Most of us are aware of the hazards presented by poorly cooked foods such as burgers or chicken. Failure to cook them thoroughly can lead to a nasty dose of food poisoning or worse. However, pathogens can also be found in raw foods such as salads and carrots, and care must be taken at every point along the chain from farm to fork to ensure they are safe to consume.
This was the main topic for consideration at a workshop hosted by Teagasc at the end of last year. The workshop brought together international researchers, regulators, growers and other stakeholders and focused on examining best practice for the control of human pathogenic micro-organisms in plant production systems.
“Our focus was on plants which are eaten in the raw state,” says Teagasc soil microbiologist Dr Fiona Brennan. “This includes salads, spinach, carrots, and so on. The consumption of these crops is increasing as people become more aware of the positive benefits of including them in their diets.”
But foods that are not cooked carry their own risks. “Heat attenuates pathogens,” she says. “Raw food is not heated, so if pathogens are present people will consume them.”
The workshop was the culmination of the EU-funded research project, Huplantcontrol. The focus of the project was mainly on zoonotic pathogens – those that originate from animal sources.
“There are three main pathogens of concern,” says Dr Brennan. “Shigatoxigenic Escherichia coli (Stec), salmonella enterica and listeria monocytogenes are the predominant cause of foodborne outbreaks in edible crops and are responsible for more than 80 per cent of cases. The first two are zoonotic while listeria is native to soil. The primary reservoir for shigatoxigenic Escherichia coli is bovine animals. For salmonella enterica it is chicken.”
Faecal contamination
The main sources of those two pathogens on farmland tends to be faecal contamination. “You can find it in water, or it can come from animal waste. It can also be present in the natural environment through things like bird droppings and so on. If contamination occurs there is a risk that it will end up in the final product and then be consumed.”
Fortunately, outbreaks of food poisoning associated with raw plants are not common. “They are quite sporadic but we have seen some bigger ones, such as in Germany in 2011 they had an E.coli outbreak associated with fenugreek sprouts, which can be eaten raw in salads. There was a more recent outbreak in the US associated with lettuce.”
However, changes to consumption patterns are leading to increased concern. “People are changing how they consume crops,” she adds. “For example, we would have traditionally always cooked mushrooms, but they are now going raw into salads. That changes the risk. We are also seeing more complex global distribution networks created by consumer demand for crops out of season. Trends are changing and consumers are demanding less plastic use and that changes how food is delivered.”
Increased handling
Those longer and more complex supply chains combined with diminishing use of plastic packaging exposes the crops to increased handling and potential contamination. The problem is exacerbated by the fact that the pathogens can become internalised, and washing may not be effective in removing them.
“The focus has to be on avoiding the pathogens getting into the food chain in the first place,” says Brennan. “Fortunately, we have a lot of knowledge in relation to that. Among the most important good practices is to make sure animals don’t get in and that nobody is spreading slurry that can contaminate the crop. We are also seeing more extreme weather events. During droughts, the increased demand for water can be a problem. Growers have to make sure their water is good quality. And during flooding, they have to ensure there is no contamination as a result of floodwaters.
“Good practice is to keep animals out and protect water sources. Staff training and good hygiene practice are also important. It’s about doing a lot of simple things well. Growers have to look at how they assess risk. They need to look at every stage, assess risk at every step and do their best to ensure that the crop goes out safe to consume.”
But that can be challenging for growers. “It is difficult for growers,” says Brennan. “They are operating on extremely tight margins. What we were trying to do in workshop was bring together the growers with the scientists and advisers. There can be a lot of paperwork but what happens on the ground is what really matters. We want to make sure that the guidance is workable for the growers and their staff. Consumer confidence is critical, and we want to ensure that consumers are not turned off things that are good for them. It’s one thing having guidance and regulations, but the motivation and reasoning behind them must be made clear to the growers.”