Treatments to inhibit the browning reactions in model solutions of olive fruit extracts

Crude enzymatic and polyphenol extracts from olives were subjected to reaction at diverse buffered pH values. At pH values similar to those found in olive flesh (pH 5.0), the colour of the solution increased with reaction time and, simultaneously, a consumption of phenols and oxygen in the reaction medium was observed, especially under aerated conditions. In alkaline solutions (pH 12.4), a strong initial solution browning was noticed while the phenols from the extract reacted with the oxygen present in the solution and caused a significant decrease in the total phenols and oxygen concentrations. This darkening was due to the appearance of non-enzymatic browning reactions since, at this pH, the polyphenoloxidase is not active. Under acidic conditions (pH 3.0), and in solutions with ascorbic acid added (100 mM), the consumption of oxygen and total phenols was negligible, under both aerated and non-aerated conditions; as a result, no significant changes in the colour of the solutions were observed. So, low pH or ascorbic acid solutions may be useful to prevent browning in the bruised areas of hand- or mechanically-harvested table olives.