# Chemical-Sensory Traits of Fresh Cheese Made by Enzymatic Coagulation of Donkey Milk
## 3 Results and Discussion
The different fat content in the two types of milk should play a role in the formation and release of VOCs. In this regard, it must be underlined that the results on the donkey samples (both milk and cheese) had low standard deviations, differently from those obtained in the cow cheese. It could be connected to the different concentration at which VOCs are present in the two types of samples, or to the variability of the fat content (\(3.62\pm 0.39\)) in the cow milk samples used. The most abundant volatile compounds in donkey milk were acetic acid and acetone: they can both derive from animal metabolism and microbial activity. These two compounds were also detected in cheese, but at a lower level, probably because they were lost into the whey during cheesemaking. Among the other compounds, 6-methyl-5-hepten-2-one was the third in order of abundance: it is commonly called sulactone, and presents an apple, bitter and citrus flavour. It is a powerful attractant for mosquitos, and is emitted by a variety of plants and animals, including humans, horses, cows and sheep. Sulcatone is also present in the faeces of mares in estrous and in the hair of horses [35; 36]: this can explain the presence in donkey milk and consequently in cheese, where its concentration almost doubled. As regards cheese, 18 compounds were identified in the donkey product (versus 34 in the control one). The most abundant were acetoin, 2-methylbutanal and 2-ethylhexanol, followed by 2-ethylhexanal and hexanoic acid. Acetoin and methylbutanal are commonly found in any types of dairy products; they present butter and green odors and derive from lactic acid bacteria fermentation [37; 38; 39]. 2-Ethylhexanol has a fruity, green, cucumber odour [40] and likely derives from microbial metabolism, since it was not present in milk [41]. However, it has also been reported to be a pollutant deriving from plastic tools. In particular, it is a metabolic derivative of 2-ethylxplphtalate (DEHP), an additive commonly added to plastics to make them flexible [42]. Possible pollution from the cheesemaking environment (i.e., plastic electrode, tools for milking and plastic baskets used for cheese moulding) should be ascertained. All other newly formed compounds had been widely reported in the literature for cow's cheese. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compoun.d.** & \multicolumn{2}{c}{**Donkey**} & \multicolumn{2}{c}{**Cow (Control)**} \\ \hline  & Milk & Cheese & Milk & Cheese \\ \hline Acids & & & & \\ acetic & \(5.65\pm 0.03\)\({}^{\text{b}}\) & \(0.19\pm 0.01\)\({}^{\text{d}}\) & \(2.69\pm 0.17\)\({}^{\text{c}}\) & \(66.03\pm 5.74\)\({}^{\text{a}}\) \\ butanoic & n.d. & \(0.36\pm 0.03\)\({}^{\text{c}}\) & \(5.09\pm 0.24\)\({}^{\text{b}}\) & \(8.77\pm 1.05\)\({}^{\text{a}}\) \\ hexanoic & n.d. & \(0.55\pm 0.10\)\({}^{\text{c}}\) & \(7.55\pm 0.87\)\({}^{\text{b}}\) & \(10.73\pm 0.82\)\({}^{\text{a}}\) \\ heptanoic & n.d. & n.d. & n.d. & \(0.68\pm 0.09\) \\ octanoic & n.d. & \(0.29\pm 0.07\)\({}^{\text{c}}\) & \(3.91\pm 0.33\)\({}^{\text{b}}\) & \(5.02\pm 0.22\)\({}^{\text{a}}\) \\ nonanoic & n.d. & n.d. & \(1.44\pm 0.03\)\({}^{\text{b}}\) & \(2.10\pm 0.07\)\({}^{\text{a}}\) \\ decanoic & n.d. & n.d. & \(3.22\pm 0.40\) & \(3.01\pm 0.44\) \\ Alcohols & & & & \\ ethanol & n.d. & n.d. & n.d. & \(17.46\pm 2.07\) \\
2-ethylhexanol & n.d. & \(7.16\pm 0.12\) & n.d. & n.d. \\ isoamylalcohol & n.d. & \(0.42\pm 0.02\) & n.d. & n.d. \\
3-methyl,1-butanol & n.d. & n.d. & n.d. & \(71.84\pm 6.47\) \\
3-methyl-2-buten-1-ol & n.d. & n.d. & n.d. & \(1.19\pm 0.52\) \\
1-nonanol & n.d. & \(0.16\pm 0.01\) & n.d. & n.d. \\
2-octyloxy-ethanol & n.d. & n.d. & n.d. & \(16.26\pm 3.62\) \\ phenylethyl alcohol & n.d. & n.d. & n.d. & \(1.92\pm 0.09\) \\
2-propyl-1-pentanol & n.d. & n.d. & \(1.48\pm 0.39\)\({}^{\text{a}}\) & \(0.47\pm 0.16\)\({}^{\text{b}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Volatile organic compounds (VOCs) detected in milk and cheese (\(\text{ug}/\text{kg}\pm\text{SD}\)). Figures 3 and 4 show the results of the electrophoretic study.