Nutrition

Pathogens and agricultural chemicals in fresh produce pose a risk that should be taken seriously.

Pathogens and agricultural chemicals in fresh produce pose a risk that should be taken seriously.

Question

Everywhere I went over summer, people were serving unwashed raspberries and strawberries. What are the rules here? Can you get sick from them?

Answer

Unwashed fruit and vegetables can harbour harmful bacteria and viruses that can certainly make us sick. Indeed, in March, Gisborne-based produce supplier LeaderBrand recalled some salad products because of the possibility that they had been contaminated with harmful Listeria. Contamination of produce can occur at any point, from before harvesting in the field to serving at the table, with pathogenic (disease-causing) bacteria such as Salmonella and Campylobacter to viruses such as hepatitis A and the noroviruses, and parasites such as Cryptosporidium and Giardia. These foodborne pathogens aren’t common in fresh produce, but they have all caused outbreaks at different times around the world, says microbiologist Graham Fletcher, the research team leader for food safety and preservation at Plant & Food Research.

Washing helps to remove pesticides and chemical residues on fresh produce, he says, and typically reduces the quantity of pathogens. “It does make some difference and any difference is good, but it won’t remove all contaminants.”

The more thorough the washing the better, says Fletcher, but that depends on the produce and how much washing it can withstand: scrubbing hard-skinned vegetables such as cucumbers or potatoes under running water is a good idea. “The bacteria actually stick quite hard to cucumbers.”

Obviously, berries can’t withstand vigorous scrubbing. Fruits and vegetables with convoluted surfaces, such as raspberries or broccoli, should be soaked in water, with a little agitation to loosen any matter stuck to them, and then rinsed under clean water to wash away any contaminants.

As for Listeria on salad leaves, no amount of washing can completely remove the serious health risk for people with compromised immune systems – pregnant women and their unborn babies, the very elderly and those undergoing chemotherapy. In 2015, just 26 notified cases of

listeriosis were reported, but four people died, three of them unborn babies. By contrast, campylobacteriosis is very common: there were 6218 notified cases in 2015, but no deaths. Hence the recent recall of all salad products potentially contaminated with Listeria.

Most human pathogens are transferred by infected hands touching produce or prepared meals, but Listeria is an environmental organism, says Fletcher. “It’s naturally present in the soil, in decaying leaf matter and in a lot of environments.” So it’s difficult for the food industry to keep Listeria out of the supply chain, especially in warm and moist food-processing environments

“A number of industries, particularly those dealing with meat, seafood and dairy products, where there is a lot of protein around, put a lot of effort into preventing Listeria growing in their environment.”

Cooking food at high temperatures can destroy most harmful foodborne pathogens. The Ministry for Primary Industries recommends boiling frozen imported berries, after an outbreak of hepatitis A in New Zealand was linked to them (bring frozen berries to the boil at 85°C for at least a minute). Foodborne illness outbreaks have also been linked to frozen berries in Sweden, Australia, the US and Ireland. However, this isn’t an option with fresh salads or other produce intended to be consumed raw.

Ultimately, fresh produce is grown in soil, which naturally contains bacteria, and there’s a good chance agricultural chemicals have been used on it too.

Aside from peeling and cooking, washing is our best line of defence as consumers, Fletcher says. “The more protection you have the better.”

In 2015, just 26 notified cases of listeriosis were reported, but four people died, three of them unborn babies.