Plant matrix concentration and redox status influence thermal glucosinolate stability and formation of nitriles in selected Brassica vegetable broths

Brassica vegetables are frequently consumed foods of nutritional interest, because they are rich in glucosinolates (GLSs). Among GLS breakdown products, especially isothiocyanates are known for their health-beneficial effects, while nitriles are less beneficial. To increase the understanding of the plant matrix's influence on GLS degradation, differently concentrated vegetable broths were prepared from selected Brassica vegetables (kohlrabi and red cabbage) and subsequently boiled. Altogether, heat stability and conversion of GLSs to the corresponding nitriles were both strongly influenced by vegetable type and plant matrix concentration in the broths. After boiling kohlrabi broths for 120 min, recovery of 4-(methylthio)butyl-GLS as nitrile was 55.5 % in 1 g/mL broth and 8.4 % in 0.25 g/mL broth. In follow-up experiments, a pronounced influence of the matrix's redox status was identified, with H₂S being an important factor. A better understanding of these processes will help to preserve health-promoting effects of GLSs in Brassica vegetables in the future.