CHANGES IN THE ACTIVITY AND SUBCELLULAR-DISTRIBUTION OF PPO IN DELICIOUS APPLES DURING CONTROLLED-ATMOSPHERE STORAGE

Polyphenol oxidase (PPO) activity in 4,000 x g, 100,000 x g, 200 x g and soluble fractions of 'Delicious' apples was monitored during 28 weeks of controlled atmosphere storage. PPO activity in 4,000 x g and 100,000 x g fractions decreased, while that in soluble and 200 x g fractions increased. These shifts in subcellular location occurred sooner in apples which were stored under high CO2 conditions (2.5-6% O2, 8-12% CO2) than those under normal CA conditions (2% O2, 3% CO2). Polyacrylamide gel electrophoresis of 4,000 x g fractions isolated from 'Delicious' apples at harvest showed 2 bands with PPO activity, while stored samples all had 3 bands. Isoenzyme patterns were found to vary in different subcellular fractions.