## 2 Results and Discussion  
### Volatile Organic Compounds (VOCs)  
In this study, 49 volatile compounds were detected in three durian cultivars, including 22 ester compounds, 13 sulfur compounds, 6 alcohol compounds, 3 ketone compounds, 3 aldehyde compounds and 2 olefin compounds. As shown in Table 1, a total of 27, 38 and 36 compounds were detected in BT, MT and MK, respectively. Methyl 2-methyl butyrate, ethyl 2-methyl butyrate, propyl 2-methyl butyrate, hexyl hexanoate, methyl octanoate and propyl tiglate existed in all durian cultivars. Propyl 2-methyl butyrate (1818.42 ug/kg) was the most abundant ester compound in BT durian, and it was also the characteristic ester of Chanee durian (2018). It has also been found in sea buckthorn (2018) and apple (2018), and has aromas of wine, apple and pineapple. The ester compound with the highest content in MT and MK was ethyl 2-methyl butyrate, whose contents were 11,680.31 ug/kg and 14,484.20 ug/kg, respectively. Ethyl 2-methyl butyrate has been described as a tropical fruit aroma and it is a key component of the aroma of durian (2018). Ethyl propionate, ethyl (Z)-2-crotonate and hexyl 2-methyl butyrate were only detected in BT. Ethyl acetate, diethyl carbonate, ethyl butyrate, hexyl formate and ethyl valerate were only detected in MT, which may be one of the reasons for the differences in the aroma of different durian cultivars. Ethyl mercaptan, methyl ethyl disulfide, diethyl disulfide, methyl propyl disulfide, diethyl trisulfide, 3,5-dimethyl-1,2,4-trithiolane and acetaldehyde diethyl mercaptal were detected in all durian cultivars. Diethyl disulfide was the most abundant sulfur-containing compound in all three durian cultivars, and was 17,777.04 \(\upmu\)g/kg, 8665.01 \(\upmu\)g/kg and 27,253.26 \(\upmu\)g/kg in BT, MT and MK, respectively. Diethyl disulfide is usually described as the smell of onion or garlic, and it was transformed from the less stable ethyl mercaptan and propyl mercaptan [13]. 3,5-dimethyl-1,2,4-trithiolane and acetaldehyde diethyl mercaptal are widespread in many durian cultivars. They are rare in other fruits, but they are important aroma compounds in durian. Methyl ethyl sulfide, S-ethyl thioacetate and dipropyl sulfide were only detected in MK, which may be one of the reasons for the differences in aroma of different durian cultivars. Diacetyl and acetoin are important aroma compounds in durian as well as in cheese, butter, yogurt and butter [14], and have been described as the smell of milky and sweet flavor. It is worth mentioning that heptanal (71.22 \(\upmu\)g/kg) and 1-octanal (81.84 \(\upmu\)g/kg) were only detected in MT. Heptanal has a grassy aroma, and has also been detected in persimmon and melon [15; 16]. Octanal has the aroma of citrus and orange, and is the main aroma compound in citrus [17]. The difference in aroma components between different durian cultivars may be caused by the differences in variety and growth environment. The light time temperatures during the day and at night and the rainfall during the growth stage may cause the differences in contents and types of the final aroma compounds of durian [18]. \begin{table}
\begin{tabular}{l l c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.