FIG 2.

Dietary fiber complexity relative to their bacterial degradation. Dietary fibers with simple chemical structures, such as fructooligosaccharides (FOS), require few bacterial glycoside hydrolases to degrade them, whereas more-complex molecules, such as xyloglucans, which contain a range of sugar and linkage types, require that bacteria have more glycoside hydrolases for their complete degradation. Complex physical structures, such as those found in insoluble dietary fibers (e.g., β-1,3 glucan [22]), also require that bacteria have specific and perhaps more complex machinery to access these insoluble substrates (maybe cellulosome-like appendages).