According to the European protocol, from a strictly chemical point of view an olive oil to be called "EXTRAVIRGIN" need to be within certain values for the following parameters:
• Acidity < 0,8
• Peroxides < 20
• Spectometry UV k232 < 2,5
• Spectometry UV k 270 < 0,22
• ΔK < 0,01
Polyphenols are not part of the panel but are a key element to evaluate extra virgin olive oil benefits
Polyphenols
Polyphenols in extra virgin olive oil are one of the most important parameters for determining the quality of extra virgin olive oil.
From a chemical point of view, these substances (also called biophenols) prevent oxidation reactions, and are therefore antioxidants and contribute to the stability of the oil over time by delaying the denaturation of fatty acids in it and, therefore, its rancidity.
Along with this, polyphenols can play a fundamental role in our diet; in fact, numerous studies attest to the active function of phenols as antioxidants (protecting cells from damage caused by free radicals), anti-tumours, antithrombotic (inhibiting the coagulation of bad cholesterol - LDL) and anti-inflammatory substances.
Moreover, polyphenols influence the olive oil’s organoleptic properties, determining the fruity aroma and the spicy or bitter taste characteristic of extra virgin olive oil.
A good extra virgin olive oil must contain at least 350 mg/kg of polyphenols.
From a strictly chemical point of view, for an oil to be defined as “EXTRA VIRGIN” it must have the following parameters: acidity < 0.8 peroxides < 20 UV spectrophotometry k232 < 2.5 UV spectrometry k 270 < 0.22 delta k < 0.01 5.2.2.
Acidity, peroxides and spectrometry
What differentiates a pure extra virgin olive oil is the process used to obtain it.
To be extra virgin, the oil must be extracted from the olives by purely mechanical processes, such as pressing or centrifugation.
Among these olive oils only the purest ones with the best organoleptic properties are selected as extra virgin olive oil.
The quality criteria applicable to extra virgin olive oil in general are:
Acidity.
It is a chemical parameter used to determine the amount of free fatty acids. Lower acidity corresponds to higher quality.
Thus, heartburn is a general indicator of poor-quality extra virgin olive oil.
The high acidity can be caused by the poor condition of the fruit, contamination by natural parasites and, finally, poor preservation.
By law, the acidity limit for an extra virgin olive oil is 0.8%, but in a quality extra virgin olive oil the values are much lower (0.1-0.3%).
Peroxides.
These determine the initial oxidation of an oil, and also indicate the damage that may have affected natural antioxidants such as tocopherols and polyphenols.
It is measured in mEqs of active oxygen per kg. According to the law, the limit on the number of peroxides in an extra virgin olive oil is 20, above which the oil is considered to be lampante oil and therefore of low quality.
The unit of measurement of peroxides is expressed in mEq O2/kg (milliequivalents of active oxygen per kg of oil); a somewhat complicated concept but the important thing is to know that the value is considered good if below 12, excellent below 7.
A high number of peroxides shows the beginning of an irreversible oxidation process; the result is the progressive degradation of many fundamental compounds for our diet (vitamins, polyphenols, etc.) as well as the gradual rancidity of the oil which also becomes unpleasant to the taste.
UV spectrophotometry (ultraviolet) K 270, K 232.
This measures the absorption of an oil at different lengths of certain ultraviolet waves and can be useful to identify if there has been any refining or manipulation in the laboratory.
An increase of K232 shows primary oxidation, with peroxide formation. This parameter increases if excessively ripe olives have been processed, damaged by careless harvesting, strongly attacked by oil flies or stored for a long time before extraction in the oil press. Even the latter, if conducted in an inadequate manner (such as long pressing performed at temperatures above 30°c) can significantly alter the value of K232.
For extra virgin olive oils, the law sets a maximum value of 2.5.
K270 measures the absorption of ultraviolet light at a wavelength of 270 nanometres and indicates the state of secondary oxidation with the formation of aldehydes and ketones.
As previously reported, these compounds are closely related to the rancidness and, therefore, are a very important indicator of the state of preservation of the oil. The quality of the raw material and the conduct of the extraction operations, in fact, do not significantly influence this parameter, while the value of the same may increase during storage and aging of the product.
For extra virgin olive oils, the law sets a maximum value of 0.22.
ΔK measures absorption at a wavelength of 268 nm and expresses, like K270 , the secondary oxidation state not affected by the quality of the raw material.
For extra virgin oils, the law sets a value of ΔK ≤ 0.01.
In refined oils the values of K270 and ΔK are generally much higher than those found in virgin oils and, therefore, it is possible to use these parameters to detect fraud and possible contamination.
Alkyl-Esters (AE)
During 2011, the European Community formalised a new parameter for assessing the quality of olive oils: alkyl esters.
Alkyl esters (ethyl and methyl esters of fatty acids) are organic compounds that originate from the esterification of fatty acids with alcohols.
This is due to fermentation and degradation phenomena that develop into poor quality olives and lead directly to the production of lampante oils.
The more alkyl esters there are, the poorer the quality of the oil as the olives from which it was extracted were poor. It is not possible to eliminate them through illegal processes of deodorisation to which poor quality oils can be subjected.
Deodorisation is a fraudulent treatment that eliminates most of the volatile compounds, including those responsible for bad odours or defects in the oil. During this treatment, the alkyl esters remain in the oil, thus constituting excellent tracers to really establish the original quality of the product.
For extra virgin olive oils the EU Regulation 61/2011 has established a total value in alkyl esters (sum of ethyl and methyl esters) not exceeding 75 mg/kg. This parameter is to be considered very high compared to the normal values of total alkyl esters (much lower) that an extra virgin olive oil must possess.
Precisely for this reason, at the request of some European countries, it was considered necessary to initiate procedures to lower this threshold to 15-20 mg/kg, a value found in quality extra virgin olive oil.