## 2 Results and Discussion  
### GC-O Results for Truffles  
The aroma substances of three kinds of fresh truffles were extracted by HS-SPME and characterized by GC-O. The results were summarized in Table 1, which listed 38, 37 and 38 odor-active compoundscorresponding to T1, T2 and T3 truffle samples, respectively. Three samples were characterized by comparison with their retention indices (RIs), aroma description and mass spectra with authentic standards. The aroma intensities (AIs) of volatile components ranged from 1.2 to 8.7 for T1, 1.2 to 9.2 for T2, 1.1 to 8.8 for T3.  
In T1 sample, dimethyl sulfide (8.7), dimethyl disulfide (8.5), octanal (8.4) and 1-octen-3-one (8.3); in T2 sample, dimethyl sulfide (8.6), 3-octanone (8.9), bis(methylthio) methane (8.4), 1-octen-3-one (8.8), 3-octanol (8.6) and 1-octen-3-ol (9.2); in T3 sample, dimethyl sulfide (8.3), 2-methyl-butanal (8.8), 2-methylbutanol (8.1), 3-(methylthio)propanal (8.4) and benzeneacetaldehyde (8.3) had relatively higher aroma intensities (AIs).  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & & & & & & & & & & & & \\ \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Component 4**} & \multicolumn{3}{c}{**H1 (Colorable)**} & \multicolumn{3}{c}{**H1 (Referenced 8**} & \multicolumn{3}{c}{**Anema**} & \multicolumn{3}{c}{**Monification 9**} & \multicolumn{3}{c}{**Anema**} & \multicolumn{3}{c}{**In  
As was shown in the Table 1, the aroma frequencies of ten panelists during GC-O experiment were presented. Dimethyl sulfide, 2-methyl-butanal, 3-methyl-butanal, hexanal, heptenal, 2-methylbutanol, 2-pentyl-furan, 3-octanone, dimethyl disulfide, bis(methylthio) methane, 2-octanone, octanal, 1-octen-3-one, 3-octanol, 1-octen-3-ol, 3-(methylthio)propanal, benzeneacetaldehyde had relatively higher frequency than other compounds. There was no doubt that most of these higher frequency components had high AIs simultaneously. Thus, the method through combining AIs with frequency of volatiles probably could find out potential important compounds in truffle [21; 22].  
From Table 1, the three samples differed greatly in sensory olfaction. Dimethyl sulfide and dimethyl disulfide had high AIs in T1 sample, which brought more decayed cabbage odor and sweet smell of popcorn (Table 1). Both of the compounds were also considered to represent the aroma of black truffles [23]. Eight carbon volatile compounds accounted for large proportion of aroma compounds in T2 samples, including 3-octanone, 2-octanone, 1-octen-3-one, 3-octanol, 1-octen-3-ol. Eight carbon alcohol and ketone mainly provided aroma of mushroom, earthy and herbal. These compounds had been found in most fungi, which gave samples typical mushroom odors [24; 25]. Bis(methylthio)methane has always been considered as the most important sulfide in Italian white truffle (_Tuber magnatum Pico_) research [26] and it has also been found to play an important role in T2 samples. In addition to sulfur compounds, 2-methyl-butanal and 3-methyl-butanal were studied as important aroma compounds in different truffles [27; 28], however, T3 samples had much less rough sulfide odor and more focused on 2-methyl-butanal and 3-methyl-butanal, which provided strong nutty and grain aroma. The AI of phenylacetaldehyde was also very high in T3 sample.