MIGRATION FROM PACKAGING MATERIALS

Food contact materials. Food packaging. History. Types.

Food contact materials are materials created and designed to be in contact with food. Most often these are the materials used in a great number of equipment and packaging. Food contact materials include a variety of materials like plastics, rubber, paper, coatings, metal etc. In a lot of cases a combination of those mentioned above is used (Mathlouti et al., 1994). Since the package or the container is in contact with the food most of its shelf life, the following essay will mainly treat the interaction of packaging with food, migration from the materials of the container. Also, legislation on food contact materials will be presented.

Food packaging has always been an important issue for human development, since humans have always had competitors for their sources of nourishment. Animals, especially rodents, insects and microorganisms, all of them are causing the spoilage at different stages in the growth, harvesting, processing, storage, transport and the sale of food. These organisms can even sometimes make the food poisonous for humans. The oldest packaging materials were leaves from larger plants, animal skins, and also other materials originating from plants. With the development of society, people started using more complicated technologies for the production of food containers, like metal, ceramics, etc. Since its starting in the 19th century, modern food packaging has advanced as results of global trends and consumer preferences. These advances are made in order to obtain improved food quality and safety. Moreover, with the globalization, food packaging requires also longer shelf life, monitoring of safety and quality, and compliance with international standards (Silvestre, Duraccio, & Cimmino, 2011). Biodegradability is another concern because of the increasing rates of pollution. Companies that aim to switch completely to biodegradable packaging

Some basic principles that have lead to the development of food packaging are:

• Food must be available in interesting variety, all year round, irrespective of the growing season wherever there are people.
• Food must be presented in a way that is convenient to purchase and use and in most instances that presumes packaging. (Paine F.A. et al., 1992)

Plastics used as food contact materials (FCM)

Over the last half of century, the use of polymers in food packaging has increased due to their advantages over other traditional materials. Polymer packaging has many properties including strength and stiffness, barrier to oxygen and moisture, resistance to food component attack and flexibility (Silvestre et al., 2011) (Paine F.A. et al., 1992) Plastics for food packaging are polymers that contain different additives that enhance different properties of plastics like elasticity, permeability etc. ( Knight D.J. et al., 2004). Usually these additives are small molecules that are capable to migrate in the food matrix. These chemicals are bisphenol-type contaminants, isocyanides, styrene, vinylchloride, antioxidant, light stabilisers and thermal stabilisers, plasticizers, lubricants and slip-additives (Lee, Son, & Hong, 2008).

Most used plastics:

1. Polyethylene (PE) – high density polyethylene (HDPE) is used in rigid plastic containers and the low density polyethylene (LDPE) is used in films (Arvanitoyannisa, Biliaderis, Ogawab, & Kawasakib, 1998).
2. Polypropylene (PP) – multifunctional plastic used in rigid and flexible plastic.
3. Polystyrene (PS) – the high-impact polystyrene is used for thermoformed containers.
4. Polyvinyl chloride (PVC) – used for oil containers and films for fatty foods (Knight D.J et al., 2004).

New trends in food packaging Active and intelligent packaging

Active packaging more often describes packaging which has functions beyond the passive containment and protection of the product. Active and intelligent packaging is based on a calculated and cautious interaction of the packaging with the food and/or its environment to improve food quality and safety. Such technology includes advances in delayed oxidation and controlled respiration rate, microbial growth, and moisture migration. Some other examples are carbon dioxide absorbers/emitters, odour absorbers, ethylene removers and aroma emitters. Intelligent packaging includes time–temperature indicators, ripeness indicators, biosensors and radio frequency identification (Restuccia et al., 2010). Another new trend in packaging materials is the use of biopolymer-based packaging materials originated from naturally renewable resources like polysaccharides, proteins, and lipids. They offer advantages in environment protection and are also a good choice for food packaging in terms of safety (Lee et al., 2008). The definitions stated in Regulation 1935/2004/EC and in Regulation 450/2009/EC say that active materials and articles are ‘‘materials and articles that are intended to extend the shelf-life or to maintain or improve the condition of packaged food”(Restuccia et al., 2010). They are designed to deliberately incorporate components that would release or absorb substances into or from the packaged food or the environment surrounding the food. Also, intelligent materials and articles means: ‘‘materials and articles which monitor the condition of packaged food or the environment surrounding the food”. Substances responsible for the active or intelligent function can be incorporated in the container or can be placed in a separate container, so the active ingredient is released in a controlled way (Restuccia et al., 2010).

