Störmer et al.
10.3389/fchem.2024.1397913
Correction factors were deduced from migration data and proposed by Castle (2015). Considering migration into fatty or humid foods, only a few publications are available: dialkylketones into salami, cheese, and croissant (Lestido-Cardama et al., 2020); recycling contaminants into butter (Zülch and Piringer, 2010); and PAAs into humid foods (Merkel et al., 2018).
Petersen (2013) and Wolf et al. (2023). In 2013, benzophenone transfer from a paper sample after 30 days at 34 ° C under three different rH conditions (43% – 73%), increased by a factor up to 7.3 with increasing rH. Wolf et al. investigated the effect of rH on the transfer of 59 volatile organic compounds from a paper at different rH setups and temperatures by gas chromatography – mass spectroscopy by comparing peak areas and by sensory tests. Furthermore they compared direct contact of MPPO with the indirect contact with the paper sample. Transfer of volatile substances increased with increasing rH, also depending on the polarity of the substances. The authors concluded and recommended that a de fi ned rH level needs to be established before starting migration or sensory tests to ensure suf fi cient repeatability and comparability of such tests. In general, touching contact of MPPO with paper led to considerably higher migration values than indirect ones. The in fl uence of humidity from foodstuffs in contact or the environment of storage was also reported by Zülch and Piringer (2010) and Hauder et al. (2013). 5.2.8 Other foods Bradley et al. (2014; 2015) compared the migration from paper into MPPO with fresh fruit (apples and bananas), potatoes, mushrooms, and raisins, which have different characteristics than typical dry foods such as polenta. Storage tests with fresh foods were performed under realistic time – temperature conditions, e.g., 5 days at room temperature, with raisins and MPPO under standard conditions of 10 days at 40 ° C. Target migrants were contaminants, intrinsically present in the paper samples such as DIPN or DiBP, as well as surrogates such as benzophenone and dodecane, previously spiked into the paper samples. The major objective of these studies was fi rst to assess the relationship between migration from paper into the foods versus into MPPO and second to study the migration of intrinsically present migrants versus spiked ones. Migration levels depended strongly on the nature of the substance. Migration from spiked P/B samples was more extensive (as a percentage of the available migrants) than that of intrinsic migratable substances, such as DIPN and DiBP. This was explained by a stronger bonding into the fi ber network by manufacturing than the spiking process. This difference appears to become relevant for compliance and food safety assessment versus real exposure estimation. In any case, studying spiked samples tends to be conservative. The nature of the substances and of the foods in fl uenced the migration levels much more than the characteristics of the paper samples. Migration into MPPO was up to a factor of 62 (potatoes) but at least by a factor of 10 higher compared with the fresh foods stored for 5 days at room temperature; however, it was comparable or only slightly higher compared with raisins, which due to their long shelf-life, were stored at the same time – temperature conditions as MPPO. The authors discussed the potential use and the limitations of correction factors to correlate MPPO values under standard conditions to realistic food conditions. They concluded that simple correction factors would approximate only the food characteristics but would not re fl ect the substance-speci fi c nature of chemical migration. Furthermore, they addressed ongoing developments toward a comprehensive migration model for paper that takes into account substance- and food- speci fi c characteristics as modeling parameters (Section 5.3).
5.3 Predictive migration estimation and modeling
5.3.1 Comparison of modeling in plastics with that in paper For plastics packaging, migration modeling-based conformity assessment has been of fi cially recognized since 2001 (EU Directive 2001/62/EC), proposed in Article 18 of the current EU Plastics Regulation 10/2011 (EU, 2023) and described in a JRC guideline (Hoekstra et al., 2015). Since then, this tool has been increasingly used by industry, testing laboratories, and authorities (e.g., EFSA and FDA) to evaluate polymer packaging quickly and inexpensively, as well as to cross-check experimental design and results for plausibility. The diffusion of organic substances in plastics generally follows Fick ’ s second law (Crank, 1975). The plastic layer is considered isotropic and homogeneous with an initially homogeneous distribution of the migrants in the layer. The differential equation from Fick ’ s law can be solved using numerical simulation (Roduit et al., 2005; Tosa et al., 2008; Nguyen et al., 2013) and is implemented in commercial or free software. The diffusion coef fi cient(s) D P of a migrant in the plastic layer(s) and partition coef fi cients K between the layers are required as input parameters. In plastics, D P depends mainly on its molecular size, which allows the estimation of D P using relatively simple formulas (Begley et al., 2005; Piringer, 2008; Welle, 2013; Hoekstra et al., 2015; Mercea et al., 2018). As partition coef fi cients into food (simulant), if known values are not available, default values for high (K P,F = 1) or low (K P,F = 1,000) solubility in food are employed (Hoekstra et al., 2015). The assumption of the homogeneity and isotropy of the layer loses its validity in the case of fi ber-based packaging materials. Paper mainly consists of cellulose fi bers, creating a porous structure, and may contain other additives, fi llers, and fi nishing agents. The transport mechanism can essentially be understood as a sequence of desorption/evaporation steps into the vapor phase of the pores and adsorption/condensation of the migrating substances (Aurela and Ketoja, 2002; Zülch and Piringer, 2010). Nevertheless, various authors considered paper materials as a quasi-homogeneous, isotropic layer and described migration kinetics with the simpli fi ed model for plastics.
5.3.2 Models following Fick ’ s second law of diffusion
The extensive kinetic migration dataset elaborated in EU Project FAIR-CT98-4318 (Raffael and Simoneau, 2002; Castle and Franz, 2003) was used to explore whether the existing migration model for plastics according to Fick ’ s law could describe the mass transfer from paper while assuming the paper matrix as a homogeneous isotropic layer. The experimental migration curves could be well- fi tted based
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