## 3 Results
### Volatile Flavor Compounds Identified from the Braised Pork

Table 1: Identification of braised pork volatile compounds extracted using SPME-GC/MS. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**ID X**} & \multirow{2}{*}{**RI Y**} & \multirow{2}{*}{**RI Z**} & \multicolumn{2}{c}{**Peak Area (\%)**} \\ \cline{5-6}  & & & & **A** & **B** \\ \hline \multicolumn{6}{c}{Esters and lactones} \\ \hline Methyl bunanoate & S & 1011 & & nd & 0.07 \(\pm\) 0.02 \\ \(\gamma\)-Butyrolactone & M & 1630 & 1647 m & 0.03 \(\pm\) 0.01 & nd \\ Styrally acetate & S & 1737 & & 0.03 \(\pm\) 0.01 & 0.05 \(\pm\) 0.01 \\ Benzyl isovalerate & S & 1938 & & nd & 0.03 \(\pm\) 0.01 \\ Total & & & & 0.06 & 0.14 \\ \hline \multicolumn{6}{c}{Phenols} \\ \hline Phenol & S & 2072 & & 0.02 \(\pm\) 0.01 & 0.03 \(\pm\) 0.01 \\ Total & & & & 0.02 & 0.03 \\ \hline \multicolumn{6}{c}{Ethers} \\ \hline Estragole & M & 1656 & 1655 m & nd & 0.04 \(\pm\) 0.01 \\ Anethole & S & 1821 & & 1.31 \(\pm\) 0.05 & 1.32 \(\pm\) 0.03 \\ Total & & & & 1.31 & 1.36 \\ \hline \multicolumn{6}{c}{Sulphur compounds} \\ \hline Methanethiololol & M & 711 & 696 m & 2.87 \(\pm\) 0.11 & 3.12 \(\pm\) 1.01 \\ Allyl mercaptan & S & 916 & & 0.34 \(\pm\) 0.06 & 1.31 \(\pm\) 0.08 \\ Allyl methyl sulfide & S & 981 & & 0.07 \(\pm\) 0.01 & 0.10 \(\pm\) 0.02 \\
2-Methylthiophene & M & 1110 & 1084 m & nd & 0.06 \(\pm\) 0.01 \\ Dially sulfide & S & 1165 & & nd & 0.11 \(\pm\) 0.07 \\ Thiophene & M & 1178 & 1150 m & 0.02 \(\pm\) 0.01 & nd \\ Thiazole & M & 1271 & 1286 s & 0.02 \(\pm\) 0.01 & nd \\ Allyl methyl disulfide & S & 1298 & & nd & 0.07 \(\pm\) 0.02 \\
2-Methyl-3-furanthiol & M & 1310 & 1339 s & 0.03 \(\pm\) 0.01 & nd \\ Furfuryl mercaptan & M & 1431 & 1432 m & 0.05 \(\pm\) 0.01 & nd \\ Methional & M & 1484 & 1458 m & 0.16 \(\pm\) 0.02 & nd \\
2-Acetylthiazole & M & 1686 & 1692 s & 0.08 \(\pm\) 0.03 & 0.10 \(\pm\) 0.03 \\ Total & & & & 3.65 & 4.87 \\ \hline \multicolumn{6}{c}{Nitrogenous compounds} \\ \hline Pyrazine & M & 1235 & 1254 s & 0.05 \(\pm\) 0.01 & nd \\ Methanamide & S & 1605 & & 0.02 \(\pm\) 0.01 & nd \\
2-Amino-6-methylbenzoic acid & S & 1781 & & nd & 0.20 \(\pm\) 0.09 \\
2-Acetylpyrrole & M & 2037 & 2027 s & 0.02 \(\pm\) 0.01 & nd \\ Dimethylamine & S & 2232 & & 0.01 \(\pm\) 0.00 & 0.11 \(\pm\) 0.04 \\ Total & & & & 0.11 & 0.31 \\ Oxygen-containing heterocycles & & & & & \\
2-Ethylfuran & M & 979 & 986 s & nd & 0.05 \(\pm\) 0.01 \\
2-Penylfuran & M & 1243 & 1240 m & 0.10 \(\pm\) 0.03 & 0.12 \(\pm\) 0.05 \\
2-Methyltetrahydro-3-one & M & 1278 & 1299 s & 0.12 \(\pm\) 0.04 & nd \\ Furfural & M & 1461 & 1455 m & 0.22 \(\pm\) 0.11 & 0.04 \(\pm\) 0.01 \\
5-Methyl-2-furfurfural & M & 1570 & 1560 m & 0.06 \(\pm\) 0.01 & nd \\ Furfuryl alcohol & S & 1647 & & 0.03 \(\pm\) 0.00 & nd \\
2,3-Dihydro-3.5-dihydroxy-6-methyl-4H-pyran-4-one & S & 2359 & & 0.24 \(\pm\) 0.10 & nd \\
5-Hydroymethyl-2-furfural & S & 2512 & & 0.13 \(\pm\) 0.03 & nd \\ Total & & & & 0.91 & 0.20 \\ \hline \end{tabular} The data is mean \(\pm\) standard deviation of triplicate analysis. nd: not found. X: Identification method (ID): S, mass spectrum and RI agree with that of the authentic compound run under similar GC-MS conditions; M, mass spectrum and RI agree with literature data. Y: Linear retention indices (RI) calculated of unknown compounds on a HP-Wax (HP-PEG-INNOWAX) (60 m \(\times\) 0.25 mm \(\times\) 0.25\(\upmu\)m) with a homologous series of n-alkanes (C6-C30). Z: m: RI from the flavoured database [16]; g: references [17; 18]; A: sample A prepared from self-made praised sauce; B: sample B prepared from white granulated sugar. SPME: solid phase microextraction; GC: gas chromatography; MS: mass spectrometry; ID: Identification method; RI: retention indices.  
\end{table} 
Table 1: _Cont._