Salmonella warning over supermarket salad bags
18th November 2016 -- Juice leaking from damaged leaves in supermarket bags of salad could encourage Salmonella bacteria to grow, according to University of Leicester research.
However, food safety officials are playing down the risk to health.
There are more than 500,000 cases of food poisoning in the UK each year.
Poultry meat is most often to blame, but around 48,000 cases are caused by fresh vegetables, fruit, nuts and sprouting seeds.
Bagged salads are a quick way to get some green leaves onto the dinner table, but the Leicester scientists wanted to investigate the risk of food poisoning they may pose - and whether this could be prevented.
Laboratory tests were done on salad leaves to see if bacteria grew on them in the lab. Although there could be implications for salad bags, the research didn't look directly for traces of Salmonella in bags. However, damaged leaves were studied individually.
They found that juices seeping out of any broken or cut leaves were far more likely to help Salmonella grow - even stored correctly in the fridge.
The findings are published in the journal Applied and Environmental Microbiology.
Dr Primrose Freestone from the University's Department of Infection, Immunity and Inflammation says in a statement: "Salad leaves are cut during harvesting and we found that even microlitres of the juices (less than 1/200th of a teaspoon) which leach from the cut-ends of the leaves enabled Salmonella to grow in water, even when it was refrigerated.
"These juices also helped the Salmonella to attach itself to the salad leaves so strongly that vigorous washing could not remove the bacteria, and even enabled the pathogen to attach to the salad bag container."
She says the findings are important for the food industry: "This strongly emphasises the need for salad leaf growers to maintain high food safety standards as even a few Salmonella cells in a salad bag at the time of purchase could become many thousands by the time a bag of salad leaves reaches its use by date, even if kept refrigerated. Even small traces of juices released from damaged leaves can make the pathogen grow better and become more able to cause disease."
Dr Freestone says there's also a message for consumers about storing salad after the bag has been opened: "It also serves as a reminder to consume a bagged salad as soon as possible after it is opened. We found that once opened, the bacteria naturally present on the leaves also grew much faster even when kept cold in the fridge."
So should you be concerned next time you are in the supermarket salad aisle?
We asked the Food Standards Agency to comment on the research. "Salmonella is not a problem regularly linked with bagged salads – there has only been one incident reported to the FSA in the past 5 years," the agency says in an emailed statement.