Polyphenols in Olive Oil Explained: Benefits, Sources, and Uses

Summary: Polyphenols in olive oil

Polyphenols are antioxidant compounds in olive oil responsible for its bitterness and pungency, and most of its health benefits. The main polyphenols in olive oil are oleacein, oleocanthal, oleuropein, hydroxytyrosol, and tyrosol, each having its own sensory characteristics and health benefits. Polyphenols are antioxidants, anti-inflammatories, and anti-cancer, and are reported to prevent metabolic disorders and chronic diseases. Only olive oils that have 5 mg of biophenols per 20 g of oil can make the health claim, as per the European Commission Regulation No. 432/2012.

Key Takeaways

• Polyphenols are the most important compounds in olive oil from sensory and health  benefit perspectives.
• Oleuropein and its derivatives, oleacein, are responsible for bitterness at the back of the tongue.
• Oleocanthal and ligstroside bring spiciness (pungency) or a burning sensation to the throat.
• Tyrosol, hydroxytyrosol, oleacein, oleocanthal, and oleuropein are the major phenolic compounds in olive oil.
• Phenolic compounds are reported as anti-oxidant, anti-inflammatory, and anti-microbial, and provide several health benefits to humans. 
• Polyphenols can have therapeutic effects against chronic and inflammatory diseases, such as cardiovascular disease, diabetes, Alzheimer’s, obesity, and aging, etc.
• Polyphenols are said to have anti-inflammatory, antioxidant, neuroprotective, cardioprotective, gastroprotective, anti-obesity, and anti-microbial effects.
• Biophenols such as hydroxytyrosol and oleocanthal have chemopreventive effects against several cancers.
• The only olive oil that has at least 0.025% (wt/wt) of polyphenols (tyrosol, hydroxtyrosol, and their derivatives) (or 5 mg of polyphenols in 20 g of oil) is eligible to claim health benefits as per EU regulation (European Commission Regulation EC No. 432/2012). 
• Polyphenols provide stability to oil from oxidation and heat. They extend the shelf life of oil. This makes makes high polyphenol olive oil such as Picual oil suitable for cooking.
• Several factors, genetic (cultivar or variety of olive), geographical/ climatic,        agronomic, fruit ripeness and its storage time, and technical aspects of the oil        extraction  process, affect the polyphenol content in olive oil.
• Polyphenol content claimed on the label should be taken with caution. Without a unit of measurement, it is not meaningful.
• Total polyphenol is usually measured in terms of caffeic acid, and biophenol in terms of tyrosol. 

What are polyphenols?

Phenolic compounds, aka polyphenols, are the most important and engaging group of natural chemicals for any olive oil consumer. Despite a general understanding of them being a single compound, polyphenols in the EVOO are a group of compounds having broad functional groups (chemical families). They are a constituent of the polar fraction (water-soluble) of olive oil.

Generally speaking, benzene rings bearing one or more hydroxyl groups are identified as phenols. In addition, their derivatives are also phenolic compounds.

Main phenolic compounds in olive oil

There are about 30 different phenolic compounds in olive oil. These compounds are mainly categorized into five different polyphenol classes. Some of the phenolic compounds in olive oil are simple phenolic acids and phenolic alcohols.

Some phenolic compounds are derivatives (connected with other molecular subunits) of phenolic alcohols.

Gallic acid, para-hydroxybenzoic acid, and caffeic acid are a few examples of the simple phenolic acids. Likewise, hydroxytyrosol, tyrosol, and tyrosol acetate are examples of phenolic alcohols.

Phenolic alcohols (tyrosol, hydroxytyrosol) and secoiridoids are the most important polyphenol class and represent around 90% of the total phenolic compounds. The secoiridoids are the ester derivatives of phenolic alcohols, such as hydroxytyrosol and tyrosol, with elenolic acid. Oleuropein and ligstroside are the secoiridoid derivatives of hydroxytyrosol and tyrosol, respectively.

Oleacein, oleocanthal, oleuropein, tyrosol, and hydroxytyrosol are the main polyphenols in olive oil.

How olive oil polyphenols form and relate

Chemically, secoiridoids have three subunits in their molecular structures: a glucose unit, elenolic acid, and phenolic alcohol. Oleuropein and ligstroside are two major secoiridoid derivatives of hydroxytyrosol and tyrosol, respectively.

Oleuropein = glucose + elenolic acid + hydroxytyrosol, and

Ligstroside = glucose + elenolic acid + tyrosol

During the malaxation process (or mixing or churning of the olive paste), polyphenols transfer from the fruit to the oil.

During this process, certain enzymes present in the olive fruit catalyze the removal of a glucose unit from oleuropein and ligstroside, forming their corresponding aglycones (Structure without the glucose subunit. Aglycone = elenolic acid + phenolic alcohol).

More water-soluble polyphenols stay with the vegetable water, while more oil-soluble polyphenols migrate to the oil.

The aglycones are less soluble in water due to the loss of the glucose unit and dissolve more in the nonaqueous medium of olive oil. In the oil matrix, they modify into open-ring dialdehydic forms, such as oleocanthal and oleacein, and other cyclic monoaldehydic forms.

