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<p>As a major part of the dietary fiber classification, plant polysaccharides often have
chemically complex structures which may differ by genera and species, and perhaps even by
genotype and growing environment. Arabinoxylans from cereal cell walls are known to
differently impact human gut microbiota composition and fermentation metabolites due to
variability in chemical structure, though specificities of structure to these functions are not
known at the level of genotype ́ environment. In the first study, corn bran arabinoxylan (CAX)
extracted from 4 genotypes ́ 3 growing years at the Purdue Agronomy Farm was compared in
human fecal fermentations to test the hypotheses that, 1) CAXs extracted from brans from
different corn genotypes and grown over different years (environments) show distinct structures,
and 2) these cause differences in gut microbiota response and fermentation metabolites.
Monosaccharides and linkage analysis revealed that CAXs had different structures and the
differences were genotype-specific, but not significantly due to environment. PCA analysis
revealed that both short chain fatty acid production and the microbial community shifted also in
a genotype-specific way. Thus, small structural changes, in terms of sugar and linkage
compositions, cause significant changes in fermentation response showing very high specificity
of structure to gut microbiota function.
</p>
<p>Insoluble fermentable cell wall matrix fibers have been shown to support beneficial
butyrogenic Clostridia, but have restricted use in food products due to their insoluble character.</p></div></div>
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<p>In the second study, a soluble fiber matrix was developed that exhibited a similar fermentation
effect as fermentable insoluble fiber matrices. Low arabinose/xylose ratio CAX was extracted
with two concentrations of sodium hydroxide to give soluble polymers with relatively low and
high residual ferulic acid (CAX-LFA and CAX-HFA). After laccase treatment to make diferulate
crosslinks, soluble matrices were formed with average size of 3.5 to 4.5 mer. In vitro human
fecal fermentation of CAX-LFA, CAX-HFA, soluble crosslinked ~3.5 mer CAX-LFA (SCCAX-
LFA), and ~4.5 mer SCCAX-HFA revealed that the SCCAX matrices had slower fermentation
property and higher butyrate proportion in SCCAX-HFA. 16S rRNA gene sequencing showed
that SCCAX-HFA promoted OTUs associated with butyrate production including Unassigned
Ruminococcaceae, Unassigned Blautia, Fecalibacterium prausnitzii, and Unassigned
Clostridium. This is the first work showing the fabrication of soluble crosslinked fiber matrices
that favors growth of butyrogenic bacteria.
</p>
<p>Moreover, these same SCCAXs exhibited an interesting gel forming property on simple pH
reduction, which is similar in gelling property to low acyl gellan gum, though is differently
readily soluble in water. Both of the SCCAXs formed gels at pH 2, with SCCAX-HFA forming
the stronger gel. Gels showed shear-thinning behavior and a thermal and pH reversible property.
A gel forming mechanism was proposed involving noncovalent crosslinking including hydrogen
bonds and hydrophobic interaction among the SCCAX complexes. This mechanism was
supported by structural characterization of SCCAX complexes using a Zeta-sizer and FT-IR
spectroscopy. SCCAX-HFA could be used in low sugar gels and has the above property of
promoting butyrogenic bacteria in the gut.
</p>
<p>In conclusion, gut microbiota responds differentially to CAXs with various fine structures. This
probably due to dietary fiber-gut microbiota relationships have been evolved over time to be highly specific. Forming soluble fiber matrices could be a good strategy to promote butyrogenic
bacteria and improve gut health, in a readily usable form in beverages.</p></div></div></div>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8014988 |
| Date | 25 June 2020 |
| Creators | Xiaowei Zhang (5930483) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/DIFFERENTIAL_GUT_MICROBIOTA_AND_FERMENTATION_METABOLITE_RESPONSE_TO_CORN_BRAN_ARABINOXYLANS_IN_DIFFERENT_CHEMICAL_AND_PHYSICAL_FORMS/8014988 |
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