Typical diffusion behaviour in packaging polymers - application to functional barriers

When plastics are collected for recycling, possibly contaminated articles might be recycled into food packaging, and thus the contaminants might subsequently migrate into the food. Multilayer functional barriers may be used to delay and to reduce such migration. The contribution of the work reported here is to establish reference values (at 40°C) of diffusion coefficients and of activation energies to predict the functional barrier efficiency of a broad range of polymers (polyolefins, polystyrene, polyamide, PVC, PET, PVDC, [ethylene vinyl alcohol copolymer], polyacrylonitrile and [ethylene vinyl acetate copolymer]). Diffusion coefficients (D) and activation energies (Ea) were measured and were compiled together with literature data. This allowed identification of new trends for the log D = f(molecular weight) relationships. The slopes were a function of the barrier efficiency of the polymer and temperature. The apparent activation energy of diffusion displayed two domains of variation with molecular weight (M). For low M (gases), there was little variation of Ea. Focusing on larger molecules, high barrier polymers displayed a larger dependence of Ea with M. The apparent activation energy decreased with T. These results suggest a discontinuity between rubbery and glassy polymers.     

Modelling of migration from multi-layers and functional barriers: Estimation of parameters

Functional barriers form parts of multi-layer packaging materials, which are deemed to protect the food from migration of a broad range of contaminants, e.g. those associated with reused packaging. Often, neither the presence nor the identity of the contaminants is known, so that safety assessment of the materials has to rely on predictive tools. Several complementary freeware described here allow one to model diffusion in multi-layer films. These tools require the input of parameters that are not easy to determine or predict. Previous work has focused on the prediction of diffusion coefficients at storage temperatures of packaging in contact with food. However, many other kinetic and thermodynamic parameters are needed to describe transport properties during the processing of a material at high temperature and during its shelf-life. All parameters needed for the calculations are discussed. In order to propose default values, the approach consists of (1) reviewing the available literature data, (2) running experiments on polypropylene, polyethylene and poly(ethylene vinyl alcohol) in typical conditions (separately diffusion during processing and migration) and (3) simulating numerical sets for typical situations. Several freeware are proposed to simulate migration from multi-layers and functional barriers using the default parameters.     

Novel chromatographic separation — The potential of smart polymers

‘Smart’ or stimuli-responsive polymers represent new classes of materials that are currently under development. These novel polymeric materials undergo conformational rearrangement in response to small changes in their environment, such as temperature, pH, UV irradiation, ionic strength or electric field. These environmental changes alter the structure of stimuli-responsive polymers and increase or decrease their overall hydrophobicity, resulting in reversible collapse, dehydration or hydrophobic layer formation. With further research into their synthesis, behaviour and application, these novel materials have great potential to become the ‘next generation’ of separation media for cost-effective and environmentally-friendly extraction and purification of high value biomolecules from agri-food and other raw materials.Industrial relevanceThe growing demand for functional food ingredients is requiring the development of selective, cost-effective isolation techniques. Chromatography is one technique employed to produce novel food ingredients. Chromatography procedures often require the use of large quantities of solvents, which must be removed from food products, increasing processing input costs (solvent and energy), and creating an environmental disposal issue. Smart polymers are novel materials that change phase with temperature or other types of operational conditions, and have the potential to offer a cost and environmentally attractive means of producing functional food ingredients. This paper presents a review of smart polymers as novel separation media, and their potential application in the food industry.     

