Carbon Dioxide Injury in ‘Honeycrisp' Apple: Dose Response and Induction of Fermentative Volatiles

Controlled atmosphere (CA) storage at low temperature has been widely used to successfully extend the marketing period of many apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivars. However ‘Honeycrisp’ fruit are very sensitive to injury by CA storage, developing brown lesions and lens-shaped cavities in the cortex in response to elevated CO₂ and, to a lesser extent, to low O₂. To investigate the effect of CA conditions on injury of ‘Honeycrisp’, fruit were subjected CO₂ levels of 0, 1.5, 3, 10, and 20 kPa in combination with 3 kPa O₂ during storage at 3 °C. In addition, fruit were treated with diphenylamine (DPA) drench (1000 µL·L^-1, 30 s) to control CO₂ injury and held in two different CA conditions (3 kPa CO₂ + 3 kPa O₂; 10 kPa CO₂ +3 kPa O₂). Fruit were assessed on day 7, 14, 21, 28, 35, 42, 56, 70, 84, 112, 140, and 168 of storage for incidence and severity of CA injury, bitter pit, and decay and fermentative volatile emissions (acetaldehyde, ethanol, and ethyl acetate) were measured on tissue samples removed from the cortex. None of the CA conditions affected incidence of bitter pit or decay. CA injury increased with increasing CO₂ level and with increasing storage duration for the first 50 days of storage. Fruit exposed to 10 and 20 kPa CO₂ had somewhat elevated levels of fermentative volatiles relative to fruit stored at lower levels of CO₂. DPA completely suppressed CA injury at 3 and 10 kPa CO₂. Interestingly, there were approximately the same levels of fermentative volatiles under both CA regimes. It is suggested that fermentative metabolism is influenced by CA conditions, but that the volatiles may not be indicative of CA-related injury per se. The role of DPA in suppressing CA-related injury needs to be investigated.