Chemicals not needed in storing apples

EAST LANSING, Mich. – Researchers at Michigan State University have found a way to prevent apple scald without chemicals when storing apples.



When refrigerated long term in controlled-atmosphere storage, apples will often react by developing scald, a physiological disorder. This scald can ruin millions of tons of apples annually unless the fruit is first treated to a dip in diphenylamine (DPA) and a fungicide before going to storage.



Michigan State University horticultural researchers David Dilley, Zhenyong Wang and John Golding have found an alternative method of controlling apple scald without any chemicals. This method involves subjecting the fruit to certain oxygen levels that keep the apples scald free as well as flavorful and firm.



After more than 30 years of research, this is an important breakthrough for apple storage and marketing in Michigan and the United States.



“Numerous countries have banned the use of DPA and prohibited importation of fruits so treated,” said Dilley.



“We were able to completely control scald in apple by subjecting them to an initial low oxygen stress at 0.5 percent oxygen for three weeks at the start of the storage period and then holding them at 1.5 percent oxygen for the remainder of the eight-month storage period.



The researchers used highly susceptible cultivars (apple varieties prone to scald) from 10 different grower orchard blocks in Michigan. This was a repeat of a large experiment conducted at the MSU Clarksville Horticultural Experiment Station in 1997-98.



Dilley noted the incidence of decay in the apples was very low, apple firmness was high and flavor quality was excellent.



“Our storage regimen that controls scald is completely applicable and readily possible by all controlled-atmosphere storage operators using equipment already in place at most storage facilities in Michigan and elsewhere,” Dilley said.



“This means apples do not have to be drench-treated with DPA before storage to control scald. Moreover, the use of the thiabendazole fungicide required to control decay when fruits are drenched with DPA can be avoided.



“Collectively, this means more wholesome, higher quality and less chemically burdened apples for the consumer,” he said.



Also important is the cost savings to growers and operators. In Michigan alone, more than $500,000 is spent annually to treat apples with DPA to control scald in controlled-atmosphere storage.



Nationally, the cost savings approach $2 million to $3 million annually. It also means an expansion in marketing opportunities for apple growers and processors.



Dilley said many Michigan apple storage operators and many in Washington state have begun using this storage regimen.