For producers and bottlers of extra virgin olive oils, controls that determine their quality and freshness are essential. The checks to be carried out concern chemical and sensory analyses. The main chemical analyses that provide the first and fundamental indications on quality are: theof lactic acidity; peroxides; the K232 values, 270, Delta K; total polyphenols and tocopherols.
The chemical parameters
Olive oil, as we know, is made up of 98-99% fats - triglycerides - where each of them is given by a chemical bond where the three fatty acids join with an alcohol molecule, glycerol. This bond between fatty acids and glycerol is not strong and even simple actions, such as the contact of the oil with air or the work of enzymes, cause their splitting, which is defined as oxidation. The oxidation process, which releases glycerol from the three fatty acids, results in a increase in acidity. The acidity of an olive oil, therefore, measures the amount of free fatty acids present there. To define its acidity it was taken as reference conventional oleic acid, because it is the fat mostly present in olive oil. This is why the acidity of olive oil is expressed in grams of free oleic acid per 100 grams of oil and, to belong to the extra virgin category, this value must be equal to or less than 0,8%.
Another chemical analysis to be performed is the determination of peroxides, which they indicate the oxidation of unsaturated fats and are expressed in milliequivalents/kilogram. Peroxides are formed byaction of oxygen present in the air which oxidizes fats, but it can also happen due to the effect of enzymes naturally contained in the olive, such as lipase and lipoxidase. The legislation requires that the values of peroxides be equal to or less than 20, above there would be a lampante oil. The oxidations that occur in the oil will, over time, give rise to aldehydes and ketones, compounds that are responsible for the rancid sensorial defect.
The tests on the evaluation of fat oxidation continue with investigations on subsequent transformations of fatty acids after oxidation, which lead to the formation of compounds with double bonds, called dienes, or with three double bonds, called trienes. These new compounds are determined based on the their ability to absorb ultraviolet light at wavelengths of 232 – 270 – 268 nanometers.
So we have two values: the value called K232 which detects the formation of dienes, which arise when land olives are overly ripe o damaged or attacked by the fly, or if one is implemented kneading in non-optimal conditions or if there is afraudulent addition of rectified oil. High K232 values give rise to the presence of defects such as wormy or cooked. The current legislation provides one maximum value for extra virgin olive oil equal to 2,50.
The other value is called K270 and detects the formation of trienes, which are able to compromising the taste and quality of the oil itself and not to make it extra virgin anymore: its value can also increase following a prolonged storage. According to current legislation the maximum value for extra virgin olive oil it is 0,22.
Il Delta K parameter, finally evaluates the state of secondary oxidation of extra virgin olive oil, i.e. if the structure of the oil has changed further after the formation of the double bonds into conjugated triple bonds. The maximum value expected for extra virgin olive oil is 0,01.
Polyphenols
The quality of an oil is also expressed by the presence of polyphenols, responsible for the bitter and spicy taste: they are antioxidant substances and help the oil to be preserved over time as they protect it from the oxidative action of air and enzymes. There is no precise and universal value that defines an "excellent" polyphenol content, since this can vary significantly based on different factors (variety of olives, production area, degree of ripeness, processing method, etc.) Generally, a good extra virgin olive oil is considered to be one with a polyphenol content greater than 200 mg/kg. However, high quality oils can reach levels exceeding 500 mg/kg, and in some cases even 1000 mg/kg. Another important group of antioxidants are tocopherols, also defined as provitamin E.
The panel test
European legislation (EC Regulation 2568/91 and following) It also provides for the correct classification of virgin olive oils, the obligation of sensory analysisThis occurs through the panel tests entrusted to a qualified group of tasters who objectively evaluates the organoleptic characteristics of a product, assigning it the correct commercial category (extra virgin, virgin, lampante).
The classification is given taking into account the positive attributes (fruity, bitter and spicy) and the possible presence of defects (heated, lees, mould, winey, vinegary, rancid, others).
AIPO Director
Interregional Association
Olive producers
