By reducing reliance on refrigeration, a new method of sealing organic Granny Smith apples before they go into cold storage could result in lower prices for organic food. It could also make produce from the developing world more available for export, says a recently released study in the Journal of the Science of Food and Agriculture.
In an experiment conducted by Edna Pesis and her team at the Agricultural Research Organization at the Volcani Center, part of Israel’s Ministry of Agriculture and Rural Development, organic Granny Smith apples were pretreated for cold storage according to a method that requires less refrigeration than current methods do.
On the day of harvest, the organic fruit was sealed in jars that had been flushed with low-grade nitrogen. This lowered the oxygen content of the environment to 3 percent. The storage jar was then kept at normal room temperature (20 °C, or 68 °F) for one week. The apples in the jar were then moved into cold storage, where they maintained most of their taste and appearance for six to eight months.
The treatment works, Pesis says, because it “reduced ethylene during storage.” Ethylene is produced when the apple reacts to oxygen in its environment and advances ripening. Reducing the oxygen content when sealing the apple reduces ethylene production and slows apples’ ripening process.
Apples that aren’t sealed through chemical or low-oxygen treatments before they are put into cold storage begin to decay and show what researchers and farmers call superficial scald symptoms. This browning and wrinkling of the peel does not render the apple inedible, but the dehydration does make the fruit less crisp and attractive. Consequently, the apples are saleable for shorter periods of time.
After six months in cold storage, 90 percent of the fruit treated according to Pesis’s method showed no sign of scald. All the untreated control apples were lost after the same amount of time.
The advance is being welcomed by organic apple farmers.
“Anything that helps to store apples better, and doesn’t deteriorate the quality or health benefits, will be a real bonus to apple growers,” says Harry Burton of Apple Luscious Organic Orchards, in British Columbia, Canada.
Currently, organic apples that go into storage are refrigerated at 0 °C (32 °F) under low oxygen conditions. The reduced oxygen content is maintained by a constant flow of low-grade nitrogen, the researchers explained in the paper. (The use of nitrogen and the manipulation of oxygen levels are not considered violations of organic growing principles because the storage environment, rather than the produce itself, is affected.) The refrigeration process is so expensive to maintain that most organic orchards have their fruit turned into apple butter, juice, and sauce rather than put into cold storage. As a result, few organic apples are available past the harvest months, driving up the price of the fruit.
“Refrigeration is very expensive, and we try to have all our apples sold fresh or made into organic cider for sale in the health-food market at the end of the season,” says Gaye Trombley, an organic apple farmer at Avalon Orchards, in Ontario, Canada. “If refrigeration costs were less and quality could be retained, we would consider storage, as the value of the fruit would increase over the winter months.”
Nonorganic apples are usually treated with inexpensive preparations of antioxidant diphenylamine (DPA) or 1-methylocylopropene (1-MCP) before they are put into cold storage for consumption up to 12 months after they are harvested. While untrained taste testers in Pesis’s study believed that the apples treated with 1-MCP tasted better after storage than the organic apples, the organic fruit subjected to the new method alone was considered almost as good as that treated with chemicals.
The study says that variations in the method could be used to extend the shelf life of other organic produce, including strawberries, tomatoes, persimmons, and other varieties of apples.
While less of a reliance on refrigeration should make organic produce easier and cheaper to store, the research team’s report states that “the simplicity, low cost and efficacy of this new apple treatment” also make it suitable for use in developing countries. In the developing world, where refrigeration is less available and power supplies to maintain low temperatures are less reliable, it’s difficult for food producers to get their less expensive produce to richer Western markets. Avoiding chemical treatments also lowers the cost of apple storage for developing-world producers.
“I cannot tell you if the treatment will be cheaper than the use of DPA,” Pesis says, “but I am sure it can be cheaper than use of MCP.”
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