Is salad really 'rocket' science?

This week saw the start of planning for a new module in Fresh Produce Post Harvest Quality Management. This is so new that we only just preparing a draft “Module Description Form”, the first piece of documentation, presented at a University Board of Studies meeting which, when finally ratified, provides the quality assurance for teaching, learning outcomes, assessment mechanisms and delivery methods which bears the university’s stamp of approval.

Now this subject is my closest colleague and partner in coffee drinking’s bag, so to speak. Carol Wagstaff, that is, Director for the AFTP, Associate Professor in Crop Quality for Health and a real-life rocket scientist (and avocado, lettuce, strawberries, in fact fresh produce generally).

So, what better subject for conversation than the headline to hit the news recently about deadly bagged salad. In our house we buy bagged salad. I’m not terribly comfortable with that, I reckon I’m pretty good a taking a leaf off a lettuce every now and then. But the bagged salad certainly means we waste less, unless of course it gets trampled to puree by the dog or it freezes to the back of the fridge and turns to some sort of soup. So it was with interest I read about the deadliness that my husband puts in his lunch every day.

Online the Sun, Express, Huffington Post, Metro, CNN, CBS, BBC, the Telegraph….all carry terrifying warnings about the salmonella breeding grounds we buy every week. According to the Metro “experts” are warning us to avoid ready cut salad whenever possible but if you have to eat then wash it thoroughly. Now what the expert actually said, the person who did this piece of research, Dr Primrose Freestone from the university of Leicester, was that it should be eaten as soon as possible after opening the packet. She didn’t mention avoiding it. And that washing didn’t make much difference.

So I asked Carol what the fuss was about. Was it going to give my husband a bacterial infection to end all bacterial infections? She said that from a consumer perspective there was an enormous misconception in that sterilisation and sanitation are believed to be the same, when in fact they are poles apart. Your bagged salads are not supposed to be sterile, simply sanitised which means that they are free from bacteria that cause human disease. Washing makes a limited difference to the total numbers of bacteria on the leaf  – bacteria can hide in all sorts of nooks and crannies on the surface of the leaf, the stomata are full of them. But this isn’t a problem, they are naturally there, supposed to be there. All but only a vanishingly small proportion of them are non-pathogenic and even Cecil the Very Hungry Caterpillar wouldn’t be likely to eat enough to make him sick. In fact, going back to our news articles, hidden amongst the terrifying “facts” were figures from the FSA (Food Standards Agency) which said that there are 500,000 cases of food poisoning in the UK a year but in the last 5 years there has only been one case of salmonella poisoning linked to bagged salad. That’s one in 2,500,000 cases over five years!!! Now I’m not a betting person, but those are not exactly death-defying odds.

So, is it a breeding ground for salmonella? Yes, of course it is. Will it make us sick? “How could it?” Carol said. Confused look from me. “Well you wouldn’t eat it anyway” she said. “It smells rank”. OK. Fair point well made. As she said, human biology is pretty well evolved to tell us what not to eat – if it’s gone hairy or smelly we tend to turn our nose up at it and for good reason. She did concede that biology doesn’t always get it right and shell fish is a good example where humans can get food poisoning from a product that looks and smells okay. The bacteria that do remain on a leaf in your salad are either completely inert, i.e. they landed their by accident when the plant was growing, or they are linked to causing food spoilage – i.e. they are the cause of the rank smell and the soupy contents at the bottom of an aged salad bag that makes it unattractive to eat - thereby protecting you from inadvertently consuming pathogenic bacteria that like to multiply using the broken down leaf material as a source of nutrients and energy.

Most food-borne illnesses tend to be associated with contaminations from the field. Because most salads are washed before they are processed then this point of contamination is removed. This care in the processing order of events helps to protect the sanitation of the crop. And this is exactly what Carol covers in “Sustaining Quality in Raw Material Supply Chains” and she and Emma Bennett draw on in the Sustainable Supply Systems Workshops, particularly part 1 from Production to Processing.

A couple of the articles talked about the packaging and this, she said, is where it gets really clever. Now I assumed that there was some sort of special gaseous atmosphere introduced to the packets to prevent spoiling, a bit like they do with meat products but I must confess that I was a bit unsure about this because one year, as part of Sustainable Supply Systems, we went to Vitacress’ factories and I don’t remember seeing gas lines on the plant. You might not have heard of Vitacress, I hadn’t, but if you eat salads and herbs then you will know their products very well. Carol and her PhD students at Reading have done an awful lot of research with Vitacress over the years so they were a natural place for us to visit. They took our participants around their site which grows the herbs in pots and the factory which produces the bagged up versions. We saw the whole supply chain, from production to processing and with a number of major supermarkets being represented by our participants I guess you could say that we had the whole chain pretty much covered.

Anyway, back to the packaging. Carol described is as active packaging – it has laser micro-perforations, which are at a pore size and density that are matched to the respiration rate of the leaf inside with the general aim of reducing the oxygen level and increasing the carbon dioxide. This keeps the leaves alive and off-sets the spoiling. Once the packet is opened though, the mixture of gases instantly reverts to an atmospheric composition that things are more likely to grow in, aerobes such as E. coli and Salmonella.

And then there are hands – no matter how sanitised your hands are, introducing them into the bag to take a handful of leaves will accelerate this process. Carol says that her group have done a lot of research into this and multiple servings from the same bag remains the biggest problem to overcome.

So what about chopped up salad versus baby leaf? Is one more predisposed to spoiling than the other? She says that with baby leaves being whole they have a greater integrity but they are juvenile and therefore break easily. Mature leaves, however are more robust and less prone to damage but the very fact that they have been chopped means that there are wounds which are sites for infection. So, as they say, you pays your money and you makes your choice.

Finally, spare a thought for the unfortunate Spanish cucumber industry. You may remember in 2011 there was an outbreak of E. coli poisoning in beansprouts produced in Germany, which unfortunately killed 29 people. This was sensationally reported by such publications are we talked about earlier who jumped straight to cucumbers from Spain as being the source of the food poisoning. They did eventually switch to beansprouts from Germany, but not before irreparable damage had been done to Spain’s cucumber industry, which took several seasons to fully recover from the impacts of the panic.

My colleague David Jukes leads our programme which looks at managing risk and food safety with modules such as food law, regulations and risk analysis and our partners at Leatherhead Food Research are world leaders in this area. Tony Hines, their Head of Corporate Affairs and Crisis Management, has worked with David on our Risk Analysis in the Food Chain module. Here they look at situations just like the beansprouts and show the steps that need to be taken to mitigate the risk, reduce the impact and provide informed guidance to organisations such as government bodies and food standards agencies and the press. Without these processes there would have been many more deaths from E. coli in 2011 as people continued to eat the contaminated beansprouts and there would have been many more Spanish cucumber farmers who went bust.

So once again, please use your judgement with food and health related headlines, read between the lines and don’t make panic your first response. After all, it really isn’t rocket science.

If you would like to know more about our sustainable food chain, risk and safety management or nutrition for the consumer please take a look at The AFTP website.

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