Analysis of the transformation mechanisms of alliin during the thermal processing of black garlic

S -allyl- l -cysteine sulfoxide (alliin) levels decrease greatly during the processing of black garlic. However, the transformation pathways of alliin are unclear. The present study explored three of its possible transformation pathways, thermal decomposition, the Maillard reaction, and enzymatic reaction, by performing in vitro simulations combined with in vivo experiments. Results showed that alliin was thermally unstable at 75 °C. Its content decreased by 87.6% during thermal decomposition and 87.7% during Maillard reactions. Thermal-degradation products of alliin were found to include S -allylcysteine (SAC) and S -Allyl Mercapto-Cysteine (SAMC). In enzymatic reactions, the enzymatic-product content of allicin initially increased and then decreased. After 4 h at 75 °C and 85% relative humidity, alliinase was completely inactivated and no further enzymatic reaction occurred. Thermal decomposition and enzymatic reactions were proven to be the main transformation pathways of alliin during black-garlic processing. • Alliin content decreased 87.6% by thermal decomposition at 75 °C. • SAC and SAMC could be produced through the thermal breakdown of alliin. • Alliin did not participate in the Maillard reaction with D-fructose at 75 °C. • Alliin participated in enzymatic reactions in the first 4 h under 75 °C and 85%RH.