Canned Foods: Invisible Health Risks?

It is necessary to further investigate the possible interactions between packaging and food. This is what emerges from analyses carried out on canned tuna and drinks by researchers from the University of Santiago de Compostela, in Spain, in collaboration with the National Agency for Food Safety and Nutrition (AESAN).

They are part of any survival kit, and many of them are essential for students' university life. If we don't feel like cooking or are short on time, they are the best option, and they are essential if we go camping. We are, of course, talking about canned goods, which allow us to keep different types of food and drinks in perfect nutritional and organoleptic conditions.

This method of preservation has been used for decades in our food system. Among its many benefits, it allows us to keep food in our cupboards for years thanks to its very long expiration date.

Therefore, traditionally, in society, cans are associated with a safe way of preserving food. However, from a chemical point of view, it is necessary to further study the possible interactions between the packaging and the food it contains in order to ensure their safety.

Generally, unless we noticed dents or rust marks on the cans , we considered that we could rest easy. A shock put us on alert, and rightly so, because it can damage the integrity of the can to the point of causing small perforations that are not always visible, which facilitates the entry of bacteria and, consequently, the contamination of the food inside the can.

What has generally been ignored or, at the very least , insufficiently addressed are food safety issues related to can components, for example the potential increase in exposure to hazardous substances that would result from dressing a salad with the oil that accompanies canned tuna.

What substances are we talking about? And, more importantly, what risks are we exposed to? Metal packaging generally contains polymer coatings that act as a barrier between the food and the metal. This coating prevents corrosion of the can and preserves the organoleptic properties and quality of the food.

However, some of its components can end up in food through a process called migration . This can affect the quality of the product and, in some cases, pose a potential health risk to the consumer, either due to ingestion in large quantities or due to cumulative exposure throughout life through food.

Endocrine disruptors in canned food

The FoodChemPack (Research, Development and Assessment of Chemical Safety of Food and Materials in Contact with Food) group at the Faculty of Pharmacy of the University of Santiago de Compostela (USC), Spain, is investigating coatings for metal cans, both for beverages and canned food, through several projects (MIGRAEXPO, MIGRACOATING, BACFood4Expo and ACHED), in collaboration with the Spanish Agency for Food Safety and Nutrition (AESAN).

In recent years, we have noticed that many coatings contain epoxy resins based on bisphenol A diglycidyl ether (BADGE), synthesized from epichlorohydrin 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 dangerousness of this compound led to its ban in baby bottles .

European authorities are increasingly reducing the maximum amount of bisphenol to which the general population should be exposed. So much so that the European Commission recently banned the use of BPA and its derivatives in materials intended to come into contact with food.

Tuna, rather in its natural state than in oil or pickled

In the beverages we studied (alcoholic, energy, soft drinks, or mineral water), the migration of these bisphenol A-derived compounds was found to be low. In contrast, higher migration levels were measured in canned foods, particularly those with a high fat content.

For example, canned tuna, such as tuna in tomato sauce, pickled tuna, or tuna in oil, has been found to have higher concentrations of another compound called cyclo-di-BADGE than tuna in brine. Unlike BPA, this compound is not yet regulated due to a lack of toxicological information.

For all these reasons, we consider it not a good habit to season pasta or salads with the liquid contained in cans, as this could increase our exposure to these substances.

Furthermore, it has been observed that heating food directly in the can, a practice associated with specific contexts, such as camping, can increase the migration of these compounds. This is because heat accelerates the transfer of substances from the inner layer of the packaging to the food, which could increase health risks.

In recent studies , we have found that the bioaccessibility of these substances, that is, the amount that could be absorbed by the body, increases considerably when they are ingested with fatty foods.

To reach this conclusion, we attempted to simulate how our digestive system processes these compounds. To do this, we used the I NFOGEST in vitro gastrointestinal digestion protocol, which, among other things, simulates the composition of saliva and gastrointestinal fluids, the duration of each phase, temperature, and body pH values. This allowed us to observe how different population groups 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 acidic gastric pH.

In most cases, the quantities detected were below the limits set by the European Commission. However, it is important to consider potential exposure through different routes and cumulative exposure over a lifetime. Indeed, a person can come into contact with the same substance in different ways, not only orally, through water or food, but also through other routes, such as the respiratory or skin. This can increase the body's total exposure to that substance.

Even at low levels, prolonged exposure can have negative health effects, particularly in the most vulnerable population groups.

An informed society, safer food

Knowledge of these and future results will enable consumers to make informed decisions regarding the use of this type of packaging (e.g., not heating cans directly on the fire when camping) and food consumption (e.g., avoiding reusing covering liquids to dress salads), thus contributing to safer food.