Polymer additive migration to foods-a direct comparison of experimental data and values calculated from migration models for polypropylene

To reduce the amount of compliance testing for food contact polymers the use of migration modelling is under discussion and being evaluated by an EU Commission funded project (Evaluation of Migration Models No. SMT4-CT98-7513). The work reported in this paper was exclusively funded by industry to provide data for the independent evaluation of a diffusion based model using eight different samples of polypropylene (PP) covering the range of polymers specification and five commonly used plastics additives. One hundred and fifty experimental migration data have been obtained in triplicate and used to evaluate a Fickian-based migration model in the prediction of specific migration of five additives into olive oil. All tests were conducted using olive oil, representing the most severe case for fatty foods, with test conditions of 2h at 121 ° C, 2h at 70 ° C and 10 days at 40 ° C, representing short term exposures at high temperatures and room temperature storage. Predicted migration values were calculated using the Piringer 'Migratest Lite' model by entering the measured initial concentration of additive in the polymers(C_p,0) in to the equations together with known variables such as additive molecular weight, temperature and exposure time. Where necessary the data generated in this study have been used to update the model. The results indicate the Piringer migration model, using the 'exact' calculations of the Migratest Lite program, predicted migration values into olive oil close to, or in excess of, the experimental results for > 97% of the migration values generated in this study. For all measurements, the predicted migration from the Migratest Lite program was greater than 70% of the observed value. This study has identified the possibility that random co-polymers of propylene and ethylene give higher migration than other grades of polypropylenes and could be treated as a separate case. However, further work on more samples of random co-polymers is required to confirm this finding.     

A study on the equivalence of olive oil and the EU official substitute test media for migration testing at high temperatures

As a consequence of an increasing awareness and findings about the technical and analytical difficulties related to the employment of triglycerides as fatty food simulants in migration testing, EU Directive 82/711/ EEC on the basic rules of migration has been amended for the second time and adapted with the recent Commission Directive 97/48/EC. The major merit of this important amendment is to authorize alternative tests such as extraction tests and to allow substitute tests for the fat test with concrete indication of corresponding test conditions to be applied. As a novelty in food law compliance testing it authorizes a modified polyphenylene oxide (MPPO), well-known as Tenax®, a thermostable and highly adsorptive porous polymer, as a 'solid' matrix to substitute fat simulant D at temperatures equal to or higher than 100°C. In the study presented here, comparative migration testing overall and specific was carried out between fat simulants olive oil and ¹⁴C-labelled HB 307 and the substitute test media iso-octane, 95% ethanol and MPPO using polypropylene materials as examples at test temperatures of 100°C to 120°C and prescribed corresponding substitute test conditions. As a consequence, a number of conclusions were drawn which are relevant for overall and/or specific migration testing under the investigated test conditions. One of the major findings was that MPPO was generally more equivalent to the fat test than the other two substitute test media. The presence of volatile hydrocarbons in the test samples was found to play a crucial role with respect to the equivalence of the iso-octane-based substitute test. At high volatile concentrations in the test sample the iso-octane test underestimated the olive oil benchmark whereas low volatile concentrations led to satisfying equivalence. It is therefore recommended that the procedure is modified and GC-FID screening of the isooctane extract is carried out. As a logical consequence, the possibility of quantitative determination of the overall extract by GC-FID is recommendable and should be investigated in more depth. Concerning the overall migration test procedure in olive oil, the vacuum pre-conditioning at 60°C should be given re-consideration to avoid the possibility of loss of volatile migrants whose determination should be within the scope of the overall migration test method itself. Finally, the specific migration related equivalence between olive oil, MPPO and iso-octane needs further investigations to clarify the net effect of strongly increased diffusion rates at the regular high temperature versus the substitute test solvent accelerated extraction effect at 60°C. Stability aspects of migrants at the different test temperatures deserve further consideration.     

Application of Finite Element Analysis (FEA) for the simulation of release of additives from multilayer polymeric packaging structures

Computer programmes are available to predict, for consumer protection purposes, the migration of additives from a polymeric package during its contact with food. However most of these programs were developed to estimate migration only from single layer polymeric packaging under isothermal conditions. In this work a diffusion model was developed to simulate the migration from multilayer packaging and under non-isothermal temperature conditions, too. Finite Element Analysis (FEA) is used as a numerical approximation method to solve the diffusion equations describing such processes. The possibilities and limitations of the FEA method are presented and the correlation between experimental and computed results is discussed.     

