Some typical substances found in oil

SAPONIFIABLE FRACTION: TRIGLYCERIDES OF FATTY ACIDS

Fatty acids
Fatty acids are present in the oil as components of triglycerides and glycerides, glycerine esters (free fatty acids are very few: when they are in large quantities, they increase the acidity rate, so the possibility for oils to oxidise, starting from free radicals), esters with other fats, or mixed esters. Fatty acids are formed by molecules containing carbon atoms, which are linked through simple links (saturated, forma cis into natural acids: palmitic acid 7/15 %, stearic acid 1.5/3.5 %) or one or more double links (monounsaturated, oleic acid 70/80%, and polyunsaturated, linoleic acid 10%, and others). 
The % composition varies according to climate and agronomic conditions; however, some differences and similarities can be found between oils from different regions.
Triglycerides are originally found almost exclusively in olive pulp; they a source of energy for our body, provide essential fatty acids (which cannot be reproduced by the body), facilitate the absorption of fat-soluble vitamins, have a plastic action in structuring cell membranes, functional action as prostaglandin precursors, protective (the unsaturated one) for the action towards free radicals and cholesterol in the body.

UNSAPONIFIABLE FRACTION:
These substances are responsible for important properties of oils: the organoleptic properties, such as scents (fruity), smells (apple, artichoke, almond, pine nut, grass, leaf), typical tastes (bitter, spicy, sweet...), biological properties, such as antioxidant and healthy properties; they are also markers to identify the presence of any frauds.

Alcohols
These are usually very volatile molecules. In fact, when they evaporate at low temperatures, they characterise the smells of oil (although they are light and hard to feel). These substances are also very labile chemically; therefore, while olives get riper and riper, the oil tends to loose its smells. This happens also to aging oil.

Sterols
Unsaturated monovalent cyclical alcohols (C27/C29), called phytosterols, presents in oils as free or estherified fatty acid esters: e.g. beta-sitosterol, stigmasterol, campesterol, brassicasterol, also cholesterol (whose presence shows contamination from olive fly). Due to oil saponification, they remain free with the unsaponifiable fraction. Every oleaginous species has a typical sterolic composition (so they are important for the marker action in the analysis of oils: they are like a fingerprint to identify fatty substances with a different origin).

Polyphenols
Antioxidant substances: these substances give oils the property to resist oxidation (oil going rancid), i.e. their effect is to oxidise instead of fats and are consumed through time: they have this protective action (on the oil and as biological activity on human body cells); their quantity is an index of the aging degree of oil and its preservability. Their quantity also depends on the type of cultivar and harvest period (higher in green olives, they decrease with olive ripening).
Their quantity in the fruit is at the maximum level at the beginning of olive ripening, then they start decreasing.
They are macromolecules containing phenolic nuclei linked with various kinds of radicals: oleuropein (bitter principle), hydroxytyrosol (from decomposition of the previous principle; more active than vitamin E, it has antioxidant activities also in human body, anti-herpes activity, anti free radicals, hypotensive, platelet antiaggregant), luteolin, elenoic acid, flavones, and phenolic acids.
Their presence is felt when the oil taste is bitter and spicy, but also fruity; these are thermolabile molecules and are affected by mechanical processing (refined oil does not contain these substances).
In olives, phenolic substances are in the form of glucosides, esters, and various complex substances not soluble in oil; in crushing and kneading, enzyme hydrolysis liberates simple soluble phenolic substances in oil, according to processing time and temperature.

Tocopherols
Antioxidants: among these compounds, the alpha-tocopherol has the highest biological activity and forms the vitamin E (approx. 150-300 mg/Kg of oil); it is lipophile and provided with a strong antioxidant power especially on polyunsaturated fatty acids, which tend more to oxidise.
These substances can easily oxidise, and capture free radicals formed during oxidation in the air of unsaturated compounds; they have the same functions in both food and cell tissue. Technical oil processing (refining, in particular) inevitably reduces the quantity of this substance, with losses in vegetation water during extraction.

Other substances 
Fat-soluble vitamins: A and D (steroid derivatives) and E (antioxidant);
vitamin A, not directly present in oil, is formed by b-carotene breakdown, which is operated by the carotenase enzyme present in liver; for this reason, b-carotene is defined as provitamin A.

Pigments
Carotenoids (including b-carotene) give oil its yellow colour, and chlorophylls (also with antioxidant action, but only if oil is kept in a dark place, together with vitamin E) its green colour (higher rate in unripe olives).
Carotenes act on oxygen molecules, in the presence of light, by deactivating their radical chain production action (antioxidant action).
Chlorophylls degrade in the presence of light; they change the oil colour to yellow and have a harmful effect on fatty acids, because they allow their oxidation. On the contrary, in the absence of light, they behave as antioxidants together with polyphenols.

Olive oil in food 
From ancient times, olive oil has always been considered as an excellent food and medicinal product. In ancient Greece, during the second century AD, the Greek doctor Gallianus considered olive oil as an excellent food for treatment of intestinal diseases, and another doctor, Dioscarides, considered it as very appropriate in the composition of unguents.

Through time, olive oil has also been used to treat arthritis, gout, for scalp treatment against dandruff, to remove thorns from the skin, etc… As concerns its digestibility, assuming that it is 100 for olive oil, it is 83 for sunflower oil, 81 for peanut oil, and 36 for corn oil. Olive oil is now recommended, raw or for cooking, in food for its full seasoning qualities and varied and typical taste. It is also recommended for its healthy action: for this reason, the use of extra-virgin olive oil is indicated for its excellent quality!