Reaction pathways and kinetics of tryptophan in hot, compressed water

The reaction pathways and chemical kinetics of tryptophan and its products were elucidated under hydrothermal conditions from experiments at 265, 280, 295, and 310 °C. Tryptophan participates in several primary reactions leading to the formation of six identified primary products. The primary reactions include decarboxylation, deamination, and cleavage of C–C bonds. Several of the primary products are also formed via secondary reactions. A chemical kinetics model based on the reaction pathways provides excellent correlation of the experimentally observed trends. The model indicates that both the reaction temperature and the initial concentration of tryptophan are influential on the selectivity of the parallel primary reaction pathways, as formation of higher molecular weight products directly from tryptophan is a second order reaction and has the highest activation energy. These new results and the reaction model provide insights into the chemistry that occurs during hydrothermal valorization of proteinaceous biomass.