## 2 Materials and Methods
### General Characterisation Methods
#### 2.3.3 Analysis of Volatile Compounds by HS-SPME-GC-MS  
HS-SPME Extraction Procedure  
The sample (1.00 \(\pm\) 0.01 g) was mixed with 1 mL of distilled water and 2 \(\upmu\)L of internal standard 4-methylstyrene (8 mg/kg, Sigma-Aldrich Inc., St. Louis, MO) and a small magnetic stirrer were placed in a 20 mL amber vial sealed with an aluminium pressure cap provided with a pierceable silicone septum. The extraction was carried out using the SPME fibre made of divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) 50/30 mm, StableFlex, 1 cm long, mounted on a manual support set SPME (Supelco, Bellefonte, PA, USA) [31; 32]. The vial with the sample was placed in a water bath under a specific temperature. After 10 min of equilibrium of the sample, the SPME needle was inserted into the vial and exposed to the headspace of the vial for a specific time. After extraction, the fibre desorption was performed in the GC-MS injection port at 250 \({}^{\circ}\)C for 12 min (splitless mode). Blank tests were performed prior to the analysis of the samples to ensure that there was no contamination that could cause memory effects. GC-MS Parameters  
The analysis of the volatiles was carried out using an Agilent 6890N GC model gas chromatograph coupled to an Agilent 5973N MS mass spectrometer (Agilent Technologies, Palo Alto, CA, USA) with impact ionization source of electrons (EI 70 eV) and quadrupole analyzer. The temperatures of the transfer line \"ion source\" and GC-MS were 230 and 250 \({}^{\circ}\)C, respectively. A TRB-624 column (30 m \(\times\) 0.25 mm \(\times\) 1.4 \(\upmu\)m) of Teknokroma was used, which was programmed from 50 \({}^{\circ}\)C (maintaining 2 min) to 250 \({}^{\circ}\)C (isotherm for 7 min) at 10 \({}^{\circ}\)C/min. Helium was used as the carrier gas (1.5 mL/min). The volatile compounds were identified in \"scan\" mode (m/z 30-550) by comparing their mass spectra with those of the standard compounds and the Wiley compound library. When standards were not available, volatile compounds having \(\geq\)80% similarity with Wiley library were tentatively identified using GC-MS spectra only. All patterns obtained from the commercial house Sigma-Aldrich, St. Louis, were quantified by HS-SPME-GC-MS using standard calibration curves. For this, mother solution (5 mg/kg) and working solutions were prepared using distilled water as a solvent. The HS-SPME and GC-MS sampling procedures were carried out as described for the samples. The analytical method used for the quantification was validated in terms of linearity, repeatability and limits of detection (LOD) and quantification (LOQ). The calibration curves were performed at five concentration levels, in triplicate, using adequately diluted standards and adjusted by linear regression. Optimization of HS-SPME Extraction Parameters Box-Benhken Experimental Design (BBD)  
The extraction of volatile compounds from PHAs was performed under different extraction conditions according to the experimental design shown in Table 2. The parameters considered during HS-SPME optimization were extraction temperature (50, 70 and 90 \({}^{\circ}\)C), and extraction time (15, 37.5 and 60 min) and sodium chloride addition (0, 0.5 and 1 M) in a final vial volume of 1 mL. The P3 HB sample was selected for the optimization of HS-SPME conditions. The range of studied variables was selected on the basis of results obtained in previous studies reported in the literature [31; 32; 33]. A Box-Behnken design (BBD), comprising 12 experimental runs and four central points, was used, and experiments were carried out in randomized order from the experimental design were evaluated in terms of the sum of the peak areas of volatile compounds identified with a library similarity higher than 80%