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Relevant academic research and scientific papers

Structure-Odor Correlations in Homologous Series of Mercapto Furans and Mercapto Thiophenes Synthesized by Changing the Structural Motifs of the Key Coffee Odorant Furan-2-ylmethanethiol

Furan-2-ylmethanethiol (2-furfurylthiol; 2-FFT, 1) is long-known as a key odorant in roast and ground coffee and was also previously identified in a wide range of thermally treated foods such as meat, bread, and roasted sesame seeds. Its unique coffee-like odor quality elicited at very low concentrations, and the fact that only a very few compounds showing a similar structure have previously been described in foods make 1 a suitable candidate for structure-odor activity studies. To gain insight into the structural features needed to evoke a coffee-like odor at low concentrations, 46 heterocyclic mercaptans and thio ethers were synthesized, 32 of them for the first time, and their odor qualities and odor thresholds were determined. A movement of the mercapto group to the 3-position kept the coffee-like aroma but led to an increase in odor threshold. A separation of the thiol group from the furan ring by an elongation of the carbon side chain caused a loss of the coffee-like odor and also led to an increase in odor thresholds, especially for ω-(furan-2-yl)alkane-1-thiols with six or seven carbon atoms in the side chain. A displacement of the furan ring by a thiophene ring had no significant influence on the odor properties of most of the compounds studied, but the newly synthesized longer-chain 1-(furan-2-yl)- and 1-(thiophene-2-yl)alkane-1-thiols elicited interesting passion fruit-like scents. In total, only 4 out of the 46 compounds also showed a coffee-like odor quality like 1, but none showed a lower odor threshold. Besides the odor attributes, also retention indices, mass spectra, and NMR data of the synthesized compounds were elaborated, which are helpful in possible future identification of these compounds in trace levels in foods or other materials.

Identification of Potent Aroma Compounds in Thermally Treated Mixtures of Glucose/Cysteine and Rhamnose/Cysteine Using Aroma Extract Dilution Techniques

Application of an aroma extract dilution analysis on extracts prepared from either thermally treated solutions (20 min, 145 °C) of glucose/cysteine (I) or rhamnose/cysteine (II) led to the identification of 2-furfurylthiol (roasty, coffee-like), 5-acetyl-2,3-dihydro-1,4-thiazine (roasty), 3-mercapto-2-butanone (sulfury, rotten), 3-mercapto-2-pentanone (catty), and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like) with the highest odor activities among the 34 odor-active volatiles detected in I. In II, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 3-hydroxy-6-methyl-2(2H)-pyranone (seasoning-like), 5-methyl-2-furfurylthiol (roasty, coffee-like), 2-furfurylthiol, and 5-acetyl-2,3-dihydro-l,4-thiazine appeared with the highest flavor dilution (FD) factors among the 18 compounds detected by HRGC/O. Among the flavor compounds identified, 2-propionyl-2-thiazoline is reported for the first time among the flavors of Maillard model reactions or foods, respectively. The odorant elicited an intense roasty, popcorn-like odor at the low odor threshold of 0.07 ng/L in air.