# Electronic Nose Analysis to Detect Milk Obtained from Pasture-Raised Goats
## 2 Materials and Methods
### Electronic Nose Analysis  
Individual milk samples, provided by each goat, from the five different milking periods (for a total of forty-five P and forty-five S samples) were used for electronic nose measurements. An aliquot of 2 mL of each milk sample, previously defrosted for 24 h at 4 \({}^{\circ}\)C, were transferred into 20 mL glass vial with a Teflon/silicon septum in the screw cap in order to analyse the odour fraction by means of an electronic nose. A portable electronic nose PEN2 (WMA Airsense Analytics GmbH, Schwerin, Germany), operating with 10 Metal Oxide Semiconductor sensors (MOS), was used.  
Before the electronic nose acquisition, the vials were incubated in a thermostat-controlled bath at 25 \({}^{\circ}\)C for 30 min to allow the equilibrium of volatile compounds in the sample headspace [28]. The headspace odour sampling system consisted of an air injection needle and a sample aspiration needle which extracted and transferred the volatile fraction to the electronic nose sensors at constant velocity (400 mL/min). Data was recorded every second by a computer and the experiment lasted 60 s. Recovery time for the flushing of sensors with reference air was 240 s. The electronic nose was used at 25 \({}^{\circ}\)C \(\pm\) 1 during all experiments. The mean G/G\({}_{0}\) values of each sensor response were calculated from measurements in the 55-59 s range (sensors stability) using Winnuster v.1.6 software (Airsense Analytics GmbH, Schwerin, Germany).  
\begin{table}
\begin{tabular}{c c c c} \hline
**Code** & **Type of Milk** & **Milking Date** & **Type of Forages** \\ \hline P1 & Pasture milk & 27 April 2021 & _Ampelodesmos mauritanicus, Anthoxanthinum ovatum_ Lag., _Borago officinalis_ L., _Beta vulgaris_ L., _Trifolium repens_ L., _Cistus monspeliensis_ L., _Medicago lupulina_ L., _Quercus pubescens [PERSON]_, _Quercus llex_., _Myrtus communis_ L., _Ranniculus macrophyllus_. \\ \hline P2 & Pasture milk & 11 May 2021 & _Crataegus monogyna, Tanaectum partheinium, Malva sylvestris, Carpinus betlulus, Rubus ulmifolius, Rubia peregrina, Dorycium pentaphyllun_, _Clematis vitalba_, _Quercus llex_., _Mycelis muralis_. \\ \hline P3 & Pasture milk & 25 May 2021 & _Crataegus monogyna, Rosa canina, Cirsium aronese, Carpinus betlulus, Rubus ulmifolius, Mentha suauceolens, Quercus cerris, Quercus llex L., _Clematis vitalba_, _Prunus spinosa_. \\ \hline P4 & Pasture milk & 8 June 2021 & _Crataegus monogyna, Rosa canina, Urtica dioica, Polygonum aviculare_, _Rubus ulmifolius, Mentha suauceolens, _Euonymous europeans, Clematis vitalba, Sambucus nigra_, _Chondrilla junca_. \\ \hline P5 & Pasture milk & 22 June 2021 & _Crataegus monogyna, Medicicago sativa, Frazinus ornus, Carpinus betlulus, Rubus ulmifolius, Acer campestre, Quercus cerris, Quercus llex L., _Clematis vitalba, Pyrus pyraster_. \\ \hline S1 & Stall milk & 27 April 2021 & Hay ad libitum and fresh alexandrine clover \\ \hline S2 & Stall milk & 11 May 2021 & Hay ad libitum and fresh alexandrine clover \\ \hline S3 & Stall milk & 25 May 2021 & Hay ad libitum and fresh alexandrine clover \\ \hline S4 & Stall milk & 8 June 2021 & Hay ad libitum and fresh alexandrine clover \\ \hline S5 & Stall milk & 22 June 2021 & Hay ad libitum and fresh alexandrine clover \\ \hline \end{tabular}
\end{table}
Table 1: Milk samples measured by electronic nose, evaluated by sensory panel and analysed by GC/MS.