Alexandre Feigenbaum

Evaluation of migration models that might be used in support of regulations for food-contact plastics

Materials and articles intended to come into contact with food must be shown to be safe because they might interact with food during processing, storage and the transportation of foodstuffs. Framework Directive 89/109/EEC and its related specific Directives provide this safety basis for the protection of the consumer against inadmissible chemical contamination from food-contact materials. Recently, the European Commission charged an international group of experts to demonstrate that migration modelling can be regarded as a valid and reliable tool to calculate ‘reasonable worst-case’ migration rates from the most important food-contact plastics into the European Union official food simulants. The paper summarizes the main steps followed to build up and validate a migration estimation model that can be used, for a series of plastic food-contact materials and migrants, for regulatory purposes. Analytical solutions of the diffusion equation in conjunction with an ‘upper limit’ equation for the migrant diffusion coefficient, D P, and the use of ‘worst case’ partitioning coefficients K P,F were used in the migration model. The results obtained were then validated, at a confidence level of 95%, by comparison with the available experimental evidence. The successful accomplishment of the goals of this project is reflected by the fact that in Directive 2002/72/EC, the European Commission included the mathematical modelling as an alternative tool to determine migration rates for compliance purposes.

Influence of the nature and treatment of starch on aroma retention

The retention of aroma compounds (d-limonene, ethyl hexanoate, octanal and 1-hexanol) on different starch matrices was measured using inverse gas chromatography. The starch materials were native, acetylated and pregelatinised corn starches, maltodextrin and extruded corn starches. The influence of the amylose content and of the physical characteristics of starch (specific area, particle shape and size) were studied. Whatever the type of starch, retention increased with the polarity of the flavour molecules in the sequence: d-limonene<ethyl hexanoate<octanal<1-hexanol. Maltodextrin appeared to be the most efficient matrix for flavour retention, followed by pregelatinised starches, extruded high-amylose starch and finally granular starches (native and acetylated starches). Retention on native starches did not follow the amylose content, unlike that on extruded starches. Specific area was the main factor, which could explain the different behaviour of samples.

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.

Functional barriers: Properties and evaluation

Functional barriers are multilayer structures deemed to prevent migration of some chemicals released by food-contact materials into food. In the area of plastics packaging, different migration behaviours of mono- and multilayer structures are assessed in terms of lag time and of their influence of the solubility of the migrants in food simulants. Whereas barriers to oxygen or to aromas must prevent the diffusion of these compounds under conditions of use, a functional barrier must also be efficient under processing conditions, to prevent diffusion of substances when the polymer layers are in contact at high (processing) temperatures. Diffusion in melted polymers at high temperatures is much slower for glassy polymers, than in polymers that are rubbery at ambient temperature. To evaluate the behaviour of functional barriers under conditions of use, a set of reference diffusion coefficients in the 40-60°C range were determined for 14 polymers. Conditions for accelerated migration tests are proposed based on worst-case activation energy in the 40-60°C range. For simulation of migration, numerical models are available. The rules derived from the models can be used both by industry (to optimize a material in terms of migration) or by risk assessors. Differences in migration behaviour between mono- and multilayer materials are discussed.

Food and packaging interactions: determination of the kinetic parameters of olive oil diffusion in polypropylene using concentration profiles

The penetration of olive oil into polypropylene was studied in order to allow a complete modellization of food and packaging interactions. Oil concentration profiles through polypropylene food trays were determined by FTIR-microscopy measurements along the thickness at various times. Calculations of the relevant parameters characterizing Fickian diffusion, namely constant diffusivity, coefficient of convective mass transport on the surface and concentration at equilibrium were carried out. This way of working has proven to be considerably shorter and more accurate than the method consisting of recording the global absorbance of the substance absorbed, especially when the amount of diffusing fat is low. Major conclusions are: that absorption of olive oil is strongly influenced by convection; the diffusion coefficient of olive oil in polypropylene is constant. Possible consequences to simplify global migration testing are discussed.

