Effect of pH, temperature and some chemicals on polyphenoloxidase and peroxidase activities in harvested Deglet Nour and Ghars dates

The influence of pH, temperature and some chemicals on polyphenoloxidase and peroxidase activities in harvested Deglet Nour and Ghars dates was studied. These activities were tested for optimum pH and temperatures. Their stability was assessed as a percentage of remaining activity after incubation at different pH and temperatures and in the presence of some chemicals. The determination of phenol content and antiradical activity of fruit extracts in the presence of these chemicals was also carried out. Optimal pHs and temperatures for polyphenoloxidase activity in Deglet Nour and Ghars are pH of 6.4 and 7.2 with temperatures of 35 degrees C and 40 degrees C respectively. For peroxidases the conditions are 5.6, 6.2 and 35 degrees C, 30 degrees C respectively. The most inhibitory chemicals to both enzymes were ascorbic acid, sodium metabisulfite and cysteine. The highest phenol content of both varieties is in the presence of sodium metabisulfite. The highest anti-radical activity is that in the presence of ascorbic acid. Deglet Nour and Ghars enzymatic browning can be completely inhibited by some chemicals and extreme pH and temperatures. (C) 2015 Elsevier B.V. All rights reserved.