Fecal excretion of Maillard reaction products and the gut microbiota composition of rats fed with bread crust or bread crumb.

A comparison between the impacts of advanced (N-carboxymethyllysine - CML) and terminal (melanoidins) Maillard reaction products from bread on gut microbiota was carried out in this study. Gut microbiota composition as well as fecal excretion of CML from both bread crust and bread crumb, and of melanoidins from bread crust were assessed on a rodent model. Rats were fed with pellets supplemented or not with 13% of bread crust, bread crumb, a fiber-free bread crust model (glucose, starch and gluten heated together) or a fiber-free-melanoidin-free bread model (glucose-starch and gluten heated separately) for four weeks. These model systems were developed to limit the presence of wheat-native dietary fibers such as cellulose, hemicelluloses and lignin. CML and melanoidins in pellets and feces were evaluated by LC/MS-MS and HPLC/fluorescence respectively, and gut microbiota composition was determined by cultivation and molecular approaches. Diets supplemented with crumb or the fiber-free-melanoidin-free model contained respectively 17% and 64% less melanoidins than their respective controls. A higher excretion of melanoidins was observed for rats fed with crust or bread crust model compared to their controls, confirming that melanoidins are in contact with gut microbiota. No impact of diets was observed on Firmicutes, Bacteroidetes and lactic flora. A decrease of enterobacteria was only observed for rats fed with the diet supplemented with the fiber-free bread crust model. Moreover, a significant increase of bifidobacteria numbers in the presence of crust, crumb and both bread models was observed, showing that this bifidogenic effect of bread is not due to the presence of melanoidins or wheat-native dietary fibers.