Understanding degradation of phenolic compounds during olive oil processing by inhibitor addition

Abstract

The aim of this work was to study, under different conditions, degradation of secoiridoids during extraction of extra virgin olive oil by following the effect of ascorbic and citric acid addition. Their effect was evaluated on oil obtained from both damaged olives and undamaged fresh olives. Addition of enzyme inhibitors to damaged olives during olive milling allowed us to obtain oil with a higher phenolic compound content. Conversely, addition of the same inhibitors to undamaged fresh olives, during oil milling, resulted in no significant improvement in the phenolic compound content of oil. A high presence of PPO was thus indirectly confirmed, as damaged olives were only found to be sensitive to action of inhibitors. Ascorbic acid was found to be more effective than citric acid in preserving phenolic compounds of oil. Trials on undamaged fresh olives confirmed occurrence of hydrolytic transformation phenomena for secoiridoids during extra virgin olive oil production process. In particular, the quantitatively most representative component for Frantoio cultivar was found to be 3,4-DHPEA-EDA. This compound may be considered a direct marker for the degree of transformation of secoiridoids during production process. Practical applications: The processing of undamaged olives resulted in the extraction of extra virgin olive oil with a higher phenol content. It could be indirectly inferred that a reduced activity of PPO caused a low secoiridoid degradation both before and after malaxation. Lightly scratched, overripe olives could be used in those markets where the addition of oxidation-inhibiting substances is allowed. Using inhibitors can be suggested for olive washing step.