## 3 Results
### Volatile Flavor Compounds Identified from the Braised Pork
This result might be attributed to the evaporation step during the SDE process that might lead to more complex side reactions and the loss of some volatile compounds. From the semi quantitation results, the most abundant class of compounds from SPME was the sulphur compounds in both samples, followed by aldehydes. A different situation was observed in SDE; the most abundant class was the aldehydes, followed by ethers. Furthermore, aldehydes \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}{Acids} \\ \hline Butanoic acid & M & 1610 & 1619 m & 0.01 \(\pm\) 0.01 & nd \\ Heptanoic acid & S & 1935 & & 0.01 \(\pm\) 0.01 & nd \\ Tetredecanoic acid & M & 2094 & 2094 s & 0.05 \(\pm\) 0.02 & nd \\ Nonanoic acid & M & 2193 & 2202 m & 0.01 \(\pm\) 0.01 & nd \\ Decanoic acid & M & 2333 & 2361 m & 0.03 \(\pm\) 0.01 & nd \\ Oleic acid & M & 2374 & 2430 m & 0.05 \(\pm\) 0.02 & nd \\ Hexadecanoic acid & S & 2468 & & 0.16 \(\pm\) 0.07 & 0.46 \(\pm\) 0.11 \\ Total & & & & 0.32 & 0.46 \\ \multicolumn{6}{c}{Lactones and esters} \\ \hline \(\gamma\)-Butyrolactone & M & 1630 & 1647 m & 0.11 \(\pm\) 0.03 & nd \\ \(\gamma\)-Nonalactone & M & 2014 & 2042 m & 0.06 \(\pm\) 0.01 & nd \\ \(\gamma\)-Undecalactone & M & 2145 & 2270 m & 0.27 \(\pm\) 0.06 & 1.58 \(\pm\) 0.31 \\ Ethyl cinnamate & M & 2158 & 2139 m & 0.01 \(\pm\) 0.01 & nd \\ Total & & & & 0.45 & 1.58 \\ \hline \multicolumn{6}{c}{Phenols} \\ \hline Phenol & S & 2072 & & 0.78 \(\pm\) 0.11 & 1.05 \(\pm\) 0.12 \\ Total & & & & 0.78 & 1.05 \\ \hline \multicolumn{6}{c}{Ethers} \\ \hline Estragole & M & 1656 & 1655 m & 0.02 \(\pm\) 0.01 & 0.98 \(\pm\) 0.09 \\ Anethole & S & 1821 & & 1.78 \(\pm\) 0.08 & 1.16 \(\pm\) 0.21 \\ Total & & & & 1.80 & 2.15 \\ \hline \multicolumn{6}{c}{Nitrogenous compounds} \\ \hline
2-Acetylpyrrole & M & 2037 & 2025 s & 0.02 \(\pm\) 0.01 & nd \\ Total & & & & 0.02 \\ \hline \multicolumn{6}{c}{Oxygen-containing heterocycles} \\ \hline Furfuryl alcohol & M & 1157 & 1199 m & 0.07 \(\pm\) 0.02 & nd \\ Furfural & M & 1461 & 1455 m & 0.06 \(\pm\) 0.02 & nd \\
2-Acetylfuran & M & 1511 & 1490 m & 0.01 \(\pm\) 0.01 & 0.01 \(\pm\) 0.01 \\
5-Methylyl-2-furfurfural & M & 1570 & 1560 m & nd & 0.05 \(\pm\) 0.02 \\
5-Methylyl-2-furfurfuryl alcohol & S & 1700 & & 0.03 \(\pm\) 0.01 & nd \\
3,4-Dihydro-2H-1-benzopyran & S & 2275 & & nd & 0.33 \(\pm\) 0.13 \\
2-Methyltetrahydrohydrofuran-3-one & S & 2393 & & 0.02 \(\pm\) 0.01 & nd \\ Coumarin & M & 2465 & 2465 m & 0.03 \(\pm\) 0.01 & 0.31 \(\pm\) 0.12 \\ Total & & & & 0.22 & 0.70 \\ \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 (60 m \(\times\) 0.25 mm \(\times\) 0.25 mm) with a homologous series of n-alkanes (C6-C30). Z: m: RI from the flavornet database [16]; g: references [17; 18]. A: sample A prepared from self-made braised saucoe; B: sample B prepared from white granulated sugar; SDE: simultaneous distillation and extraction.  
\end{table} 
Table 2: _Cont._considered to be formed by the mono-unsaturated fatty acids and Strecker oxidative degradation of amino acids, which made a great contribution to the flavor of braised pork due to their low odor threshold [19; 20; 21]. Nine kinds of aldehyde compounds were commonly identified in these two methods including 3-methylbutanal, pentanal, hexanal, heptanal, benzaldehyde, phenylacetaldehyde, (E,E)-2,4-decadienal, 4-methoxybenzaldehyde and (\(Z\))-cinnamaldehyde. Moreover, SPME detected more low-molecular-weight aldehydes, such as hexanal, heptanal, (E)-2-heptenal, and nonanal.