Olive Oil Alterations
Are there many?
The main alterations that olive oil will incur are hydrolysis and oxidation. Hydrolysis takes place mainly in the olive-crop, whereas oxidation takes place only afterwards, following the separation of olive oil from the olive-crop. The latter is due to inadequate conditions during its storage. Olive oil’s appearance can also be altered due to variations in temperature, a phenomenon called ‘Olive Oil Blurring’.
Hydrolysis
Hydrolysis [lipolysis] constitutes one of the main alterations of olive oil and is owed to the release of fatty acids from triglycerides. The outcome is an increase in acidity levels and a change in the flavour of the oil, resulting in α loss of quality. The factors that affect hydrolysis are humidity, temperature, ferments and various micro-organisms.
Hydrolysis of triglycerides takes place when micro-organisms develop in the flesh of the olive fruit [bacteria, mushrooms, insects, yeasts]. Hydrolytic alteration occurs in the olive-crop, when the storage conditions are inadequate [elevated humidity and temperature].
Enzymatic hydrolysis is initiated by natural ferments [lipases] of the olive-crop and from ferments released by various micro-organisms that are developed, all this during storage under inadequate conditions. Fermentation activity is predominantly found in the more mature olive-crop [Winter Harvest] than in the less matured olive-crop [Fall Harvest], hence a higher acidity level in the matured-crop olive oil. The ferments’ activity is favoured in environments where acidity levels of pH 8.3 and temperatures of above 45°C are found. OxidationIn addition to other fatty substances that contain unsaturated fatty acids, olive oil oxidizes when it comes into contact with oxygen. The by-products of oxidation emanate an unpleasant flavour and odour, which downgrade the quality of the oil and are considered toxic, when in large quantities. These oxidation by-products are saturated and non-saturated aldehydes. The oxidized olive oil’s content in linoleic and α-linolenic fatty acids is decreased considerably and the lipid-soluble vitamins are destroyed. However, it should be noted that olive oil is very resistant to oxidation [self-oxidation], because of its small content of fatty acids compared to its large content of antioxidative substances. It presents however, sensitivity to photo-oxidation [oxidation due to light exposure], which is related to the action of certain olive oil pigments, such as chlorophyll and pheophytin. For this to occur, these pigments must come into contact with light [direct solar light, diffuse light in room or fluorescent light]. This clearly happens when olive oil is packaged in transparent containers. As well, metals such as iron and copper act as catalysts in the oxidative alteration of olive oil. Present in olive oil is also magnesium, a constituent of chlorophyll. Iron, found in a higher than natural level, originates from the metal surfaces of the oil factory’s instruments and means of storage.
Blurring of Olive OilMany times, when olive oil is stored at low temperatures [just above 00C], it blurs. This is due to the solidification of its components, stearin and palmitin, at low temperatures. The solidification process of these triglycerides occurs because the molecules of the corresponding fatty acids [saturated stearic and palmitic acids], align in a straight line and do not leave any space amongst them, thus leading to a blurred appearance of olive oil at low temperatures. The contrary though can be said about the molecules of esterified glycerol oleic acids. They present a change in the provision of the molecule in the part of their non-saturated double bond, resulting in no presentation of solidification. For this reason they are found in liquid form even when stored at low temperatures.
Light blurring is even present in fresh olive oils. This is not the sign of a deficiency. The receipt of a clear/transparent olive oil from the oil factory testifies to the utilisation of water with a high temperature in the various stages of the olive-crop’s treatment. In this case, the high temperatures [when above 28 0C] destroy some of the components of olive oil, mainly the volatile ones, to which are attributed its characteristic odour.
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The Olive Oil 