Polyphenols and quality of olive oil

Polyphenols are key to the quality of olive oil. The flavors such as bitterness, spiciness, and astringency are due to polyphenols. The positive gustatory (taste) attributes, such as bitterness, are due to oleacein and oleuropein, and spiciness or pungency is due to oleocanthal.

Bitterness and pungency indicate the freshness of olive oil and signal that the olive oil is healthy.

Due to the high antioxidative property, a polyphenol-rich olive oil is resistant to oxidation during cooking and storage. For instance, KORAJE is high polyphenol Picual oil has a longer shelf life due to its high polyphenol content.

An early-harvest olive oil has a higher content of polyphenols and tastes more bitter and spicy than a late-harvest or ripe olive oil.

As the olive fruit ripens, its polyphenol content goes down. For that reason, an early harvest olive oil has higher polyphenols and a late harvest olive oil oil has lower polyphenols.

Factors affecting phenolic content in olive oil

Genetic or cultivated variety (Cultivar) is the variable that determines the polyphenol content in olive oil the most. For instance, Picual and Cornicabra are high polyphenol Spanish olive varieties.

The climatic (altitude, temperature), agronomic (irrigation, soil chemistry), health, stage of ripeness, and duration of storage of the fruit, and extraction conditions (temperature, oxygen level), etc., also are the significant factors affecting phenolic content in olive oil.

Health benefits of polyphenols

Polyphenols in olive oil are reported to have several health benefits. The health benefits of polyphenols are mainly due to antioxidant, anti-inflammatory, cardioprotective, and neuroprotective properties of hydroxytyrosol, oleocanthal, oleacein, and oleuropein.

Several scientific studies have shown that regular olive oil consumption may lead to a decrease in the chances of metabolic disorders and other chronic diseases, such as diabetes, obesity, stroke, high blood pressure, asthma, arthritis, atherosclerosis, and cholesterol-related conditions.

According to European Commission Regulation EC No. 432/2012, only olive oil that has at least 5 mg of tyrosol, hydroxytyrosol, and their derivatives in 20 g of olive oil can claim olive oil health benefits.

KORAJE has 8 mg+ of bioactive healthy polyphenols per 20 g of the oil.

How polyphenols are metabolized in the human body

In the fruit, the polyphenols exist in glycoside (glucose derivative) forms. Since they are polar and are soluble in water, olive oil mainly contains water-insoluble aglycone forms.

In an acidic environment of the stomach, they undergo partial hydrolysis, releasing free acidic phenol or phenolic alcohol forms- tyrosol, and hydroxytyrosol.

However, this reaction occurs only to a small extent, and the majority of the phenolic compounds remain unmetabolized. When they reach the small intestine, their main absorption happens.

Measurement of phenolic compounds in olive oil

Measurement of phenolic compounds in olive oil can be done by a number of analytical techniques. Gas chromatography-mass spectrometry (GCMS), high-performance liquid chromatography-diode array detector (HPLC-DAD), colorimetry, and Nuclear Magnetic Resonance (NMR) spectroscopy are some of the common techniques.

Total phenolic content in olive oil is analyzed by colorimetric method using Folin-Ciocalteu reagent (FC reagent) and the biophenols in olive oil are measured by HPLC-DAD method. Both of the techniques measure relative and not absolute amount of polyphenols or biophenols. The FC reagent method measures total polyphenols as caffeic acid equivalent and the HPLC method measures tyrosol equivalent in terms of mg of either caffeic acid or tyrosol in one kilogram of oil.

The polyphenol amount without a unit does not mean anything. So, whatever the number, large or small, they mean the same thing depending on the unit in which they are expressed. For that reason, polyphenol value on the label of an olive oil should be read with caution.

FAQ

Are biophenols and polyphenols the same?

Polyphenols and biophenols are sometimes used interchangeably. However, they are not the same terms. Polyphenols are an umbrella term under which fall biophenols. Not all polyphenols have biological activity. So, phenols or polyphenols having bioactivity are called biophenols.

To distinguish, gallic acid, ferulic acid, or caffeic acid are polyphenols and may or may not have a strong therapeutic effect, so they are not biophenols. In contrast, hydroxytyrosol or oleocanthal are polyphenols and have multiple therapeutic effects and thus are biophenols.

Simply, all biophenols are polyphenols, but not all polyphenols are biophenols.

Which olive oil polyphenol is like ibuprofen in function?

Oleocanthal is similar to ibuprofen in its anti-inflammatory effect. It is the polyphenol responsible for the peppery back of throat- kick produced by fresh olive oil. 

What causes the bitterness in olive oil?

Oleacein and oleuropein are polyphenols that cause bitterness in the mouth when tasting olive oil. Bitterness is a positive olive oil quality indicator. A fresh and unoxidized olive oil has higher bitterness intensity than an old and oxidized olive oil. The early-harvest olive oil is more bitter than the late-harvest olive oil.

Is hydroxytyrosol good for you?

Hydroxytyrosol is good for human health. It has strong antioxidative potency and destroys disease-causing free radicals by its scavenging effect. It has shown positive effects on several diseases.

References

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