## 3 Results and Discussion
### Sulfur Compounds Analysis Using GC-Orbitrap-MS  
Sulfur compounds have been considered as critical volatile compounds that primarily determine the featured aroma of tropic fruits, although these compounds exist in fruits with a trace amount level [9]. In the present study, a total of 17 sulfur compounds were detected in passion fruit wine samples (Tables 2 and S1). Different yeast strains resulted in a variation in the sulfur compounds composition and concentration in the passion fruit wine samples. Among these compounds, methionol was the most prominent sulfur compounds in all samples and was reported as the most abundant sulfur compound in wine [27], and can confer odors of cauliflower and potato at a concentration above its perception threshold (1000 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{L}\)) [9]. Although methionol was found in a variety of tropical fruit juice [10], the formation of methionol in wine is clearly related to the metabolism of L-methionine during alcohol fermentation [28]. As shown in Table 2, the content of methionol was significantly higher in the sample fermented by ES488 than other yeasts; this suggested that the methionine metabolism routes of the strain ES488 were more robust than others in passion fruit wine. It has been reported that 3-mercaptoethanol(3 MH) is a featured aromatic compound in passion fruit [10]. Its precursor, cysteine conjugate, exists in fruit juice and can be cleaved into 3 MH through enzymes in yeast during alcoholic fermentation in wine [29]. 3 MH has been reported to further interact with acetic acid through the esterification reaction in fruit wine to yield 3-mercaptoethanol acetate (3 MHA), another important sulfur volatile responsible for passion fruit's featured aroma [29]. 3 MH significantly contributed its flavor notes to the overall aroma in these passion fruit wines due to its high odor activity value (OAV) in the current study (Table 2). Meanwhile, the passion fruit wine fermented by ES488 exhibited a lower level of 3 MH than the other wine samples. Regarding 3 MHA, only ES488-femented wine was found to contain this sulfur compound, but there is very limited information on the clear correlations between 3 MH and 3 MHA in the passion fruit matrix, and additional research is required. 2-methyl-4-propyl-1,3-oxathiane (MPO), another sulfur compound, provides the most characteristic passion fruit odor and occurs naturally in passion fruit juice, especially in the yellow fruits [10]. It was recently identified and quantitated in wine, and has a close relation to 3 MH during wine fermentation and ageing [30]. As shown in Table 2, MPO was found in all samples; meanwhile, the passion fruit wine fermented by CY3079 had a significantly lower level, which was more than seven times  
Figure 1: Principal component analysis of passion fruit wine fermented by commercial yeast strain ES488 (ES), BV818 (BV), VIC (VI) and CY3079 (CY). (**A**) The scores plot of passion fruit wine samples and (**B**) the loadings analysis of different metal oxide semiconductor (MOS) \(-\) type chemical sensors: 1 (aromatic), 2 (broad range), 3 (aromatic), 4 (hydrogen), 5 (arom \(-\) alph), 6 (broad \(-\) methane), 7 (sulfur \(-\) organic), 8 (broad \(-\) alcohol), 9 (sulph \(-\) chlor) and 10 (methane \(-\) alph). lower than the others. On the basis of OAV, it seemed that the contribution of MPO to the aroma of CY30079 wine was not significant, but, with its highest content of 3 MH, it seems necessary to conduct further studies to better elucidate the sensory impact on the passion fruit wine aroma according to the research of [30]. It has been reported that 3-(methylthio) propyl acetate exhibits herbaceous and vegetable-like odor notes [9], and that these passion fruit wine samples possess different levels of 3-(methylthio) propyl acetate (Table 2). Similarly, 3-(Methylthio)propanoic acid ethyl ester can significantly contribute its fruity and cheese-like scents to the overall aroma of these passion fruit wines.