## 2 Results and Discussion
### Volatile Profile of Marinated Pork Hocks Characterized by GC-MS/O
#### 2.1.1 Volatile Composition of Marinated Pork Hocks
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Code** & **Compound** & **Formula** & **DB-wx\({}^{*}\)** & **DB-g\({}^{\dagger}\)** & **Identification** & **\begin{tabular}{c} **\$ Odour** \\ **Descriptions** \\ \end{tabular} & \
\begin{tabular}{c} **\$ Odour** \\ **(ug-kg\({}^{-3}\))** \\ \end{tabular} &
\begin{tabular}{c} **Relative Concentration (log-kg\({}^{-3}\))** \\ \end{tabular} \\ \hline
56 & 2-Methylpyrazine & C\({}_{6}\)H\({}_{5}\)N\({}_{2}\) & 1262 & N.A. & MS, LRI, O & Popcorn & 250 & N.D. & N.D. & N.D. & 55 \(\pm\) 0.3 \\
57 & 1-Waythmalkoz & C\({}_{6}\)H\({}_{5}\)N\({}_{2}\) & 1263 & N.A. & MS, LRI & N.A. & N.D. & 85 \(\pm\) 0.4 & N.D. & N.D. \\
58 & 2-Acetylylylrazine & C\({}_{6}\)H\({}_{5}\)N\({}_{2}\)O & 1624 & N.A. & MS, LRI, O & Nurity, most & 62 & 17.8 \(\pm\) 1.8 & N.D. & N.D. & N.D. \\  & \multicolumn{2}{c}{} & & & & \multicolumn{2}{c}{12.9 \(\pm\) 12a} & 43 \(\pm\) 12c & 42 \(\pm\) 10c & 75 \(\pm\) 0.8b \\  & \multicolumn{2}{c}{} & & & & \multicolumn{2}{c}{12.9 \(\pm\) 12b} & 43 \(\pm\) 12c & 42 \(\pm\) 10c & 75 \(\pm\) 0.8b \\  & \multicolumn{2}{c}{} & & & & \multicolumn{2}{c}{12.9 \(\pm\) 12a} & 43 \(\pm\) 12c & 42 \(\pm\) 10c & 75 \(\pm\) 0.8b \\
59 & 3-Methylthiophene & C\({}_{6}\)H\({}_{5}\)S & 1083 & N.A. & MS, LRI, O & Fatty, urine & 5000 & N.D. & 43 \(\pm\) 12b & N.D. & 75 \(\pm\) 0.8a \\
60 & 2-Methylthiophene & C\({}_{6}\)H\({}_{5}\)S & 1075 & N.A. & MS, LRI, O & green & 3000 & N.D. & N.D. & 42 \(\pm\) 1.0 & N.D. \\
61 & 2-Acetylylhiacel & C\({}_{6}\)H\({}_{5}\)N\({}_{2}\)OS & 1644 & N.A. & MS, LRI, O & current & 10 & 10 \(\pm\) 15 & N.D. & N.D. & N.D. \\
62 & 3-Methylhiappened & C\({}_{6}\)H\({}_{5}\)O\({}_{5}\)S & 1712 & N.A. & MS, LRI & Sweet, potato & 123 & 22 \(\pm\) 0.8 & N.D. & N.D. & N.D. \\  & \multicolumn{2}{c}{} & & & & & \multicolumn{2}{c}{1224.2 \(\pm\) 1073.4 \(\pm\) 1791.8 \(\pm\) 822.40} & \multicolumn{2}{c}{Total} & & & & \multicolumn{2}{c}{1242.2 \(\pm\) 1073.4 \(\pm\) 1791.8 \(\pm\) 822.40} \\ \hline \hline \end{tabular}  Note: Different letters indicate significant differences (p \(<\) 0.05) among samples. All experiments were conducted for \(n\) = 3 independent maintained period shocks. Standard deviations are shown, MS, mass spectrum comparison using NIST libraries; LRI, linear retention index compared with literature value (0,0), colour descriptions. \({}^{\dagger}\) Odour descriptions were mainly gathered from the following literature and online database. [11, 12, 20, 22, 18]. ([[http://www.lower.org.it/](http://www.lower.org.it/)]([http://www.lower.org.it/](http://www.lower.org.it/))  
Another main observation from Table 1 is the relatively high odour threshold of hydrocarbons, which results in low contributions for the majority of the hydrocarbons except ethyl acetate, 3-carene, D-limonene and \(\beta\)-phellandrene. As reported, hydrocarbons can be derived from alkyl radicals via lipid auto-oxidation processes [29]. Other types of volatiles including ketones, esters and phenols are also considered as a flavour auxiliary of the marinated pork hocks, although they have relatively high thresholds. Furans refer to a group of heterocyclic compounds that were structurally characterized with the oxygen atom in the ring. [PERSON] et al. [20] reported that furans might be derived from the dehydration of carbohydrates or the Amadori rearrangement procedure. [PERSON] and [PERSON] [30] suggested that the oxidation of fatty acids could be another pathway for the formation of furans. Among six furans listed in Table 1, 2-pentylfuran with the lower threshold (6.0 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)kg\({}^{-1}\)) had the highest relative concentration in all samples, and 2-ethylfuran with the lowest threshold (2.3 \(\mathrm{\SIUnitSymbolMicro g}\)\(\cdot\)kg\({}^{-1}\)) had the highest relative concentration in only HHT. These two furans were oxidative degradation products of linolenate [11; 13] and were considered as the most important flavour compounds contributing to meat products [11].