Störmer et al.
10.3389/fchem.2024.1397913
substances, such as 2-methylnaphthalene, 2,6-DIPN, and perylene, representing MOAH in a wide range of molecular masses, chemical structures, and most importantly, volatilities (boiling point ranges from 240 ° C to 467 ° C). Migration reached equilibrium after 3 – 6 days at 60 ° C. For more volatile MOAH substances, the equilibrium levels obtained at 60 ° C were already reached after 2 h at 70 ° C. This coincides with the fi ndings of Aurela et al. (1999). In general, the migration values were higher in MPPO than in couscous and polenta, which was highly distinctive for the more volatile surrogates and less distinctive or even the same for the heavier surrogates. The authors concluded that MPPO can be considered as the worst case of the simulation of migration to dry food. 5.2.6 Additional alternative simulants for dry foods In addition to MPPO (Tenax ® ) and polenta (as a model food), other adsorbents have also been studied as potential dry food simulants: Nerín et al. (2007) performed comprehensive kinetic migration studies on three paper samples with different recycled pulp content using Porapak (a porous copolymer, not further speci fi ed in the publication) as a solid-food simulant. Target migrants were DIPN, DiBP, and diethylhexyl phthalate. The test setup was direct ( “ touching ” ) contact. Test temperatures were 25 ° C, 50 ° C, 75 ° C, and 100 ° C with contact times ranging from 5 min to 10 days. In a few selected cases, migration into MPPO and milk powder was carried out for comparison. Porapak was found to allow solid and reproducible measurement of migration kinetics comparable with those obtained with MPPO. Notably, both solid simulants covered reasonably, i.e., with a slight overestimation, and the migration into milk powder occurred at 25 ° Cand 50 ° C. Fengler and Gruber (2022) studied Sorb-Star as another alternative dry food simulant. Sorb-Star is not porous like MPPO but rod-shaped polydimethylsiloxane (20 mm, ø 2 mm), which is highly adsorptive toward low and medium volatile lipophilic organic compounds. The study compared migration kinetics (at 20 ° C, 40 ° C, and 60 ° C up to 12 days) for MOH using Sorb-Star versus MPPO in “ touching ” versus “ gas phase ” contact. The carbon fractions C10 – C16, C16 – C20, C20 – C25, C25 – C35, and C35 – C50 were investigated to obtain better volatility-resolved information. Furthermore, migration of representative single- substance surrogates for each fraction — alkanes and aromatic compounds — was compared. More polar MOAH migrated slower than MOSH. MPPO in “ touching contact ” showed the highest values. Under gas phase contact conditions (without direct contact), migration rates into MPPO were lower compared with Sorb-Star. In C25-C35, migration was found only in MPPO- touching contact and Sorb-Star at 60 ° C for MOSH. The authors concluded that the migration behavior of MOH can be depicted by the use of suitably representative surrogates, which will help ease the analytical tasks. Migration tests with these simulants (MPPO and Sorb-Star) at 20 ° C and 40 ° C can cover a wide range of real-life migration processes from paper-based food contact materials into foods, provided that appropriate conditions are chosen. 5.2.7 Impact of humidity As a potentially important factor, relative humidity (rH) — which could affect the extent of migration and the type of migrants from paper qualitatively — was studied using MPPO by Barnkob and
80% of the initial concentration in paper; however, for speci fi c substances, the ranges were narrower: DIPN 37% – 49% (with 26% for breadcrumbs). Migration of DiBP ranged from 0.22 mg/kg food to 0.54 mg/kg food (with an “ outlier ” of 0.06 for rice and biscuits as the highest) and of benzophenone (as the most prominent photoinitiator) from 24 μ g/kg food to 59 μ g/kg food (with 6 μ g/kg as the lower “ outlier ” from noodles and oatmeal as the highest). The authors commented this: “ Migration seemed to be in fl uenced more by the porosity of the food than by the fat content (for instance, MOSH migration into oatmeal was clearly higher than into fatty biscuits). ” This indicates that adsorption rather than dissolution in the fat phase constitutes the driving mechanism for migration of substances with suf fi cient volatility (according to the authors when compared with C24 or a similar substance). The steepest increase for MOSH was in the fi rst 2 months of storage (approximately 40% of potential, between 22% for noodles and 57% for oatmeal), which increased to 50% – 80% after 9 months. As a potentially logical next step, this author consortium studied the difference of more volatile versus non-volatile migrants from paper into dry foods (Eicher et al., 2015). In this study of mechanistic character, data from migration experiments using newspaper as contact with dry foods (rice, polenta, baking mix, and breadcrumbs) and MPPO was reported. The newspaper was chosen because it contained volatile MOSH ( < C24) and non-volatile polyalphaole fi nes (PAO, branched alkanes, characterized by the retention time of the respective n-alkanes) from the printing ink. The authors have differentiated between “ direct ” (touching) and indirect (gas phase) contacts. They concluded that migration into dry foods via touching contact is not necessarily negligible and could even reach considerable levels. One of the several key experiments was a comparison of 10 and 20 days of contact at room temperature with MPPO, polenta, and rice. The migration focused on three substance classes: MOSH < C24, PAO29, and PAO35, representing increasing molecular weights and decreasing volatility. Migration of MOSH < C24 was 100% on MPPO, 92% for polenta, and 71% for rice. Migration of the non-volatiles PAO29/PAO35 was much lower: 46%/20% for MPPO, 39%/20% for polenta, and 4%/2% for rice. Decreasing the particle size of the polenta from 2 mm to 1 mm led to an increase in PAO migration by factor 2.5 but not of MOSH. Further size reduction to 0.5 mm had only little effect. This was related to the density of contact points in the paper. Migration into MPPO at identical conditions at room temperature (10 days) was in the same order of magnitude as polenta yet lower than baking mix and largely higher than into rice. However, in longer-term (45 days) migration of PAO into rice (higher fat content) passed that of the fi ner breadcrumbs in contrast to the result after 8 days, in which migration into breadcrumbs was higher. Migration in both rice and breadcrumbs was lower than into polenta. Considering all fi ndings, the authors expressed their concern as to whether MPPO test would be suitable for paper to simulate touching contact: elevating temperature may volatilize non-volatile substances at room temperature, and the particle size of the food may be far from that of MPPO. The use of surrogates for MOAH while comparing migration testing with MPPO versus the dry foods polenta and couscous was the main topic of research by Jaén et al. (2022). For these kinetic experiments (at 60 ° C: 3, 6, and 10 days and 70 ° C: 2 h) cardboard samples were previously forti fi ed with 16 aromatic model
Frontiers in Chemistry
08
frontiersin.org
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