Störmer et al.
10.3389/fchem.2024.1397913
In contrast to plastics, the liquid simulants used in the conventional test methods in the paper sector, i.e., cold or hot water or solvents such as isooctane and 95% ethanol, penetrate uncoated and even often coated paper test samples, thus heavily impairing their functional consistency. This can cause physical disintegration of the paper fi ber network. Therefore, the obtained values are rather results of an extraction process and not of a migration mechanism into food. Consequently, this leads in many or even most cases to overestimations because the so- measured values represent an equilibrium between the used (extraction) solvent and the paper material. This differs from real food contact applications, in which the equilibrium is not reached during the contact time. Migration can be slowed down by the diffusion properties of the food itself, especially in the case of semisolid or solid foods. Additionally, the solubility of the migrants in real food may be lower than in simulants, i.e., partitioning is more on the food contact material side. However, tests in food cannot be seen as an alternative to routine testing as they are not possible for all substances and may fi nd their limitations in the analytical feasibility for usually very complex food matrices or even in the choice of representative foods for the intended applications. A way out or at least a supporting tool is the development and use of predictive mathematical migration models, which need to be designed such that they depict reality as closely as possible. Numerous scienti fi c papers addressed the development of analytical methods for key migrants and contaminants in paper for food contact as well as alternative migration test procedures. The latter aims to de fi ne crucial physico-chemical parameters for mass transfer from paper and to fi nd relationships between paper material properties, migrants, test conditions, and migration levels. In the following sections, an overview will be given of published experimental and theoretical scienti fi c approaches toward a better understanding and evaluation of mass transfer from paper food contact materials into foods and their safety in use. This overview is not quantitatively exhaustive but claims to address the most relevant publications with regard to the intention of this article. The conclusions of the studies may depend on the considered migrating substances and their properties, e.g., volatility. The substances used in the respective publications are compiled in the Supplementary Table S1.
understood as representatives of the fatty foods to be simulated. Lestido-Cardama et al. (2020) showed that the solvent extract could be strongly overestimating for lipophilic substance groups like dialkylketones. Solvent extracts in isooctane and dichloromethane were compared with migration into two vegetable oils and three fatty foods (croissant, salami, and two kinds of cheese) under different conditions. The migration into the solvents and oils exceeded the migration into the real foods by roughly four orders of magnitude, suggesting that the solvent and oils are far more extractive than the real foods. It seems that solvent extracts constitute an appropriate and correct tool to determine the migration potential of substances from papers but the obtained results in mass per surface unit cannot be taken as direct measures for considering real transfer to food. However, this practice is still applied. The dialkylketones — for which German BfR has set a migration limit of 5 mg/kg food — are usually directly controlled on the basis of the organic solvent extract. From the industry side, CEPI released an updated guideline regarding compliance work for food contact paper materials (CEPI, 2019/2021). The guideline is addressed to all participants in the manufacturing chain as well as to the consumers and regulators. CEPI guideline refers to the current standard procedures for testing, including cold water, hot water, and solvent extracts as well as migration into MPPO. It gives recommendations on how to handle limitations of these standards, like the possible overestimation of migration through extracts, e.g., cases in which certain solvent – material combinations could falsely lead to failing results. The solution will be a case-by-case approach, focusing on the risk assessment of the used raw materials in the context of the intended use of the material. Scienti fi c guidance for theoretically assessing, measuring, and estimating the transfer of mineral oil components was published by German Federation for Food Law and Food Science (Gruber et al., 2019). 5 Scienti fi c studies and alternative approaches including migration modeling 5.1 Introductory remarks and description of the key challenges The transfer of a migrant from a packaging material is determined by its mobility/speed (diffusion rate) inside the material and, in the case of semisolid and solid foods, additionally inside the food. The second main parameter is the partitioning between the packaging material and the food, in the case of several layers, additionally between the layers. For compliance testing of plastics, in most cases, liquid simulants are used which shall roughly represent the solubility properties of the food for the migrants. Concerning diffusion and the use of simulants, plastics appear as a simpler matrix compared with paper. The simulant liquids usually do not penetrate the plastic matrix so a kinetic migration test will monitor the time-dependent development of the migrant ’ s transfer process, ideally in a way that is comparable to the processes occurring in contact with food. Normally migration follows Fickian second law. Therefore, from kinetic data using curve fi tting, the physico-chemical key parameters; the diffusion coef fi cient, D P , in polymer; and the partition coef fi cient polymer-food, K P/F , can be derived. Both are fundamental for migration prediction and modeling (Mercea, 2008).
5.2 Experimental test approaches and key fi ndings
The scienti fi c efforts in the published literature are largely varied and have manifold details. In principle, they can be divided into three major research directions with the following objectives: (i) Exploring and developing alternative food simulants suitable to mimic food in contact with paper; (ii) Comparison of migration results obtained from simulated migration testing with realistic migration levels in foods themselves; (iii) Deriving/de fi ning migration test conditions to better simulate food contact.
Frontiers in Chemistry
05
frontiersin.org
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