Synthèse et caractérisation organoleptique de thiols polyfonctionnels : recherche de leur présence dans la bière
(2005)
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- Authors
- Supervisors
- Collin, Sonia
- Abstract
- Nowadays, thiols are considered to be among the most powerful odoriferous compounds present in foods and beverages. Because of their commercial unavailability and their high reactivity, many of them are still uncharacterized. In order to improve our knowledge, the greatest part of our work has been devoted to their synthesis as well as to their sensorial and physico-chemical characterizations. Applied on a few number of reagents, combinatorial chemistry revealed to be very rapid and efficient to obtain many structural analogues. Around hundred thiols were separated by gas chromatography and analyzed by olfactometry (GC-O) as well as mass spectrometry (GC-MS). It turns out that many of them possess fresh and fruity odors whereas others exhale onion/sweat-like notes. Their odor perception threshold is in all cases extremely low (BE-GC-LOADS generally lower than the ng level). The molecular ion M+° and the radical cation (M+°-34) related to the loss of an H2S molecule are always apparent on electron impact - mass spectra, except for the mercaptoesters which are prone to get rid of an acetic acid molecule (M+°-60). Suspecting a high organoleptic relevance of thiols in brewery, we take advantage of our combinatorial library to identify most lager beer mercaptans. Twelve polyfonctional thiols were found in selective pHMB extracts (method proposed by Dr Tominaga) : 2-methyl-3-furanthiol (MFT), 4-mercapto-4-methyl-2-pentanone (4MMP), 1-mercapto-3-pentanone (hypothesis - M3P), 3-methyl-2-buten-1-thiol (MBT), 2-mercaptoethanol (2MEol), 3-mercaptopropanol (3MPol), 3-mercapto-3-methylbutanol (3MMBol), 2-mercapto-3-methylbutanol (2M3MBol), 1-mercapto-3-pentanol (M3Pol), 3-mercaptohexanol (3MHol) as well as 2-mercaptoethyl (Ac2ME) and 3-mercaptopropyl (Ac3MP) acetates. According to experiments conducted on wort and aged beer, fermentation and storage emerged as the two key-steps where thiols are generated. Potential synthesis pathways are discussed. A new hypothesis explains for the first time how H2S (resulting from yeasts sulfur metabolism) and 3-methyl-2-buten-1-ol (coming from hop) could produce MBT in absence of light.
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Citations
Vermeulen, C. (2005). Synthèse et caractérisation organoleptique de thiols polyfonctionnels : recherche de leur présence dans la bière. https://hdl.handle.net/2078.5/124170