SULFUR-CONTAINING VOLATILES ARISING BY THERMAL-DEGRADATION OF ALLIIN AND DEOXYALLIIN

Alliin (S-allyl-L-cysteine sulfoxide) and its biochemical precursor de oxyalliin (S-allyl-L-cysteine) were heated in a closed model system at different temperatures (from 80 to 200 degrees C) in the presence of variable amounts of water (0-98%) for 1-60 min. The arising volatile c ompounds were isolated by extraction, analyzed, and identified by mean s of GC and GC/MS. The major volatile compounds generated by thermal d egradation of these amino acids were diallyl sulfides (mono-, di-, tri -, and tetrasulfide) and allyl alcohol. Other important degradation pr oducts (arising especially at temperatures higher than 140 degrees C) were sulfur-containing cyclic compounds, namely 2,5-dimethyl-1,4-dithi anes, 2-methyl-1,4-dithiepane, and dimethyl-1,2,5-trithiepanes. It was found that the typical garlic aroma can be formed nonenzymatically du ring the thermal treatment of either alliin or deoxyalliin. The major precursor of this aroma was alliin, while deoxyalliin was much more st able. The contribution of the individual volatiles to the resulting ar oma with regard to their sensory properties is discussed.