Predicting changes in the human gut microbiome is a primary goal of human nutrition researcher because those changes might be controlled to produce health-promoting metabolites and prevent or reverse dysbiosis. Carbohydrate metabolic networks are a central aspect of gut microbial ecosystems, and so deconvoluting those networks may uncover a causal link between dietary carbohydrates and microbiome function. However, the individual carbohydrate structures that compose those networks are difficult to isolate and purify, limiting mechanistic research to the most easily purifiable carbohydrates. For example, impure, branched arabinan from sugar beet is sold for research, and of pure arabinooligosaccharides, only linear ones are commercially available. In this work, the previously described “Fenton’s initiation toward defined oligosaccharide groups” (FITDOG) reaction was used to transform sugar beet pulp pellets into branched and linear oligosaccharide constituents of sugar beet polysaccharides. Because FITDOG is a non-enzymatic, relatively non-biased reaction, it may simulate the natural production of oligosaccharides from dietary polysaccharides by gut bacteria. Branched and linear sugar beet oligosaccharides derived from FITDOG were used to investigate the mechanism of sugar beet oligosaccharide consumption by human gut bacteria. It was demonstrated that in vitro fecal communities enriched by sugar beet oligosaccharides could not be distinguished from those enriched by sugar beet pulp, which implies that FITDOG products are functionally similar to FITDOG reactants. It was also shown that not all adult human Bifidobacterium species can grow on these sugar beet oligosaccharides. These findings demonstrate the potential of FITDOG as a prebiotic oligosaccharide synthesis method. However, only when it is paired with high throughput glycoanalytical tools can it be used to dissect the glycolytic capabilities of human gut bacteria. Mechanistic investigations of oligosaccharide consumption by gut bacteria have been hampered by low-resolution carbohydrate sequencing technology. However, recent advancements in liquid chromatography/mass spectrometry have enabled the performance of monosaccharide and linkage analysis with unprecedented throughput and breadth. High throughput monitoring of the structural motifs that compose even perfectly defined carbohydrate structures is required to describe the mechanism of those structures’ consumption. This is made especially salient when researching the structural specificity of the glycoside hydrolases. Here we also describe a workflow to find the structural specificity of bacterial glycoside hydrolases that mediate cross-feeding between primary and secondary dietary fiber degraders of arabinan with high throughput monosaccharide, linkage, and oligosaccharide composition analysis. Bifidobacterium pseudocatenulatum was chosen to demonstrate this workflow because it cannot metabolize arabinan, yet it metabolizes sugar beet arabinooligosaccharides and encodes the most predicted arabinosidases in human Bifidobacterium behind Bifidobacterium longum subsp. longum, which can metabolize arabinan. The specificity of arabinofuranosidases from Bifidobacterium pseudocatenulatum suggest that it cleaves arabinan and arabinofuranooligosaccharides with extracellular, substitution-intolerant, endo-arabinofuranosidases. Comparative genomics of Bifidobacterium strains that do and do not grow on sugar beet oligosaccharides and arabinan suggests Bifidobacterium pseudocatenulatum competes with Bifidobacterium longum subsp. longum and Bacteroides species for unsubstituted or lightly substituted arabinofuranooligosaccharides. FITDOG produces diverse oligosaccharides from polysaccharides without highly specific enzymes, meaning this workflow can be used to describe bacterial cross-feeding mechanisms between primary and secondary dietary fiber degraders of any carbohydrate-containing food.