Figure 4.3 represents a typical mass spectrum obtained for the durian sample at 300°C. The peaks at m/z 41, 55, 71, 83, 129, 157, 161, and 189 are observed. The peaks with low intensities at m/z 41, 55, and 71 are assigned to [H2S + Li]+, [SO+Li]+, and [SO2+Li]+, respectively. These species in durian as volatile compounds was reported in other reports (Neti et al. 2011; Wong and Tie 1995).

The H2S and SOx peaks are detected at low intensity. H2S is known to be derived from arils in ripe durian fruits (Greve 1974). Moser et al. reported negligibly small amount of H2S from immature fruits (Moser et al. 1980). For detailed investigation of reaction process of these compounds in hydrothermal reaction, the peaks were detected by SIM for quantitative analysis.

Figure 4.4 shows the relationship between the reaction time and the amount of generated sulfur compound during the hydrothermal process of durian at the sub­critical temperatures of 250, 300, and 350°C.

At all the temperatures, the released sulfur compounds increase along with the time elapsing. The compounds, except for H2S and SOx, would be resulted from extraction processes. The peak intensities, corresponding to the amounts of these sulfur compounds, drastically rise up from 250 to 300°C. However, the intensities decrease at 350°C, suggesting that the decomposition process started at this temperature.

During the hydrothermal reactions, two mechanisms likely occur, i. e., extraction and decomposition. By extraction in the reactor, the higher molecular weight com­pounds could be yielded. Decomposition of the higher molecular compounds occurs, and the lower molecular compounds could be produced at high tempera­tures, as below:

Durian ^ 1 — propanethiol, methyl phenyl disulfide, etc. (lowtemperature) (4.6)

Durian ^ H2S, CO, CO2,SO, SO2,SO3etc. (high temperature) (4.7)