The term packaging refers to any material used to protect a product when it is stored and transported. In particular, food packaging is used to protect food against microbiological, chemical and physical contamination. However, the materials that make up the container can react with the content and cause alterations in the product.
Occasionally, the interactions between the container and food entail a loss of quality, as well as the migration of toxic products into the food caused by the use of inappropriate materials. In addition, packaging materials can absorb the flavor compounds of the products, so it is important to pay attention to the mechanical properties of the packaging to avoid variations in the organoleptic properties of the food. The substances that most interact with the materials are plastics, monomers, oligomers and contaminants.
The most used type of food packaging is plastic. In plastic, additives are used as plasticizers that improve their flexibility. The most commonly used plasticizers are Butyl benzyl phthalate (BBP) and di-n-butyl phthalate (DBP) and are used in conjunction with thermal stabilizers to slow down decomposition.
Other substances that are added to plastics are the sliding additives that act as lubricants of the plastic avoiding conglomerates. Examples include esters and amides of fatty acids, polyethylene waxes, metal stearates and paraffin.
Sometimes, packaging deteriorates due to the effects of microorganisms or atmospheric agents, for this reason, antioxidants are incorporated into plastics to delay the oxidation process. In addition, antimicrobials can also be used as algaecides, bactericides and fungicides.
Migration of substances
In general, the amount of container components that can migrate to liquid or solid foods depends on the chemical and physical properties of the food and the container. The number of migrations depends on their concentration, molecular weight and solubility among other factors.
Briston and Katan classified the materials based on the limiting control mechanism:
- class 1: non-migratory materials with or without the presence of food.
- class 2: independent migration, which is not controlled by food, although the presence of food can accelerate migration.
- class 3: leaching, which is controlled by food, negligible in the absence of food, and significant in its presence.
Based on this classification, numerous analytical procedures have been determined that include chromatographic or spectrophotometric analysis to calculate the percentage of migrations of substances. These methods and protocols have been approved by regulatory agencies such as the FDA and the EC.
Some of the factors that affect this migration of substances are the glass transition temperature (Tg) of the polymer. At room temperature, polymers with a Tg lower than room temperature have a high permeability for organic compounds compared to those with a higher Tg. In addition, the degree of solubility in food allows for an increase in the speed of migration.
Interaction between food and packaging material
Often metals that are used as packaging material suffer corrosion due to a chemical or electrochemical reaction with the environment. There are numerous factors that accelerate corrosion, such as acidity, the presence of oxygen, nitrates, sulfur compounds, as well as the severity of heat treatment and storage conditions.
As we have commented in another post, canned foods using materials such as steel, are often coated with a layer of tin to avoid interaction with the food.
Other metals such as lead are dangerous if they accumulate in human tissue. Therefore, the use of welded or cemented cans of three pieces that completely prevent the migration of lead to the food has been incorporated. However, raw materials used for food can only contain 2 ppm of this metal, 0.5 ppm for baby foods and 0.2 ppm for soft drinks. In addition, canned baby foods are welded with pure tin to avoid lead contamination.
Currently, the admissible tin limit is 150 ppm although it is difficult to find lacquered cans with more than 100 ppm. The upper limits are not admissible for toxicity but for producing a bad taste.
Iron, an essential component of our diet, does not constitute a problem of toxicity, and is generally considered with a limit of 50 ppm.
The majority of documented cases of migration of cardboard laminates refer to components transferred from solvents and adhesives used for the manufacturing of materials and packages or those transferred from inks used for printing. Solvents used for paper printing are often involved in the migration of solvent residues to the packaged product, which causes an unpleasant taste.
In addition, the paper or cardboard manufacturing process itself could lead to the formation of potential migrants such as chlorophenols and nitrosamines. Other compounds with active odor that can be formed and released during heating of certain types of paperboard include acetone, chloroform, furan, methylene chloride and acetaldehyde.
Plastics are not a 100% effective barrier either, since they interact with food. The migration of plastics is mainly due to:
- residual components and reagents of the manufacturing process
- compounds formed during the conversion into packaging materials
- additives incorporated for functionality
- adhesives used during conversion
What is really important is the migration of the components of plastics and their possible toxicity. Most plastics contain residual monomers and other additives. Some of them have been linked to health problems, the most important being vinyl chloride. For this reason the standard of the National Council of Health and Medical Research in Australia has completely banned the presence of this compound in food.
The direct contact between the plastic and a food product can lead to components of the container that leach into the product, changing the flavors of the food.
The main components likely to cause damage are the amides, the thermal degradation products of the polymer base and the components of the ink. Migration can also occur from food to plastic, which can cause a loss of mechanical strength. Furthermore, during extrusion of the plastic, temperatures of more than 250 ° C are reached, the temperature at which the antioxidants disappear, giving rise to the formation of free radicals on the surface of the material and in contact with the food.
Many adhesives contain solvents that can migrate to food and some inks used to print packaging materials impart unpleasant tastes. However, proper drying of the printing materials can completely eliminate the migration of solvents from the adhesives and printing inks.
In short, the amount of substances used in food is considerable. Many of them are potentially toxic, harmful and can migrate to food. Therefore, to protect the consumer concerned about health and food safety, different countries have established regulations that outline the acceptable limits of containers. The likelihood that a substance poses a health risk depends on its concentration in the diet and its toxic potential.