## 2 Results
### GC-MS Analysis
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**RT/min \({}^{\text{d}}\)**} & \multicolumn{4}{c}{**RI**} & \multicolumn{4}{c}{**Concentration (sg/I)**} & \multirow{2}{*}{**Identification \({}^{\text{a}}\)**} \\ \cline{4-10}  & & & **Cal. * & \multicolumn{1}{c}{**Ref. \({}^{\text{f}}\)**} & \multicolumn{1}{c}{**CK**} & \multicolumn{1}{c}{**W30**} & \multicolumn{1}{c}{**W40**} & \multicolumn{1}{c}{**W50**} & \multicolumn{1}{c}{**W60**} \\ \hline \multicolumn{10}{c}{**Ketences**} \\
1 & 2-Nonanone & 14.47 & 1310 & 1366 & 0.57 \(\pm\) 0.11 & 0.50 \(\pm\) 0.23 & 0.40 \(\pm\) 0.07 & 0.47 \(\pm\) 0.10 & 0.69 \(\pm\) 0.08 & MSSTD/RI \\
2 & 2-Undecanne & 19.73 & 1509 & 1599 & 0.41 \(\pm\) 0.06 & 0.53 \(\pm\) 0.10 & 0.66 \(\pm\) 0.11 & 0.43 \(\pm\) 0.32 & 0.21 \(\pm\) 0.14 & MSSTD/RI \\
3 & Acetophenone & 20.87 & 1555 & 1627 & 0.06 \(\pm\) 0.01 & 0.03 \(\pm\) 0.00 & 0.04 \(\pm\) 0.01 & 0.07 \(\pm\) 0.03 & 0.05 \(\pm\) 0.02 & MSSTD/RI \\ Total & & & & 1.05 \(\pm\) 0.12 & 1.06 \(\pm\) 0.24 & 1.10 \(\pm\) 0.16 & 0.97 \(\pm\) 0.39 & 0.96 \(\pm\) 0.22 \\ \hline \multicolumn{10}{c}{**Acids**} \\
1 & Hexanoic acid & 25.74 & 1765 & 1850 & 1.03 \(\pm\) 0.33 & 0.47 \(\pm\) 0.35 & 0.54 \(\pm\) 0.11 & 1.33 \(\pm\) 0.01 & - & MSSTD/RI \\
2 & Octanoic acid & 30.06 & 1969 & 2038 & 7.55 \(\pm\) 2.53 & 6.48 \(\pm\) 2.16 & 6.04 \(\pm\) 0.35 & 14.75 \(\pm\) 7.97 & 4.48 \(\pm\) 2.88 & MSSTD/RI \\
3 & n-Decanoic acid & 34.07 & 2176 & 2246 & 6.60 \(\pm\) 2.06 & 4.80 \(\pm\) 0.85 & 3.88 \(\pm\) 1.13 & 9.94 \(\pm\) 4.92 & 1.59 \(\pm\) 0.64 & MSSTD/RI \\ Total & & & & 15.18 \(\pm\) 3.50  & \multicolumn{1}{c}{**J**} \\ \hline \multicolumn{10}{c}{**Aidedy \(\sim\) 0.07**} \\
1 & Octanal & 11.78 & 1214 & 1292 & - & - & 0.18 \(\pm\) 0.14 & - & MSSTD/RI \\
2 & Nomanal & 14.55 & 1313 & 1390 & 0.56 \(\pm\) 0.18 & 0.43 \(\pm\) 0.07 & 0.46 \(\pm\) 0.17 & 1.42 \(\pm\) 0.08 & 0.44 \(\pm\) 0.11 & MSSTD/RI \\
3 & Decanal & 17.23 & 1412 & 1472 & 1.27 \(\pm\) 0.81 & 0.18 \(\pm\) 0.09 & 0.98 \(\pm\) 0.37 & 1.21 \(\pm\) 0.73 & MSSTD/RI \\ Total & & & & 0.56 \(\pm\) 0.18  & \multicolumn{1}{c}{**J**} \\ \hline \multicolumn{10}{c}{**Aidedy \(\sim\) 0.07**} \\
1 & Octanal & 11.78 & 1214 & 1292 & - & - & 0.18 \(\pm\) 0.14 & - & MSSTD/RI \\
2 & Nomanal & 14.55 & 1313 & 1390 & 0.56 \(\pm\) 0.18 & 0.43 \(\pm\) 0.07 & 0.46 \(\pm\) 0.17 & 1.42 \(\pm\) 0.08 & 0.44 \(\pm\) 0.11 & MSSTD/RI \\
3 & Decanal & 17.23 & 1412 & 1472 & 1.27 \(\pm\) 0.81 & 0.18 \(\pm\) 0.09 & 0.98 \(\pm\) 0.37 & 1.21 \(\pm\) 0.73 & MSSTD/RI \\ Total & & & & 0.56 \(\pm\) 0.18  & \multicolumn{1}{c}{**J**} \\ \hline \multicolumn{10}{c}{**Aidedy \(\sim\) 0.07**} \\
1 & Octanal & 11.78 & 1214 & 1292 & - & - & 0.18 \(\pm\) 0.14 & - & MSSTD/RI \\
2 & Nomanal & 14.55 & 1313 & 1390 & 0.56 \(\pm\) 0.18 & 0.43 \(\pm\) 0.07 & 0.46 \(\pm\) 0.17 & 1.42 \(\pm\) 0.08 & 0.44 \(\pm\) 0.11 & MSSTD/RI \\
3 & Decanal & 17.23 & 1412 & 1472 & 1.27 \(\pm\) 0.81 & 0.18 \(\pm\) 0.09 & 0.98 \(\pm\) 0.37 & 1.21 \(\pm\) 0.73 & MSSTD/RI \\ Total & & & & 0.56 \(\pm\) 0.18  & \multicolumn{1}{c}{**J**} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Volatile compounds identified by GC-MS in skim millks with different preheating temperatures.