Why salads are the biggest source of food poisoning and what to do to avoid it

Just over a year ago, the United States was experiencing the largest outbreak of E. coli since 2006; affecting at least 98 people in more than 20 states. The origin was a bagged romaine lettuce. Unfortunately, this is not an isolated case. Fresh vegetables and fruit have become a real headache for food safety experts.

Today in the United States, fresh vegetables are the largest source of food poisoning. In Europe the figures are not so pristine, but the bacteria and viruses associated with this type of food are also to blame for the vast majority of poisonings. We are facing a real danger for food safety: salads.

The numbers speak for themselves

In 1990, more than 400 epidemic outbreaks associated with fresh fruits and salads were detected. Between 2001 and 2013 we are not even able to know in its entirety, some experts explain, how many related outbreaks appeared, but they are many, increasing since 2008. Arrived in 2013, in Europe these epidemics seem to reduce their growth, stagnating in number per year , as explained in this article by EFSA, the European authority on food safety.

Despite the fact that the number of appearances in Europe seems to have stabilized, in the United States they have continued to increase. The danger is still lurking, hidden between "romaine lettuce and brussels sprouts."The reason is in a "cool" words.

According to some independent experts, this increase could be related to the increased consumption of vegetables and fresh fruit in the diet. This is a consequence of the search for a better, healthier diet. But, not being processed, these foods can also bring unexpected and unpleasant surprises.

Why does my salad "bug"?

But what is the problem? What's wrong with fresh vegetables? It is not that they do not pass strict food safety controls, as happens with everything that arrives in our supermarkets, but fresh food, especially if we put them in a plastic bag, are cannon fodder for microorganisms.

When a vegetable goes through the processing and washing system, it is relatively clean and can pass the controls because it does not meet the ranges in which it would be considered dangerous. However, that does not mean that the vegetable is aseptic or that it is sterilized. These two words refer to the fact that there is no presence of microorganisms in it.

In order to delay the action of microorganisms as much as possible, it is necessary to use processing methods such as the use of preservatives or cooking. But these foods are fresh, that is, we have temporarily removed the organisms responsible for causing a food infection. But they are still there in very small quantities or in dormant forms, such as spores.

By packing fresh vegetables in plastic bags, or simply transporting them, the necessary time and humidity are given for these microorganisms, which have not been detected in the samples analyzed due to their low presence, to grow and proliferate until reaching a dangerous number. It is then when we are at risk of food poisoning.

What happens inside a salad bag?

Several issues need to be made clear. First of all, the presence of an organism is not synonymous with intoxication. This, although pathogenic, must be in a minimum number known as the infective dose. This dose is what you need to be able to cross our first defense barriers and generate an infection. Depending on the organism, these doses can be higher or lower, and serve, in part, to define the safety ranges.

Second, you have to understand what happens in a salad bag. Imagine ten little bacilli from E. coli that have managed to resist washing. Now we put them in a bag that retains the moisture transpired by the fresh leaf, which, in addition, spends a couple of hours at about 35ºC, while transporting it. Taking into account that at 37ºC this bacterium divides every 20 minutes (about 12 times in four hours), the calculation gives us about 40,960 bacteria after this time, under optimal conditions.

If we consider that the infective dose of the strain of E. coli O157: H7, the cause of the last and most important outbreaks in recent years, ranges between 100 and 2,000 microorganisms (it is especially infectious), we will realize that a perfectly edible salad has become a problem in four hours. food health.

Finally, it is important to know that not only the bacteria themselves are the cause of poisoning. Upon death, microorganisms can produce a series of substances that are toxic to other living beings, including humans. These substances are known as toxins (the real ones and not the ones the "detox methods" talk about). Therefore, it is not enough, only, to kill organisms.

Of course, measures are put in place to prevent this from happening, such as refrigerated transport, traceability, processing measures ... But, despite the attempts, fresh foods do not possess the conditions of asepsis typical of cooked foods. Also, even in the best of cases mistakes do happen. Or, sometimes, they are not errors but the tenacity of the microorganisms to survive.

The main protagonists of the food nightmare

We have talked about Escherichia coli, a ubiquitous bacterium, and not always malicious, but it can cause serious problems, especially some strains like the one we named. But it is not the only one. There are lots of pathogens associated with food. These can appear common or extraordinary due to cross contamination.

The most common in fresh vegetables are coliforms and enterobacteriaceae. These two groups overlap some species with each other, such as the own E. coli. Both are related to bacteria in the digestive system. Among them are bacteria like Klebsiella sp, Enterobacter sp, Shigella sp, Serratia sp, Yersinia sp... some are infectious and some are opportunistic. These are the bacteria analyzed compulsorily according to Regulation (EC) 2073/2005.

In addition to coliforms and enterobacteriaceae, which basically come from manure, bag salads can also be found Listeria and Salmonella. The first is typical of meat and dairy and the second appears associated with poultry, especially its digestive system. These two appear in bagged salads as a result of manipulation.

Finally, it should be noted the remarkable role that the norovirus plays in food infections from salads. This virus is responsible for a gigantic number of gastroenteritis worldwide. Due to the humidity conditions, this virus, cosmopolitan and ubiquitous, is able to resist quite well in salad bags, causing many problems.

The million dollar question: how to prevent a food infection?

There are several methods to "take apart" these bacteriological pumps. Speaking of generalities, the most common and effective method of killing pathogens in food is to heat it to 65ºC for one minute. However, remember that we are talking about salads, so it is probably not possible.

In this case, the only thing left to do is wash the salad with a disinfectant or food bleach. These substances are fully prepared to eliminate the danger without modifying the nutritional or organoleptic properties of the food.

Of course, it is necessary to avoid cross contamination, using the utensils only with the appropriate foods and, also, to avoid breaking the cold chain. Needless to say, this includes not leaving the vegetable at room temperature too long. Finally, and although it seems obvious, we should never eat a salad after its expiration date.

Let's remember that some invisible microorganisms can hide among its invisible leaves, the consequences of which can range from annoying gastroenteritis to much worse problems, in case we are unlucky enough to find an especially harmful strain.

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