# Aroma Volatiles in Litchi Fruit: A Mini-Review
## 4 Sulfur-Containing Volatile Compounds (VSCs) in Litchi Fruit  
VSCs are a class of sulfur-containing volatile compounds which are able to release intense odors with a very low olfactory threshold that renders it difficult to detect with general gas phase detection methods. Studies in fruits, including strawberries [58], durian [59], pineapple [60], and passion fruit [61], have revealed that VSCs could produce unique aromas.  
As shown in Table 3, VSCs were also found to be present in litchi fruit. [PERSON] et al. [22] found that freshly harvested litchi fruit could release benzothiazzo, a rubbery-like VSC, via a mass spectrometer and electrolytic conductivity detector. Subsequently, [PERSON] et al. [39] detected eight VSCs in three cultivars (\"Mauritius\", \"Brewster\", and \"Hak Ip\"), including hydrogen sulfide, dimethyl sulfide, diethyl disulfide, 2-acetyl-2-thiazoline, 2-methyl thiazole, 2,4-dithiopentane, DMTS, and methional. These VSCs exclude the smell of cabbage scent or garlic aroma. There were differences among these three cultivars in the intensity of garlic or cabbage scents that might be due to the differences in the ratio of these VSCs. [PERSON] et al. [24] detected two VSCs in HY with GC-MS, named 2,4-dithiopentane and 2,3,5-trithihexane, which imparted the garlic scent in litchi fruit. Interestingly, these two VSCs were only detected in HY grown in Guangxi but not in HY grown in Guangdong, suggesting that the production of 2,4-dithiopentane and 2,3,5-trithihexane might be dependent on the cultivation environment. [PERSON] et al. [23] also detected two VSCs in \"sweetheart\" litchi fruit, of which DMTS had a higher flavor dilution factor (FD) of 32, which confirmed that a lower DMTS content could trigger a strong sense of smell perception. Methional is often considered to be an important odorant-active compound in subtropical and tropical fruits [62; 63], and it has an extremely high FD factor in the \"sweetheart\" fruit, reaching an astonishing 1024, suggesting that methional might be the main source of the aroma in \"sweetheart\" litchi fruit.  
\begin{table}
\begin{tabular}{l l l l} \hline
**Method of Detection** & **Volatile Sulfur** & **Scent Descriptions** & **References** \\ \hline Electrolytic conductivity detector & Benzothiazole & Rubber-like odor & [PERSON] et al. (1980) [22] \\ and mass spectrometer & Hydrogen sulfide & Sulfur, fetid & \\  & Dimethyl sulfide & Cabbage & \\  & Diethyl disulfide & Moldy, sulfur & \\  & 2-Acetyl-2 thiazoline & Dry fruit, nutty & \\  & 2-Methyl thiazole & Roasted garlic & [PERSON] et al. (2007) [39] \\  & 2,4-Dithiopentane & Burning tire, cabbage & \\  & Dimethyl trisulfide (DMTS) & Cabbage, sulfur & \\  & Methional & Cooked potato & \\  & 2,4-Dithiopentane & Cabbage & \\  & 2,3-5-Trithihexane & N/A & [PERSON] et al. (2009) [24] \\ GC-MS/O and AEDA & DMTS & Pickled vegetable & [PERSON] et al. (2018) [23] \\ \hline \end{tabular} GC-MS: gas chromatography-mass spectrometry; GC-PFPD: gas chromatography-pulsed flame photometric detection; GC-O: gas chromatography-olfactory; AEDA: aroma extract dilution analysis. N/A: no record.  
\end{table}
Table 3: List of VSCs found in litchi fruit and their aroma description.