# Optimization and Preparation of Tallow with a Strong Aroma by Mild Oxidation
## 2 Results and Discussion
### Principal Component Analysis  
In order to further clarify the aroma characteristics of oxidized melted tallow under different conditions, principal component analysis was performed on 15 levels of oxidized melted tallow with different factors according to the compositions and contents of different aroma compounds, as shown in Figure 5. It could be seen from the figure that the samples of 15 levels of oxidation-smelting tallow with different factors were relatively concentrated and could be divided into three types after dimension reduction treatment with a principal component. Type I was oxidized melted tallow samples at different temperatures, which mainly contained five kinds of samples at 120 \({}^{\circ}\)C, 130 \({}^{\circ}\)C, 140 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, and 160 \({}^{\circ}\)C. The content of 1-pentanal (almond), 1-hexanal (green, grassy), (_E_)-2-pentenal (fruity), 1-heptanal (fatty), 1-octanal (fatty), (_E_)-2-heptenal (fatty), 1-nonal (fresh), (_E_)-2-octenal (cuucumber), (_E_)-2-nonenal (cuucumber), (_E_)-2-decenal (fatty), 2-undecanal (orange peel), and (_E_,_E_)-2,4-decational (fried) compounds were relatively high, and the characteristic odor of these compounds affected the overall odor of the five samples. The interaction between each odor caused each sample in Type I to, overall, present strong fruity and animal fat notes. Type II samples mainly included 25 min, 35 min, 45 min, 55 min, and 65 min. The content of 1-pentanal (almond), (_E_)-2-decenal (fatty), (_E_)-2-heptenal (fatty), benzaldehyde (nutty), (_E_,_)-2,4-heptadienal (fatty), (_E_,_)-2,4-decadienal (fried), 1-octanal (fatty), 1-hexanal (green, grassy), (_E_)-2-pentenal (fresh), 1-heptanal (fatty), 2-tridecanone (creamy), 2-pentadecanone (floral), 2-octanone (fresh), 2-nonone (fresh), 2-decanone (orange peel), and 3-ethyl-cyclopentane-1,2-dione (caramel) were relatively high, and the characteristic odor of aldehyde and ketone compounds affected the overall odor of these five samples, it made the overall odor profiles of each sample in Type II show the odor of animal fat, muttony and sweet. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Condition** & **Number** & **Aldehyde** & **Alcohol** & **Ester** & **Sour** & **Ketone** & **Heterocycle** & **Other** \\ \hline \multirow{6}{*}{Temperature} & 120 \({}^{\circ}\)C & 56.00\% & 12.00\% & 12.00\% & 12.00\% & 0.00\% & 8.00\% & 0.00\% \\  & 130 \({}^{\circ}\)C & 58.33\% & 4.17\% & 12.50\% & 16.67\% & 0.00\% & 8.33\% & 0.00\% \\  & 140 \({}^{\circ}\)C & 60.00\% & 4.00\% & 4.00\% & 16.00\% & 0.00\% & 12.00\% & 0.00\% \\  & 150 \({}^{\circ}\)C & 60.00\% & 4.00\% & 4.00\% & 16.00\% & 0.00\% & 12.00\% & 0.00\% \\  & 160 \({}^{\circ}\)C & 60.00\% & 4.00\% & 4.00\% & 16.00\% & 0.00\% & 12.00\% & 0.00\% \\  & 25 min & 59.26\% & 0.00\% & 11.11\% & 14.81\% & 3.70\% & 7.41\% & 0.00\% \\  & 35 min & 51.72\% & 3.45\% & 10.34\% & 20.69\% & 3.45\% & 6.90\% & 0.00\% \\  & 45 min & 50.00\% & 6.67\% & 10.00\% & 20.00\% & 6.67\% & 6.67\% & 0.00\% \\  & 55 min & 41.67\% & 5.56\% & 11.11\% & 16.67\% & 16.67\% & 8.33\% & 0.00\% \\  & 65 min & 38.89\% & 8.33\% & 11.11\% & 16.67\% & 16.67\% & 8.33\% & 0.00\% \\  & 18 L/h & 36.36\% & 13.64\% & 13.64\% & 31.82\% & 0.00\% & 0.00\% & 4.55\% \\  & 48 L/h & 40.00\% & 12.00\% & 12.00\% & 32.00\% & 0.00\% & 0.00\% & 4.00\% \\ Air velocity & 78 L/h & 40.00\% & 12.00\% & 12.00\% & 32.00\% & 0.00\% & 0.00\% & 4.00\% \\  & 108 L/h & 48.28\% & 10.34\% & 10.34\% & 27.59\% & 0.00\% & 0.00\% & 3.45\% \\  & 138 L/h & 51.85\% & 7.41\% & 11.11\% & 25.93\% & 0.00\% & 0.00\% & 3.70\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The proportion of aroma compounds in oxidized melted tallow under different conditions. Type III mainly consisted of five samples at 18 L/h, 48 L/h, 78 L/h, 108 L/h, and 138 L/h.