Quick summary: While the skin on whole fruits and vegetables protects them, sliced and chopped produce has more vulnerable exposed surface area and can easily support microbial growth. Pre-cut produce, from zucchini zoodles to apple slices, needs to be refrigerated and will likely spoil in obvious ways before it becomes unsafe to eat. However, some less acidic fruits and vegetables, like melons, have been implicated in food-borne illness outbreaks and it’s wise to give some deference to the printed dates on pre-cut produce.
Cutting into produce shortens its shelf life significantly
Whole fruits and vegetables typically don’t bear date labels – their outer skins usually protect them as long as possible, and when they start to spoil, often due to a combination of cells weakened by aging and opportunistic spoilage microorganisms (not microbes that cause human disease), it will be apparent. No expiry date needed.
But once produce is cut, chopped, sliced and diced, it loses the protection of the outer skin and cells are busted open, releasing moisture and nutrients that can immediately support microbial growth. This is why we can store whole bananas and apples on the counter, for example, but need to put them in the fridge once they’re peeled and sliced. And it’s why some pre-chopped fruits and vegetables do bear “use by,” “best by” or “sell by” dates. Without their protective outer skin and with loads of vulnerable surfaces exposed, pre-chopped fruits and vegetables decline much faster than their intact counterparts.
Within the world of pre-cut produce, there’s a wide range of how long the food will last and how much care it needs. In short, be extra cautious with low-acid produce with a lot of vulnerable surface area, especially foods that contact dirt while they’re growing. Melons are high on that list. But even with chopped melon, odds are good that spoilage bacteria will destroy the food before pathogenic bacteria can boost their numbers enough to make you sick. And, if you’re looking for a little more reassurance, high-heat cooking will kill the disease-causing bacteria of top concern on fresh produce.
Produce can have high loads of bacteria and be safe – as long as it’s the right bacteria
After being washed and packaged, fresh produce can have between 1,000 and a million units of bacteria per gram, according to a review in Frontiers in Microbiology And that’s perfectly fine, explains the book, Postharvest Technology of Horticultural Crops: “Products that are visually acceptable to consumers may have high microbial populations. The total microbial population, however, has no direct bearing on the safety of the product.”
This is because most microorganisms won’t make us sick. In fact, some of them, like the type of bacteria used to make yogurt, which is widespread in the environment, are probiotics that are healthy to eat. (Though deliberately eating unknown microbes is obviously inadvisable.)
While outbreaks are rare, it is possible for pathogens including salmonella, pathogenic E. coli and listeria to land on food. If a bacterial cell lands on the raincoat-like outer peel or skin of an intact produce item, the cell will probably just sit there. If, however, a cell lands on the cut-side of a sliced food, it’ll have access to cellular juices and nutrients that will enable it to reproduce over and over again. More bacterial cells make an illness-causing infection more likely. Fortunately, salmonella and E. coli bacteria struggle to grow when food is properly refrigerated (keep your fridge at 40 degrees or less!). L. monocytogenes, which causes a rare, but serious illness, can, however, grow at refrigeration temperatures.
But even listeria can’t usually grow as fast as the spoilage organisms. And those spoilage organisms are pretty good at making their presence known with calling cards that can include slime, odors, a “tangier“ taste and even some fizzing.
Many factors affect how produce ages
Every type of produce is different–variations in acidity, respiration rate, moisture, temperature tolerances, tissue structure and outer skins all contribute to how long a food will stay in peak condition. And that’s even before you cut into the food. According to Postharvest Technology, you can expect a shelf life of about 10 to 14 days for shredded lettuce and cabbage, mixed salads, washed and trimmed spinach, peeled “baby” carrots, cauliflower and broccoli florets and cleaned and diced onions. Fruit, which is biologically programmed to sweeten and soften as it works to spread seeds in the wild, typically doesn’t last as long.
Why does produce turn brown where it’s cut?
Physiologically, a lot happens when you cut into a piece of produce. By breaking open cells, you trigger a defensive response. Compounds normally kept separate within the cells mix with each other and oxygen in a series of reactions believed to ward off insects and microbes. The consequence of all that mixing and oxidizing is the dark coloration that often develops on cut and bruised surfaces, like in apples, avocados and mushrooms.
