## 3 Results and Discussion
### Changes of Volatile Flavours in Cooked Marinated Pork Kunckle During Processing
Moreover, some short-chain fatty aldehydes (C5-C9) derive from the rapid oxidation of polyunsaturated fatty acids in lipids, and these changes are also critical to the overall flavours of cooked marinated pork knuckle. For instance, hexanal (OT = 5 \(\upmu\)g/kg) has tallow, grass, and fat odours; heptanal (OT = 3 \(\upmu\)g/kg) has sweet apricot, nutty aroma; octanal (OT = 0.7 \(\upmu\)g/kg) has a strong fruity aroma; and nonanal (OT = 1 \(\upmu\)g/kg) has fat and sweet orange notes. Benzaldehyde, which exhibits pleasant almond and burnt sugar odours (OT = 350 \(\upmu\)g/kg), had higher (\(p<\) 0.05) contents in T\({}_{4}\) than the other treatment groups and is generated from the degradation of phenylalanine [20]. In addition, trans-2-octanal has a fatty and meaty aroma; cis-2-nonenal has a roasted pork aroma. These aldehydes from lipid oxidation attend in the Maillard reaction during the heating stages. Ketones have little contribution to the overall flavour of cooked marinated pork knuckle due to lower concentration and higher threshold, and hydroxyacetone was from the Maillard reaction. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number** & **Compound** & \begin{tabular}{c} **RI** \\ **Value** \\ \end{tabular} & **T1** & **T2** & **T3** & **T4** \\ \hline \multicolumn{5}{c}{Esters} & \multirow{2}{*}{35} & \multirow{2}{*}{\begin{tabular}{c} 20.66 \(\pm\) 0.67 b \\ \end{tabular} } & \multirow{2}{*}{10.34 \(\pm\) 1.21 c  } & \multirow{2}{*}{\
\begin{tabular}{c} 2.50 \(\pm\) 0.22 d \\ \end{tabular} } & \multirow{2}{*}{37.57 \(\pm\) 1.34 a  } \\ V37 & 12,15-Octadecylic acid methyl ester & & & & & & \\ V38 & Isopropyl Palmitate & & & & & & \\ V39 & Methyl cinnamate & & & & & & \\ V40 & Ethyl octanoate & & & & & & \\ V41 & Ethyl decanoate & & & & & & \\ V42 & Isopropyl Myristate & 1573 & 1.06 \(\pm\) 0.01 d  & 2.33 \(\pm\) 0.04 b  & 1.60 \(\pm\) 0.08 c  \\ V43 & Ethylene glycol laurate & & & & & & & \\ V44 & Ethyl hexanoate & & & & & & \\ V45 & Octyl octanoate & & & & & & \\ V46 & 2-Ethylhexyl ester & & & & & & \\ \hline \multicolumn{5}{c}{Acids} & \multirow{2}{*}{1154} & \multirow{2}{*}{2.70 \(\pm\) 0.06 b  } & \multirow{2}{*}{91.75 \(\pm\) 0.78 a  } \\ V47 & Acetic acid & & & & & & \\ V48 & Octanoic Acid & & & & & & \\ V49 & Decanoic acid & & & & & & \\ V50 & Nonanoic acid & & & & & & \\ V51 & Benzoic acid & & & & & & \\ V52 & Hexanoic acid & & & & & & \\ V53 & Levulinic acid & & & & & & \\ V54 & Butanoic acid & & & & & & \\ V54 & 4-(hydroxyphenyl) phosphonic acid & & & & & & \\ \hline \multicolumn{5}{c}{Others} & \multirow{2}{*}{1425} & \multirow{2}{*}{
\begin{tabular}{c} 2.53 \(\pm\) 0.60 b \\ \end{tabular} } & \multirow{2}{*}{20.29 \(\pm\) 0.20 a  } & \multirow{2}{*}{19.30 \(\pm\) 33.77 b  } \\ V56 & Anethole & & & & & & \\ V57 & 2-Pentyl-Furan & & & & & & \\ V58 & Styrene & 942 & 2.53 \(\pm\) 0.60 b  & 20.29 \(\pm\) 0.20 a  & & & & & \\ V59 & L-camphor & & & & & & \\ V60 & Dodecane & 828 & n.d. & 21.06 \(\pm\) 1.65 a  & 33.22 \(\pm\) 7.39 a  & 25.35 \(\pm\) 9.62 a  \\ V61 & Pently-cyclopropane & & & & & & & \\ V62 & Tetadecane & & & & & & \\ V63 & Heptadecane & & & & & & \\ V64 & Terpinen-4-ol & & & & & \\ V65 & Furfural & & & & & & \\ V66 & 5-methyl-furfurral & & & & & & \\ \hline \multicolumn{5}{c}{804.97 \(\pm\) 62.88 ab  } & \multirow{2}{*}{19.17 \(\pm\) 1.69 b  } \\ Total & & & & & & & \\ \hline \multicolumn{5}{c}{n.d.: volatile compounds not detected. Different lowercase letters (a–d) in the same row indicate significant differences among different samples (\(p<\) 0.05). Treatments: T1: raw meat stage; T2: marnade stage; T3: summer in brine soup stage; T4: finished product stage.} \\ \end{tabular}
\end{table} 
Table 1: _Cont._Alcohols accounted for the majority of the total volatile flavour compounds in this study, which originate from fat oxidation. Saturated alcohol has a high threshold and therefore has little effect on flavour.