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Abstract
Glucosinolate-derived isothiocyanates are valuable for human health as they exert health promoting effects. Here, the stability and reactivity of 12 different isothiocyanates during aqueous heating at 100 °C and pH 5 to pH 8 were investigated. The formation of their corresponding amines and N,N’-dialk(en)yl thioureas was quantified. Further, the potential to form odor active compounds was investigated using a HRGC-MS-olfactometry approach. A strong structure-reactivity relationship was found for the isothiocyanates: shorter side chains and electron withdrawing groups increase the reactivity of the isothiocyanate and 3-(methylsulfonyl)propyl isothiocyanate was least stable. The main degradation product was found to be the corresponding amine (up to 69% recovery after 4 h of heating at pH 5) and formation of N,N’-dialk(en)yl thioureas is only relevant at neutral to basic pH values. Apart from allyl isothiocyanate also 3-(methylthio)propyl isothiocyanate is precursor to many sulfur containing odor active compounds that will contribute to the boiled cabbage flavor.
Supplementary materials
Title
Supplemental Figure 1
Description
Effect of aqueous heating of isothiocyanates (ITC) at 100°C at pH 5 (A), pH 6 (B) and pH 8 (C) on the formation of N,N’-dialk(en)ylthioureas. The abbreviations of the alk(en)yl residues of the thioureas (TUs) correspond to the ITC-side chains depicted in Figure 1.
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Title
Supplemental Figure 2
Description
Obtained EI mass spectra of unknown products from A) 3-butenyl isothiocyanate (ITC), and B) 4-(methylthio)butyl ITC by GC-MS-olfactometry.
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Supplemental Tables 1, 2, and 3
Description
Supplemental Table 1: Heat treatment times (100°C) of models and plant homogenates.
Supplemental Table 2: Half-lifes of isothiocyanates (ITCs) heated at 100°C in model systems or as natural ITCs in plant homogenates. AV- average, SD- standard deviation
Supplemental Table 3: Overview of isothiocyanate (ITC) and N,N-dialkenylthiourea (TU) levels (mM) after aqueous heating for different times at 100°C levels and calculated recovery of the ITC as TU in %.
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