Volatile compounds generated from thermal interaction of glucose and alliin or deoxyalliin in propylene glycol

Alliin and deoxyalliin, the two important nonvolatile flavor precursors of garlic, were reacted with and without glucose in propylene glycol, respectively. The reactions were accomplished in a closed sample cylinder at 180°C for 1 h. The volatile compounds generated were isolated and analyzed by GC and GC-MS. A considerable amount of allylthio-containing and cyclic sulfur-containing compounds were found in deoxyalliin systems. No allylthio-containing compounds and only a small amount of cyclic sulfur-containing compounds were found in alliin systems. Some pyrazines were identified from both alliin and deoxyalliin model systems even in the absence of glucose. Propylene glycol was proposed to participate in the formation of some pyrazines. More thiophenes were generated in deoxyalliin model systems than in alliin model systems, while more thiazoles were generated in alliin model systems than in deoxyalliin model systems.