A Research Note Low pH Inactivation of Polyphenoloxidase in Apple Juice

Apple polyphenoloxidase (PPO) was inactivated to 98%, 63% and 34% of the initial activity after 20 min at adjusted pH values of 2.00, 2.25 and 2.50, respectively. Higher pH values resulted in slower inactivation. In a pilot plant study, juice was acidified with HCI to pH 2.00 for 45 min and subsequently raised to the original pH with NaOH. PPO activity decreased by 88% and filtration of the juice was improved. Sensory analysis of the juice indicated that the acidified samples had a lighter but less preferred color and a disagreeable salty taste. No aroma difference was recognized.