According to the Federal Institute for Risk Assessment high bacteria loads in fresh packaged sprouts and ready-to-eat salads are likely caused by a combination of factors including poor processing hygiene and humid conditions fostered inside plastic packaging. Contribution to contamination also occurs during the growth and harvesting of the products because bacteria are carried by animals and occur naturally in the environment. Studies found that while both products are stored under refrigerated conditions they still carry a risk of contamination with bacteria such as Listeria monocytogenes, Salmonella and E.coli, as well as viruses such as Norovirus and Hepatitis A. The Federal Institute for Risk Assessment found that samples of fresh packaged sprouts and shoots had bacteria numbers “increase considerably within a few days” and had an above average microbial load when they reach the best before date”. They report that a study of 133 bagged salads in 2008 found five per cent contained Listeria, particularly mixed salads consisting of white cabbage.
The Federal Institute for Risk Assessment has listed a range of potential causes for bacterial contamination including:
Irrigation with contaminated water or use of manure
The cultivation of sprouts in special containers promotes the growth of bacteria
A lack of hygiene during processing such as the use of contaminated washing water or a lack of refrigeration
Whole lettuce and white cabbage can provide natural protection against bacteria but this is broken once the vegetables are cut, with the release of cell sap providing a medium for the bacteria to multiply
Bacteria can also adhere to the surface of plants, especially white cabbage.