# Electronic Nose Analysis to Detect Milk Obtained from Pasture-Raised Goats
## 2 Materials and Methods
### Analysis of Volatile Organic Compounds  
The extraction of volatile organic compounds (VOCs) was carried out, as described by [PERSON] et al. [31]. A total of 22.5 g of milk, 20 uL of 2-methyl-3-heptanone (99% purity, Sigma-Aldrich, St. Louis, MO, USA) as internal standard (389 mg/L, in water solution) and 2.75 g of sodium phosphate monobasic (NaH\({}_{2}\)PO\({}_{4}\)) (Sigma-Aldrich) were added into a 50 mL dark glass bottle. The sample was magnetically stirred for 5 min at 55 \({}^{\circ}\)C. SPME fibre was inserted through the Teflon septum in the bottle and exposed to sample headspace for 60 min at 55 \({}^{\circ}\)C while stirring. The SPME device (Supelco Co., Bellefonte, PA, USA) was equipped with a 50/30 \(\upmu\)m thick divinyl-benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre coated with 2 cm length stationary phase. Then, the VOCs were desorbed directly in the injector port of GC kept at a temperature of 250 \({}^{\circ}\)C in split mode with a 4:1 split ratio, for 10 min. Volatile compounds analyses were performed on an Agilent 7890A GC System gas chromatograph coupled to an Agilent 5975C VI MSD with Triple-Axis-Detector mass spectrometer (Agilent Technologies, Inc., Palo Alto, CA, USA). GC was equipped with a Zebron ZB-WAX capillary column (60 m \(\times\) 0.25 mm i.d. \(\times\) 0.25 \(\upmu\)m film thickness 100% polyethylene glycol; Phenomenex, Torrance, CA, USA). The carrier gas was helium with a flow of 1 mL/min. The temperature program was 40 \({}^{\circ}\)C for 10 min, then raised at 5 \({}^{\circ}\)C/min to 240 \({}^{\circ}\)C and held for 11 min [32]. Mass spectra were recorded at 70 eV. The source temperature was 230 \({}^{\circ}\)C, the quadrupole temperature was 150 \({}^{\circ}\)C and the interface temperature was 250 \({}^{\circ}\)C.  
The identification of VOCs was performed by comparing retention times and mass spectra obtained by analysing pure reference compounds in the same conditions. The identification was confirmed by comparing mass spectra with those of the National Institute of Standards and Technology (NIST) database. All chemical standards were supplied by Sigma-Aldrich (St. Louis, MO, USA). The fibre was conditioned at 270 \({}^{\circ}\)C for 1 h before the analysis. A blank test was performed before each analysis. The quantitative data of milk volatile compounds was carried out by normalising the peak areas of each compound with respect to the area of the internal standard peak. Peak area data were processed by MSD  
\begin{table}
\begin{tabular}{c c c} \hline
**Attribute** & **Definition** & **Reference** \\ \hline Sweet aromatic & Odour associated with materials having a sweet taste & Vanillin \\ Cream & Aromatics characteristic of milk fat and lactones & Heavy cream \\ Butterscotch & Butterscotch candies odour & Butterscotch candies \\ Goaty & Aromatics associated with goat fresh cheese & Goat fresh cheese \\ Feed/malty/silage & Aromatics associated with silage, hay and cattle feed & Malt extract \\ Grassy & Aromatics associated with cut green grass & Fresh-cut grass \\ \hline \end{tabular}
\end{table}
Table 2: Definitions and reference standards of odour attributes used in the sensory analysis of raw goat milk samples.  
ChemStation 5975 TAD Data Analysis software (Agilent Technologies, Palo Alto, CA, USA). The analysis of volatile compounds was performed in triplicate on the bulk milk samples for each of the five milking periods.