A new study shows that broken leaves in bags of prepared salad may increase risks of salmonella. juices which leach from salad leaves cut during harvesting enabled salmonella to grow in water, even when refrigerated. The study carried out at the University of Leicester (1) also showed that the 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.
This 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 refrigerated.
Each year more than 500,000 cases of food poisoning are recorded in the UK, according to a recent report from the Food Standards Agency. While poultry meat was the most common source of infection, some 48,000 cases were linked to fresh non-meat produce including vegetables, fruits, nuts and sprouting seeds.Some recent outbreaks of food poisoning have been associated with contaminated salad or vegetable products, and more specifically, pre-bagged salads. For example, in 2007 a Salmonella outbreak in the UK was traced back to imported basil, and an E. coli outbreak in the USA in 2006 was traced to contaminated pre-packed baby spinach
Professor Frankel Imperial College London (2) says “even though a very small minority of cases are currently linked to salads, the numbers are likely to increase in coming years. In their efforts to eat healthily, people are eating more salad products, choosing to buy organic brands, and preferring the ease of 'pre-washed' bagged salads from supermarkets, then ever before. All of these factors, together with the globalisation of the food market, mean that cases of Salmonella and E. coli poisoning caused by salads are likely to rise in the future”.
1. Koukkidis, G., Haigh, R., Allcock, N., Jordan, S., & Freestone, P. (2017). Salad Leaf Juices Enhance, 83(1). http://doi.org/10.1128/AEM.02416-16
2. How Salmonella bacteria contaminate salad leaves – it's not rocket science. Sept (2008) http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_3-9-2008-10-4-59