A team of researchers at the University of Leicester found that juices released from the cut ends of salad leaves enabled Salmonella to grow in water.
The study, published in the journal Applied and Environmental Microbiology reads: “Salad leaves are an important part of a healthy diet but, in recent years, have been associated with a growing risk of food poisoning from bacterial pathogens such as Salmonella.
“Although this is considered a significant public health problem, very little is known about what happens to the behaviour of Salmonella when in the actual salad bag.”
Salad juice exposure not only encouraged Salmonella growth but helped the cells attach to leaves so strongly that they could not be removed by washing, they discovered.
Salmonella poisoning symptoms include severe diarrhoea, fever and abdominal cramps – which can last up to seven days. In most cases, individuals recover without treatment but it can be fatal.
Stuart Kelly, managing director of food safety specialists Acoura, told The Morning Advertiser (MA): "Chlorine-free washes for fruit and salad such as Sustain are becoming increasingly popular and are now being used by some of the UK's largest pub and restaurant chains.
"We've found them to be an excellent alternative to chemical-heavy options, which can often leave food with an unnatural flavour."
He added: "Obviously there are real benefits in preserving the taste customers expect when dining out while also protecting them from harm, so we'd recommend exploring these options."
Public Health England (PHE) issued a warning to operators earlier this year urging them to wash all salads thoroughly after two people died of E.coli and a further 62 were hospitalised.
PHE discovered several of the individuals affected had eaten mixed salad leaves prior to becoming unwell and admitted it was a possible cause.