Temporal metabolomic analysis of o-glucoside phenolic compounds and their aglycone forms in olive tree and derived...

Maturity is one of the most important factors associated with evaluation of the quality of fruit and vegetables. In olive oil, maturation plays a key role in the kinetics of biosynthetic pathways of the secondary metabolism. One of the most relevant pathways is that catalysed by beta-glucosidases, which are involved in olive oil debittering. Therefore, the knowledge of this influence can be of particular interest for olive oil industry.

To monitor the profile of O-glucoside phenols and their aglycone forms in olive oil, alperujo (the semisolid residue resulting in the production of olive oil), stones, leaves and branches in order to interpret its evolution according to the sample and the period of the season (October, when olive drupes are green; December, when these drupes are green-purple; and February, when they are mostly black).

Targeted phenols were extracted by previously optimised methods assisted by auxiliary energies (i.e. ultrasound, microwaves or superheated liquids) according to the characteristics of the sample. The analysis was carried out by liquid chromatography-tandem mass spectrometry with a triple quadrupole mass detector. Highly selective identification and sensitive determination of metabolites was performed in multiple-reaction monitoring mode. Statistical analysis to evaluate differences in the profile of the target compounds was based on principal compounds analysis.

The evolution of the analytes concentration is strongly related to the role of beta-glucosidases. An explanation for this evolution in olive oil, alperujo and stones is given by relation to the industrial process for olive oil production. For leaves and small branches, the concentration was practically constant over the season, which was foreseeable because of the perennial character of olive trees. Leaves and branches were found to be highly concentrated in O-glucoside derivatives, demonstrating their capacity for phenolic compounds storage.

Targeted metabolomic profiling has proved a useful tool to monitor O-glucoside phenolic compounds and their aglycone forms in olive materials. The profile of target compounds enables interpretion of their evolution according to the olive material and the period of the season.