Date of Award

January 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Food Science

First Advisor

Bruce R Hamaker

Committee Member 1

Osvaldo H Campanella

Committee Member 2

Bradley L Reuhs

Committee Member 3

John Patterson


Dietary fiber has gained an increasing attention in recent years due to the myriad of health benefits attributed to it. The majority of these arise from their fermentative properties and their effects on gut microbiota. Cereals and pseudocereals are important sources of insoluble dietary fibers that are recalcitrant to solubilization by non-chemical methods and poorly fermented. This warranted an effort to make these fibers more susceptible to microbial degradation and a resulting improved fermentability. Insoluble dietary fibers from four alternative grains, sorghum and pearl millet of African origin, and quinoa and amaranth of Andean origin, were subjected to a combination of microwave treatment and sequential enzymatic hydrolysis in order to effect solubilization and improve fermentability. Characterization of the dietary fibers revealed that, besides cellulose and lignin, insoluble fiber from pseudocereals consisted of pectic polysaccharides and xyloglucans, and that arabinoxylans were the main hemicellulose found in cereals. Subjecting insoluble fibers to microwave radiation resulted in low solubilization, but in combination with enzyme hydrolysis solubilization was significantly higher. Quinoa and amaranth were more susceptible to treatments (increase to ~50% soluble fiber) than pearl millet (increase to ~20 soluble fiber). In addition to solubilization, a portion of the fiber that remained insoluble after treatments became susceptible to microbial degradation and fermentation. Thus, treatments of insoluble fibers generated fiber substrates that were constituted by 3 types of fiber: 1) soluble-fermentable, 2) insoluble-fermentable, and 3) insoluble-nonfermentable. Accordingly, fermentability of treated fiber substrates (TFS) significantly improved to levels higher than predicted solely by increase in soluble fiber content. Improved fermentability was evident in increased total short chain fatty acid production and slow rates of gas production for TFS from pearl millet. Furthermore, fermentation of TFS resulted in significant changes in human fecal microbiota composition following in vitro fermentation. Next-generation sequencing (SBS) of genomic DNA extracted from fecal samples after incubations with TFS showed that the abundance of bacterial groups changed as a response to differences in composition, structure, and degree of fermentability. In general, TFS promoted greater diversity and richness than the single soluble-fermentable control, FOS. In comparison to their untreated counterparts, TFS caused a significant increase in Lachnospiraceae and a decrease in Bacteroidaceae. Substrates from quinoa significantly promoted the Ruminococcaceae family and substrates from pearl millet were more bifidogenic. These results lay the groundwork for the design of fermentable carbohydrates using insoluble fibers to potentially create fiber substrates for improvement of gut health.