The Olive Oil Quality Criteria

Olive Oil Quality Criteria
The Olive Oil Quality Criteria

The quality of the olive oil is significantly influenced by a multitude of factors that may be present even during the fruit's development stage due to contact with pests, micro-organisms, humidity, oxygen, bright light, temperature and is determined by measuring certain physico-chemical parameters.


  • Free acidity
  • Number of peroxides
  • Absorption in the ultraviolet
  • Moisture and volatile matter
  • Impurities
  • Traces of metals
  • Alkyl esters


Sensory evaluation (only for virgin olive oils)


Free acidity in olive oil is defined as the determination of the free fatty acid content of olive oil and is expressed in grams of oleic acid per 100 grams of olive oil.
A special enzyme, lipase, found in the olive fruit, acts lipolytically specifically on positions 1 and 3 of triglycerides and results in the production of free fatty acids (responsible for the acidity of olive oil).

Factors that affect acidity:

  • Humidity
  • Temperature
  • Enzymes
  • Various microorganisms

Olive oil acquires higher acidity when:

  • The olive has remained on the tree for a long time.
  • The olive has been infested by olive fly larvae.
  • The cells of the olive have been damaged.
  • The olive has been stored in a pile for an extended period.
  • The olive oil comes into prolonged contact with waste water.
  • The temperature is 35-40o C.

Olive oil acquires lower acidity when:

  • The olive is healthy, with no damaged cells
  • The olive is stored in a cool, well-ventilated place during the period when it has to be kept in a mill.
  • The time the olives remains in the mill is limited.

Number of peroxides

Peroxide are chemical compounds created by the effect of oxygen in the olive oil. The number of peroxides is due to hydroperoxides, which are products of the primary stage of oxidation of the unsaturated fatty acids of triglycerides.

The oxidation may be enzymatic or chemical

Enzymatic oxidation is due to the action of lipoxidases, enzymes present in the olive. When the olive oil is separated from the wastewater in the mill, these enzymes, which are water-soluble proteins, are removed with the wastewater. In this way the olive oil ceases to be subject to the action of the enzymes. Chemical oxidation takes place during the preservation of the olive oil through a free radical mechanism.

Factors that affect the number of peroxides

The application of proper agricultural practices during cultivation and harvesting, the observance of proper storage practices, as well as the application of proper industrial practices throughout the olive oil production process at the mill, promote the production of low peroxide olive oil.
Lipoxidase enzymes act oxidatively as long as there is contact between the oil and the wastewaters, either because the cells have been broken during harvesting and storage or during breaking and milling operations.

Lipoxidase activity varies with temperature, but these enzymes are active even at -40o C. Chemical oxidation is favoured by light, high temperature, the presence of oxygen, and metallic elements. High peroxides indicate that the olive oil has undergone radical oxidative or other deterioration and are associated with a reduction in shelf life. Determining the concentration of peroxides therefore allows us to draw conclusions about the age and type of storage (under appropriate or inappropriate conditions) of the olive oil.

Spectrophotometric examination in ultraviolet

The spectrophotometric examination in the UV is the absorptions at wavelengths of 232nm and 270nm, conventionally represented by K. The IC index is defined as a mathematical relationship for calculating UV absorption coefficients.

The absorption at 232nm is due to

  • Hydroperoxides, which are produced in a primary oxidation step.
  • Cybrid dienes, which are produced in an intermediate oxidation state.
    (The value of the absorption coefficient K232 increases when the olive is stored for several days before it is crushed and the olive oil has been stored in unsuitable conditions).
    The absorption at 270nm is due to:
  • Carbonyl groups (ketones and aldehydes), which are secondary oxidation products.
  • Containing trienes, which are produced when the olive oil is subjected to industrial processing.

The value of the absorption coefficient K270 depends on how fresh the olive oil is. Old olive oil or blends with old olive oil have increased K270 values. In addition, the value of K270 is very low immediately after bottling and increases with the age of the olive oil. Exposure of the olive oil to sunlight or high temperatures accelerates the progress of ageing

Factors that affect ultraviolet absorption as a quality criterion

Taking into consideration the fact that the substances responsible for ultraviolet absorption (as a quality criterion) are products of oxidative reactions, it is obvious that air, light, temperature and traces of metallic elements are factors that affect ultraviolet absorption.

Therefore, prolonged storage of olive oil must be avoided and care should be taken during storage to ensure that the olive oil:

  • is protected from light.
  • is protected from air.
  • is carefully decanted during the process of removing the solid residue that has settled, avoiding contact with air and exposure to light.
  • is not stored in iron barrels.
  • is kept in clean and cool places.
  • is stored in glass containers, kept in a dark place.

Organoleptic evaluation of virgin olive oils


Organoleptic evaluation is the detection and description of the qualitative and quantitative olfactory-tasting characteristics of virgin olive oil using the human senses and its classification according to its organoleptic characteristics.

Method for the organoleptic evaluation

The method uses a group of tasters selected and trained and is applied only to classify it according to the perceived intensity of the defect perceived with the greatest intensity and the presence or absence of fruitiness.

The organoleptic characteristics of virgin olive oil are divided into three categories

  • Negative properties
  • Positive properties
  • Other negative properties

Research has shown that

The substances responsible for the negative organoleptic properties are not present in good quality olives. These substances are secondary products of oxidation or enzymatic reactions.

Factors adversely affecting organoleptic characteristics

  • Unhealthy olives.
  • Unfriendly way of harvesting the olives.
  • Prolonged storage of the olives or storage in unsuitable conditions.
  • Fermentation of the pulp remaining in the olive oil.
  • Excessive or prolonged heating during the production of olive oil, particularly during the heat treatment of olive paste.
  • Incomplete or untimely separation of the olive oil.
  • Use of equipment in the mill that may cause contamination of the olive oil.
  • Inappropriate or prolonged storage of olive oil.