Modulation of gut microbiota and its environment using starch-entrapped microspheres and cereal arabinoxylans

Consumption of large amounts of readily fermentable fibers results in rapid gas production often leading to flatulence, bloating, and pain. It also limits delivery of carbohydrate substrate to the distal colon likely predisposing this region to diseases like ulcerative colitis. Two types of fibers with initial slow and extended fermentation, starch-entrapped microspheres and alkali-soluble corn bran arabinoxylans (AXs), have been developed and researched in our laboratory. Fermentation of starch-entrapped microspheres has been shown to generate high butyrate and positively impact fecal microbiota of inflammatory bowel disease patients. The present thesis study was designed with the following objectives: 1) Use starch-entrapped microspheres as a benchmark slow fermenting fiber against a wide range of claimed slowly fermentable fibers and demonstrate their efficacy, 2) Test starch-entrapped microspheres in an animal model for their slow fermenting, high butyrogenic property, as well as evaluate the physically inaccessible (starch-entrapped microspheres) versus accessible (raw potato, resistant starch type 2) starches with regards to their favoring certain bacterial groups within the colon microbiota, and 3) Elucidate the effect of variably fermentable cereal AXs on human fecal microbiota. The results showed that among the claimed slowly fermentable fibers, alkali-soluble corn bran arabinoxylan and long-chain β-glucan initially were slower fermenting, but later fermented rapidly with little remaining in the final half of the fermentation period. Long-chain inulin and psyllium had slow and moderate, but incomplete, fermentation. It was found that none of the tested fibers indeed had an extended rate of fermentation and only starch-entrapped microsphere fermentation resulted in significantly higher short-chain fatty acids (SCFAs) and butyrate between 24-48 h. However, the extended fermentation of the starch-entrapped microspheres that has been demonstrated in vitro was not observed in the mouse distal gut when animals were fed with 10 % (w/w) fiber in the diet. This was speculated to be due to an overly slow fermentation rate that may be compensated for by microbiota adaptation over time or a change in the microsphere composition to increase rate. In comparison, resistant starch type 2 had an extended fermentation profile with maximum total SCFAs in the distal colon. Both the starches were equivalent with respect to amount of butyrate, but fermentation of starch-entrapped microspheres led to highest mole percent butyrate in the distal gut, which is desirable in part due to its anti-inflammatory property. Both starches shifted the luminal and mucosal microbiota with respect to a non-fermentable control. Furthermore, physically inaccessible starch in the microspheres clearly promoted growth of different bacterial groups than the accessible resistant starch; the former resulting in substantially lower Bacteroidetes and higher Firmicutes. Lastly, alkali-soluble AXs from corn, rice, sorghum, and wheat were shown to promote Bacteroides-Prevotella group, but all in different patterns indicating that rate of fermentation cannot be directly related to the changes in certain bacterial classes. None of the AXs (except rice AX) promoted bifidobacteria and lactobacilli between 0-12 h, but did so between 12-24 h indicating metabolic cross feeding by these bacteria on AX-generated-oligosaccharides. The above studies bring us one step closer to substrate-microbiota specificity, but future research is warranted for a better understanding of how rates of fermentation and availability of dietary fiber substrate affects microbiota composition