Use of nanomaterials in food packaging

Another new trend in food packaging is the incorporation of nanoparticles in the packaging polymer. Nanoparticles are particles with the diameter between 1 nm and 2500 nm. Applications of polymer nanotechnology can provide improved mechanical and antimicrobial properties, together with nano-sensors for tracing and monitoring the condition of food during transport and storage (Silvestre et al., 2011), but successful technical development of polymer nanomaterials for food packaging (PNFP) has to overcome barriers in safety, technology, regulation, standardisation, trained workforce and technology transfer. Also, apart from the fact that they have direct toxic properties, nanomaterials due to their specific form, surface or charge may also interact with food components and bind nutrients. Moreover, the nanomaterials once entered in the environment have the potential to accumulate in the environmental organisms. Metal nanoparticles, metal oxide nanomaterials and carbon nanotubes are the most used nanoparticles to develop antimicrobial active particles (Silvestre et al., 2011). Nanoparticles can also be used as nanosensors to respond to environmental changes (e.g., temperature or humidity) http://www.efsa.europa.eu/.

Migration of substances from packaging materials

Migration of toxins

Food packaging and other materials that come in contact with food can interact during different technological treatments and storage. The toxins that migrate from materials which come in contact with food represent an important source of contamination (Paine F.A. et al., 1992). Most of the studies made in this field are focussed on the migration of toxins from plastics of traditional packaging. Considering the development of new packaging techniques like active packaging and use of nanoparticles, new and more complicated analyses are required for the determination of migration levels. Also, since paper, especially recycled paper starts to gain popularity more research is needed for this type of material.

Migration from plastics: the case of phthalates. Phthalates are organic lipophilic compounds that are mainly used as plasticizers to increase the flexibility of plastic polymers. Human exposure to phthalates mainly occurs during food ingestion and can provoke undesired health effects. Researchers have demonstrated that di-n-butyl phthalate (DnBP), benzylbutyl phthalate (BBP), DEHP and DiNP can adversely affect the male reproductive system, causing DNA damage in human sperm. Tolerable daily intakes (TDIs) have been specified by the European Food Safety Authority (EFSA) for these phthalates, namely 0.01 mg/kg bw for DnBP (EFSA, 2005a), 0.05 mg/kg bw for DEHP (EFSA, 2005b), 0.50 mg/kg bw for BBP (EFSA, 2005c) and a group TDI of 0.15 mg/kg bw for DiDP and DiNP (EFSA, 2005d,e) (Fierens et al., 2012).

In many countries studies were made for the determination of the level of contamination of different products available on the market. In one study, the presence of eight phthalate compounds – dimethyl phthalate (DMP), diethyl phthalate (DEP), diisobutyl phthalate (DiBP), di-n-butyl phthalate (DnBP), benzylbutyl phthalate (BBP), di(2-ethylhexyl) phthalate (DEHP), dicyclohexyl phthalate (DCHP) and di-n-octyl phthalate (DnOP) – was investigated in 400 food products, divided over eleven groups, and packages sold on the Belgian market. For this specific study suitable extraction techniques were developed and validated for four different matrices, namely high-fat foods, low-fat food products, aqueous-based beverages and packaging materials.

