Degradation of glucosinolates and formation of isothiocyanates, nitriles, amines, and N,N'-dialk(en)yl thioureas during domestic boiling of red cabbage

Red cabbage is a popular vegetable in Central Europe and a rich source of glucosinolates (GLSs). Upon hydrolysis, GLSs form health-promoting isothiocyanates (ITCs), but also nitriles and epithionitriles. Recently, ITCs were shown to undergo further hydrolysis, yielding amines. Here, we analyzed the degradation of GLSs and the formation of ITCs, nitriles, epithionitriles, and amines during domestic-like cooking of red cabbage with addition of vinegar or baking soda. Both additives strongly affected the stability of GLSs and the formation of nitriles during boiling. Primary amines were found as a major degradation product of GLSs. In control and vinegar samples, formation of methylsulfinylalkyl amines increased during boiling. Additionally, for the first time, the formation of several N,N'-dialk(en)yl thioureas during boiling of Brassica vegetables was demonstrated, resulting from the reaction of GLS-derived ITCs and amines, and they were subsequently quantified. As references, five N,N'-dialk(en)yl thioureas were synthesized and characterized by NMR and HRMS.

Automated summary

Red cabbage, a popular vegetable in Central Europe, contains glucosinolates (GLSs), which can be hydrolyzed to form health-promoting isothiocyanates (ITCs), nitriles, and epithionitriles. This study found that vinegar and baking soda significantly affected the stability of GLSs and the formation of nitriles during cooking of red cabbage. Primary amines were identified as the major degradation product of GLSs. Additionally, the formation of various N,N'-dialk(en)yl thioureas during boiling of Brassica vegetables was demonstrated for the first time.