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The presence of polymerized triacylglycerides or chlorophyll degradation products in olive oil indicates that the oil has been refined or subject to other thermal treatment processes. In this study, several olive oils were analyzed using the Agilent 1260 Infinity LC with refractive index and fluorescence detection.
Virgin olive oil can be created only by mild, cold pressing of olives (Olea europea L.). In addition to the determination of stigmastadienes (1), the quantification of polymerized triacylglycerides and chlorophyll degradation products in olive oil is another important factor to determine whether thermal treatment was used.
Table 1: Polymerized triacylglycerides.
During different refining steps, the oil components are chemically altered (2). Polymerized triacylglycerides are normally not present in crude vegetable oils. During the extraction processes, the chlorophyll a and b pigments are converted into the more stable pheophytins (3), which in turn undergoes slow decarboxymethylation to give pyropheophytin.
Table 2: Chlorophyll degradation products.
In contrast to virgin olive oil, the partly refined olive oil chromatogram showed dimerized triacylglycerides (Figure 1a). In addition, a higher percentage of chlorophyll a degradation products are found in partly refined olive oils (Figure 1b).
Figure 1: Detection of (a) polymerized triacylglycerides and (b) chlorophyll degradation products in partly refined olive oil.
Only negligible amounts of polymerized triacylglycerides were detected in all six virgin olive oils. In addition, in fresh virgin olive oils, only a minor amount of pyropheophytin was detectable, but as it develops slowly during storage, higher amounts were detected in several longer stored virgin olive oils as well as in the partly refined olive oil.
(1) Quality Analysis of Virgin Olive Oils – Part 1, Agilent Application Note, Publication Number 5991-1894EN, 2013.
(2) G Billek, European Journal of Lipid Science and Technology94(5), 161–172 (1992).
(3) K Aitzetmueller, European Journal of Lipid Science and Technology91(3), (1989).
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