The influence of the malaxation temperature on the activity of polyphenoloxidase and peroxidase and on the phenolic composition of virgin olive oil

The effect of the malaxation temperature under sealed conditions on the qualitative and quantitative composition of the phenolic compounds in virgin olive oils produced from four Italian cultivars was assessed for two atmospheric conditions. In both cases, the results show a positive relationship between temperature and the concentration of the derivatives of the secoiridoid aglycones; the effect of the temperature on the oxidoreductases that promote oxidation (polyphenoloxidase and peroxidase) was investigated to determine their optimal temperatures and thermal stability. While olive peroxidase (POD) showed the highest activity at 37 degrees C and high stability in the temperature range tested, polyphenoloxidase (PPO) exhibited the optimum activity at approximately 50 degrees C, but showed low stability at 40 degrees C, with a large variation in stability according to the olive cultivar. These results may contribute to an understanding of the increase in the phenol concentration found in virgin olive oils obtained following higher temperatures of malaxation. (C) 2012 Elsevier Ltd. All rights reserved.