Multi-Glycomic Characterization of Fiber from AOAC Methods Defines the Carbohydrate Structures

Dietary fiber has long been known to be an essential
component
of a healthy diet, and recent investigations into the gut microbiome-health
paradigm have identified fiber as a prime determinant in this interaction.
Further, fiber is now known to impact the gut microbiome in a structure-specific
manner, conferring differential bioactivities to these specific structures.
However, current analytical methods for food carbohydrate analysis
do not capture this important structural information. To address this
need, we utilized rapid-throughput LC-MS methods to develop a novel
analytical pipeline to determine the structural composition of soluble
and insoluble fiber fractions from two AOAC methods (991.43 and 2017.16)
at the total monosaccharide, glycosidic linkage, and free saccharide
level. Two foods were chosen for this proof-of-concept study: oats
and potato starch. For oats, both AOAC methods gave similar results.
Insoluble fiber was found to be comprised of linkages corresponding
to β-glucan, arabinoxylan, xyloglucan, and mannan, while soluble
fiber was found to be mostly β-glucan, with small amounts of
arabinogalactan. For raw potato starch, each AOAC method gave markedly
different results in the soluble fiber fractions. These observed differences
are attributable to the resistant starch content of potato starch
and the different starch digestion conditions used in each method.
Together, these tools are a means to obtain the complex structures
present within dietary fiber while retaining “classical”
determinations such as soluble and insoluble fiber. These efforts
will provide an analytical framework to connect gravimetric fiber
determinations with their constituent structures to better inform
gut microbiome and clinical nutrition studies.