Stability and bioaccessibility during ex vivo digestion of glucoraphenin and glucoraphasatin from Matthiola incana (L.) R. Br

The glucosinolates (GSLs) of Matthiola incana were characterized and quantified as desulfoGSLs in different plant tissues (seeds, siliquae, stems, leaves, and flowers) using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-DAD-MS/MS). The major GSL detected in all plant parts was 4-(methylsulfinyl)but-3-enyl GSL (glucoraphenin, 1), followed by 4-(methylsulfanyl)but-3-enyl GSL (glucoraphasatin, 2), while indol-3-ylmethyl GSL (glucobrassicin, 3) was also found in the flowers. GSL 2 was found to be the dominant in the plants analysed after only 2 days of drying, contrary to all analyses performed after longer storage of plant material, thus suggesting an oxidation of 2 into 1. The stability of GSLs was monitored over a one-month period. The desulfo-counterpart of 1 was unstable in water, showing a dramatic decrease (ca 80%) during the observation time, with spontaneous conversion into cyclic thioimidate N-oxides. Bioaccessibility of GSLs through the simulated ex vivo gastrointestinal digestion was determined using human gastrointestinal juices. Glucoraphenin 1 showed high bioaccessibility in the gastric phase (> 90%), while both GSLs 1 and 2 were transformed in the intestinal phase.