They are part of any survival kit and many of them are essential to the university life of students. If we don’t want to cook or when we run out of time, they are the best option. And they are essential if we leave to camp. We are of course talking about preserves that keep different types of food and drinks in perfect nutritional and organoleptic conditions.
This conservation mode has been used for decades in our food system. Among its many advantages, it allows in particular to keep food in our cupboards for years thanks to their very long consumption date.
As a result, traditionally, in society, cans are associated with a sure way to keep food. However, from a chemical point of view, it is necessary to study more in depth the possible interactions between the packaging and the foods it contains in order to guarantee their innocentity.
In general, unless we build bumps or traces of rust on the canned (PDF), we consider that we could be quiet. A shock put us on alert, rightly, as it can damage the integrity of the box to the point of causing small perforations which are not always visible, which facilitates the entry of bacteria and, therefore, the contamination of food inside the canne.
What has generally been ignored or, at least insufficiently addressed, are the food security issues linked to the components of the canned box, for example the potential increase in exposure to dangerous substances that would be the seasoning of a salad with the oil that accompanies the canned tuna.
The risks linked to the components of the cans
What substances are we talking about? And above all, at what risks are we exposed? Metal packaging generally contains polymer coverings which act as a barrier between food and metal. This coating prevents the corrosion of the box and preserves organoleptic properties and the quality of food.
However, some of its components can be found in food by a process called “migration”. This can affect the quality of the product and, in some cases, represent a potential risk for consumer’s health, either because of their ingestion in large quantities, or due to cumulative exposure throughout food by food.
Endocrine disruptors in the cans
The Foodchempack group (Research, development and evaluation of chemical safety of food and materials in contact with food) of the Faculty of Pharmacy of the University of Santiago de Compostela (USC), in Spain, studies the coatings of metal boxes, for drinks as for food preserves, within the framework of several projects (migraexpo, migracoating, bac Collaboration with the Spanish agency dedicated to food security and nutrition (AESAN).
In recent years, we have found that many coatings have contained epoxy resins based on diglycidyl ether from bisphenol A (badge in English), synthesized from epichlorhydrine and bisphenol A (BPA), an endocrine disruptor that interferes with the hormonal system. It thus contributes to the development of metabolic diseases, such as diabetes or obesity, and can affect the reproductive system, among other harmful effects. In 2011, the danger of this compound thus led to its ban in baby bottles.
The European authorities increasingly reduce the maximum quantity of bisphenol to which the general population should be exposed. So much so that in December 2024, the European Commission prohibited the use of bisphenol A and its derivatives in materials intended to come into contact with foodstuffs.
Tuna, rather natural than in oil or escabèche
In the drinks that we have studied (alcoholic, energizing, refreshing or mineral water), the migration of these bisphenol A compounds has proven to be low. On the other hand, in canned foods, in particular in those with high fat content, higher levels of migration have been measured.
For example, in preserves, such as tomato tuna, escabèche or oil, higher concentrations than natural tuna were noted for another compound called cyclo-di-badge. Unlike bisphenol A, this compound is not yet regulated due to the lack of toxicological information.
For all these reasons, we consider that it is not a good habit of seasoning pasta or salads with the liquid contained in the cans, as this could increase our exposure to these substances.
In addition, it has been observed that reheating food directly in the cans, a practice associated with specific contexts, such as camping, can increase the migration of these compounds. Indeed, heat accelerates the transfer processes from substances from the inner layer of the packaging to food, which could increase health risks.
What do we absorb, how and in what quantity?
In a 2021 study, we found that the bioaccessibility of these substances, that is to say the quantity which could be absorbed by the body, increases considerably when they are ingested with fatty food.
To achieve this conclusion, we have tried to simulate the way in which our digestive system deals with these compounds. To do this, we used the gastrointestinal in vitro infogestine digestion protocol which, among other things, simulates the composition of saliva and gastrointestinal fluids, the duration of each phase, the temperature or the values of body pH. We have thus been able to observe how different groups of populations are exposed differently to these substances, mainly depending on the basal pH of the stomach, which is 1.5 in adults, while children and the elderly have a less acid gastric pH.
In the majority of cases, the quantities detected were lower than the limits set by the European Commission. However, it is important to take into account the potential exposure by different ways and cumulative exposure throughout life. Indeed, a person can be in contact with the same substance in different ways, not only orally, by water or food, but also by other ways, such as respiratory or skin tracks. This can increase the total exposure of the body to this substance.
Even at low levels, prolonged exposure can have negative health effects, especially in groups of the most vulnerable populations.
Knowledge of these results – and of those to come – will allow consumers to make informed decisions concerning the use of this type of packaging (for example, do not directly heat the cans on fire when camping) and food consumption (for example, avoid reusing the coverage liquids to season salads), which will thus contribute to a safer food.