Of course the brown, black or gray colors that result from this oxidation are harmless to us humans and their presence alone doesn’t mean the food is no longer good to eat (though injured food will clearly go bad faster). Still, I love the drama with which Harold McGee describes the phenomenon in On Food and Cooking: “The brown pigments that we see are essentially masses of spent weapons.”
A faster respiration rate also causes pre-cut produce to age faster
Raw produce is still alive; it takes in oxygen and expels carbon dioxide. Cut surfaces increase the rate of this respiration. For example, according to Postharvest Technology, salad-sized kale leaves respire twice as fast as intact kale leaves. This matters for shelf life because the faster a produce item respires, the more it uses up its limited stash of nutrition. Because the produce is no longer in the ground or attached to the rest of the plant, it can’t replenish those supplies and will eventually fall apart. Like produce weakened by age, produce weakened by cutting is more vulnerable to hungry microbes. The point in its life cycle when a food is harvested also affects its respiration. Postharvest Technology notes that young leaf tissue takes in oxygen and expels carbon dioxide at a higher rate than more mature tissue.
You can slow respiration by keeping produce cool. Refrigeration, of course, also slows microbial growth. (However not all intact produce does well in the fridge, which can actually reduce shelf life for some foods, like squash or eggplant.)
Increased handling of fresh-cut produce provides more opportunity for contamination
By necessity, produce that’s cut and prepped before you purchase it has been touched by more people, utensils, surfaces and machines than the same produce sold in whole form. That additional handling provides more opportunities for bacteria and other microbes to hitch a ride to your kitchen.
Additionally, produce that travels farther from the farm to your store has more time to be contaminated.
Bacteria grow much faster outside the fridge
If chopped fruits or vegetables are left out of refrigeration for a long time, bacteria can grow faster. And, more types of human pathogens can grow at room temperature. So, if, for example, you see cups of chopped fruit displayed without refrigeration, you may want to skip them or commit to eating your purchase right away.
Any packaged, pre-cut produce held outside of refrigeration for an extended period of time could easily go south before it hits its printed date.
So, how should you judge the “best by,” “sell by” or “use by” dates on pre-cut produce?
No matter what date is printed on your pre-cut product, remember that these dates are not “expiration dates.” If the food looks fine, smells fine, has been properly refrigerated and is only a couple days past the printed date, it’s probably OK; though you won’t want to wait much longer as, at the very least, it’s probably about to go slimy or smelly. If you are immunocompromised or risk averse, you may choose to stick to the date. Although disease-causing bacteria are usually outcompeted by spoilage bacteria, Faith Critzer, a food science professor at the University of Georgia, cautions that that doesn’t mean eating slightly spoiled food is risk-free or a good idea.
Even if the food still looks great, Critzer says she tries to eat pre-cut fruit by the “sell by” date. If the date passes and the food still looks good, she said “I would try and consume it two days, three days max after the date.”
Date labels on pre-cut fruits and vegetables may be stamped with a variety of different phrases (“sell by,” “use by,” “best by”). These phrases aren’t regulated and reflect how the company has decided to present its product. That said, the FDA Food Code, which is law in many states, requires that any food prepared on-premises in a grocery store be sold within seven days, a time period designed to prevent listeria infections. This standard, which has a built-in safety buffer, may be why you see “sell by” on pre-cut produce at your local store.
“So it’s not like on the eighth day, everything’s going to explode,” Critzer said. “They’ve added in a bit of a safety factor because they know that we are human beings. Maybe our refrigerators aren’t running right at 40 degrees? Or maybe we temperature abuse our foods and leave them sitting out you know for a brunch or something like that.”
Critzer noted that while it’s less likely, it is possible that older pre-cut produce can look fine, even as it accumulates a larger pathogen load.
“If those spoilage organisms either weren’t there in very high concentrations or there was something that impeded their growth ultimately then the food will look perfectly fine, and [a pathogen] may be there in sufficient numbers to make you ill.”
How long does a party veggie tray last?
