Thermolysis kinetics and thermal degradation compounds of alliin

•Thermal degradation kinetic of alliin could be described by first order reaction.•Thermal degradation compounds of alliin were identified.•Reaction mechanisms for the thermal degradation of alliin were proposed.•Allyl alanine tetrasulfide was identified for the first time in heat treated alliin.

To investigate thermolysis kinetics and identify degradation compounds, alliin solutions were heated at 60, 80, and 89 °C. The degradation compounds of alliin were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS), tandem mass spectrometry (MS/MS) and ultra-pressure liquid chromatography-high resolution mass spectrometry (UPLC-HRMS). The results showed that the thermal degradation kinetic of alliin could be described by a first-order reaction and k = 4.38 × 1017exp (−142494/RT), where k is the reaction rate constant, min−1; R is gas constant; T is the absolute temperature, K. Degraded compounds, including S-allyl-l-cysteine and ethers, such as allyl alanine disulfide, allyl alanine trisulfide, allyl alanine tetrasulfide, dialanine disulfide (cysteine), dialanine trisulfide and dialanine tetrasulfide, were identified by HPLC-MS, MS/MS and UPLC-HRMS. Allyl alanine tetrasulfide was identified for the first time in alliin. The results show that alliin is unstable and significant numbers of organosulfur compounds are generated under high temperature treatment.