## 3 Experimental Section
### HS-SPME and GC/MS Analysis of VOCs  
Five SPME fibers and different extraction times were tested to select the optimal conditions: polydimethylsiloxane (PDMS, 100 \(\,\)m), carboxen-polydimethylsiloxane (CAR-PDMS, 75 \(\,\)m), polydimethylsiloxane-divinylbenzene (PDMS-DVB, 65 \(\,\)m), (divinylbenzene-carboxylate-polymethylsiloxane (DVB-CAR-PDMS, 50/30 \(\,\)m), polyacrylate (PA, 85 \(\,\)m) (Supelco, Bellefonte, PA, USA). Prior to analysis, each fiber was preconditioned in the injector port of the gas-chromatograph during desorption at the temperature and for time suggested by the manufacturer. In order to test the fibers, 1 g of cling film was placed in a hermetically sealed glass vial and the samples were subjectedto different extraction times (15, 45, 60, 90, 120, 180, 240 min). Finally, 5 g of cheese and 1 g of each cling-film or \"mandrino\" cardboard prepared as previously described underwent SPME-GC/MS analysis. All samples of cheese or film were put in a 20 mL glass vial, fitted with cap equipped with silicon/PTFE septa (Supelco), and by adding 1 mL of the internal standard solution (IS) in water (camphor, 1 \(\upmu\)g mL\({}^{-1}\), CAS 21368-68-3). At the end of the sample equilibration period (1 h), a conditioned (1.5 h at 280 \(\lx@math@degree\)C) 50/30 \(\upmu\)m Divinylbenzene/CarboxenTM/polydimethylsiloxane (CAR/PDMS/DVB) StableFlexTM fiber (Supelco) was exposed to the headspace of the sample for extraction (3 h) by CombiPAL system injector autosampler (CTC analytics, Zwingen, Switzerland). The extraction temperature was 50 \(\lx@math@degree\)C to obtain VOC adsorption. To keep the temperature constant during analysis the vials were maintained on a heater plate (CTC Analytics). HS-SPME analysis was performed using a Trace GC Ultra (Thermo-Fisher Scientific; Waltham, MA, USA) Gas Chromatograph coupled to a quadrupole Mass Spectrometer Trace DSQII (Thermo-Fisher Scientific) and equipped with an Rtx-Wax column (30 m; 0.25 mm i.d. ; 0.25 \(\upmu\)m film thickness, Restek, Bellefonte, PA, USA). The oven temperature program was: from 35 \(\lx@math@degree\)C, hold 8 min, to 60 \(\lx@math@degree\)C at 4 \(\lx@math@degree\)C/min, then from 60 \(\lx@math@degree\)C to 160 \(\lx@math@degree\)C at 6 \(\lx@math@degree\)C/min and finally from 160 \(\lx@math@degree\)C to 200 \(\lx@math@degree\)C at 20 \(\lx@math@degree\)C /min. Carry over and peaks arising from the SPME fiber were checked by regularly running blank samples. After each analysis the fibers were immediately thermally desorbed in the GC injector for 5 min at 250 \(\lx@math@degree\)C to prevent contamination. The injections were performed in splitless mode (5 min). The carrier gas was helium at the constant flow of 1 mL\({}^{-1}\). An _n_-Alkanes mixture (C\({}_{8}\)-C\({}_{22}\), Sigma-Aldrich, St. Louis, MO, USA) was also run under the same chromatographic conditions as the samples to verify Kovats retention indices (KI) of the detected compounds confirming the identity of compounds. The transfer line to the mass spectrometer was maintained at 230 \(\lx@math@degree\)C, and the ion source temperature was set at 250 \(\lx@math@degree\)C. The mass selective detector parameter were set as follow: electronic impact at 70 eV, a multiplier voltage of 1456 V, and the mass spectra were obtained by collecting the data at rate of 1 scan s\({}^{-1}\) over the _m/z_ range of 45-450. Selected Ion Monitoring (SIM) was selected for acquisition of compounds investigated in the process of migration from cling-film to cheeses. For each compound, two ions were chosen as qualifier ions and one as quantifier ion (Table S5, Supplementary Material). Authentic compounds were analysed under the same conditions to identify and compare the retention times of peaks when available, or by comparing the Kovats retention indices with literature data. The identification of MS fragmentation patterns was performed either by comparison with those of standard compounds or using the National Institute of Standards and Technology (NIST) MS spectral database.