The most important advice Jim Mattheis can give packers regarding applications of MCP is to know your variety and its postharvest disorder risks. In other words, know ahead of time what you’re trying to manage for.
The compound that blocks ripening is a good tool, but applying it right away is not always the wisest plan. That’s not necessarily breaking news, but, too often, lessons are forgotten amid change and turnover in the industry.
Mattheis, the research leader for the U.S. Department of Agriculture’s Agricultural Research Service in Wenatchee, Washington, reminded growers about the lessons learned over 20 years of research on MCP, funded by the Washington Tree Fruit Research Commission, at the Pace Postharvest Academy in Cle Elum, Washington, in May 2018.
Not all varieties respond to MCP (1-methylcyclopropene) the same way and Mattheis continues to study the effects of MCP on newer varieties.
For one thing, the risk of controlled-atmosphere injury generally decreases with a delay in MCP treatment, while controlled-atmosphere storage can mitigate some of the effects of delaying MCP application. However, “this isn’t something you can apply across all varieties,” he said.
For example, he suggests minimal delay on applying MCP on varieties that tend to soften in storage, such as Gala, Red Delicious and Golden Delicious or varieties for which superficial scald is a risk, such as Red Delicious or Granny Smith. In those instances, it makes more sense to apply MCP quickly after harvest.
Other times, delaying MCP treatment may be beneficial, such as on varieties that are sensitive to controlled-atmosphere storage disorders such as carbon dioxide injury. Varieties in that category include Fuji, Braeburn and Cameo.
When stored in air, Galas react in a predictable way to delays of MCP. The longer the delay in MCP application, the more the fruit softened.
However, when Golden Delicious apples were stored in controlled-atmosphere, the picture started to change. A 15-day delay in MCP treatment resulted in almost no firmness change to fruit stored in controlled-atmosphere for four months. However, that same delay led to significant softening after being stored for eight months in controlled-atmosphere storage. The benefits of CA were greater over a long period of time than short.
“This is a place where you see that CA plus MCP is a different beast than either one of them alone,” Mattheis said.
Timing of MCP also tends to affect apple skin color, especially with Golden Delicious. Apples stored in controlled-atmosphere with a delayed MCP treatment turned from green to yellow faster.
Granny Smith in cold storage treated with MCP eight weeks after harvest stayed firmer than the untreated apples but lost all protection against superficial scald after only a four-week delay in treatment.
In Fujis, delaying MCP treatment helped reduce internal browning almost to zero, especially when stored in air as opposed to controlled atmosphere. However, the delays did not affect how much firmness the fruit lost. Fujis are not very prone to softening when controlled atmosphere or MCP are delayed.
Braeburn, on the other hand, turned softer with longer delays in MCP treatment, whether stored in air or controlled-atmosphere storage. However, core browning did not follow a clean model.
“There’s no single formula,” he said.
That’s why Mattheis recommends showing up to the warehouse with clear postharvest management goals. If preventing a disorder is the highest priority, then apply MCP for that outcome. And, consult user guides from providers.
“Really it gets back to what the goals are of any particular variety as far as what you’re trying to do with it in a postharvest environment,” he said. •
—by Ross Courtney