Conditioning of ‘Honeycrisp' Apple to Prevent Injury by Controlled Atmosphere Storage: Testing a Matrix of Temperatures and Exposure Durations

‘Honeycrisp’ apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit are susceptible to damage by the low O₂ and elevated CO₂ partial pressures in controlled atmosphere (CA) storage. The injury takes the form of small to extensive dark brown lesions in the cortex and lens-shaped openings typical of CO₂ injury reported for other apple varieties. The browning is somewhat more patchy and less smooth-edged than that of the chilling injury soggy breakdown when viewed in transverse cross section. Previously we have shown that a prestorage conditioning treatment can suppress CA injury.  However, the conditioning treatment has not been optimized.  To better understand the relationship between the duration of the conditioning treatment and the temperature during conditioning, we exposed ‘Honeycrisp’ fruit from 6 different orchards to combinations of temperature (3, 10, 15, 20 and 25 °C) and conditioning durations (0, 1, 3, 5, and 7 days).  After conditioning, fruit were held at 3 °C in CA (3 kPa O₂ and 3 kPa CO₂) for 7 months and subsequently evaluated for CA injury, aroma profile, fruit firmness, °Brix and titratable acids and subjected to a sensory evaluation of degree of ripeness.  We found that increasing the conditioning time reduced susceptibility to CA injury at all temperatures.  Use of a 10 °C conditioning temperature was not sufficient to reduce injury to acceptable levels.  A minimum of 3 days at 20 or 25 °C was required to effectively suppress CA injury.  Increasing the temperature and duration of the conditioning period tended to increase ripeness-related volatiles, but only the most extreme treatment (7 d at 25 °C) resulted in a discernable advancement in ripeness as determined by a trained panel.