In vitro utilization of barley husk by human gut microbiota depends on husk composition and particle size.

Particle size had no significant effect on overall SCFA production except for butyrate, which was significantly higher after fermentation of the coarsest particles at 48 hours.

• Barley husk samples were milled to four particle sizes with D[4,3] ranging from 20 to 1085 µm.
• Butyrate production was specifically elevated for the coarsest particle fraction at the 48-hour fermentation timepoint.
• No significant effect of particle size was observed on total SCFA production.
• Samples were pre-digested with the INFOGEST protocol before in vitro fermentation.

Barley husk samples with higher starch content produced higher levels of SCFAs during in vitro fermentation.

• Two different barley husk samples with two different levels of starch were used.
• Higher starch content was associated with greater total SCFA production.
• Starch content was identified as a key compositional driver of fermentation outcomes.
• Fermentation was conducted with a human fecal inoculum pooled from five healthy adult volunteers.

Reduction of particle size increased phenolic acid bioaccessibility, particularly for ferulic and coumaric acid, during in vitro digestion and fermentation.

• Smaller particle sizes led to greater release of ferulic and coumaric acid.
• Enhanced phenolic acid release was observed both during in vitro digestion (INFOGEST protocol) and during in vitro fermentation.
• Barley husk is described as rich in phenolic acids including ferulic and coumaric acid.
• Both particle size and composition were evaluated for their effects on phenolic acid bioaccessibility.

Starch content, rather than particle size, drove microbial community variation at 48 hours of fermentation as determined by PERMANOVA analysis.

• Gut microbiota composition was determined using 16S rRNA gene amplicon sequencing.
• PERMANOVA analysis was used to assess drivers of microbial variation.
• The effect of starch content on microbial composition was significant at the 48-hour timepoint.
• Particle size did not emerge as a significant driver of microbial community composition.
• Fecal inoculum was prepared by pooling donations from five healthy adult volunteers.

Barley husk is a cereal by-product rich in dietary fibers and phenolic acids that was evaluated for its potential as a food ingredient with health benefits.

• Barley husk samples with two different levels of starch were studied.
• Each starch level was milled to produce four samples with D[4,3] particle sizes ranging from 20 to 1085 µm.
• Outcomes evaluated included fiber fermentability, phenolic acid release, fecal microbiota composition, and microbiota activity.
• The study used both composition and physical structure manipulation to assess their respective roles.