Bagged salads such as the ones displayed at a Trader Joe's in Arlington, Mass., were the subject of a recent food safety study at the University of Leicester in the United Kingdom.
Bagged salads such as the ones displayed at a Trader Joe's in Arlington, Mass., were the subject of a recent food safety study at the University of Leicester in the United Kingdom.

Food safety experts and salad companies expressed skepticism about a recent study in the United Kingdom that raised concerns of salmonella in bagged salads.

Researchers at the University of Leicester found that if salmonella makes it into a bagged salad, the juice from damaged salad leaves will encourage the growth of salmonella and enable bacteria to adhere so strongly to the salad leaves that they cannot be removed even with “vigorous” washing, according to a news release. The study also said exposure to leaf juice can make salmonella more likely to cause infection.

The study found, too, that salmonella can grow in a salad bag even when the bag is refrigerated.

Bruce Taylor, CEO and founder of Salinas, Calif.-based Taylor Farms, emphatically denounced the study.

“We find the artificial conditions created by this study to be ridiculous,” Taylor said in an e-mail. “Producers of bagged salads do not have ‘juice’ in the salad bag, and producers take painstaking steps to avoid the introduction of salmonella or any other pathogen.”

The conclusion regarding refrigeration was the only notable one in the study, said Trevor Suslow, a member of the technical committee of the Center for Produce Safety. Scientists would expect salmonella to be able to survive at the temperature recorded in the study but would not expect it to grow, he said.

“People will definitely be trying to reproduce their results as far as growth under refrigeration temperature for salmonella,” Suslow said. “That’s, for me, the key issue.”

Suslow, an extension research specialist at the University of California-Davis, said it is already known that a bagged salad is an environment in which salmonella can have the nutrients it needs to grow, which is why the industry has focused so intently on ensuring no pathogens make it into bags into the first place.

Drew McDonald, vice president of quality, food safety and regulatory affairs at Salinas-based Church Brothers Farms, said in an e-mail that, although the researchers did some things well, he also had some issues with the study.

“From my read, the study essentially grew salmonella in juices extracted from actual bagged salads in a mixture of sterile water,” McDonald said. “The issue is that in the ‘real’ world the salmonella has to come from somewhere (the surface of the leaf for example) but along with this would be many other microorganisms. That they were able to grow salmonella under these forced, artificial conditions without any competition from other organisms is not surprising.”

Along with the growth conditions, the washed status of the lettuce also gave McDonald pause.

“From my understanding, (the) project used ‘bagged salad,’” McDonald said. “I am assuming this means it was already washed. The fact that they added salad juice and salmonella after it had already been bagged and washed really just shows how important it is to not cross-contaminate cleaned product.”

The researchers, as a result of their findings, suggested people eat bagged salads as soon as possible after purchase to minimize risk. They wrote in a question-and-answer supplement to the release that they no longer keep their bagged salads in the refrigerator longer than one day.

“Ridiculous recommendation,” Taylor said in his e-mail. “For 30 years consumers have enjoyed hundreds of millions of bagged salads weekly with great benefit to their health and wellbeing.”

Jennifer McEntire, vice president of food safety and technology at United Fresh Produce Association, also disagreed with the recommendation.

“People should always follow the instructions, including best-by dates, on packages, mainly so that they experience the best quality product,” McEntire said in an e-mail. “People shouldn’t be afraid to keep salad in their refrigerators for the full duration of the shelf life.”

McDonald also suggested the recommendation should not have gone as far as it did.

“I would edit the recommendation to state that eating fresh vegetables — cut, uncut, fresh, or washed and bagged — is important for our health, but ensuring the produce is healthy-looking, clean, and relatively free of defects or poor quality such as pooled water in the bag is important to reduce food safety risks, too,” McDonald said in his e-mail.

Suslow described the study as another piece of the puzzle in trying to find long-term solutions for food safety issues, but he was not impressed by it.

“Sort of generating a lot of additional concern and fear without any real basis for changing what (is) sort of standard practice isn’t necessarily helpful,” Suslow said. “Could hurt the category, but probably no more so than other things such as those instances when there are outbreaks or recalls.

“I think consumers understand that there’s no such thing as zero risk,” Suslow said. “They understand and appreciate the convenience of packaged salads with multiple ingredients with very healthy mixed leafy greens, and that’s how the category has grown.”

McEntire also said she expected the effect of the study on the category to be minimal.

“I hope people realize that salmonella won’t grow in salad, or any other produce, if it’s not there to begin with, and the industry does an incredible job producing safe fruits and vegetables,” McEntire said in her e-mail. “This study shouldn’t change people’s perception of the safety of these products. Additionally, with so much conflicting information regarding all types of foods, consumers may be desensitized to these types of reports.”

McDonald, too, didn’t expect many to abandon their bagged salads in reaction to the study.

“I would expect, at worst, some might respond to the potential underlying message of the ‘dangers of lettuce juices’ and stop their home-juice diets while others perhaps might become more sensitized to decaying produce or pooled water in bagged salad bags,” McDonald said in his e-mail. “Of course, I would anticipate that many will continue to eat their delicious, healthy fresh-cut salads.” 

The study was posted Nov. 18 on the website of the journal Applied and Environmental Microbiology.