Some cold storage operators could lower MCP concentrations, reducing costs without losing effectiveness, according to some research data from Michigan State University. MSU scientists also found that although the material extends firmness retention, there is a limit to how long apples can be stored and still be –marketable.

MCP (1-methylcyclopropene), an ethylene action inhibitor, is used in 26 countries on more than 20 plant materials under the brand name of SmartFresh. The product is registered and manufactured by AgroFresh.

Dr. Randy Beaudry, postharvest physiologist at MSU, learned during research about MCP that much of the material was absorbed by materials in the experimental storage chambers, including wood and corrugated cardboard. "Everything living and nonliving that we’ve tested absorbs MCP," he said. Beaudry presented findings of the MSU research during the Great Lakes Fruit, Vegetable, and Farm Market Expo held in Grand Rapids, Michigan.

Bins

They found that when wooden bin material was in the chamber, it took 200 to 300 parts per billion concentration of MCP to achieve the same concentration that 60 ppb achieved without wood. Other tests showed that about 90 percent of the MCP was absorbed within about six hours when wood was in the chamber.

Beaudry said that while a higher concentration of MCP is needed when you have wood present, the normal dose used is around 1,000 ppb, more than enough to make up for the wood absorption.

But it means that if you use 1,000 ppb in a wood chamber, you could probably use only 200 ppb in a nonwood room with plastic bins, he added.

"The take-home point is that the data demonstrates that MCP efficiency is reduced by wooden materials, in some cases," Beaudry said. "If you use plastic bins, you can probably get away with lower MCP concentrations, which could reduce costs."

Length of storage

MSU researchers also wanted to know how long fruit can be stored and still be marketable under MCP programs. Storage trials evaluated Empire and Red Delicious varieties of apples, assessing their firmness and internal quality. Fruit treated with MCP were held for 6, 9, and 12 months, and were evaluated from one day to two weeks after removal from cold storage.

Throughout the study, fruit remained very firm. "We can retain firmness with MCP. That’s not a problem," Beaudry said. However, packers are pulling fruit out of storage later than ever before, he added.

Some of the fruit, being held for the sliced-apple market, is coming out of storage when new crop is going into –storage. In the past, he said, Empire apples didn’t last much past six months—the limit before core browning and other internal problems began showing up.

Their research showed that the incidence of core browning in MCP-treated Empire apples was about 5 percent at 9 months, but 25 percent at 12 months. "The fruit is still firm and still in good condition in terms of texture, but internal quality is beginning to suffer."

Beaudry explained that when Empire apples are 12 months old, there is little difference in fruit quality between MCP-treated and untreated Empires. "Fruit cells are dying. They’re just beyond the fruit’s life."

For Red Delicious, at 9 months of storage, the core browning showed up in 10 percent of the MCP-treated fruit and worsened within a few days of being taken out of cold storage. At 12 months, there was little difference between the treated and nontreated fruit in terms of internal browning, as both treated and untreated fruit had browning.

Rots

Fruit rots showed similar patterns, increasing from 4 percent incidence in treated fruit held for 9 months to 13 percent in fruit held for 12 months. Organisms causing decay are picking up their activity as disease resistance decreases.

"MCP is a marvelous compound and can extend the firmness retention remarkably well beyond the storage life of the fruit," Beaudry said. "Now, odds are, there are some tricks we’ll be able to use that will be developed in the next few years." The ultimate storage life is cultivar dependent, and there probably is about a three-months difference between Empire and Red Delicious, he added.

"So, while MCP enables us to preserve some quality attributes to record durations, it can take us beyond the natural capacity of the life of the fruit and that leads to increased disorders like those we’ve seen in the past couple of years, especially in the sliced apples," he –concluded.