# Effects of Isochoric Freezing on the Quality Characteristics of Raw Bovine Milk
## 3 Results and Discussion
### SPME GC/MS Analysis
The three most abundant compounds present in the initial milk sample were methoxyphenyl-oxime (36%), acetone (23%), and 2-butanone (13%). While there is little information regarding the flavor characteristics of methoxyphenyl-oxime, its presence in milk has been reported elsewhere [13; 53]. Acetone and 2-butanone, both ketones, are common milk aromas which might originate from the cow's metabolism. Ketone aromas contribute to floral or fruity aromas in milk. The remaining compounds are classified as free fatty acids (FFAs), branched hydrocarbons, alcohols, and aromatics. In the context of flavor, FFAs are of particular importance. FFAs can come from various sources, such as in the lipolysis of milk triglycerides, lipid oxidation reactions, or microbial growth. Thus, high concentrations of (volatile) FFAs suggests the degradation of milk quality and flavor. After two weeks of storage, a significant increase (\(p<0.05\)) in FFAs (-11\(\times\)) was observed in the refrigerated samples (RF). In addition to the increase in all formerly \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Volatile** \\ **Compound** \\ \end{tabular} } & \multirow{2}{*}{\(RI\)} & \multirow{2}{*}{\(RI\)} & \multirow{2}{*}{\(\dfrac{\text{Initial}}{\text{{RF}}}\)} & \multirow{2}{*}{\(\dfrac{\text{{HTST}}}{\text{{HST}}}\)} & \multicolumn{3}{c}{\(\dfrac{\text{{IF (-5}}^{\circ}\text{C)}}{\text{{IF (-10}}^{\circ}\text{C)}}\)} \\ \cline{4-14}  & & & & **0 Weeks** & & **2 Weeks** & **0 Weeks** & **2 Weeks** & **5 Weeks** & **2 Weeks** & **5 Weeks** \\ \hline \multirow{2}{*}{2-Nonanone} & \multirow{2}{*}{1094} & \multirow{2}{*}{1073} & \multirow{2}{*}{ND} & \(0.61\) & \multirow{2}{*}{ND} & \(0.88\) & \multirow{2}{*}{ND} & \(0.88\) & \(\dfrac{\text{{(0.15)}}}{\text{{ND}}}\) & \(\dfrac{\text{{ND}}}{\text{{ND}}}\) & \(\dfrac{\text{{ND}}}{\text{{ND}}}\) & \(\dfrac{\text{{ND}}}{\text{{ND}}}\) \\ \hline \multirow{2}{*}{2-Undecanone} & \multirow{2}{*}{1279} & \multirow{2}{*}{1276} & \multirow{2}{*}{ND} & \(11.81\) & \(15.32\) & \(9.71\) & \(8.27\) & \(14.89\) & \(10.34\) & \(7.91\) & \(10.01\) & \(8.82\) \\ Compounds & & & \((2.32)^{\text{ab}}\) & \((2.26)^{\text{c}}\) & \((1.07)^{\text{ab}}\) & \((0.66)^{\text{ab}}\) & \((2.97)^{\text{c}}\) & \((1.34)^{\text{b}}\) & \((0.9)^{\text{a}}\) & \((2.51)^{\text{ab}}\) & \((0.49)^{\text{ab}}\) \\ \hline \multicolumn{2}{c}{Oxime-,} & \multirow{2}{*}{\(-\)} & \multirow{2}{*}{890} & \(11.81\) & \(15.32\) & \(9.71\) & \(8.27\) & \(14.89\) & \(10.34\) & \(7.91\) & \(10.01\) & \(8.82\) \\ \multicolumn{2}{c}{-} & \multirow{2}{*}{\(-\)} & \multirow{2}{*}{890} & \((2.32)^{\text{ab}}\) & \((2.26)^{\text{c}}\) & \((1.07)^{\text{ab}}\) & \((0.66)^{\text{ab}}\) & \((2.97)^{\text{c}}\) & \((1.34)^{\text{b}}\) & \((0.90)^{\text{a}}\) & \((2.51)^{\text{ab}}\) & \((0.49)^{\text{ab}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 7: Relative abundance of volatiles by chemical classes for all storage treatments (Initial, HTST, IF, and RF) measured over a 5-week period. identified FFAs, newly formed FFAs included butanoic acid and decanoic acid. Ethanol was also detected in the refrigerated raw milk samples only. The newly formed ester, ethyl acetate, contributes to the sourness of the milk and is an indicator of milk quality degradation. Significant increases in aliphatic hydrocarbons were also observed, however their impact on the milk's flavor is considered secondary due to their high odor thresholds. Same-day pasteurization of the initial milk sample did not result in substantial changes in nearly all chemical categories. However, small amounts of newly formed decanoic acid were detected. The formation of nonanal, which delivers sweet grass-like odors was also observed. Milk pasteurization followed by 2 weeks of refrigeration (HTST) led to a significant increase in aliphatic hydrocarbon content but a decline in overall ketone amounts. The net outcome of these changes likely signifies the onset of milk flavor degradation.