Different phthalate concentrations were observed in different groups. DEHP was found in the highest concentration in almost every group. Also, DEHP was the most abundant phthalate compound, followed by DiBP, DnBP and BBP. In packaging materials, especially in cardboard, phthalate contamination was primarily due to the presence of DiBP. The explanation of this is that this phthalate compound is often used as additive in printing inks and lacquers of food contact materials (Fierens et al., 2012).

Studies made in Japan also lead to the discovery of phthalate contamination in ready-to-heat meals from Japanese shops. In that case the phthalates originated from the gloves of the workers that have prepared the meals. Two months after the research gloves containing PVC were forbidden for cooking purposes. Studies made on different products from retail shops in Germany, Italy, Slovakia have confirmed the contamination with different phthalates and have proven the occurrence of migration (Fierens et al., 2012).   

The presence of phthalates, mainly DBP in some samples of Moldovan wine has lead to the blocking of exports to Russia. Right after that, studies, including more than 2000 samples of the bottled wine and base-wine, for the presence of DBP were performed. The purpose of that study was mainly to determine the origin of phthalate contamination. It was found that the contamination of phthalates is the result of contact with polymeric materials used in equipment (Duca G. et al., 2011).

Migration from paper Paper and paperboard are often used as food packaging materials, frequently in forms that are created to be in direct contact with foodstuffs. A number of chemicals, like slimicides, bleaching agents, and inks, are used during the production process(Ozaki, Yamaguchi, Fujita, Kuroda, & Endo, 2004). Recycled fiber materials can be used in certain limits as food contact materials. Recycled paper is mainly used in direct contact with dry foodstuffs like flour, grain, sugar, salt, rice and pasta(Triantafyllou, Akridademertzi, & Demertzis, 2007). Toxic components found usually in paper are 1,2-benzisothiazoline-3-one (BIT), 2-(thiocyanomethylthio) benzothiazole, 2,4,5,6-tetrachloro-isophthalonitrile, 2,4,6-trichlorophenol (TCP), and pentachlorophenol. Although, migration from paper is not intensively studied, it was demonstrated that migration from paper and board occurs even to dry food. Migration to dry foods was reported at least for phthalates, diisopropylnaphthalenes(DIPNs) and benzophenone (Triantafyllou et al., 2007)(Ozaki et al., 2004).

Migration of nanoparticles Not so many studies can be found in the literature on the migration of nanoparticles from packaging material to food. Two studies analyzed the migration of clay from PET bottles and films of potato-starch and potato starch polyester blends. In both cases insignificant detectable migration of nanoclay is observed. Another study reports the migration of silver nanoparticles from polypropylene nanosilver composites. The level of silver migration was found to be lower than the quantification limit. In the case of nanoparticles the most exposed are usually the workers from plants working with nanoparticles, but for the final consumer finding the level of migration into foods has great importance (Silvestre et al., 2011).

“Positive” and deliberate migration

In the case of active and intelligent packaging, as well as in the case of the use of nanoparticles, the phenomenon of migration is more often a desired and an induced one. The main problem in this case is that the level of migration must be controlled and the active substances must be stable and not lead to the formation of more toxic compounds for the whole shelf life of the food product.  Presently active PNFP have been mainly developed for antimicrobial packaging applications. These particles function on direct contact, but they can also migrate slowly and react preferentially with organic components present in the food. Silver, gold and zinc nanoparticles are the most studied metal nanoparticles with antimicrobial function, with silver nanoparticles already found in several commercial applications. “Silver, that has high temperature stability and low volatility, at the nano-scale is known to be an effective anti-fungal, anti-microbial and is claimed to be effective against 150 different bacteria. Carbon nanotubes could be used not only for improving the properties of polymer matrix, but also for their antibacterial properties(Silvestre et al., 2011). Another use of nanoparticles is the incorporation of oxygen scavengers in order to stop the oxidation of products. Also, the migration of preservatives from the package into the food is another field that is an early stage of research (Silvestre et al., 2011) http://www.efsa.europa.eu/.

