Mercapto grapefruit

Mercapto-hexyl acetate Grapefruit, passion fruit, black currant 0.12-1.3 [24] ND-0.02 [23] 0.004 [22]... 

Mercapto-4- Citrus paradisi (grapefruit juice) (Rutaceae), OD-R (catty, black-... 

Typical Scheurebe wines are characterized by a jfruity aroma, which is described as redcurrant-like, often with a grapefruit note. In 1995 Darriet et al. identified 4-mercapto-4-methylpentan-2-one (MMP), responsible for the distinctive odor of box tree and cat urine (7). The perception threshold of this compound in wine has been reported to be very low (3 ng/1). Recent studies by Guth and coworkers (2) showed that MMP also significaiitly influences the aroma of Scheurebe wines. 

The especially fresh, juicy grapefruit note is due to the presence of R(-i-)-para-menthene-8-thiol which can be detected as a trace constituent in the ppb range of grapefruit oils ]46]. Other important potent odour-active volatiles of grapefmit juice are l-penten-3-one, l-hepten-3-one, hex-anal, 4-mercapto-4-methylpentan-2-one and 4,5-epoxy-(E)-2-decenal ]47]. 

Analysis of grapefruit juice [71] gave high OAV for 4-mercapto-4-methylpentan-2-one (MMP), ethyl (S)-2-methylbutanoate, (Z)-3-hexenal, ethyl butanoate, decanal, ethyl methylpropanoate and l-p-menthen-8-thiol (MTO, probably the R-enantiomer). The aroma of a solution containing 19 odorants in the levels found in grapefmits was very similar to the natural aroma of this fmit [71 ]. 

The characteristic aroma of blackcurrants (varieties oiRibes nigrum, Grossulariaceae) is mainly a consequence of aliphatic and aUcycUc thiols. The bearer of the characteristic cat odour is 4-methoxy-2-methyl-2-thiol, called blackcurrant mercaptan (8-124), which occurs also in olive oil and green tea. Other important components are 4-mercapto-4-methylpentan-2-one called cat ketone (8-125) and (lS,4R)-p-menthan-8-thiol-2-one (see Section 8.2.13.1.1). Cat ketone is also found in grapefruits, some hop cultivars, basil and some aromatic wines. The leaves contain about 0.7% essential oil, whose main component isp-cymol, the sulfur compounds of which contribute to the strong smell, mainlyp-menthan-8-thiol-2-one. 

The key components of fresh grapefruit juices with a typical grapefruit odour are both isomers of p-mentha-l-en-8-thiol (8-188). The (- -)-(Ji)-enantiomer is present in minute concentrations (less than 1 (xg/kg), but has a very low odour threshold concentration. The (-)-(S)-p-mentha-l-ene-8-thiolhas aweak and non-specific smell. Of the other sulfur compounds, 4-mercapto-4-methylpentan-2-one (8-125) is significant, and also occurs in blackcurrants, some hop cultivars, aromatic wines and basil. A relatively high content of sesquiterpenoids is also typical. The smell and bitter taste of grapefruits arise from (-l-)-nootkatone and (-1-)-8,9-didehydronootkatone. Important odour-active compounds are numerous cyclic ethers, which are likewise found in other essential oils. For example, the essential oil contains about 13% of hnalool oxides that arise from linalool via 5,6-epoxide, and another important epoxide is ( )-4,5-epoxydec-2-enal. The fresh odour of juices is mainly influenced by aliphatic aldehydes, such as acetaldehyde. 

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