Quantitative Analysis of GSLs and GHPs

GSLs and GHPs were extracted following the methods described by Bell et al. [43 (link)] and Bell et al. [44 (link)], respectively, with modifications as described in our earlier paper Oloyede et al. [38 ]. GSLs were extracted with 70% methanol, analysed by LC-MS/MS (Agilent, Bracknell, UK), and quantified using sinigrin hydrate standard. Six concentrations of sinigrin hydrate (14–438 µg/mL) were prepared with 70% methanol and used to prepare an external calibration curve (r² = 0.996). Compounds were identified using their mass parent ion, characteristic ion fragments and through comparing with ion data from literature (Table 1).
GHPs were extracted using dichloromethane and analysed by GC-MS (Agilent, Manchester, UK). Compounds were identified using the literature on ion data (Table 2; see Supplementary Figure S1 for GC-MS chromatograms) and quantified based on an external standard calibration curve. Five concentrations (0.15–0.5 mg/mL) of sulforaphane standard (Sigma Aldrich, UK) were prepared in DCM (r² = 0.99). Data analysis was performed using ChemStation for GC-MS (Agilent, Manchester, UK).