Parameters influencing migration from FCM

Analyzing many studies on toxin migration from food contact materials, the parameters that influence the level of migration were determined. The most important that can be listed are:

• The composition of the food matrix and its properties (pH, fat content, sugar content, volatility etc.)
• The composition of the FCM
• The contact surface area
• The wetting properties of the plastic
• Storage conditions (temperature, time, light)
• The contact time

“Wetting is defined by the contact angle formed between the test liquid and the film. As the contact angle increases, the potential of interaction between the two, decreases” (Meiron & Saguy, 2007). The tendency of food to interact with the FCM is a major factor that affects quality, appearance and shelf life. Moreover, the affinity of the products to the packaging material could increase the level of migration of some of the package compounds, or in enhanced adsorption of off flavours, or it may even affect the barrier characteristics (Meiron & Saguy, 2007). During the DBP analysis, the optimal conditions of extraction from liquid samples were determined. It has been established, that significant influence on extractability is performed by pH value and sugar content, the alcohol content in synthetic wine has not displayed significant effect (Duca et al., 2011)(Report & Bureau, 2008).

When studying the migration kinetics in the case of paper and paperboard, it was found dependent on the on the temperature, the nature (mass, thickness and composition) of the paper sample and the nature (molecular size, chemical structure, fat content and volatility) of the food. Migration tests have demonstrated that migration occurs rapidly at elevated temperatures, so to keep migration in acceptable limits a low storage temperature should be applied in combination with a barrier layer for indirect contact (Triantafyllou et al., 2007). “The highest level of migration of organic pollutants was observed for the substrate with the highest fat content. Furthermore, it is shown that contact time and temperature have a significant effect on migration of model contaminants into foods”(Ozaki et al., 2004). Another factor that influences the level of migration is the surface of the contact. Small amounts of food are generally in contact with more packaging material (higher surface area: volume), so the migration from the package will be more efficient, thus the concentration of the migrants will be higher.

 

Legislation of food contact materials

Considering the fact that food should be safe, the area of food industry is heavily regulated, including the part that concerns the materials which come in contact with foods. The regulation of this sector depends on the type of food, the type of material and on the country. As an example, the legal measures differ a lot between EU and USA (Knight D.J. et al., 2004). The US approach gives credibility to the idea that ‘‘the dose makes the poison” so that toxicological justification is not needed, or is greatly minimized by exposure assessments, while the European approach begins with the principle that toxicological data on all substances is necessary, regardless of the level of anticipated exposure (Restuccia et al., 2010).

International legislation and Codex Alimentarius

The reference made to Codex food safety standards in the World Trade Organizations’ Agreement on Sanitary and Phytosanitary measures (SPS Agreement) makes Codex alimentarius an important tool in the regulation in trade disputes including the differences between legal provisions on food contact materials from different countries. Different provisions on FCMs are stipulated in different Codex standards and guidelines (e.g. General Principles of Food Hygiene). WTO members that wish to apply stricter food safety measures, including measures that limit the migration from food contact materials, than those set by Codex may be required to justify these measures scientifically (www.codexalimentarius.org).

Legislation in EU

In Europe the EC 1935/2004 on materials and articles intended to come into contact with food sets the legal framework for FCMs. This regulation, apart from general requirements and definitions, presents special requirements for active and intelligent materials and articles, as well as the specific measures for groups of materials and articles (see Annex I “EU food contact materials legislation”) and describes the role of the European Food Safety Authority, the procedure for authorization of new products. The Annex II of the same regulation presents the symbol of food contact materials.

For every group of materials there are specific measures stipulated in different documents. Annex I and Annex II of this essay present the general scheme of EU legislation and specific legislation for each group of materials used as FCMs.

