# Electronic Nose Analysis to Detect Milk Obtained from Pasture-Raised Goats
## 3 Results and Discussion
### Analysis of Volatile Compounds
The VOCs most abundant in P milk are, generally, responsible for green, sweet, fragrant and fruity notes [42; 45; 46; 47; 48]. On the contrary, [Z]-2-heptenal, maltol and 2,3 pentanedione, reported in higher amount in S milk samples, have biscuit, milky, caramel and buttery odours. According to [PERSON] et al. [50], 2,3 pentanedione, with a cheesy odour, was found to be lower in the milk of ruminants fed fresh fodder. [PERSON] et al. [43] have recently reported higher amounts of maltol in raw milk from indoor-fed animals than in pasture-fed animals. According to the authors, since maltol derives from the Maillard reaction, its presence in raw milk leads to the hypothesis of its microbial origin. However, further investigation would be needed. A cluster analysis was performed on the significant volatile compounds in order to classify and discriminate the two types of milk based on milking period and diet. The results were plotted into a heatmap (Figure 3). The cluster lines on the left side of Figure 3 represent volatile compounds clusters. Volatile compounds were grouped into three main clusters. The first two, starting from the top of the map, were represented by the terpene compounds and the acids, most abundant in P milk. The other cluster was represented by the molecules most present in S milk. The cluster lines on the top of Figure 3 represent the milking period and type of diet. Pasture milk of the last period, P5, was grouped with S milk samples, due to a lower quantity of some terpene compounds and acids that helped discriminate pasture milk from previous periods. The exclusive presence of terpene compounds in the milk of pasture-fed goats suggests how the terpene profile of the milk of grazing ruminants can help in the authentication of milk. The content of terpenes in milk is higher when animals are fed in highly biodiverse pastures rich in dicotyledons than monotonous forage [51]. [PERSON] et al. [35] identified \(\alpha\)-terpineol and \(\beta\)-caryophyllene only in the milk of goats fed on Caatinga native high-biodiverse pasture with concentrate supplementation compared to \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Volatile Compound** & **Pasture Milk** & **Stall Milk** & \(p\)**-Value** & **Odour Descriptor** \\ \hline
**Acids** & & & & \\ butanoic acid & + & \(-\) & 0.0043 & sweet, sweaty, cheesy \({}^{\text{a,e}}\) \\ hexanoic acid & + & \(-\) & 0.0106 & pungent, sweaty \({}^{\text{a}}\), goaty, cheesy \({}^{\text{b}}\) \\ heptanoic acid & & & 0.0729 & rancid, sour, cheesy, sweaty \({}^{\text{b}}\) \\ octanoic acid & + & \(-\) & 0.0119 & medicinal, fatty, musty \({}^{\text{a}}\), camphor, nutmeg \({}^{\text{b}}\) \\ nonanoic acid & & & 0.0706 & goaty, fatty \({}^{\text{a}}\), grassy \({}^{\text{b}}\) \\ decanoic acid & + & \(-\) & 0.0040 & grassy, fatty, goaty \({}^{\text{a}}\), sour \({}^{\text{b}}\) \\ undecanoic acid & & & 0.2256 & \\ dodecanoic acid & + & \(-\) & 0.0021 & soapy, goaty \({}^{\text{a}}\) \\ tetradecanoic acid & + & \(-\) & 0.0026 & sweet, animal \\
**Others** & & & & \\ methyl octanoate & + & \(-\) & 0.0010 & green, fruity, citrus \\ dimethyl sulphone & & & 0.6905 & sulphurous, burnt \({}^{\text{b,g}}\) \\ maltol & \(-\) & + & \(<\)0.0001 & caramel, cotton-candy \({}^{\text{d,f}}\) \\ \(\delta\)-octalactone & & & 0.1389 & coconut \({}^{\text{a}}\), fruity (peach), sweet \({}^{\text{e}}\) \\ \(\delta\)-dodecalactone & + & \(-\) & 0.0454 & coconut \({}^{\text{b}}\), floral, sweet \({}^{\text{e,f}}\), flowery, daisy-like \({}^{\text{a}}\) \\ \hline \hline \end{tabular}  
* A higher (+) or lower (\(-\)) quantity of compound has been reported for VOCs that exhibited statistically significant differences (\(p\leq 0.05\)). nf = not found. a = [PERSON] and [PERSON] [45]; b = [PERSON] et al. [47]; c = [PERSON] et al. [44]; d = [PERSON] et al. [43]; e = [PERSON] [42]; f = [PERSON] et al. [48]; g = [PERSON] et al. [46].  
\end{table} 
Table 4: _Cont._small-fed goats with elephant grass, hay and concentrate.