Fermentation of barley flour with Lactobacillus reuteri

Abstract: Fermentation of foodstuffs has beneficial effects on shelf life, taste and texture and possibly also health of the consumer. Products containing microbes with beneficial health effects for the host are defined as probiotics. One probiotic bacterium, Lactobacillus reuteri, has been shown to exert positive effects on a number of diseases and disorders, including a possible protective role against increased intestinal permeability or ‘leaky gut’. Increased intestinal permeability has been linked to e.g. inflammatory bowel disease (IBD), irritable bowel disease (IBS), coeliac disease and infectious diarrhoea. This study examined the effect of different cereal substrates on the growth, general metabolism and production of potential bioactive compounds by L. reuteri, with the aim of establishing a synbiotic formulation effective against increased intestinal permeability. Combinations of six barley varieties and six strains of bacteria were evaluated using standard plate counts, chemical analysis (1H-NMR) and a small intestinal epithelial cell model (IPEC-J2). The overall growth of L. reuteri in barley flour was good and reached higher densities in untreated compared with heat-treated flours. Differences in growth were also seen between bacterial strains and barley varieties. The general metabolism was similar for all strains with a few exceptions, e.g. lower production of succinate from L. reuteri DSM 17938. Two potentially bioactive compounds, γ-aminobutyric acid (GABA) and 3-hydroxypropionic acid (reuterin), were detected in barley fermented by L. reuteri. GABA was present in unfermented flour at similar levels as in the fermented counterpart, indicating no or low production by L. reuteri. Reuterin production was detected as formation of 1,3-propanediol and was strain-specific, being present in fermentation with DSM 17938 and ATCC PTA 6475. Experiments with IPEC-J2 cells revealed an increase in epithelial permeability caused by untreated flour, both fermented and unfermented. Treatment with heat-treated flour had a slight increasing effect on permeability, but recovered over time. Pre-treatments with live bacteria or fermented heat-treated flour before challenge with enterotoxigenic E. coli revealed significantly lower leakage of a molecular probe (FITC-dextran, 4 kDa). However, neither live bacteria nor their metabolites had a protective effect on epithelial permeability, measured as transepithelial electrical resistance (TEER).