Exploring the bioaccessibility, in vitro colonic fermentation, and the impact on the intestinal microbiota of allyl-and benzyl-isothiocyanate from white and Ethiopian mustard.

The aim of this research was to study the formation and bioaccessibility of allyl- and benzyl-isothiocyanate (ITC) resulting from the gastrointestinal digestion (small and large intestine) of green parts from Ethiopian and white mustard. In addition, a GC-MS methodology was validated to determine these compounds in bioaccessible and non-bioaccessible fraction. Plant clumps were divided into two batches: fresh and freeze-dried samples. ITC bioaccessibility was low in the small intestine, with values ranged between 11 and 53 % and mean values of 26 %. These results are in agreement with the fact that ITCs are poorly water-soluble compounds. Bioaccessibility values for lyophilised samples were lower than those obtained in fresh samples. This could be due to the degradation of the precursor glucosinolates (sinigrin and glucotropaeolin respectively). The simulation of the colonic fermentation reduced allyl - and benzyl - ITC levels from the non-bioaccessible fraction of Ethiopian and white mustard (values between 0.009 and 0.087 mg/g). In both cases, ITCs concentration dropped dramatically, i.e. with a ten-fold reduction. Nevertheless, this result does not necessarily indicate that ITCs have not been produced in the large intestine. Bacterial microbiota plays a key role in generating ITCs; however, ITCs are not always the final products of this process. The metagenomic analysis of colonic samples revealed that ITCs and cruciferous matrix significantly influenced the composition of gut microbiota, inhibiting potentially pathogenic bacteria such as Enterobacter and Klebsiella, while promoting beneficial bacteria such as Bifidobacterium, Faecalibacterium, Blautia, and Ruminococcus. Interestingly, ITCs-rich environments selected bacterial species (i.e. Enterobacter ludwigii) and promoted metabolic pathways involved in glucosinolate/ITCs metabolism.