Chemical analyzes of an olive oil are a fundamental step (although not the only one) for evaluating its quality and categorization as Extra Virgin Olive Oil (EVO).
The reports issued by ACCREDIA accredited laboratories should always be requested from the mill or the farm that sells the oil before purchase.
Too often we read advertisements with claims such as “very high quality”, “very low acidity”, vague in meaning and without any independent proof.
But even once you have obtained the report, you must know how to read it and then form an opinion based on valid scientific data for all oils of any origin and variety.
The values present in the report, as for blood tests, give indications on the general health of the oil or on the contrary indicate where there is a “suffering”.
In this article we will describe their meaning and indicate the values that determine good, very good or sufficient quality.
What does it indicate
Acidity indicates a lipolytic alteration, expressed in grams of oleic acid per 100 grams of oil (%); it is determined by laboratory analysis (acid-base titration), while it is not perceptible at the organoleptic level. The acidity limit for an extra virgin olive oil is 0.8%, but in a quality oil the values are much lower (0.1-0.3%). Higher values often indicate problems that have arisen during the production chain (olives that are too ripe, or are attacked by the fly, or stored for a long time …) and are often accompanied by sensory defects (in particular wine, heating, mold).
Low acidity is not enough
Low acidity is a necessary, but not sufficient, condition to demonstrate a high quality level of the oil; the support of other qualitative parameters is required, in particular the organoleptic examination.
What do they indicate
Peroxides indicate an oxidative alteration, synonymous with degradation and aging, expressed in milliequivalents of active oxygen per kilo of oil (meq O2 / kg). The limit relating to the number of peroxides is 20, above which the oil is clear.
What are good values?
A value is good if below 10-12 (but recommended below 7); a high number of peroxides highlights a primary oxidation process already started and irreversible, while a low number of peroxides is not necessarily linked to high quality, as it may already be in the presence of the secondary phase of oxidation, in which the peroxides are they are decomposed into aldehydes and ketones, which give the sensation of rancid. It is therefore necessary to accompany the analysis of peroxides with the spectrophotometric examination and the organoleptic test.
What are polyphenols?
Polyphenols are among the most precious components of extra virgin olive oil, the only one among vegetable fats to be rich in it. These substances, which determine its characteristic spicy and bitter taste, have an antioxidant and protective action for the oil, giving it stability, health qualities and sensory peculiarities.
Phenolic compounds, also referred to as polyphenols or biophenols, are the main antioxidants present in extra virgin olive oils and intervene in the prevention of oxidation by capturing free radicals that form during storage. This parameter can be considered a quality indicator and related to the other quality parameters linked to the oxidation process.
Legal limits and reference values
Currently the polyphenol content, expressed in milligrams per kilogram of oil, is not regulated. For an extra virgin olive oil, the minimum reference value of 150 mg in one kilogram of oil.
What do they indicate
Spectrophotometric analysis highlights refining processes or oxidation and aging phenomena of the oil.
The Kreiss assay (delta K) is a chemical assay used to qualitatively determine the degree of rancidity of an edible oil. The test is used to identify the secondary products of auto-oxidation of fatty acids and is accompanied by the determination of the number of peroxides (primary products of auto-oxidation).
The reference values
The K232, K270 and DK are determined with the spectrophotometer in the laboratory by reading the absorptions at 232 and 270 nanometers. The limits for an extra virgin olive oil are 2.5 for K232, 0.2 for K270 and 0.01 for DK. An increase in K232 highlights primary oxidation (excessively ripe olives, damaged or attacked by the fly, processing problems in the press, fraudulent addition of rectified oil) with the formation of peroxides, while an increase in K270 highlights secondary oxidation (problems in the conservation, fraudulent rectification treatments) with the formation of aldehydes and ketones.
- K232 : This parameter indicates the absorbance of extra virgin olive oil at a wavelength of 232 nm. The absorbance at this wavelength is affected by the presence of oxidized compounds in the oil, such as aldehydes. A high K232 value may indicate oxidation and degradation of the oil.
- K264 : Similar to K232, K264 represents the absorbance of extra virgin olive oil at a wavelength of 264 nm. Again, a high K264 value may indicate a higher presence of oxidized compounds in the oil.
- K268 : This parameter measures the absorbance of the oil at 268 nm and is used to evaluate the presence of polycyclic aromatic substances (PAHs), which may be present in traces due to combustion processes or environmental contamination. A high K268 value may indicate possible contamination by PAHs.
- K272 : Similar to K268, K272 measures the absorbance of oil at 272 nm and is also used to evaluate the presence of polycyclic aromatic substances. A high K272 value may indicate possible contamination by PAHs.
- Delta-K (ΔK) : This parameter represents the difference between the values of K232 and K270 and is used to evaluate the evolution of oil oxidation over time. An increase in the ΔK value may indicate deterioration of the oil due to oxidation.
In summary, spectrophotometric parameters such as K232, K264, K268, K272 and Delta-K provide valuable information on the quality and state of conservation of extra virgin olive oil, allowing its integrity and freshness to be assessed. High values of these parameters can indicate oxidation and degradation of the oil, while lower values are indicative of an oil of better quality and preservation.
Now that you know how to read the chemical analyzes of EVO oil, look at the analyzes of Casa Julia EVO oil
Learn to also interpret the sensorial and organoleptic analysis (Panel Test) of an EVO Oil : How to read the organoleptic analyzes of EVO oil (Panel Test)
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