Carbon Dioxide Treatments for ‘McIntosh’ Apples before CA Storage1

In a collaborative study at 5 North American locations, treatment with 12% CO 2 and 3 to 5% O 2 for 2 weeks at 0° to 3°C at the beginning of controlled atmosphere (CA) storage significantly delayed softening of ‘McIntosh’ apples ( Malus domestica Borkh.). Softening was retarded further when treatment time and CO 2 concentration were increased, and when fruit was harvested less mature. The effect was diminished by treatment at 0°, and was nullified by delayed treatment and slow cooling during treatment. Softening response to CO 2 was not influenced by O 2 concentration or storage humidification during treatment. CO 2 treatment reduced the rates of CO 2 and ethylene evolution from the fruit, even after 4 to 5 months of subsequent CA storage, but affected neither soluble solids nor titratable acidity of fruit after storage. When taste panelists could distinguish CO 2 -treated from nontreated CA apples, they preferred the treated fruit. These beneficial results were usually accompanied by external CO 2 injury, and occasionally by internal CO 2 injury; 30 to 50% of the fruit were injured in some tests. Treatment in a non-humidified room reduced CO 2 injury without also reducing treatment benefits. We conclude that for ‘McIntosh’, the potential for injury outweighs the benefits obtained from CO 2 pre-treatment in CA storage.