The olive tree generally grows under rain conditions. The Mediterranean region has limited water resources and olive orchards are getting adopted to new irrigation techniques.
The chemical compounds which are effected mostly by irrigation are the phenols, which effect the oxidation and bitterness. The right level of irrigation could enhance these characteristics. The required water for the irrigation of the olive tree is regulated.
The olive tree that is rain-fed is of a lesser production than the irrigated one.
The acidity in olive oil is measured by the milliequivalents of active oxygen per kilogram with analytical methods of the European regulations.
The irrigation effects the fruitiness, bitterness and pungency. The pungency and mainly the bitterness are related to the phenolic content in olive oil. Both were higher in olive oils produced by rain-fed olive trees.
The fatty acid composition is performed under the European regulations. When the fruit ripens, the content of the palmitic acid decreases.
Under irrigation treatments the oleic and linoleic acids content decreases. That decrease is because of the triacylglycerols’s active bio-synthesis, that happens during the ripening of the olive fruit, which causes the decrease of the olive oil’s content in palmitic acid. The increase of the linoleic acid is because of the conversion of the oleic acid into linoleic acid. The rest of the fats do not change during the ripening process.
The olive oils that are produced from rain-fed crops show higher oleic acid content and the ones that are produced from irrigated fed crops show higher content in linoleic and palmitic acids.
The conclusion is that rain-fed crops produce oils that are higher in mono-unsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs).
The phenolic compounds in extra virgin olive oil decreases when the water dose increases. Studies have shown that low phenolic content decreases the self life of extra virgin olive oils.
The amounts of water in irrigating olive trees, not only effect the phenolic content in extra virgin olive oil, but the profile of the olive oils also. The bitterness decreases as the supplied amount of water decreases.
Irrigating the olive trees from the beginning of August when the accumulation of the oil starts in the olive fruit, is giving better results.