Influence of ReTain, DPA, 1-MCP, and CO₂ on ‘Empire’ Quality

The objectives of this study were: 1) to determine the effects and interactions of 1-MCP, ReTain, and DPA on the quality of 'Empire' apples during storage, and 2) to investigate the effects of CO₂ in the CA regime for 'Empire' apples treated with 1-MCP. 'Empire' apples that had been treated with and without ReTain (200 ppm, ~ 4 weeks prior to harvest) were harvested, treated with or without DPA (~1000 ppm) and 1-MCP (1 ppm, 24 hours at 0°C), and subsequently stored in CA of 2.5% O₂ with either 2% or 0% CO₂ for 120 and 240 days at 2^oC.

There was no significant effect of ReTain on fruit firmness, CO₂ production, and total volatiles after storage, although there was slightly less ethylene production in ReTain-treated fruit compared to those not treated. DPA treatment had no significant effect on CO₂ production, ethylene, and total volatiles, but when fruit were treated with 1-MCP then DPA resulted in firmer fruit (+ 0.7 lb) than when no DPA was applied. 'Empire' treated with 1-MCP had similar firmness after 1 or 7 days at ~23°C following 120 days of CA storage with or without CO₂.

However, of the fruit not treated with 1-MCP, only those in the CA regime without CO₂ exhibited reduced firmness retention (- 1.8 lb) during the 7 days at ~23°C. After 240 days of storage, apples that were treated with 1-MCP also had reduced firmness retention (- 0.4 lb) without CO₂ in the CA regime, while the effect of 0% CO₂ was even stronger on the fruit not treated with 1-MCP.

These results clearly show the importance of CO₂ in the CA regime regardless of 1-MCP treatment, for maintaining fruit firmness, especially after long-term storage. However, due to increased sensitivity to CO₂ in 1-MCP treated apples, DPA should always be used to control any possible CO₂ injury.