The rheology of starch dispersions at high temperatures and high shear rates: a review

Engineering design of continuous processes for liquid and semi-liquid foods involves a complex heat transfer and fluid flow coupling, which strongly depends on the rheological behaviour of fluid foods. Most of these processes are performed at temperatures above 95°C. Lack of rheological data is one major problem encountered during numerical simulation and equipment design of liquid food processing at high temperatures. Insufficient rheological studies in the literature have been conducted with food products under these conditions. This paper presents a literature review of experimental devices and methods used to obtain rheological data for starch dispersions at temperatures below and above 95°C. Results and gelatinization models from the literature are analysed and discussed.     

Correlation of foodstuffs with ethanol–water mixtures with regard to the solubility of migrants from food contact materials

Today most foods are available in a packed form. During storage, the migration of chemical substances from food packaging materials into food may occur and may therefore be a potential source of consumer exposure. To protect the consumer, standard migration tests are laid down in Regulation (EU) No. 10/2011. When using those migration tests and applying additional conservative conventions, estimated exposure is linked with large uncertainties including a certain margin of safety. Thus the research project FACET was initiated within the 7th Framework Programme of the European Commission with the aim of developing a probabilistic migration modelling framework which allows one (1) to calculate migration into foods under real conditions of use; and (2) to deliver realistic concentration estimates for consumer exposure modelling for complex packaging materials (including multi-material multilayer structures). The aim was to carry out within the framework of the FACET project a comprehensive systematic study on the solubility behaviour of foodstuffs for potentially migrating organic chemicals. Therefore a rapid and convenient method was established to obtain partition coefficients between polymer and food, K_P/F. With this method approximately 700 time-dependent kinetic experiments from spiked polyethylene films were performed using model migrants, foods and ethanol–water mixtures. The partition coefficients of migrants between polymer and food (K_P/F) were compared with those obtained using ethanol–water mixtures (K_P/F’s) to investigate whether an allocation of food groups with common migration behaviour to certain ethanol–water mixtures could be made. These studies have confirmed that the solubility of a migrant is mainly dependent on the fat content in the food and on the ethanol concentration of ethanol–water mixtures. Therefore dissolution properties of generic food groups for migrants can be assigned to those of ethanol–water mixtures. All foodstuffs (including dry foods) when allocated to FACET model food group codes can be classified into a reduced number of food categories each represented by a corresponding ethanol–water equivalency.     

The specific diffusion behaviour in paper and migration modelling from recycled board into dry foodstuffs

Recycled board plays an important role in food packaging, but the great variety of organic impurities must be considered as potential food contaminants. The diffusion behaviour of the impurities is significantly different from that in plastic materials. The two-layer concept for paper and board introduced recently is now treated in more detail. In the rate-determining surface region the diffusion coefficients of the n-alkanes in the homologous series with 15–35 carbon atoms decrease proportionally as their vapour pressures. This leads to a different equation of the diffusion coefficients in comparison with that for the core layer. Different polarities of the migrants have additional influences on the diffusion due to their interactions with the fibre matrix. A new analytical method for the quantification of aromatic impurities has previously been developed. Based on this method and on the described diffusion behaviour, a migration model for specific and global mass transfer of impurities from recycled board into dry food and food simulants is given.     

Migration of substances from food packaging materials to foods

The employment of novel food packaging materials has increased the number of occurring hazards due to the migration from packaging material to the packaged food. Although polymers have mainly monopolized the interest of migration testing and experimentation, recent studies have revealed that migration also occurs from "traditional" materials generally considered to be safe, such as paper, carton, wood, ceramic, and metal. The regulations and the directives of the EU tend to become stricter in this respect. The emphasis is on reaching a consensus in terms of food simulants and testing conditions for migration studies. Furthermore, the list of hazardous monomers, oligomers, and additives continues to augment in order to ensure that the consumer safety is in current agreement with the HACCP, which is continuously gaining ground.     

