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The metabolism of methylsulfinylalkyl- and methylthioalkyl-glucosinolates by a selection of human gut bacteria

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Abstract

Scope

Certain myrosinase-positive human gut bacteria can metabolize glucosinolates (GSLs) to produce isothiocyanates (ITC) as chemopreventive agents. We investigated glucoerucin, glucoiberin, and glucoraphanin (present in broccoli) metabolism by human gut strains.

Methods and results

All tested bacteria metabolized glucoerucin to completion within 16 h to erucin and erucin nitrile (NIT). Lactobacillus agilis R16 metabolized only 10% of glucoiberin and glucoraphanin with no detectable products. Enterococcus casseliflavus CP1, however, metabolized 40–50% of glucoiberin and glucoraphanin producing relatively low concentrations of iberin and sulforaphane. Interestingly, Escherichia coli VL8 metabolized 80–90% of glucoiberin and glucoraphanin and also bioconverted glucoraphanin and glucoiberin to glucoerucin and glucoiberverin, respectively, producing erucin, erucin NIT, iberverin, and iberverin NIT from the two GSLs. The putative reductase enzyme in the cell-free extracts of this bacterium required both Mg2+ and NAD(P)H as cofactors for bioconversion. The cell-free extract of E. coli VL8 containing the reductase enzyme was able to reduce both the GSL glucoraphanin and its hydrolysis product sulforaphane to glucoerucin and erucin/erucin NIT, respectively.

Conclusion

The composition and metabolic activity of the human gut bacteria can indirectly impact on the potential chemopreventive effects of GSL-derived metabolites.

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