The effect of dietary fibres and starch on the anaerobic gut microbiota and the potential for bacterial encapsulation for oral delivery

The human gut is rich with anaerobic bacteria which have a fundamental role in maintaining homeostasis of the intestinal ecosystem. Carbohydrates are the main nutritional substrates for these beneficial gut bacteria. However, some bacteria cannot utilise these substrates, thus they rely on other bacteria to gain these molecules by cross-feeding mechanisms. During an in vitro study, Eubacterium rectale PC25 (a butyrate-producer) showed the highest microbial activity including optical density, pH change and gas production during growth on most fibres and starches, and in co-culture it cross-fed with a putative Eubacterium ventriosum PC31 strain. Dietary fibre and starch can significantly affect the composition of gut microbiota as well as impacting their fermentation acid production, and several bacterial species are associated with specific carbohydrates intake. In an in vivo study, consuming diets rich with barley β-glucan and whole grain wheat had different effects on the gut bacterial composition in eight hypercholesterolaemic volunteers, and there was a detection of Eubacterium genus within the bacterial composition before and after the diets. There was no significant change in concentrations of the major short-chain fatty acids or the cholesterol levels for these volunteers after consuming the diets. New techniques were developed to encapsulate an obligatory anaerobic bacterium for potential subsequent use as a probiotic or synbiotic. Microencapsulation with alginate was evaluated as a potential technique to enhance viability of E. rectale PC25 due to its observed abundance in vivo, and its high butyrate production in vitro. The microencapsulation technique showed promising results in protecting E. rectalePC25 from exposure to oxygen during storage and following exposure to simulated gastrointestinal conditions. In conclusion, E. rectale might be considered for development as a potential probiotic due to its beneficial health effects by producing high amount of butyrate, its ability to degrade many carbohydrates, and its interactions with other gut bacteria.