Investigation on mercury migration discipline in different paper-plastic food packaging containers

The understanding of the migration of mercury from packaging materials to food stuffs is the prerequisite for the development of food safety regulations. In this article, the migration of mercury from food paper-plastic packaging containers to four food stimulants under different migrated temperatures is studied. The results show that the mobility and the maximum migration volume of mercury increase at certain temperatures when the migration time is extended. It is also noted that the time to reach equilibrium is reduced as the temperature increases. Meanwhile, different solvents appear various different while the rates of migration are 3% acetic acid >10% ethanol >20% ethanol >50% ethanol. But they show the same trend at the different temperatures. Our data suggest that different solvents, temperatures, and food stimulants affect the migration rates, and ameliorate those conditions will reduce migration and promote food quality.     

Modelling of simultaneous two-sided migration into water and olive oil from nylon food packaging

Nylon 6 and nylon 12 food packaging materials used as sausage casings are typically exposed to fatty food on one side and boiling water on the other during the cooking process. To simulate the migration behaviour under these conditions, a special migration cell was constructed and filled with olive oil on one side of the polymer and water on the other to find out what amounts of the migrants will transfer to either side and phase at 100 °C. Results show that when a nylon 6 film is exposed to the conditions as described above, total mass transfer of the monomer—caprolactam—into the water phase occurs after 2 h at 100 °C. Nylon 12 sausage casings release similar amounts of their monomer—laurolactam—into both the aqueous and oil phase. An existing computer migration model was adapted to simulate the situation of simultaneous two-sided migration applying previously determined diffusion and partitioning coefficients. The suitability of the model was confirmed by experimental data.     

Migration and sensory properties of plastics-based nets used as food-contacting materials under ambient and high temperature heating conditions

Overall migration from a wide range of commercial plastics-based netting materials destined to be used as either meat or vegetable packaging materials into the fatty food simulant isooctane or the aqueous simulant distilled water, respectively, was studied. In addition, sensory tests of representative netting materials were carried out in bottled water in order to investigate possible development of off-odour/taste and discoloration in this food simulant as a result of migration from the netting material. Sensory tests were supplemented by determination of the volatile compounds' profile in table water exposed to the netting materials using SPME-GC/MS. Test conditions for packaging material/food simulant contact and method of overall migration analysis were according to European Union Directives 90/128 (EEC, 1990) and 2002/72 (EEC, 2002). The results showed that for both PET and polyethylene-based netting materials, overall migration values into distilled water ranged between 11.5 and 48.5 mg l^-1, well below the upper limit (60 mg l^-1) for overall migration values from plastics-packaging materials set by the European Union. The overall migration values from netting materials into isooctane ranged between 38.0 and 624.0 mg l^-1, both below and above the European Union upper limit for migration. Sensory tests involving contact of representative samples with table water under refluxing (100°C/4 h) conditions showed a number of the netting materials produced both off-odour and/or taste as well as discoloration of the food simulant rendering such materials unfit for the packaging of foodstuffs in applications involving heating at elevated temperatures. GC/MS analysis showed the presence of numerous volatile compounds being produced after netting materials/water contact under refluxing conditions. Although it is extremely difficult to establish a clear correlation between sensory off-odour development and GC/MS volatile compounds' profile, it may be postulated that plastics oxidation products such as hexanal, heptanal, octanal and 2,6 di-tert-butylquinone may contribute to off-odour development using commercially bottled table water as a food simulant. Likewise, compounds such as carbon disulfide, [1,1'-biphenyl]-2-ol and propanoic acid, 2 methyl 1-(1,1-dimethyl)-2-methyl-1,3-propanediyl ester probably originating from cotton and rubber components of netting materials may also contribute to off-odour/taste development.     

