Problems with pear ripening
MCP-treated pears store longer but ripen differently.
The ripening inhibitor SmartFresh (MCP) holds promise for maintaining pear quality over a longer period of time and reducing disorders such as scald, but the pear industry reports that some treated pears won’t ripen.
Dr. Eugene Kupferman, retired Washington State University postharvest specialist, said Bartlett pears, which are harvested in August in the Pacific Northwest, can normally be stored until December or January. Shippers are starting to use MCP to extend the season as well as to maintain the quality of pears during shipment to distant markets, but there’s a risk, he said, that the pears might still be rock hard when they reach the consumer.
“It’s like the Viagra ad,” he said. “You can’t get them to relax and ripen after you apply too high a concentration of SmartFresh.”
Dr. Amit Dhingra, a researcher with Washington State University, estimates that between 5 and 10 percent of Northwest pears are being treated with MCP, based on a survey of warehouses that he recently conducted for the Fresh Pear Committee.
Last season, some Bartlett pears exported to Brazil were rejected by retailers and sent back to the wholesaler because the fruit remained hard, even though it turned color, said Jeff Correa, director of export promotions with the Pear Bureau Northwest. Brazil is the Northwest pear industry’s largest offshore market for MCP-treated Bartlett pears, and there’s concern about the impact of unripenable pears on consumer demand.
During the Pear Bureau’s annual meeting this summer, Dennis Kihlstadius, a ripening consultant for the Pear Bureau, reported a similar situation in Vladivostok, Russia. An importer he visited last season had bought eight loads of Bartlett pears from Argentina that had been shipped in March. When Kihlstadius was there in October, the pears still would not ripen, and the importer had been able to sell only one load because he was getting no repeat sales.
Bob Koehler, a regional manager for the Pear Bureau covering the northeastern United States and Canada, said he saw Bartlett pears on the domestic market at the end of April that had been treated with MCP and looked ripe, but the pressure stayed high and they never got juicy.
“They had a little bit of flavor, but they were not like we expect out of a Bartlett on a regular basis,” he said. “The retailer was happy he could carry Bartletts into January or February, but the fruit was not something that you would want to give the consumer and pin your label on it.”
In fact, for the domestic market, the Pear Bureau has been strongly encouraging shippers to supply pears that have been conditioned with ethylene so they are ripe when purchased, based on the theory that pear sales increase when consumers don’t have to wait several days for the pears to ripen.
Dr. Jim Mattheis, postharvest physiologist with the U.S. Department of Agriculture in Wenatchee, Washington, has done extensive research with MCP on both apples and pears. In the controlled conditions of laboratory research, MCP treatment of pears has been successful, he said, but in commercial settings, where conditions are variable, pears have responded inconsistently to treatment.
“If we could predict the responsiveness and adjust the treatment protocol accordingly, I think you could probably get it right every time,” he said. “But right now, nobody knows how to do that.”
The recommended rate is 100 to 300 parts per billion for pears, compared with 1 part per million for apples. Mattheis said that in lab tests a rate of 300 ppb has provided a nice response in terms of maintaining pear quality, and the effect wears off after several months, allowing the pears to ripen. But it’s not possible to know exactly how many months the effect will last, he said, “and that’s fundamentally the problem.”
If the pears are removed from storage too early, they will ripen very slowly and the only way for a warehouse to know when they’re ready to sell is to keep taking samples of fruit out of storage at intervals and trying to ripen them.
“It’s a commitment,” Mattheis said. “It’s for fruit that you’re not planning to sell, that you want to hold on to for several months. If you get an order and that’s all you’ve got, you’re kind of stuck. There’s no means that I’m aware of to accelerate that process in a really short period.”
Mattheis has done tests at storage and at room temperatures and found that the higher temperature gave a stronger response in terms of delaying ripening.
The reason MCP-treated pears can look ripe even though they’re still hard is because not every aspect of ripening
is controlled to the same degree by ethylene, he said.
MCP is also being used to extend the season for d’Anjou pears and control scald. Packers can potentially save money by treating them with MCP and holding them in regular storage instead of putting them in CA and having to apply a scald control.
Research has shown that the combination of MCP and CA has given the strongest response and longest duration of ripening inhibition, Mattheis said. Long-term exposure to CA makes the fruit inherently less capable of ripening.
Eric Strutzel at Blue Star Growers, Cashmere, Washington, said his company tried using MCP on d’Anjou pears but won’t treat any more because a significant proportion of the pears it sells are conditioned, either before shipment or at the retailer’s distribution center, and the treated pears were difficult to ripen.
“We used it once, and when we took the fruit out and ran it through our preconditioning program, it took five to six times as long to ripen as untreated fruit and never got ripe to the same degree,” he said. However, Strutzel expects the industry will use MCP to lengthen the Bartlett season. If California producers use it to ship pears longer, there will be more overlap with the Northwest season, putting pressure on Northwest packers to shift their season later also. The increasing size of the Northwest crop could also be a factor, he said.
Brad Tukey, with AgroFresh’s research and development department in Yakima, Washington, said MCP-treated pears do ripen, but they ripen differently from untreated fruit, and fruit in CA storage ripens differently from fruit in regular storage. Results also differ depending on variety.
“Apples are very cookie-cutter, but the varieties are different in pears and you have to understand that,” he said.
Nate Reed, director of pome fruit research and development at AgroFresh, said that although MCP-treated d’Anjou pears typically come out of storage 1.0 to 1.5 pounds firmer than nontreated fruit, they eventually ripen to the same point. Fruit held for five to seven days at 50°F should ripen well, even without ethylene, he said.
“I think one of the theories in the commercial world is that a SmartFresh-treated d’Anjou doesn’t ripen. That’s not the case.”
Reed said side-by-side comparisons would show that SmartFresh-treated pears do ripen. Though the time frame might not be exactly the same as with untreated pears, it’s not extended to the point of being commercially not feasible.