Glucoraphanin is hydrolyzed by lactobacilli in vitro and rat cecal microbiota in vitro and in situ.

Abstract

Glucoraphanin (GP) is a major glucosinolate in broccoli. To become active as an anticarcinogen, GP needs hydrolysis to the isothiocyanate sulforaphane (SF), either by the endogenous plant enzyme myrosinase or possibly by microbiota in the GI tract. Five Lactobacillus species (L. gasseri, L. acidophilus, L. casei, and two of L. plantarum) and rat cecal digesta (containing live microbiota) were evaluated for GP metabolism. The degradation of GP by the tested Lactobacillus spp. ranged from 36 to 49% after 24 h incubation, but the major hydrolytic product was a nitrile, which has no bioactivity, and no SF was found. The cecal digesta from naïve and GP pretreated rats showed 40 and 56% degradation of GP, respectively, after 24 h incubation in MRS, a medium that supports growth of lactobacilli. Again, the major hydrolytic product was a nitrile, although one sample produced SF (36% of the GP substrate). Also, when GP was injected directly into the cecum of rats, isothiocyanate metabolites were found in the portal blood stream. This is the first study to show directly that GP can be metabolized by cecal microbiota to SF in situ, and then absorbed at the cecum. Supported by USDA/NRI 05‐02622 and a University of Illinois Toxicology Fellowship to RHL.