Food Safety News – July 2011
Why are Sprouting Beans such a Problem for Food Safety?
Following further cases of E. coli in France, the Food Standards Agency has revised its guidance on the consumption of sprouted seeds such as alfalfa, mung beans (usually known as beansprouts) and fenugreek.
As a precaution, the Agency advises that sprouted seeds should only be eaten if they have been cooked thoroughly until steaming hot throughout; they should not be eaten raw. The Agency also advises that equipment that has been used for sprouting seeds should be cleaned thoroughly after use. You should always wash your hands after handling seeds intended for planting or sprouting.
The European Food Safety Authority (EFSA) has published its report in the possible sources of the outbreaks in Germany and has concluded that fenugreek seeds, originally supplied from a company in Egypt to a German company, are the most likely link between the two outbreaks. A UK company that has been linked to the outbreak in France is the only UK business currently known to have received the implicated fenugreek seeds via the German importer of the affected batch. Samples of these implicated seeds are currently being tested for E. coli O104:H4
It is not the first time sprouting seeds - including adzuki, alfalfa, lentils and mung beans - have been associated with food poisoning. Most recently they were linked to the German E.coli outbreak; they have also been linked to a salmonella outbreak in the UK and at least 30 outbreaks in the USA since 1996.
Mung beans (beansprouts) are the most popular variety in the UK, however a number of sprouts are now eaten raw as a salad item including alfalfa, lemon grass and fenugreek creating a potential for outbreaks. Imported seeds may also come from sources where Good Agricultural Practice Guidelines do not apply.
Sprouted seeds present a food safety problem because bacteria including Salmonella and E.coli may grow and therefore increase in number during germination and sprouting. Dr Stephen Smith, a clinical microbiologist at Trinity College Dublin, said: "E. coli can stick tightly to the surface of seeds needed to make sprouts and they can lay dormant on the seeds for months, during germination the population of bugs can expand 100,000 fold. Prevention of contamination is probably the most efficient method of ensuring food safety. Seeds can become contaminated from:
- Soil
- Insects during seed development
- Animals and birds
- Animal manure
- Irrigation water
- Harvest of seeds
- Seed processing and shipping
- Damaged/cracked seeds
The risk of contamination of seeds from soil is dependent on the organisms ability to survive in soil. Research suggests Listeria moncytogenes can survive in soil for several months, and salmonella for 200 days (depending on pH, nutrient availability etc.) Research has also found that if soil pores do not become clogged E.coli 0157:H7 is able to travel and survive below the top layers of soil for more than 2 months after initial application.
The use of raw or inadequately treated animal manure as a fertiliser during the growing of seeds is also a likely source of contamination by pathogens such as salmonella and E.coli 0157:H7. For example, E.coli normally lives in the guts of animals and E.coli outbreaks can start when faeces are used as fertiliser or when they contaminate water.
Contamination during harvest of seeds often occurs as the intended use of the crop is only decided after harvesting and there is therefore little incentive to follow good manufacturing practice for human food production during the growth and harvest of seeds. A large outbreak of Cyclospora poisoning involving 1465 cases was linked to poor field handling by workers.
Damaged seeds can also cause issues for food safety. Bacterial cells can lodge in cracks and crevices where they may be protected from, chemical and antibacterial solutions. Bacteria can also live inside the sprout tube as well as outside. Thus washing probably has limited effect. Hence the new advice to only eat cooked sprouted seeds.
Most guidance on sprouting seeds originates from the USA and recommendations include:
- Growing seeds under Good Agricultural Practice (GAP)
- Seeds for sprouting should undergo one or more treatments that have been approved for reduction of pathogens
- Sprout producers should conduct microbiological testing of spent irrigation water.
- Procedures should be in place so that seeds and sprouts can readily be traced to source.
- Planting of seeds should be delayed by 12 months if the land has been grazed by cattle and 6 months if grazed by other livestock.
- Council Directive 686/278/EEC (1996) states sludge should not be used in ground intended for cultivation of fruit and vegetable crops normally eaten raw for a period of 10 months preceding the harvest of the crops and during harvest itself.
- After processing, seeds should be stored in clean areas, and off the floor and away from walls to avoid contamination due to rodents.
- Seed contamination is sporadic and unequally distributed throughout batches, therefore a negative result is not a guarantee of the absence of pathogens.
- There is currently no decontamination method that totally eliminates pathogens.
With all the above in mind, sprouting seeds could potentially be contaminated with a number of pathogenic bacteria. This is why you should treat them as high risk produce. It is essential to source them from reputable suppliers and if you use them only serve them cooked. Ensure that any equipment that comes into contact with the sprouting seeds is thoroughly disinfected and always wash hands after handling this produce.
For more information on how to handle and prepare fresh produce including sprouting seeds safely, click here.
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