Ultraviolet absorption to detect oxidation and refining

Instead, when there are peaks, indicating UV absorption, this is a clear indication that the oil has undergone either 1. an oxidation process or 2. a thermal deodorizing or bleaching treatment in the presence of active earth during the refining processes. 

The UV method is based on measurements of extinction or optical density in the 232 nm and 270 nm regions in which diene and triene conjugated systems are known to absorb UV. The intensity of the UV spectral absorption band at 232 nm and 270 nm is also useful to detect, and also in part to quantify, both the extent of the oxidation of monounsaturated and polyunsaturated acid moieties 

An additional parameter derived from measuring the extinction coefficient in the 270 nm region is the extinction coefficient variation A K defined by the equation 

Measurements of the first three categories of virgin olive oil must give a A K value not higher than 0.01 for refined olive oil and olive oil the limits are set at 0.16 and 0.13 values, respectively, whilst for oils of types 8 and 9 A K should not exceed the values 0.25 and 0.20, respectively. 

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