In vitro fecal microbiota modulation properties of pectin and xyloglucan from hazelnut (Corylus avellana L.) skin, an industrial byproduct, and their incorporation into biscuit formula

The aim of this study was to extract water-soluble dietary fibers (WSDF_skin), pectin (PEC_skin), and xyloglucan (XG_skin) from hazelnut skin and to determine their impacts on colonic microbiota and metabolic function. WSDF_skin, PEC_skin, and XG_skin were extracted by water, acid, and alkali treatments, respectively. Monosaccharide analysis revealed WSDF_skin and PEC_skin were dominated by uronic acids, while the XG_skin was found to contain xyloglucan- and pectin-associated sugars. In vitro fecal fermentation analysis showed that WSDF_skin, PEC_skin, and XG_skin are fermented to different microbial short-chain fatty acid profiles by identical microbiota. 16S rRNA sequencing demonstrated that PEC_skin promoted Faecalibacterium prausnitzii and Lachnospiraceae related operational taxonomic units (OTUs), which are recognized as beneficial members of the human gut, whereas WSDF_skin and XG_skin stimulated Bacteroides OTUs. Interestingly, increased abundances of F. prausnitzii and Lachnospiraceae OTUs in PEC_skin were higher than those in commercially available pectin. Finally, PEC_skin and XG_skin were tested in a biscuit model and the results showed that either PEC_skin or XG_skin can be incorporated into biscuit formulations without impacting physical, textural, and sensory properties of the final product. Overall, our results demonstrated that hazelnut skin, an industrial byproduct, can be utilized for the production of functional dietary fibers, especially pectin, to improve colonic health.