Formation of oxidised chlorophyll catabolites in olives

Even though chlorophyll catabolism has been studied in depth, there is a parallel oxidation metabolism for chlorophylls which is hardly known. This work describes the oxidised chlorophyll profile of two varieties of olives (of high and low pigmentation) and how they relate to the possible enzymatic mechanisms involved in this oxidation. For the first time, the results showed in vivo evolution of “oxidised chlorophyll a”, a catabolite generated by the enzyme peroxidase, and a very different oxidative chlorophyll profile between the two varieties (up to 12% of 132-OH-chlorophyll for Arbequina fruits and almost 1% of 151-OH-lactone-chlorophyll for Hojiblanca fruits). While the participation of peroxidase in the oxidative metabolism of chlorophylls was demonstrated in the fruits of the Hojiblanca variety (due a good correlation between peroxidase activity and chlorophyll catabolite profile in the fruits), it was not possible to conclude the same for the Arbequina variety fruits. The latter variety demonstrated in vitro competition between chlorophyllase and peroxidase, which made it difficult to interpret the results. Finally, there was a clear difference observed in the specificity of the enzymes peroxidase and chlorophyllase for the substrate chlorophyll a (and not for its epimer), which is explained by the steric changes involved in the epimerisation.