Whereas the sterols and fatty acid profile of olive oil are examined to assure authenticity, other tests are aimed at assessing quality and freshness.
The free fatty acid level, peroxide value and UV absorbency are the traditional tests used for this purpose. Two other tests that have been in use in the Northern European olive oil trade since at least 2006 measure pyropheophytin (PPP) and diacylglycerols (DAGs).
Pyropheophytins (PPP) are chlorophyll pigment breakdown compounds from the thermal degradation of olive oil. Heat and long storage time break down chlorophyll into pheophytins then into PPP. Used to indicate the presence of adulteration with refined oil.
The PPP test measures degradation products of chlorophyll in olive oil. This degradation of chlorophylls to pyropheophytin was found to take place at a predictable pace making it possible to gain information about the age of an olive oil. The rate at which the degradation occurs can be accelerated by even short periods at high temperatures — such as those present during the deodorizing or soft column refining process — making it a useful indicator of the presence of deodorized olive oil as well as of the age of an oil.
The DAGs test measures the proportion of two forms of diacylglycerol: 1,2 and 1,3. In oil freshly made from sound, good quality olives, the prevalent form of DAG is the 1,2 form, where the fatty acids are bonded to a glycerol molecule in the 1 and 2 positions. The bond on the 2 position is weak and easily broken, leading to the migration of that 2 position fatty acid to the 3 position. This results in the much more stable 1,3 DAG. This makes the ratio of 1,2 DAGs to the total DAGs a good indicator of the quality of the olive fruit and the processing. It is also an indicator of the age of an oil, since the migration from 1,2 to 1,3 DAGs takes place naturally as oil ages. Warmer storage temperatures and higher free fatty acid levels will both accelerate this process, but DAGs are not affected by the short exposure to high heat that is characteristic of deodorizing.
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