# Electronic Nose Analysis to Detect Milk Obtained from Pasture-Raised Goats
## 3 Results and Discussion
### Analysis of Volatile Compounds  
The SPME-GC/MS analysis was conducted to understand the volatile compounds that most contributed to discriminate the odour of the two types of milk. Table 4 shows the VOCs identified in the milk samples P and S, as well as their odour descriptors based on the available literature [42; 43; 44; 45; 46; 47; 48]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Volatile Compound** & **Pasture Milk** & **Stall Milk** & \(p\)**-Value** & **Odour Descriptor** \\ \hline
**Hydrocarbons** & & & & \\ hexane & \(-\) & \(+\) & 0.0041 & pungent, solvent \\ toluene & & & 0.3116 & earthy, nutty, bitter, plastic \({}^{\text{c,d}}\) \\ p-xylene & & & 0.3717 & \\ styrene & & & 0.2588 & rubber, plastic \({}^{\text{c}}\) \\
**Terpenes** & & & & \\ \(\alpha\)-pinene & \(+\) & nf & \(<\)0.0001 & green, woody, piney \({}^{\text{e}}\) \\ \(\beta\)-pinene & \(+\) & nf & \(<\)0.0001 & green, woody, piney, fragrant \({}^{\text{e}}\) \\ \(\alpha\)-limonene & \(+\) & nf & \(<\)0.0001 & fresh, lemon, orange \({}^{\text{e}}\) \\ eucalypt & \(+\) & nf & \(<\)0.0001 & \\ \(\beta\)-caryophyllene & \(+\) & nf & \(<\)0.0001 & berry-fruit, orange, green \({}^{\text{e}}\) \\ \(\alpha\)-caryophyllene & \(+\) & nf & \(<\)0.0001 & spicy, woody, green \\
**Aldehydes** & & & & \\ pentanal & & & 0.9174 & grassy, fruity, green \({}^{\text{c,g}}\) \\ hexanal & & & 0.0839 & fresh, herbaceous \({}^{\text{d}}\), cooked \({}^{\text{e}}\) \\ heptanal & \(+\) & \(-\) & 0.0257 & herbaceous, fruity (citrus) \({}^{\text{c}}\), soapy \({}^{\text{g}}\) \\ [E]-2-hexanal & & & 0.1557 & fruity, herbaceous, flowery \({}^{\text{c,e}}\), sour, cream \({}^{\text{e}}\) \\ octanal & & & 0.3377 & fatty, soapy \({}^{\text{a,g}}\), green, fruity (grape) \({}^{\text{c,g}}\) \\ [Z]-2-heptenal & \(-\) & \(+\) & 0.0371 & biscuit, fresh milk \({}^{\text{e}}\) \\ nonanal & \(+\) & \(-\) & 0.0286 & green, grassy fruity (citrus) \({}^{\text{c,g}}\), fresh \({}^{\text{d}}\), stale \({}^{\text{f}}\) \\ [E]-2-octeral & & & 0.4902 & green, fatty \({}^{\text{a}}\) \\ decanal & & & 0.1822 & green, grassy, floral \({}^{\text{d,g}}\) \\ [E,E]-2-4-heptadiene & & & 0.2005 & green, fatty \\ [E]-2-nonenal & & & 0.7669 & fatty, green \({}^{\text{a}}\), cardboard-like \({}^{\text{c}}\), hay \({}^{\text{f}}\) \\
[E,E]-2-4-decaional & & & 0.8193 & fatty, green \({}^{\text{a}}\), fried \({}^{\text{f}}\) \\
**Ketones** & & & & \\ acetone & \(+\) & \(-\) & 0.0052 & solvent, sweet, woody \\
2-butanone & & & 0.9125 & butterscotch, chocolate \({}^{\text{c}}\) \\
2-pentanone & & & 0.7500 & sweet, fruity \\
2,3-pentanedione & \(-\) & \(+\) & 0.0054 & buttery \\
2-nonanone & \(+\) & \(-\) & 0.0122 & hot milk, fruity \\
**Alcohols** & & & & \\
1-pentanol & & & 0.5730 & sweet, fruity, plastic \({}^{\text{d}}\) \\
1-hexanol & & & 0.1732 & green \({}^{\text{g}}\) \\
1-octen-3-ol & & & 0.0759 & mushroom \({}^{\text{c,g}}\) \\
1-heptanol & & & 0.5450 & green, pungent \\
1-octanol & & & 0.9894 & stale, mushroom \({}^{\text{d}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Quantitative data of volatile organic compounds identified in bulk milk samples obtained from goats fed on a pasture (P) or stall (S)-based diet. A total of 4 hydrocarbons, 6 terpenes, 12 aldehydes, 5 ketones, 5 alcohols and 9 acids have been identified in milk samples. For the volatile compounds, which had a significant difference between P and S milk samples (\(p\leq 0.05\)), the relative abundance was also reported (Table 4). Hydrocarbons, terpenes, and acids are the chemical classes that most differentiate the two types of milk samples, where terpene compounds qualitatively characterised the P milk samples. Heptanal and nonanal, which can result from lipid oxidation, had a higher intensity in P milk. The greater amount of unsaturated fatty acids, more susceptible to oxidation, increases the amount of aldehydes in pasture milk [36; 49]. We found no significant differences in the concentration of alcohols for the two types of milk.