Critzer said that leaving freshly cut fruits or vegetables out for the length of a typical party would probably not be enough time for listeria to grow sufficiently to cause an infection in a healthy person. But, let’s not push it.
As with all the pre-cut veggies we’ve discussed in this post, with enough time, the leftovers on the tray would probably spoil before anything harmful to humans could grow, though there’s a non-zero chance that if you waited too long a problematic amount of listeria could grow.
And, different veggie tray items will have wildly different shelf lives. Intact cherry tomatoes don’t even technically need refrigeration. And a whole mini pepper will last longer than a sliced bell pepper. A slice of cucumber, with its exposed sides, will succumb faster than a celery stick that’s only been sliced on each end. While broccoli’s florets can eventually go bad, with only the bottom of the floret sliced, it will probably last longer than the cucumber.
Personally, I try to quickly cook any veggie tray extras. I’ve even been known to take stray carrots, broccoli and pickled veggies home from events where they otherwise might have been trashed. Sautéed alongside some scrambled eggs, they make a great lunch the next day.
What produce is the riskiest?
Generally, fresh produce is healthy to eat and the risks of foodborne illness don’t outweigh the raw foods’ benefits. Outbreaks are fortunately rare and vary from year to year. Multi-state outbreaks often involve food that’s fresh and looks fine, but was contaminated with a large load of invisible-to-the-naked eye pathogenic bacteria. Some outbreaks are also very isolated–think restricted to a single household–and it’s hard to know if the problem was with the food itself or with how consumers handled the food.
Still, microbiologists I’ve interviewed are often wary of sprouts, because the seeds can’t be disinfected and sprouting occurs in a warm, humid, nutrient-rich environment that could nurture pathogenic bacteria. Generally, acidic pre-cut fruits, like oranges, will be better able to hold off pathogens than less acidic fruits like melons (though most fruits won’t last as long as many veggies for reasons we’ve mentioned above). And, as stated earlier, produce with a lot of cut surface area will be more vulnerable.
Recent examples of listeria outbreaks (we’re focusing on listeria as that’s the disease-causing bacteria best able to grow after extended storage in the fridge) include a 2018-2023 outbreak that sickened at least 19 people and was tied to leafy greens (but no specific type or producer was ever pinpointed) and a 2022-2023 outbreak associated with enoki mushrooms that sickened at least five people.
Overall, pre-cut or whole fresh produce is safe and healthy to eat!
Critzer said she avoids sprouts, but that overall, outbreaks are rare and fruit and vegetable growers, shippers and processors are doing the best they can to keep food safe.
“I would say that based upon my knowledge of everything that’s going in in the fresh produce industry, I feel very confident and safe in consuming those food products.”
- Faith Critzer. Associate Professor and Undergraduate Coordinator. Food Science & Technology Dept. College of Agricultural and Environmental Sciences. University of Georgia. Interview Fall 2023.
- Douglas L. Marshall. Chief Scientific Officer. Eurofins Microbiology Laboratories. Also: Technical Director, Refrigerated Foods Association.
- Jeremy Runyan. Business Development. Alliance Analytical Laboratories, Inc. Interview Fall 2023.
- Kathleen Glass. Associate Director. Food Research Institute at the University of Wisconsin.
- Postharvest Technology of Horticultural Crops. Edited by Adel A. Kader. 2002. Chapter: 36. Postharvest Handling Systems: Fresh-Cut Fruits and Vegetables by Marita I. Cantwell and Trevor V. Suslow
- List of Multistate Foodborne Outbreak Notices. Centers for Disease Control and Prevention. Accessed October 2023.
- Zielińska D, Kolożyn-Krajewska D. Food-Origin Lactic Acid Bacteria May Exhibit Probiotic Properties: Review. Biomed Res Int. 2018 Oct 1;2018:5063185. doi: 10.1155/2018/5063185. PMID: 30402482; PMCID: PMC6191956.
- Carstens CK, Salazar JK, Darkoh C. Multistate Outbreaks of Foodborne Illness in the United States Associated With Fresh Produce From 2010 to 2017. Front Microbiol. 2019 Nov 22;10:2667. doi: 10.3389/fmicb.2019.02667. PMID: 31824454; PMCID: PMC6883221.
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