Novel transformation products from glucosinolate-derived thioglucose and isothiocyanates formed during cooking

Glucosinolates are plant secondary metabolites occurring in Brassicaceae plants. Upon tissue disruption, these compounds can be enzymatically hydrolyzed into isothiocyanates, which are very reactive and can react with nucleophiles during thermal processes such as boiling. Here, a novel type of glucosinolate degradation product was identified resulting from the reaction of thioglucose with the isothiocyanates sulforaphane or allyl isothiocyanate during aqueous heating. The two heterocyclic compounds 4-hydroxy-3-(4-(methylsulfinyl)butyl)thiazolidine-2-thione and 3-allyl-4-hydroxythiazolidine-2-thione were isolated and their structure elucidated by NMR spectroscopy and high-resolution mass spectrometry. Based on a set of chemical experiments, a reaction mechanism was proposed. Finally, the formation of the two 3-alk(en)yl-4-hydroxythiazolidine-2-thiones was quantified in boiled cabbage samples using a standard addition method in which 92 pmol/g and 19 pmol/g fresh weight of the sulforaphane and allyl isothiocyanate derivatives were found, respectively.