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Wooden apple bins absorb MCP in storage, reducing the amount available to be absorbed by the fruit, research in Michigan has shown. In contrast, plastic bins absorb little or no MCP. However, AgroFresh, which sells MCP, is not recommending any changes in the rates of MCP used.

MCP (1-methylcyclopropene) is applied to apples in storage to preserve quality. The MCP binds to the ethylene-binding sites in the apples, preventing the ripening action of ethylene.

It was originally thought that when apples were treated, only the fruit absorbed the MCP, but Dr. Randy Beaudry, postharvest physiologist at Michigan State University, noticed that the amount of MCP in the treatment chamber declined faster than expected and decided to find out why.

In experiments, Beaudry and colleagues found large differences in the absorption of MCP by the different bin materials. Oak absorbed significant amounts of MCP, while plastic absorbed little or none. Absorption by plywood was between that of oak and plastic. Wetting of the wood, as would happen when bins of apples are drenched before storage, speeded up the absorption.

In experiments where the researchers simulated a controlled-atmosphere storage treatment room, half the MCP was depleted in about 12 hours when apples were stored alone. But when they were stored with wet oak, the MCP concentration dropped to 50 percent within two hours, and within six hours, only 10 percent of the initial concentration was left.

But Beaudry said even though the wooden bins absorb a significant amount of the MCP, under normal treatment conditions, there should be enough left to obtain the desired response in the fruit. This is because the recommended treatment rate is so high. The 1-part-per-million rate used in the United States is ten times higher than the amount necessary to get the effect, he said, and significantly higher than used in some other countries. In the United Kingdom, for example, the product is used at only 0.625 ppm.

“So, if you lose a third or 20 percent to the bin, it’s not a big problem,” he said.

However, if there was a leak in the room or anything else in the storage environment taking up MCP, the losses could be greater, he added.

Lower rates

In theory, lower concentrations of MCP than the recommended rate should work when plastic bins are used, and Beaudry said there is no regulatory reason why producers can’t use less than the labeled rate of a product.

Reducing the rate might be appealing to packers using plastic bins because of the high cost of AgroFresh’s SmartFresh brand. However, packers may be prevented from doing so by their agreement with AgroFresh, which not only sells the product, but makes the applications.

“This is the first time, as far as I know, where a company has said, ‘We’re going to control everything associated with the application of the chemical. It’s not yours to apply, and we’re providing a service and treatment.’” Beaudry said.

Robin Sprague, global communications manager for AgroFresh, said the company does not recommend using lower rates than on the label. “Lower rates would likely prevent our customers from receiving the full benefits of the SmartFresh Quality System,” she wrote in an
e-mail message.

In a press release, AgroFresh stated that based on thousands of applications worldwide, its customers have found that SmartFresh works effectively and equally with either wooden or plastic bins. In tests and studies, they found no instances where the label rate did not work effectively due to the composition of the bins.

“The rate used is the rate set by EPA (Environmental Protection Agency), which was established based on efficacy studies which tested different storage regimes and conditions to ensure a maximum benefit for packers, retailers, and consumers,” the release states. “Findings concluded that success of the SmartFresh Quality System is influenced by several key factors, such as room air tightness, fruit maturity, and harvest-to-application timing, but bin composition, in commercial practice, is not a factor.”