A new technology that determines low-oxygen thresholds in controlled-atmosphere-stored apples

HarvestWatch is a new chlorophyll fluorescence (F)-based technology that identifies the low-oxygen threshold for apple (Malus x domestica) fruit in dynamic low-O-2 controlled atmosphere (DLOCA) storage environments [e.g., <1% oxygen (O-2)]. Immediately following harvest, 'Cortland', 'Delicious', 'Golden Delicious', 'Honeycrisp', 'Jonagold' and 'McIntosh' fruit were cooled and loaded into 0.34 m(3) (12.0 ft(3)) storage cabinets. A static controlled atmosphere (CA) regime of 1.5% 021 1.5% carbon dioxide (CO2) and 3degreesC (37.4 degreesF) [0 degreesC (32.0 degreesF) for 'Delicious' an 'Golden Delicious'] was established for the control fruit, while the low-O-2 threshold was identified by a spike in the fluorescence parameter, Fec, as the O-2 levels in the DLOCA cabinets were lowered below 1%. The DLOCA storages were then maintained at O-2 levels of 0.1% to 0.2% above the threshold value for each cultivar, which returned Falpha to prethreshold signatures. Quality measurements following 5 to 9 months of storage and a 7-day shelf life of 20 degreesC (68.0 degreesF), showed that the HarvestWatch fruit were generally firmer, had no incidence of superficial scald in 'Cortland' and 'Delicious' apples, and did not accumulate fermentative volatile compounds. The HarvestWatch system permits rapid, real-time measurements of the status of stored apple fruit in ultra low-O-2 environments without the inconvenience of breaking the room's atmosphere. Our results indicate that HarvestWatch facilitates what may be the highest possible level of fruit quality retention in long-term, low-O-2 apple storage without the use of scald-controlling or other chemicals before storage.