# Internet of Food (IoF), Tailor-Made Metal Oxide Gas Sensors to Support Tea Supply Chain
## 2 Materials and Methods
### GC-MS Analysis Conditions  
After closure, vials were placed in the autosampler HT280T (HTA s.r.l., Brescia, Italy) to proceed with vial conditioning and volatile organic compound (VOC) extraction. Conditioning of the sample was performed as follows: filled vials were maintained for 15 min at 40 \({}^{\circ}\)C in order to equilibrate the headspace (HS) of the sample and to remove any variables. Afterward, VOCs extraction was performed using solid-phase microextraction (SPME) analysis, and the fiber used for the adsorption of volatiles was a divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) 50/30 \(\upmu\)m (Supelco Co. Bellefonte, PA, USA) placed on the HT280T autosampler. The fiber was exposed to the vial HS in the HT280T oven thermostatically regulated at 40 \({}^{\circ}\)C for 15 min. The GC instrument used in this work was a Shimadzu GC 2010 PLUS (Kyoto, KYT, Japan), equipped with a Shimadzu single quadrupole mass spectrometer (MS) MS-QP2010 Ultra (Kyoto, KYT, Japan). Fiber desorption took place in the GC-MS injector for 6 min at 250 \({}^{\circ}\)C. GC was operated in the direct mode throughout the run, while the separation was performed on a MEGA-WAX capillary column, 30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m film thickness, (Agilent Technologies, Santa Clara, CA, USA). Hydrogen was used as the carrier gas and has been produced by GENius PF500, FullTech Instruments Srl. (Rome, Italy) at a constant flow rate of 2.34 mL/min. The GC oven temperature programming was applied as follows: at the beginning, the chromatographic column was held at 40 \({}^{\circ}\)C for 2 min and, subsequently, the temperature was raised from 40 to 100 \({}^{\circ}\)C at 2 \({}^{\circ}\)C/min. Next, the temperature was raised from 100 to 180 \({}^{\circ}\)C, with a rate of 5 \({}^{\circ}\)C/min; finally, the temperature was raised from 180 to 230 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C/min and was maintained for 5 min, for a total program time of 58 min [21; 23; 24]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Kind**} & \multirow{2}{*}{**Code**} & \multirow{2}{*}{**Description**} & \multirow{2}{*}{**Components**} & \multicolumn{2}{c}{**Number of**} \\  & & & & **Replicates** \\ \cline{5-6}  & & & & **GC-MS** & **S3** \\ \hline \multirow{6}{*}{Green tea} & \multirow{2}{*}{TGO} & Green tea with & 88\% Green tea + 10\% & & \\  & & orange aroma & natural orange aroma + 1\% & 3 & 5 \\  & & & loto flower + 1\% orange skin & & \\ \cline{2-6}  & SGP & Pure green tea & 100\% Green tea & 3 & 12 \\ \cline{2-6}  & \multirow{2}{*}{SGL} & Green tea with & Green tea 83\% + lemon & & \\  & & lemon aroma & aroma + lemon juice & 3 & 12 \\  & & & concentrate 4\% & & \\ \cline{2-6}  & SGM & Green tea with & Green tea + green tea & & \\  & & Match tea & Matcha & 3 & 12 \\ \hline \multirow{6}{*}{Black tea} & \multirow{2}{*}{TBV} & Black tea with & 91,5\% tea + 8\% aroma + & \\  & & vanilla aroma & 0.5\% vanilla & 3 & 5 \\ \cline{2-6}  & \multirow{2}{*}{TBC} & Pure black tea from & 100\% Black tea Ceylon Sri & \\  & & Ceylon & Lanka & 3 & 12 \\ \cline{2-6}  & \multirow{2}{*}{EBL} & Black tea with lemon & Black tea from India and & \\  & & aroma & lemon aroma & 3 & 12 \\ \cline{2-6}  & \multirow{2}{*}{EBB} & Black tea Earl Grey & Black tea from India + & \\  & & & bergamot juice & 3 & 12 \\ \cline{2-6}  & EBP & Pure black tea & Biological black Tea & 3 & 12 \\ \cline{2-6}  & \multirow{2}{*}{SBL} & Black tea with lemon & Black tea + aroma + 1.04\% & \\  & & aroma & powder of lemon juice & 3 & 12 \\ \hline \multirow{2}{*}{White tea} & \multirow{2}{*}{BWL} & White tea with & White tea leaf 90\%, dried & \\  & & lemongrass & lemongrass 10\% & 3 & 8 \\ \hline \multicolumn{6}{c}{Total number of samples for each technique} & 33 & 114 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Samples description.