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Left: In carbon dioxide-sensitive apple varieties, like these Golden Delicious, fruit harvested early tends to have peel injuries. Right: Internal breakdown occurred in this Golden Delicious apple, as a result of carbon dioxide injury.

Left: In carbon dioxide-sensitive apple varieties, like these Golden Delicious, fruit harvested early tends to have peel injuries. Right: Internal breakdown occurred in this Golden Delicious apple, as a result of carbon dioxide injury.

All apples release carbon dioxide as part of the fruit respiration process. But some varieties, like Golden Delicious and Empire, are more sensitive to carbon dioxide and require special postharvest management strategies. However, cold-storage operators have several options available to avoid peel and internal injuries associated with carbon dioxide injury.    

Dr. Jim Mattheis  specializes in postharvest physiology of apples, pears, and cherries with the U.S. Department of Agriculture in Wenatchee, Washington. He has developed strategies to help cold-storage operators better manage carbon dioxide injury that can occur in Golden Delicious, Empire, ­Jonagold, Fuji, ­Braeburn, and Honeycrisp.

Carbon dioxide injury shows up as browning and cavities in the peel, flesh, and core. Injury tends to differ from other storage disorders, Mattheis said, in that it usually occurs during the first four months of storage.

Mattheis believes that with the widespread use of MCP or SmartFresh (methylcyclopropene), the carbon dioxide sensitivity for some varieties that used to be more sporadic is now more consistent and needs to be managed on a routine basis. “There’s no way to know if a lot of fruit will be sensitive or not, so we now have to manage for the risk of sensitivity being there,” he said. “But we have tools to make it possible to manage risk.”

The process of fruit respiration produces energy (which drives the continued life of the fruit), carbon dioxide, water, and heat, Mattheis explained. “The challenge is in managing the negative aspects of carbon dioxide and slowing down the amount of carbon dioxide that will be released.” Research has shown that managing the factors that affect fruit ­respiration (ethylene, stage of fruit development, atmosphere, and temperature) can help control carbon dioxide injury.

Management tools

Harvest maturity: Fruit maturity at harvest makes a big difference in the amount of respiration and ethylene produced by the fruit. Apples picked early in the season produce very little ethylene, and there’s little respiration (carbon dioxide) produced during storage. “But the later you pick, the higher the capacity for the fruit to produce carbon dioxide, which adds to the challenge of limiting carbon dioxide in the atmosphere,” Mattheis said. “That’s why fruit is picked early if it’s going to be stored for long periods—the maturity stage naturally helps keep the carbon dioxide and respiration rates lower.”

Mattheis noted that in carbon dioxide-sensitive varieties, apples harvested early tend to have increased peel injury risk, while fruit harvested later have more internal injury. Matching fruit development to storage potential in sensitive varieties is one tool to help manage carbon dioxide injury.

Temperature management:  Temperature control is important and ­provides an avenue to manage injury, he said. Low temperatures help to reduce ­production of carbon dioxide.

Control carbon dioxide accumulation: Mechanical devices like scrubbers can remove carbon dioxide from the atmosphere. Low oxygen also reduces respiration, the driver for carbon dioxide production. However, a small amount of carbon dioxide in the atmosphere can actually help slow down the carbon dioxide production by the fruit, Mattheis said. “The amount of carbon dioxide is important and the amount of oxygen is important. Lower amounts of oxygen mean that you need to keep the carbon dioxide levels low as well.” Research showed much more injury at 5 percent carbon dioxide than 0.5 percent. Mattheis acknowledged that 5 percent carbon dioxide is an artificially high rate, but it’s used for research purposes to help show effects.

Exposure and SmartFresh: If you can delay when fruit is put into controlled atmosphere, you can avoid some risk of injury, Mattheis said. A study found less injury on fruit that was treated with MCP and put into CA after a delay of five weeks. “There’s less risk of carbon dioxide injury when fruit is held in regular air, and the SmartFresh maintained the quality of fruit during this period and kept it from getting soft, even though it was not held in CA.”

Carbon dioxide sensitivity is highest right after harvest on mature fruit, so it’s important to have a strategy for sensitive varieties before they arrive at the cold storage. When ethylene is inhibited, as is the case after SmartFresh treatment, the fruit tends to have a prolonged sensitivity to carbon dioxide.

Mattheis added that because carbon dioxide injury is a result of oxidative metabolism, reducing potential for ­oxidative injury through the application of DPA (diphenylamine) may be a ­treatment to consider.

Support for his research comes from the Washington Tree Fruit Research ­Commission and AgroFresh.