkaline β-glucosidase isolated from an olive brine strain of Wickerhamomyces anomalus. FEMS Yeast Research. 11. 6. 2011. 487–493. 1567-1356. 10.1111/j.1567-1364.2011.00738.x. 21575132. free.
  12. Kumral. A.. Basoglu. F.. Darkening methods used in olive processing. Acta Horticulturae. 791. 2008. 665–668. 0567-7572. 10.17660/ActaHortic.2008.791.101.
  13. 10.1016/S0308-8146(00)00338-1 . Phenolic compounds change during California-style ripe olive processing . Vincenzo Marsilio . Cristina Campestre . Barbara Lanza . Food Chemistry . 74 . 1 . July 2001 . 55–60.
  14. Katsiki. Magda. Chondrogianni. Niki. Chinou. Ioanna. Rivett. A. Jennifer. Gonos. Efstathios S.. June 2007. The olive constituent oleuropein exhibits proteasome stimulatory properties in vitro and confers life span extension of human embryonic fibroblasts. Rejuvenation Research. 10. 2. 157–172. 10.1089/rej.2006.0513. 1549-1684. 17518699. 2020-10-15. 2020-11-15. https://web.archive.org/web/20201115110544/https://pubmed.ncbi.nlm.nih.gov/17518699/. live.
  15. Zou. Ke. Rouskin. Silvia. Dervishi. Kevin. McCormick. Mark A.. Sasikumar. Arjun. Deng. Changhui. Chen. Zhibing. Kaeberlein. Matt. Brem. Rachel B.. Polymenis. Michael. Kennedy. Brian K.. 2020-08-01. Life span extension by glucose restriction is abrogated by methionine supplementation: Cross-talk between glucose and methionine and implication of methionine as a key regulator of life span. Science Advances. en. 6. 32. eaba1306. 10.1126/sciadv.aba1306. 32821821. 7406366. 2020SciA....6.1306Z . 2375-2548. free.

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