Intact Glucosinolate Profiles of Oldenbor F1 and Redbor F1 Curly Kale Under Iodine Biofortification and Thermal Processing

This study investigated intact glucosinolate (GLS) profiles in two curly kale cultivars, Oldenbor F1 and Redbor F1, subjected to iodine biofortification and thermal processing. Plants were grown as non-biofortified controls or biofortified with potassium iodate (KIO3) or 5,7-diiodo-8-quinolinol (5,7-diI-8-Q). Unprocessed, non-biofortified kale samples were used as RAW references, while leaves from all iodine-treatment conditions were subjected to blanching, boiling or steaming. Ten intact GLS, comprising five aliphatic, four indole and one aromatic compound, were quantitatively analyzed using LC–Q-Exactive Orbitrap HRMS. The GLS profiles showed pronounced cultivar- and processing-related differences. Redbor F1 was characterized by a strong contribution of indole GLS, whereas Oldenbor F1 showed a comparatively greater contribution of aliphatic GLS. Across all cultivar × biofortification combinations, steamed samples showed the highest summed concentrations of quantifiable GLS among the thermally processed samples. Responses associated with KIO3 and 5,7-diI-8-Q were compound and cultivar dependent rather than uniformly directed. Principal component analysis (PCA), based on standardized QC-corrected LC–HRMS peak areas of the ten GLS, showed that PC1 and PC2 explained 66.1% and 25.5% of the total variance, respectively. PC1 reflected a pronounced processing-associated gradient, whereas PC2 primarily reflected cultivar-related differences in GLS composition. Because cooking water was not analyzed for GLS and a complete mass balance was not performed, the observed differences are interpreted as differences in post-processing tissue concentrations rather than true GLS retention.