What you see: Brownish discoloration inside a plum
What it is: Likely flesh browning from too-cold storage
Eat or toss: The plum doesn’t taste good, right? It’s probably mealy and relatively flavorless. It won’t hurt you, but if you aren’t enjoying it, go ahead and toss.
There are a couple things that could be going on here. This plum could be genetically programmed to have different colored flesh. Or it could have gotten so much sun exposure that it “burned” and some of its flesh turned brown. But most likely, somewhere along the line, this plum was too cold for too long. And it started changing for the worse.
Plums, like most produce, are often chilled to help keep them fresh between the farm and the store. Consumers might also stash them in the fridge, thinking it will keep them fresher longer. But, while properly executed chilling extends their lifespan, it can be hard to get right. The stone fruits generally aren’t happy at refrigerator temperatures or cooler for long stretches. A series of awful things occurs.
Flavor goes first
First, the volatiles, the compounds that give plums their yummy flavors, start to abandon ship. Volatiles are the result of certain enzymatic activity. Macarena Farcuh, an assistant professor in horticulture at the University of Maryland, points out that temperature change does a number on how enzymes function in certain fruits.
Then, texture suffers
After the tastiest volatiles flee, the texture suffers. Cold temperatures mess with cell walls and moisture migrates away, making the fruit flesh feel dryer and softer—ultimately mealy. Bite into a nicely ripened fruit, and you’ll encounter cells that are like tightly filled water balloons; your teeth will bust them open, releasing bursts of juice. But when you bite into mealy fruit, your teeth don’t break open cells. Rather, your teeth cause the cells to separate and slosh around and you get dry fruit tissue with little flavor.
This plum may also be displaying what’s called “gel breakdown.” Another symptom of too-cold storage, this happens when fluids leak out of cells and are absorbed by certain compounds in the fruit, leading to a loss of juiciness and a translucent-looking flesh.
Finally, the flesh turns brown
Now that we’ve lost flavor and texture, the next stop on the fruity chilling injury train is browning. At this stage, the cells leak various chemicals normally kept apart. Those chemicals react, creating an unappealing brown color.
By this point, the fruit has lost flavor, texture and visual appeal. As long as you didn’t spot any mold or rotting areas, it’s unlikely to hurt you, but it’s also unlikely to provide a pleasant fruit eating experience. If you’re enjoying eating this fruit though, keep eating. Otherwise, you have our permission to drop it in the compost.
Lots of factors to balance
Making sure that fruit reaches consumers in the best possible condition is challenging for the fruit industry, said Farcuh, whose Ph.D. work focused on plums. Careful temperature management—including some cold storage—can extend the life of the stone fruits without quality consequences, but factors like harvest timing and variety can make such treatment hard to calibrate. Often, the fruit can look fine and the chilling injury doesn’t become apparent until the consumer takes a bite.
“Many times in order to make the fruit able to be shipped you have to compromise a little of the flavor,” Farcuh said. “At the end the consumer is the one who pays for the problem.”
How to store your plums
But, to be fair, the consumer can also cause the problem. If you buy hard plums and plan to let them ripen at home, don’t put them in the fridge. The cold temperatures could cause the issues described above. Instead, Farcuh says, keep them on the counter, stem-side down, until they soften. Don't stack them as this could lead to bruising. Once they're ripe, either eat them right away or put them in the fridge to slow aging. Fully ripened fruit is less susceptible to cold temperatures than fruit that’s still softening and developing its flavors.
Dr. Macarena Farcuh, PhD. Assistant professor in horticulture. College of Agriculture and Natural Resources. University of Maryland.
Physiological Disorders. Book chapter made available by the Institute of Food and Agricultural Studies at the University of Florida.
Fruit Ripening & Ethylene Management Workshop: Cold Storage Disorders of Fruits and Vegetables. Slide deck by Mikal E. Saltveit. Department of Plant Sciences. University of California, Davis. 2017.
Cell wall modifications in chilling-injured plum fruit (Prunus salicina). G.A. Manganaris, A.R. Vicente, C.H. Crisosto, J.M. Labavitch. Post Harvest Biology and Technology. 2008
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M. A. Taylor, G. Jacobs, E. Rabe & M. C. Dodd. Physiological factors associated with overripeness, internal breakdown and gel breakdown in plums stored at low temperature. Journal of Horticultural Science. 1993.