Olive oil (Olea europaea) is a major vegetable oil obtained from the mesocarp of the fruits of the olive tree. The oil has a long history with many biblical references. Olive trees bear fruit for over 100 years.
Annual production is around three million tonnes with commercial cultivation of the tree confined almost entirely to the Mediterranean countries of Spain, Italy, Greece, Tunisia, Morocco, Syria, and Turkey. Olive oil is an important part of the Mediterranean diet associated with low incidence of coronary heart disease. Its oxidative stability and unique flavour are linked to the fatty acid composition of the oil, particularly its high level of oleic acid, and to its many minor components still present in virgin (i.e. unrefined) oil. However new sources of olive oil are being developed in Australia and in California.
Virgin olive oil is produced from the first pressing of olives, and other grades of lower quality are produced subsequently. The oil is recovered without use of solvent and the highest quality oil is used without further refining. The quality and processing of several grades of olive are defined by Codex Alimentarius and by EU Commission Regulations (European Communities Commission 1991, 1998, and 2001). The regulations provide defined value ranges for physical and chemical properties and for composition of minor fatty acids and sterols.
Olive oil is characterised by a high level of oleic acid with Codex ranges of 8-20% for palmitic acid, 55-83% for oleic acid, and 4-21% for linoleic acid. Other acids present in trace amounts include myristic, palmitoleic, heptadecanoic, heptadecenoic, linolenic, and C20, C22, and C24 saturated acids. A mean fatty acid composition of 78 Greek olive oils indicates the presence of palmitic (10.5%), stearic (2.6%), oleic (76.9%), and linoleic acids (7.5%) in addition to nine other acids each present at a level of less than 1.0%.
Olive oil is characterised by a range of unsaponifiable constituents (total 0.5-1.5%), some of which confer high oxidative stability. They include tocopherols (usually 100-300 mg/kg and almost entirely α-tocopherol) and squalene, which may be 40-50% of total unsaponifiable material. This acyclic C30 hydrocarbon is the biological precursor of the sterols and is present at a higher level (700-12000 mg/kg of oil) in olive oil than in other vegetable oils (usually only 50-500 mg/kg). It can be recovered from olive oil deodorizer distillate. Other minor components include carotenoids, chlorophylls responsible for the greenish colour of virgin olive oil, sterols (desmethylsterols, 4α-methylsterols, 4,4-dimethylsterols or triterpene alcohols, triterpene dialcohols, and hydroxyterpenic acids), fatty alcohols and waxes, polyphenols, and volatile and aroma compounds. Several of these show antioxidant properties and add to the nutritional value of this oil.