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But sometimes, as is the case with our recent tests of frozen fruits and veggies, we get good news. Our food scientists recently tested more than 300 samples of eight types of frozen produce and didn’t find any harmful bacteria.
Most frozen vegetables are blanched in hot water or steamed before freezing, which may lead many to think they are already cooked and risk free — people let their toddlers snack on frozen veggies, or might toss them into a salad without cooking them first. But though frozen produce is convenient and generally safe, it may still harbor bacteria that cause foodborne illness such as Listeria monocytogenes or salmonella.
In 2016, there was a recall of more than 450 frozen produce items from at least 42 brands because they were linked to a multistate outbreak of listeriosis, the disease caused by Listeria monocytogenes. Since then, frozen fruits and vegetables have been recalled at least 20 times because of possible contamination with listeria, hepatitis A or norovirus, according to data from the Food and Drug Administration — often discovered as a result of routine testing, not because someone got sick.
“Produce can be contaminated at a farm or when it’s harvested,” says Sana Mujahid, manager of food safety research and testing at Consumer Reports. “Any additional step — including packaging at a processing facility — can create another opportunity to introduce foodborne pathogens like Listeria monocytogenes or E. coli to food.”
Listeria is of particular concern. Most healthy adults exposed to the bacteria typically don’t get very sick, though some may have fever and diarrhea, similar to other foodborne germs. But people who do develop listeriosis often need to be hospitalized, and about 20 percent die, according to the Centers for Disease Control and Prevention. Those at highest risk are immunocompromised people, newborns, older adults and pregnant people (an infection can lead to miscarriage). And once listeria contaminates a production facility, getting rid of it can be extremely difficult, especially because freezing doesn’t kill it, and it can grow and thrive at refrigerator temperatures.
What our tests found
With that history in mind, CR’s food scientists wanted to evaluate frozen fruits and veggies to assess how high the risks are — especially because frozen food sales have increased during the pandemic, according to the American Frozen Food Institute. Sales of frozen fruit spiked almost 30 percent during the first year of the pandemic, and sales of frozen vegetables grew about 15 percent, according to a 2021 AFFI report.
For our tests, we looked for E. coli, listeria and salmonella, types of bacteria that commonly cause foodborne illness, in eight frozen categories — avocado, berries, corn, mangoes, peaches, pineapple, spinach and smoothie mixes. In total, we included 369 items from big brands, private label and store brands, including 365 by Whole Foods, Blendtopia, Birds Eye, Campoverde, Dole, Great Value, O Organics and Trader Joe’s.
The results were reassuring. “We didn’t detect bacteria that could make someone ill,” Mujahid says. “We consider frozen fruits and vegetables to be low-risk in general, though people at high risk for foodborne illness may always want to take certain precautions.”
Since 2017, the frozen food industry has taken steps to try to reduce the risk for listeria, according to the AFFI. In 2019, the group published its Listeria Control Program resources, which recommended best practices for frozen food manufacturers, including sampling for listeria and ways to routinely clean and sanitize industrial freezing equipment.
Still, there’s always some risk, and our findings don’t mean that all frozen produce is pathogen-free. We didn’t check for hepatitis or norovirus, which require a different test. From 2017 to 2021, frozen fruits and vegetables were responsible for more recalls because of listeria, norovirus or hepatitis A than any other frozen food category, according to CR’s food safety team. “That’s why heating frozen vegetables is important, especially for people at high risk,” Mujahid says.
Yet it’s a common misconception that you don’t need to cook frozen vegetables, even when packaging says these products are meant to be cooked. And many people eat frozen fruit without cooking it — when making smoothies, for example — which is why the FDA has been sampling frozen berries to look for pathogens. (Berries and other frozen fruit are considered ready to eat, the AFFI says.)
Frozen vs. fresh benefits
Most of us need to eat more fruits and vegetables — approximately 90 percent of adults don’t meet the recommended intake, according to the CDC.
Frozen produce can make that goal easier to reach. It requires no washing or chopping, and, as anyone who has reached into a crisper drawer to find a withered head of broccoli or a package of limp carrots can attest, they’re less likely to go bad before you get a chance to use them. The average American family of four wastes about $1,500 worth of food each year, according to the Agriculture Department — and tossing fresh fruits and vegetables accounts for a large portion of that.
Frozen also is comparable to fresh nutritionally. “Fruits and vegetables are packed with nutrients — and that doesn’t change when they are frozen,” says Amy Keating, a CR nutritionist. “Consumers should buy what is available, and fits their storage needs and their budget, and not worry about any variability in fresh versus frozen.”
Nutrient levels can be affected by a number of factors, including how fruit and vegetables are grown and how long they spend in storage before being sold. Because produce is frozen close to harvest, it may in some cases maintain its nutritional profile longer than fresh fruits and veggies that can lose vitamins on the journey to the grocery aisle and then while stored in your fridge.
Research has generally found that the nutritional differences between fresh and frozen produce are small. In one 2015 study, researchers compared the level of four nutrients in eight types of fresh and frozen produce and found that in some cases, frozen versions of a food had higher vitamin levels. Another study, from 2017, that looked at a form of vitamin C, provitamin A, and total folate in eight fruits and veggies found that for the most part, vitamin levels in frozen produce were similar to those in fresh produce. Frozen versions were better than fresh items that had been stored in a refrigerator for five days.
None of this means that people should avoid fresh produce and seek out frozen or vice versa, Keating says. “Choosing a variety of types and sources, including fresh and frozen produce, is your best bet,” she says.
Copyright 2022, Consumer Reports Inc.
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