Hydroxytyrosol is a natural phenolic substance that has the chemical formula (HO)2C6H3CH2CH2OH and is classified as a phenyl ethanoid, i.e., a related compound of phenethyl alcohol. Its derivatives are found in natural sources, mainly in olive oil and wine. As a compound it is colourless and solid[1][2] although commercial samples are beige in colour. It is a derived compound of catechol, the presence of which is very important in both edible olives and virgin olive oil[3][4].


Oleuropein, a bitter component found in the skin of the green olive, is an ester of hydroxytyrosol.

Olives, olive leaves and olive pulp contain large amounts of a derivative of hydroxytyrosol, oleuropein. Unprocessed green (unripe) olives contain between 4.3 and 116 mg of hydroxytyrosol per 100 g, while unprocessed ripe black olives contain up to 413.3 mg per 100 g.[5] Olive ripening significantly increases the amount of hydroxytyrosol. [6] Processed olives, such as the common canned olive containing ferrous gluconate (II), contained little hydroxytyrosol, as iron salts are catalysts for its oxidation.[7]



Hydroxytyrosol is considered safe as a novel food for human consumption, with an unobserved adverse effect level of 50 mg/kg body weight per day, as assessed by the European Food Safety Authority (EFSA).8]

In the United States, hydroxytyrosol is considered a safe ingredient (GRAS) in processed foods at levels of 5 mg per serving.[9]

In nature, hydroxytyrosol is produced after the hydrolysis of oleuropein that occurs during olive ripening. Aleuropein accumulates in the leaves and fruits of the olive as a defence mechanism (see secondary metabolites) against pathogens and herbivorous micro-organisms.

During olive ripening or when the olive has been degraded by pathogens or mechanical damage, the enzyme β-glucosidase catalyses the synthesis of hydroxytyrosol through hydrolysis by oleuropein.[10]




Mediterranean diets, characterized by regular olive oil intake, have been shown to have a positive impact on human health, including reduced rates of cardiovascular disease.3][11][12] Research on the consumption of olive oil and its constituents includes hydroxytyrosol and oleuropein, which may inhibit the oxidation of LDL cholesterol - a risk factor for atherosclerosis, heart attack or stroke.[13]

The daily intake of hydroxytyrosol in the Mediterranean diet is estimated to be between 0.15 and 30 mg/day. [14]

The European Food Safety Authority has issued a scientific opinion on health claims related to dietary consumption of hydroxytyrosol and related polyphenol compounds from fruits and olive oil and the protection of blood lipids from potential oxidative damage.[15]

The Authority also concluded that there was a cause and effect relationship between the consumption of hydroxytyrosol and phenolic compounds from olives and olive oil and the protection of blood lipids from oxidative damage,[15] providing a health claim for consumption of olive oil polyphenols containing at least 5 mg of hydroxytyrosol and its derivatives (oleuropein complex and tyrosol) per 20 g of olive oil.[16]


References


1.    «Factors influencing phenolic compounds in table olives (Olea europaea)». Journal of Agricultural and Food Chemistry 60 (29): 7081–7095. July 2012. doi:10.1021/jf3017699. PMID 22720792.
2.    «Hydroxytyrosol, Tyrosol and Derivatives and Their Potential Effects on Human Health». Molecules 24 (10): 2001. May 2019. doi:10.3390/molecules24102001. PMID 31137753.
3.    «Bioactive compounds in wine: Resveratrol, hydroxytyrosol and melatonin: A review». Food Chemistry 130 (4): 797–813. 2012-02-15. doi:10.1016/j.foodchem.2011.08.023. ISSN 0308-8146.
4.    «Hydroxytyrosol and its potential therapeutic effects». Journal of Agricultural and Food Chemistry 62 (7): 1449–1455. February 2014. doi:10.1021/jf405820v. PMID 24479643.
5.    «Showing all foods in which the polyphenol Hydroxytyrosol is found - Phenol-Explorer». phenol-explorer.eu. Ανακτήθηκε στις 2 Ιουλίου 2021.
6.    «Table olives and health: a review». Journal of Nutritional Science 9: e57. 2020. doi:10.1017/jns.2020.50. PMID 33354328.
7.    «Phenolic compounds change during California-style ripe olive processing». Food Chemistry 74 (1): 55–60. July 2001. doi:10.1016/S0308-8146(00)00338-1.
8.    «Safety of hydroxytyrosol as a novel food pursuant to Regulation (EC) No 258/97». EFSA Journal. European Food Safety Authority 15 (3): e04728. March 2017. doi:10.2903/j.efsa.2017.4728. PMID 32625437.
9.    «GRAS notice for hydroxytyrosol». US Food and Drug Administration. 13 Μαΐου 2016. Ανακτήθηκε στις 2 Ιουλίου 2021.
10.    «Factors influencing phenolic compounds in table olives (Olea europaea)». Journal of Agricultural and Food Chemistry 60 (29): 7081–7095. July 2012. doi:10.1021/jf3017699. PMID 22720792.
11.    «Hydroxytyrosol and its potential therapeutic effects». Journal of Agricultural and Food Chemistry 62 (7): 1449–1455. February 2014. doi:10.1021/jf405820v. PMID 24479643.
12.    «The Mediterranean Diet and Cardiovascular Health». Circulation Research 124 (5): 779–798. March 2019. doi:10.1161/CIRCRESAHA.118.313348. PMID 30817261.
13.    «Effects of Olive Oil and Its Minor Components on Cardiovascular Diseases, Inflammation, and Gut Microbiota». Nutrients 11 (8): 1826. August 2019. doi:10.3390/nu11081826. PMID 31394805.
14.    «Hydroxytyrosol protects from aging process via AMPK and autophagy; a review of its effects on cancer, metabolic syndrome, osteoporosis, immune-mediated and neurodegenerative diseases». Pharmacological Research 143: 58–72. May 2019. doi:10.1016/j.phrs.2019.03.005. PMID 30853597.
15.    «Scientific Opinion on the substantiation of health claims related to polyphenols in olive and protection of LDL particles». European Food Safety Authority (στα Αγγλικά). Ανακτήθηκε στις 13 Απριλίου 2021. From oxidative damage (ID 1333, 1638, 1639, 1696, 2865), maintenance of normal blood HDL cholesterol concentrations (ID 1639), maintenance of normal blood pressure (ID 3781), “anti-inflammatory properties” (ID 1882), “contributes to the upper respiratory tract health” (ID 3468), “can help to maintain a normal function of gastrointestinal tract” (3779), and “contributes to body defences against external agents” (ID 3467) pursuant to Article 13(1) of Regulation (EC) No 1924/2006
16.    «EU Register of nutrition and health claims made on foods (v.3.6)». ec.europa.eu. Ανακτήθηκε στις 13 Απριλίου 2021.