Pentose-cysteine model systems

Parliment T.H. and Stahl H.D. (1994) Generation of furfuryl mercaptan in cysteine-pentose model systems in relation to roasted coffee. Am. Chem. Soc. Symp. Ser. 564, 160-70. 

Generation of Furfuryl Mercaptan in Cysteine—Pentose Model Systems in Relation to Roasted Coffee... 

T. H. Parliment and H. D. Stahl, Generation of Furfuryl Mercaptan in Cysteine-Pentose Model Systems in Relation to Roasted Coffee, in Sulfur Compounds in Foods (C. Mussinan and M. Keelan, eds.), American Chemical Society, Washington,... 

Model Systems. Model system studies have investigated the reaction of sulfiir sources and pentoses and have established that furfuryl mercaptan may be a significant product. The study of the cysteine/xylose model system under aqueous conditions at ISO C and pH 5 led Tressl to propose a mechanism for the production of furfuryl mercaptan via dehydration and reduction of the 3-deoxpentosone which is a known Maillaid reaction product (8). 

The routes involved in the formation of the various furan sulphides and disulphides involve the interaction of hydrogen sulphide with dicarbonyls, furanones and furfurals. Possible pathways are shown in Scheme 12.8. Furanthiols have been found in heated model systems containing hydrogen sulphide or cysteine with pentoses [56-58]. 2-Methyl-3-furanthiol has also been found as a major product in the reaction of 4-hydroxy-5-methyl-3(2H)-furanone with hydrogen sulphide or cysteine [21, 59]. This furanone is formed in the Maillard reaction of pentoses alternatively it has been suggested that it may be produced by the dephosphorylation and dehydration of ribose phosphate, and that this may be a route to its formation in cooked meat [21, 60]. 

The investigation of characteristic flavors associated with cooked meats has been the subject of much research over the past four decades but, although compounds with "meaty" aromas had been synthesized, compounds with such characteristics were not found in cooked meats until recently (1). In the search for compounds with characteristic aromas it was found that furans and thiophenes with a thiol group in the 3-position possessed meat-like aromas (2). The corresponding disulfides formed by oxidation of furan and thiophene thiols were also found to have meat-like characteristics, and exceptionally low odor threshold values (3). A number of such compounds are formed in heated model systems containing hydrogen sulfide or cysteine and pentoses or other sources of carbonyl compounds (4,5), The thermal degradation of thiamine also produces 2-methyl-3-fiiranthiol and a number of sulfides and disulfides (6J). 

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