Characterizing the migration of antioxidants from polypropylene into fatty food simulants

The migration (diffusion and equilibrium) processes of antioxidants (AOs) from polypropylene (PP) films of different thicknesses into n-heptane and 95% ethanol as fatty food simulants were analysed at 20, 37 and 60°C. Heptane fully extracted the AOs from the polymer while a partition equilibrium described the migration to ethanol. The kinetics of migration were also studied via the diffusion coefficients. As expected, diffusion was found to be faster when the polymer was in contact with heptane, due to polymer swelling by the solvent. The kinetics of the process in ethanol was described by different theoretical expressions which are discussed. Equations disregarding partition equilibrium failed to describe the process and the diffusion coefficient values obtained through them were much smaller than the actual ones and dependent on film thickness. The results also showed the significance of food simulant selection in the analysis of food-packaging interactions and migration variability with thickness.     

EVALUATION OF PLASTICS PACKAGING MATERIALS FOR FOOD PACKAGING APPLICATIONS: FOOD SAFETY CONSIDERATIONS

In evaluating a packaging system for food packaging applications, consideration must be given to the physical properties, chemical composition and extractivity of the packaging material. The last point, extractivity, or migration from the packaging material to a food contact phase, is of major concern in the selection and use of plastics packaging materials for food packaging.
The present article deals specifically with migration of indirect food additives from plastics packaging materials and the scientific principles related to migrant transport or diffusion, as they apply to food safety. These principles and their experimental basis are discussed.     

Migration of bisphenol A from can coatings—effects of damage, storage conditions and heating

Bisphenol A (BPA) is an important monomer used in the manufacture of epoxy resins for internal food can linings. Experiments were conducted to investigate the effects of different storage conditions and can damage on the migration of BPA to foods. These experiments were conducted in a systematic fashion by filling empty epoxyphenolic coated cans with four foods: soup, minced beef, evaporated milk and carrots and a food simulant (10% ethanol). Filled cans of each food type or simulant were then sealed and processed using appropriate conditions, before storage at three different temperatures: 5°C, 20°C and 40°C. For each of the storage regimes, 50% of the cans were dented to establish if this would lead to increased BPA migration. Cans were removed from these stocks at intervals of 1, 3 and 9 months storage at 5°C and 20°C or 10 days, 1 and 3 months at 40°C. Some initial problems of heterogeneity between samples was overcome by determining the amount of BPA in food as well as in the can lining. It was found that 80-100% of the total BPA present in the coating had migrated to foods directly after can processing by pilot plant filling with food or simulant, sealing and sterilization. This level was not changed by extended storage (up to 9 months) or can damage, indicating most migration was occurring during the can processing step. There was no noticeable difference, in this respect, between the different foods or the food simulant. Analysis of control samples (foods fortified with ∼0.1 mg kg^-1 BPA and contained in Schott bottles) showed that BPA was stable under both processing and storage. Experiments were also conducted to investigate the potential effects, on the migration of BPA from can coatings, of cooking or heating foods in the can prior to consumption. Food cans were purchased and the food either cooked or heated in the can. BPA was analysed prior to and after the heating/cooking process. It was concluded from the results that there were no appreciable differences in the BPA level before and after cooking or heating.     

Investigation of migration from paper and board into food-development of methods for rapid testing

A range of paper and board materials including carton board, corrugated board, napkins and paper towels intended for contact with food have been solvent extracted and substances present at the highest levels identified and quantified by GC/MS. Dibutyl phthalate, and diisopropylnaphthalene (DIPN) were selected to study migration to food and potential food simulants with the aim of developing a simple quick test that will give an equivalent or higher result. Tenax was found to be a suitable food simulant for dry foods and dry 'fatty foods' such as pastry and cake and was also found to be a suitable simulant for pizza base tested at higher temperatures for short contact times. The percentage migration values from corrugated and carton boards were generally in the range 15-40%, with the highest percentage being 49% for rice using conditions representing ambient storage. Quick tests were developed using Tenax under accelerated conditions of 4h at 80°C to cover room temperature storage with dry foods and fatty dry foods. These tests are suitable for compliance testing of paperboard samples if migration limits are applied in future legislation. Migration from tissues, napkins and paper towels was found to be at very low or not detectable levels, even when the levels of DIPN and DBP were significant. It is strongly suspected that this finding is due to a combination of short contact time, low grammage and the fact that the tissues absorb fat and moisture from foods, thus minimizing extraction from the paper. In all cases, the results from migration experiments into food and Tenax indicate that for the substances found at highest concentrations in the paper, currently accepted safety limits were not exceeded where they exist in EU legislation or in working documents applying to plastics.     

