It is up to each of us, according to our knowledge and our eating habits, to find out whether the quality of an olive oil wholly satisfies our senses, whereas the evaluation of its genuineness depends on important chemical parameters gathered from more or less complicated tests. Olive oil by its nature is one of the products most exposed to adulteration and falsification by blending with less costly oils. In recent years, analytical techniques have been devised to quantify certain oil components to be used as indexes of genuineness.

In a drop of Olive Oil

Generally fats are composed of a glyceride type fraction that represents about 90%-99% of the mass, and by a numerous group of microcomponents, the non-glyceride, or unsaponifiabile, fraction, that represents 0.4%-5%, even though in some oils it can be as much as 12%. The glyceride fraction is made up of triglycerides, diglycerides, monoglycerides, free fatty acids and phospholipids. Triglycerides, diglycerides and monoglycerides are composed of a glycerol molecule to which are linked respectively three, two and one molecule of fatty acid. Depending on their origin we can distinguish oils on the basis of the fatty acids that make up our drop of oil. Every fatty acid is formed by a chain of carbon atoms combined with oxygen and hydrogen; according to the number of carbon atoms we can distinguish different fatty acids, from butyric acid with four carbon atoms, typical of butter, to caprinic, myristic, palmitic, stearic, and oleic acid, abundant in olive oil, to linoleic and linolenic acids, up to long-chain fatty acids such as montanic acid with 28 carbon atoms, characteristic of the adipose tissue of sea-fauna. The carbon atoms that form the chains of fatty acids can be connected to one another by single or double links. Fatty acids can be grouped into three different categories according to the presence or absence of double links in the chain of carbon atoms. In the absence of double links we have saturated fats, particularly abundant in the fat of animals. If only one double link is present, we have monounsaturated fatty acids, like oleic acid; if two or more double links are present, we have polyunsaturated acids, typical of seed oils.

Owing to the normal chemical reactions of hydrolysis, the fatty acids linked with glycerol can detach themselves and remain free in fat. This detachment, due to various factors, can occur both in the fruit or the seed, and in the oil. The quantity present is an important parameter in assessing the quality of an oil. The increase of free acidity in the oil is always accompanied by a series of modifications that lead to the development of components that determine the deterioration of sensory characteristics. Thus we can conclude that an olive oil with low free acidity denotes a healthier product, easier to preserve, and with superior sensory characteristics. Unfortunately few olive oil producers declare on their labels the free acidity value at the moment of packaging. Therefore it is better to look for brands that feature this indication on their labels and give your preference to those with less than 0.3% acidity.

Olive Oil chemichal-physical index chart.
The chart shows some of the main chemical-physical indexes taken into account for assessing the class of olive oils in compliance with European Regulations.

While fatty acids help us to determine the different origin of an oil, in the non-glyceride fraction we will find a great number of trace components that are even more useful for this determination. The non-glyceride fraction is mainly present in vegetable fats, and is composed of sterols, waxes, vitamins, alcohols, carotenes, chlorophyll, phenols, aroma components. Each of these families of components is very helpful in detecting olive oils adulterated with seed oils.