Influence of native and processed cereal grain fibers on gut health

Cereal fibers that can be metabolized by gut microbiota have been shown to promote the growth of beneficial bacteria in the gut. Increased consumption of cereal fibers may improve host / gut microbiota interactions in obesity and other metabolic diseases by normalizing gut dysbiosis. The present dissertation describes four research projects to assess the impact of cereal dietary fibers on gut microbiota and host metabolism. In the first study, we determined the treatment temperatures for production of soluble, non-digestible, feruloylated oligo- and polysaccharides (FOPS) from maize bran and wheat bran, and determined the fermentation properties of partially purified FOPS from maize bran and wheat bran. In vitro fermentation revealed that wheat FOPS were more bifidogenic than maize FOPS. However, maize FOPS led to continual production of short-chain fatty acids (SCFA), resulting in the highest SCFA and butyrate production at the end of the fermentation. In addition, maize FOPS showed significantly higher antioxidant activity than wheat FOPS. The study showed FOPS from maize bran may exhibit enhanced benefits on gut health compared to those of wheat bran. In the second study, we further determined whether the colonic fermentation of FOPS could counteract the deleterious metabolic effects of a high-fat (HF) diet through modulating the gut microbiota using a mouse model. Our results suggest that colonic fermentation of FOPS plays an important role in preventing metabolic disorders in HF-fed mice, and that these metabolic improvements depend on specific alterations of the gut microbiota through FOPS fermentation. Blautia and Akkermansia might be considered potential therapeutic targets for improving body and adipose tissue weights, while SCFA production seems linked to improvements in glucose metabolism. In the third study, by obtaining long-term dietary records from fecal donors, we aimed to determine the correlations between dietary intake variables and dietary fiber degradation and short-/branched-chain fatty acid (BCFA) and ammonia production during in vitro fecal fermentation. We found that butyrate production was correlated with fecal donor intake of many nutrients, of which principal component analysis revealed were mostly contributed by grain-, nut-, and vegetable-based foods. Negative correlations were found for propionate with intake of total carbohydrate, added sugar, and sucrose and for ammonia and BCFA production with intake of unsaturated fats. These results suggest that diets high in plant-based foods and high in unsaturated fats are associated with microbial metabolism that is consistent with host health. In the fourth study, we determined the impacts of long-term dietary pattern on gut microbiota composition and the change in composition of the gut microbiota during fermentation of predigested whole wheat flour. Butyrate production was significantly correlated with the abundance of Butyricicoccus, Coprococcus, Dorea, Faecalibacterium, and Lachnospiracea incertae sedis. BCFA and ammonia production displayed negative correlations with the abundance of Roseburia and Parasutterella. Bifidobacterium and Butyricicoccus were enhanced by pre-digested whole wheat flour. Taken together, these results provide new evidence for modulating the gut microbiota through dietary treatment and indicate its contribution to host metabolism