Use of inverse gas chromatography to determine thermodynamic parameters of aroma-starch interactions.

Interactions between aroma compounds (d-limonene, ethyl hexanoate, octanal and 1-hexanol) and high amylose cornstarch were studied using inverse gas chromatography. Free energies of adsorption (deltaGa) and enthalpies of adsorption (deltaHa) of aroma compounds on starch were measured in the temperature range of 33-40 degrees C. The results showed existence of interactions between aroma compounds and starch, involving hydrogen bounds and dipole-dipole interactions. Sorption isotherms and Henrys law solubility coefficients (S) were determined at 40 degrees C. Three different shapes of isotherms were obtained according to the BET classification: type III for d-limonene, type II for ethyl hexanoate and linear for octanal and 1-hexanol.

Safety and quality of food contact materials. Part 1: evaluation of analytical strategies to introduce migration testing into good manufacturing practice.

The results of a research project (EU AIR Research Programme CT94-1025) aimed to introduce control of migration into good manufacturing practice and into enforcement work are reported. Representative polymer classes were defined on the basis of chemical structure, technological function, migration behaviour and market share. These classes were characterized by analytical methods. Analytical techniques were investigated for identification of potential migrants. High-temperature gas chromatography was shown to be a powerful method and 1H-magnetic resonance provided a convenient fingerprint of plastic materials. Volatile compounds were characterized by headspace techniques, where it was shown to be essential to differentiate volatile compounds desorbed from those generated during the thermal desorption itself. For metal trace analysis, microwave mineralization followed by atomic absorption was employed. These different techniques were introduced into a systematic testing scheme that is envisaged as being suitable both for industrial control and for enforcement laboratories. Guidelines will be proposed in the second part of this paper.

Prediction of worst case migration: presentation of a rigorous methodology.

An improvement of the Piringer model, allowing the prediction of a worst case migration from packaging to food is presented here. The authors are proposing other constants for the calculation of the upperbound value of the diffusion coefficient, using experimental data determined by a film to film method. Considering the plasticizing effects of food simulants, a model involving the variation of the diffusion coefficient versus space and time must be used. Future fields of investigation are discussed: the relationship between diffusion coefficients and the volume of the migrant (instead of molar mass), and the variation of diffusion coefficient activation energy with temperature.

Migration of additives from polymers into food simulants: numerical solution of a mathematical model taking into account food and polymer interactions

The principle of a computing program describing precisely the migration of additives from a polymer into a food simulant is presented. As six parameters are used to fit the simulant sorption and additive extraction kinetics, the parameters have been determined by independent experiments. Owing to the complicated coupling between the liquid and additive diffusion processes, migration kinetics cannot be obtained by a mathematical resolution of kinetic equations, but they must be calculated by numerical analysis. The method is applied to a UV absorber in polypropylene migrating into glyceryl tripelargonate, a pure triglyceride, of which behaviour and average molecular weight are similar to official fatty food simulants. Properly designed experiments validate the model used to fit the migration kinetics. The possibility of erasing any parameters is also discussed.

Safety evaluation of an ionized multilayer plastic film used for vacuum cooking and meat preservation

The main concern in safety evaluation of ionized plastic food packaging materials is the possible formation of unsuspected potential migrants. Solvent extracts and migrates of a polypropylene-based multilayer film, beta-irradiated at 80 kGy and widely used for vacuum cooking of packaged meat were studied, using complementary analytical techniques. 1H-NMR and HPLC showed that 96% of the initial phenolic stabilizer was not found after irradiation. A phosphite stabilizer and its reaction products, identified by GC-MS, accounted for 35% of the initial amount. The sum of all potential migrants derived from the additives accounted for less than 1% of global migration. This global migration was mainly due to oligomers. By comparison our results with literature work done with the same film, but at lower doses, it was suggested that larger electron beam doses reduce the possibility of migration and enhance the consumers safety.