Mild refined olive oil obtained by neutralization and/or by soft deodorization at a low temperature and its blending with extra virgin olive oil (EVOO) is not allowed and is difficult to detect. Chlorophyll derivatives, pheophytins and pyropheophytin, and their relative proportions were proposed as parameters to detect such processes. The objective of this study is to determine changes in EVOO, in terms of pheophytins and pyropheophytin, occurring after several well-controlled mild refining processes. The changes on those chlorophyll pigments due to the processes depend on the temperature, stripping gas, acidity and oil nature. The data obtained show that, at temperatures below 100 °C, the rate at which pyropheophytin a is formed (Ra) is lower than the rate at which pheophytins a+a' disappear (Ra+a'). As a consequence, the Ra+a' and Ra ratios are considered to be directly linked to pheophytins a+a' decrease instead of to pyropheophytin a formation. Stripping gas very slightly affects the transformation of the chlorophyll pigments; actually both acidity and N2 enhance the increment in the Ra+a' and Ra ratios. In relation to the oil nature, the higher the initial pheophytin a+a' content, the higher the increase in the Ra+a' and Ra relations.
Keywords: chlorophyll pigments; olive oil; pheophytins; pyropheophytin; soft refining.