Characterization of natural polymers as functional barriers for cellulose-based packaging materials

Cellulose-based packaging materials are currently the most commonly used food packaging materials due to their light weight, stability and affordable price. However, the use of recycled paper and board adds to the risk that undesirable substances migrate into the packed goods, since contaminants are not completely removed during the recycling process and can accumulate in the final product. The only available fast and practical solution that can be used to reduce the migration of these substances is the application of functional barriers in the packaging. The applied barriers are currently mostly synthetic, which either serve only a moderate barrier function and/or have the disadvantage that it is often more complex and expensive to recycle the resulting packaging material. The aim of this project is to evaluate different bio-based or biodegradable polymers with regards to their barrier properties. Due to the fact that the transport phenomena are mainly driven by (gas phase) migration, methods based on gas chromatography (GC), including GC coupled with mass spectrometry (GC-MS) and flame ionization detection (GC-FID), GC-FID coupled online with high pressure liquid chromatography (HPLC-GC-FID), and comprehensive GCxGC-MS were used to qualify and quantify the migrated substances. This use of a wide range of different methods and instruments yielded excellent results, allowing us to comprehensively characterize the biopolymers and their barrier function.     

Migration modelling from food-contact plastics into foodstuffs as a new tool for consumer exposure estimation

One important aspect within the European Union's public healthcare is the exposure of consumers to undesirable chemicals in the diet. Food-contact materials (FCM) are one potential contamination source and therefore of particular interest for food exposure assessment. On the other hand, scientific investigations concerning the migration potential and behaviour of food-packaging materials have demonstrated that diffusion in and migration from FCM are foreseeable physical and, in principle, mathematically describable processes. Because of this situation and the current state-of-the-art in migration science, a research project was initiated within the 5th Framework Programme of the European Commission. This project, with the acronym 'FOODMIGROSURE' (European Union Contract No. 'QLK1-CT2002-2390') started on 1 March 2003, was due to last 3 years and had the participation of nine European project partners (see the project website: www.foodmigrosure.org). The aim of the project was to extend currently existing migration models (which have been demonstrated to be applicable for less complex matrices such as food simulants) to foodstuffs themselves. In this way, the project aims to provide a novel and economic tool for estimation of consumer exposure to chemicals migrating from food-contact plastic materials under any actual contact conditions. In addition, the project aims to increase knowledge of the mechanisms of diffusion of organic compounds in foodstuffs and provide data on the partitioning effects between FCM and foods. Today the latter aspect is increasingly regarded as a fundamental influence parameter for migration into foods. Based on the project achievements, a much better scientific basis is available to allow scientifically appropriate amendments of European Union Directive 85/572/EEC as well as to support further developments with the so-called Plastics Directive 2002/72/EC. The paper introduces the project and presents an overview of the project work progress.     

Perfluorinated compounds in food simulants after migration from fluorocarbon resin-coated frying pans,baking utensils,and non-stick baking papers on the Korean market

ABSTRACT

Perfluorinated compounds (PFCs) are used in manufacturing food contact materials, including non-stick cookware coatings and oil- and moisture-resistant paper coatings. The chemical stability of PFCs poses an issue for human safety, as they do not degrade well naturally and hence may accumulate in the body. In terms of food safety, since dietary intake is thought to be a major source of exposure to PFCs, it is necessary to assess the migration of PFCs from food packaging articles to food under typical cooking and storage conditions. An analytical method was developed for assessing the migration of 16 PFCs from food contact materials to food simulants using liquid chromatography–tandem mass spectrometry. The applicability of the method for regular inspection was assessed by monitoring 312 samples. Based on the results of the exposure assessment, all food contact materials deemed to be safe for use, which evaluated migrated concentrations and dietary food intake.