Organosulfur Compounds of Allium Subgenus Nectaroscordum Species.

Organosulfur compounds formed upon comminuting the bulbs of two Allium subgenus Nectaroscordum species (Allium siculum and Allium tripedale) were analyzed by HPLC-PDA-MS/MS. The major organosulfur components were isolated and structurally characterized (MS, NMR), including several previously unknown compounds. It was found that the organosulfur chemistry occurring when these plants are cut is very similar to that observed in onion (Allium cepa). In all cases, however, the organosulfur compounds found in Nectaroscordum species were higher homologues of those observed in onion, being formed by various combinations of C1 and C4 building blocks derived from methiin and homoisoalliin/butiin, respectively. Thiosulfinates, bis-sulfine, cepaenes, and several cepaene-like compounds were identified among the major organosulfur components present in the homogenized bulbs. Several groups of 3,4-diethylthiolane-based compounds, structurally homologous with onionin A, cepathiolane A, allithiolanes A-H, and cepadithiolactone A, found in onion, were also detected.

Isoalliin-Derived Thiolanes Formed in Homogenized Onion.

Several families of 3,4-dimethylthiolane-based compounds spontaneously formed upon cutting of onion (Allium cepa) were studied. We report the isolation of the first known example of a naturally occurring dithiolactone, 5-hydroxy-3,4-dimethylthiolane-2-thione (cepadithiolactone A, C6H10OS2). Furthermore, on the basis of conceivable spectroscopic evidence (MS, NMR, IR), we could disprove the structure previously proposed for onionin A (C9H16O2S2), which is shown to be in fact (E)-3,4-dimethyl-5-(1-propenylsulfinyl)thiolane-2-ol. The identification of hitherto unknown methyl and propyl homologues of onionin A (dubbed onionins B and C, respectively) is also reported. Furthermore, the existence of the methyl and propyl homologues of cepathiolanes A (C9H16O2S3), trivially named cepathiolanes B and C, respectively, has been newly revealed. The organoleptic properties of these 3,4-dimethylthiolanes and their role in the formation of the pink discoloration of processed onion were also evaluated.

Allithiolanes: Nine Groups of a Newly Discovered Family of Sulfur Compounds Responsible for the Bitter Off-Taste of Processed Onion.

The compounds responsible for the bitter off-taste of processed onion ( Allium cepa) were studied. Using a series of sensory-guided HPLC fractionations, the existence of nine groups of hitherto unknown sulfur compounds has been revealed. On the basis of spectroscopic data (MS, NMR, and IR), it was found that these compounds, trivially named allithiolanes A-I, are members of a large family of structurally closely related derivatives of 3,4-dimethylthiolane S-oxide, with the general formulas of C xH yO2S4, C xH yO3S5, and C xH yO4S6 ( x = 10-18, y = 18-30). The presence of multiple stereoisomers was observed for each group of allithiolanes. Allithiolanes possess an unpleasantly bitter taste with detection thresholds in the range of 15-30 ppm. Formation pathways of these newly discovered sulfur compounds were proposed.

Antimicrobial, Cytotoxic, Anti-Inflammatory, and Antioxidant Activity of Culinary Processed Shiitake Medicinal Mushroom (Lentinus edodes, Agaricomycetes) and Its Major Sulfur Sensory-Active Compound-Lenthionine.

The antimicrobial, cytotoxic, anti-inflammatory, and antioxidant properties of aqueous extracts of raw and culinary processed shiitake mushrooms were evaluated and compared with those of lenthionine (1,2,3,5,6-penta-thiepane), the principal aroma-bearing substance of the shiitake medicinal mushroom (Lentinus edodes). Antimicrobial activity was tested using a panel of 4 strains of bacteria, 2 yeasts, and 2 fungi. Cytotoxic properties were evaluated against 3 cell lines (HepG2, HeLa, PaTu), whereas the anti-inflammatory activity of tested samples was assayed based on their ability to attenuate the secretion of the cytokine tumor necrosis factor-α. Antioxidant activity was measured using in vitro DPPH and ABTS assays. It was found that lenthionine possesses significant antimicrobial properties; it is remarkably effective in inhibiting the growth of yeasts and fungi (minimum inhibitory concentration, 2-8 µg/mL) and thus is comparable to standard antifungal agents. Lenthionine is also able to decrease significantly the production of tumor necrosis factor-a and thus could be at least partly responsible for the observed anti-inflammatory effect of shiitake. On the other hand, lenthionine does not seem to contribute significantly to the well-known anticancer and antioxidant effects of the mushroom.