For intelligent packaging until 2004 in Europe there was a legislative lack which has lead to the decreasing of their penetration in the EU market. To face the problem Regulation 1935/2004/EC and more specifically Regulation 450/2009/EC set new legal basis for their correct use, safety and marketing. As long as the migration of components is desired, active materials are also a subject of the regulation for additives. The Framework Directive (89/107/EEC) stipulates the regulation of (direct) food additives(Restuccia et al., 2010)(Grob et al., 2007).

When evaluating active packaging materials, EFSA safety assessment will focus on three risks related to the dietary exposure of chemicals. Those include:

• the migration of active or intelligent substances;
• the migration of their degradation and/or reaction products;
• the toxicological properties of active or intelligent substances and their degradation or reaction products.

Also, for each application documentation should be present proving that:

• the information of the intelligent packaging is correct;
•  the active packaging has the intended effect on the food.

In the case of nanotechnologies used in food packaging, there is a lack in the regulatory system, although both Food and Drug Administration and European Food Safety Authority are interested in the subject. When it comes to regulation of nanotechnologies in EU, the task of assessing nanotechnologies was assigned to the European Food Safety Authority (EFSA) Scientific Committee. The EFSA concluded its assessment of the potential risks of nanotechnologies, stating that a careful, case-by-case approach is needed as many uncertainties remain over the safe use of nanotechnologies. In 2011 the Guidance for risk assessment of engineered nanomaterials was published and placed on EFSA official website. It presents a practical approach for assessing potential risks that may appear when applying nano-science and nanotechnologies (Silvestre et al., 2011) http://www.efsa.europa.eu/. Nanoparticles should be assessed in all cases until more information is known about this new technology (Restuccia et al., 2010).

Units used to express migration

The 10/ 2011 EC regulation on plastic materials and articles intended to come in contact with food describes two units for the expression of the migration from plastics into food:

‘Overall migration limit’ (OML) means the maximum permitted amount of non-volatile substances released from a material or article into food simulants;

‘Specific migration limit’ (SML) means the maximum permitted amount of a given substance released from a material or article into food or food simulants;

‘Total specific migration limit’ (SML(T)) means the maximum permitted sum of particular substances released in food or food simulants expressed as total of moiety of the substances indicated;

The OML is not derived scientifically. It should be as low as technically possible, and the fact that organic materials cannot be produced free of low molecular weight materials should be taken into account. “Plastic materials and articles shall not transfer their constituents to food simulants in quantities exceeding 10 milligrams of total constituents released per dm2 of food contact surface(mg/dm2)”(10/2011 EC).  SMLs are a risk management tool derived from toxicological data, like tolerable daily intakes (TDIs), or from a limited toxicological assessment ensuring safety only for a low migration. SMLs for different components are presented in the Annex I of 10/2011 EC. Also, EU introduced the fat consumption reduction factor (FRF), considering that on a long term average virtually nobody consumes more than 200 g fat per day. At the same time, in the case of small packs with a high surface area/volume ratio, the European system tolerates high migration, since during migration from smaller, from a large surface area the migrant concentrates into a smaller amount of food(Grob et al., 2007)(Commission, 2011).

Conclusion

Humans have always needed ways to preserve and protect food, this being the main factor that has led to the creation and development of food packaging. From leaves and animal skins, then ceramics and metals, packaging is always evolving. Nowadays, complicated and elaborated technologies are used in food packaging, such as active and intelligent packaging, or nanotechnologies. The more complicated technologies are used, the more safety and regulatory problems appear. The interaction between food and the materials that are in contact with food is proven and many legislative acts exist in order to limit the levels of interaction. The phenomenon of migration and the parameters influencing migration such as composition and properties of food, composition and properties of packaging material, storage condition, contact surface area, etc. are intensely studied, especially in plastics and synthetic materials, but new research has shown that migration of toxins can also occur from materials considered more or less traditional, like paper and paperboard. Furthermore, the development of new technologies also requires new researches regarding migration from materials which interact in even a more active way with food, therefore creating increasingly difficult safety and regulatory issues.

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