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.