The physicochemical properties that classify an olive oil are:

  • the free acidity,
  • the peroxide value and
  • the UV absorption spectrum.

Degree of free acidity: Is one of the quality parameters that determine the quality of the olive oil. Defined as the amount of free fatty acids in olive oil and is expressed as a percentage (%) of acid found in oil. The values are used to classify the various types of oil: extra virgin, virgin and simple olive oil.

Peroxide value: measures the oxidation state of the oil, by determing the concentration of peroxides in the sample. The peroxides are primary oxidation compounds that occur during processing and storage of oil, as a consequence of the presence of oxygen. In a second stage of oxidation, the peroxides decompose in different final products of oxidation. The peroxide value, as well as acidity, are used to determine the categories of oil. To classify an oil as extra virgin, the maximum peroxide value must not exceed 20 kilograms per kilo for olive oil.

UV absorption spectrum: is another indicator used to determine the quality of the oil. This measurement provides information about the quality of the oil situation and in particular to determine the extent of oxidative deterioration. It is measured at two wavelengths, 232 and 270 nm. In the first wavelength absorb primary oxidation products (conjugated peroxides), while in the second the secondary oxidation products (aldehydes, ketones). The difference (DK) absorption gives information on the state of oxidation of the oil. The lower the value, the higher the quality of the oil, with a maximum value 0.01 for the extra virgin olive oil.