Prestorage conditioning, diphenylamine improve condition of 'honeycrisp' apple

Since the introduction of 'Honeycrisp' apples in 1991, the variety has become a consumer favorite for its unusual texture and delicious flavor. Honeycrisp has increased in popularity with growers as well; Michigan, New York, and Washington boast significant numbers of 'Honeycrisp' orchards. As the growing area dedicated to the variety has grown, the need to find better methods for improving storage performance has become more important to growers. Because 'Honeycrisp' is very sensitive to low temperatures and can be damaged by controlled-atmosphere conditions, long-term storage of the apples can be challenging.

Carolina Contreras and Randy Beaudry from the Department of Horticulture at Michigan State University and Nihad Alsmairat from the Department of Horticulture and Crop Science at the University of Jordan published a study in HortScience that revealed some important information for apple producers. "Our work was conducted in two phases," Beaudry explained. "The first phase was designed to determine whether 'Honeycrisp' apples were susceptible to controlled-atmosphere injury, to determine the relative influence of O₂ and CO₂, and to identify a treatment combination that would reliably generate symptoms so that control measures could be subsequently evaluated." In the second phase, the scientists evaluated options for avoiding injury to 'Honeycrisp' during controlled-atmosphere storage. Fruit were conditioned at 3º C, 10º C, and 20º C for 5 days and then exposed to one of nine different storage treatments.

In the first experiment, 'Honeycrisp' exhibited a high sensitivity to both low oxygen and elevated CO₂ levels. "We found that the controlled-atmospheres used induced injuries typical of those associated with CO₂ (i.e., small brown lesions and associated lens-shaped cavities) and also larger dark brown lesions with often irregular margins," the authors said. "The extent of the injury was higher for those fruit in an atmosphere with elevated CO₂ for each level of O₂."

Subsequent experiments took place over 3 years, during which the researchers reproduced the controlled-atmosphere (CA) injury from the preliminary study with varied intensity. Although the researchers observed high variability between orchards and years, they found two treatments that effectively controlled the CA injury. "We found that the brown lesions in the cortex were completely suppressed by DPA application, even when the prestorage conditioning temperature was 3º C," Beaudry said. "The incidence of cavities ranged from 0.1% to 0.3% under the same DPA treatment. On the other hand, the most affected treatment was 3/3 followed by 3/0, 21/0, and 21/ 0 plus 1-MCP."

The authors noted that, while there is good progress toward determining optimal storage recommendations for 'Honeycrisp' additional studies are still warranted. "For instance, although the 7-day prestorage conditioning treatments provided some protection against the development of CA injury, shorter durations should be investigated to prevent quality loss resulting from excessive ripening, which could cause increased skin greasiness and undesirable flavor profile."

The study includes additional recommendations for handling 'Honeycrisp' in prestorage conditions.