Below is given a short description of some of the most important quality chemical parameters and their correlation with the quality of extra virgin olive oils.

ACIDITY

It shows the presence of a hydrolytic oxidation phenomenon and its progress. In a extra virgin olive oil should not exceed 0.8%.
The value of acidity gives us information about the quality of the raw material: damaged olives,
attacked by the fly, harvested in an advanced ripening state or preserved badly for a long time before squeezing give oils with a high acidity. Even kneading at high temperature or non-filtration can give high acidity values and consequently oils that, to sensory analysis will be defined as defective. In a quality extra virgin oil, the values must be around 0.1-0,5%.
This parameter, while important, not evaluable by sensory analysis, is not sufficient to define the quality of an oil and is therefore necessary to support other parameters.

PEROXIDES NUMBER’S

They are used to assess the storage status of a fat. Peroxides are in fact the product of primary rancidity reports. Over the limit of 20 meq 0₂/kg the oil is no longer marketable for food purposes.
The number of peroxides may increase due to poor raw material conditions, high temperature during kneading but above all by storage conditions of olive oil, in fact contact with oxygen can have a significant impact.

UV SPECTROPHOTOMETRY 

Includes K232, K270 and K values, parameters that measure the absorption of ultraviolet light by oil.

K232 measures the absorption of ultraviolet light at a wavelength of 232 nanometers and indicates whether the olive oil structure has changed as a result of oxidation. This parameter can increase if olives are overly ripe, damaged or attacked by the fly, if the kneading is done in non-optimal conditions and if there is a fraudulent addition of adjusted oil, conditions that sensory analysis can be detected through defects such as worm or hint of cooked. Under current law, the maximum value for extra virgin olive oil is 2.5.
K270 measures the absorption of ultraviolet light to a wavelength of 270 nanometers while K depends on the absorption of ultraviolet light at wavelengths close to 268 nanometers, both indicate the state of secondary oxidation, i.e. whether the structure of the oil has changed further after the formation of double bonds (in technical terms, if even triple conjugated bonds are formed).
Olives and the production process don’t affect these parameters, which may increase during storage and in the case of fraudulent rectification treatments.
For extra virgin olive oil, the maximum value for K270 is 0.22, for ΔK is 0.01.

PHENOLIC AND TOCOFERL COMPOUNDS

They represent the antioxidant heritage of oils. The presence of antioxidant compounds allows you to define a higher level of product quality than that related to the product classification.
The content of these compounds depends on various factors, including the maturation of olives, the parameters of processing and the preservation of olive oil over time.
Olives harvested with a high phenolic content can give rise to oils rich in compounds antioxidants if you are working under reduced oxidative stress and without the addition of water in the process.
Extra virgin olive oils is rich in antioxidants (phenolic compounds) have a high resistance to aging, a high intensity of the “bitter” and “spicy” descriptors and high health properties.