IDENTIFICATION OF KEY AROMA COMPOUNDS GENERATED FROM CYSTEINE AND CARBOHYDRATES UNDER ROASTING CONDITIONS

Application of the aroma extract dilution analysis to volatile fractio ns obtained from dry-heated (180 degrees C for 6 min on silica) mixtur es of cysteine and ribose (I), glucose (II) or rhamnose (III) revealed the following compounds with the highest flavour dilution factors: 2- furfurylthiol (FFT) and 2-acetyl-2-thiazoline in I; 2-acetyl-2-thiazol ine, 2-propionyl-2-thiazoline and FFT in II; 5-methyl-2-furfurylthiol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 2-acetyl-2-thiazoline, 2-propi onyl-2-thiazoline and (Z)-2-propenyl-3,5-dimethylpyrazine in III. A co mparison of the data with results of previous studies, in which the sa me mixtures had been reacted under aqueous conditions (145 degrees C, 20 min) revealed that the dry-heating process favoured the formation o f the roasty, popcorn-like smelling 2-acetyl- and 2-propionyl-2-thiazo line as well as the potato-chip-like 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine in all three reaction systems. 2-Ethenyl- and (2)2-propenyl-3,5-dimethylpyrazine, both having an intense roast potato smell were, however, selectively formed in the presence of ribo se or rhamnose, respectively, Based on quantitative data, pathways gen erating the latter two pyrazines via their 1-desoxyosones as key inter mediates are discussed.