Listeria in frozen vegetables: how to reduce risks
EFSA has assessed the risks to public health from Listeria contamination of vegetables that are blanched - scalded in hot water or steam for a short time - before they are frozen. They conclude that the risks associated with the consumption of these products is lower than for ready-to-eat foods such as smoked fish, cooked meat, sausages, pâté, soft cheese - which are usually associated with listeria contamination.
Food business operators often blanch vegetables before freezing them because this stops enzyme actions which can cause loss of flavour, colour and texture.
EFSA's experts identified relevant control activities that food business operators can implement to lower the risks of contamination of frozen vegetables. These range from cleaning and disinfection of the food producing environment to water, time and temperature control at different processing steps, and accurate labelling.
They stress the importance of monitoring the food producing environment for Listeria monocytogenes. This is because Listeria can persist in the food processing environment from which it can contaminate food.
EFSA also makes recommendations on how to reduce risks at home. The key is to maintain good hygiene practices such as storing frozen or thawed vegetables in a clean freezer or refrigerator at the appropriate temperature and following the instructions on labelling for safe preparation. In general, risks are much lower if vegetables are cooked properly after defrosting. This work was triggered by a multi-country outbreak that affected 53 people and caused 10 deaths between 2015 and 2018.
Listeria is a family of bacteria that contains ten species. One of these, Listeria monocytogenes, causes the disease listeriosis. According to the latest European Union One Health Zoonoses Report from EFSA and the European Centre for Disease Prevention and Control (ECDC), the number of people affected by listeriosis in 2018 is similar to 2017 (2,549 cases reported in the EU in 2018 against 2,480 the previous year). However, the trend has gone up over the past ten years.
Listeriosis symptoms vary, ranging from mild flu-like symptoms, such as nausea, vomiting and diarrhoea to more serious infections such as meningitis and other potentially life-threatening complications. The disease primarily affects the elderly, pregnant women, new-borns and people with weak immune systems.