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Interactions of 1-MCP and Low Oxygen CA Storage on Apple Quality

The objective of this research has been to investigate the interactions of 1-methyl-cyclopropene (1-MCP) and low oxygen controlled atmosphere (CA) storage on apple quality. ‘McIntosh’, ‘Empire’, ‘Gala’, and ‘Delicious’ apples harvested for two consecutive years at optimum maturity for long-term storage were treated either with 1 ppm 1-MCP or without 1-MCP at 0^oC for 24 hours. After treatment, ‘McIntosh’ and ‘Empire’ apples were placed into standard CA (3.0% O₂ + 2.5% CO₂ for 30 days then 4.5% CO₂ thereafter, and 2.5% O₂ + 2.5% CO₂ for ‘McIntosh’ and ‘Empire’, respectively) at 2½ to 3°C, and four low oxygen regimes (1% and 0.7% O₂, each with or without 0.7-1% CO₂) at either 2½ to 3°C or 0°C. ‘Gala’ and ‘Delicious’ apples were also placed into standard CA (2.5% O₂ + 2.5% CO₂) and the low oxygen regimes, but only at 0^oC. Within a specific CA regime, apples treated with 1-MCP were 1 to 2 lb firmer than comparable apples after mid- or long-term storage (120 or 240 days, respectively).

Lowering the oxygen and the presence of CO₂ did not consistently improve firmness, as many apples treated with 1-MCP exhibited the highest firmness regardless of gas concentrations during storage. Firmness of certain cultivars in specific CA regimes was influenced by 1-MCP, gas concentrations, and storage temperature. Ethylene, CO₂, and volatile production were generally lower in apples treated with 1-MCP, held at lower temperatures, and in low oxygen with CO₂, although there were some interactions of these factors. Overall, 1-MCP reduced the incidence of superficial scald, but increased core browning and CO₂ injury, and interacted with the CA regimes to influence internal breakdown. These results suggest that in combination with 1-MCP both standard and low oxygen CA recommendations require revision, since in certain cultivars there was no further quality benefit from combining low oxygen CA regimes with 1-MCP. More detailed results will become available in late spring.