Nonstarch polysaccharide-degrading enzymes alter the microbial community and the fermentation patterns of barley cultivars and wheat products in an in vitro model of the porcine gastrointestinal tract

An in vitro experiment was carried out to assess how nonstarch polysaccharide (NSP)-degrading enzymes influence the fermentation of dietary fiber in the pig large intestine. Seven wheat and barley products and cultivars with differing carbohydrate fractions were hydrolyzed using pepsin and pancreatin in the presence or not of NSP-degrading enzymes (xylanase and beta-glucanase) and the filter retentate was subsequently fermented with sow fecal bacteria. Dry matter, starch, crude protein and beta-glucan digestibilities during hydrolysis were measured. Fermentation kinetics of the hydrolyzed ingredients were modelled. Short-chain fatty acids (SCFA) production and molar ratio were compared after 12, 24 and 72 h. Microbial communities were analyzed after 72 h of fermentation using terminal restriction fragment length polymorphism. The results showed an increase of nutrient digestibility (P < 0.001), whereas fermentability and SCFA production decreased (P < 0.001) with addition of the enzyme. SCFA and bacterial community profiles also indicated a shift from propionate to acetate and an increase in cellulolytic Ruminococcus- and xylanolytic Clostridium-like bacteria. This is explained by the increase in slowly fermentable insoluble carbohydrate and the lower proportion of rapidly fermentable beta-glucan and starch in the retentate when grains were incubated with NSP-degrading enzymes. Shifts were also different for the four barley varieties investigated, showing that the efficiency of the enzymes depends on the structure of the carbohydrate fractions in cereal products and cultivars.