Effects of in vitro fermentation of barley β-glucan and sugar beet pectin using human fecal inocula on cytokine expression by dendritic cells

Abstract

Scope: This study simulates the fermentation process of barley β-glucan and sugar beet pectin in the human colon and monitors the degradation products formed. Additionally, immune effects of the degradation products were investigated.

Methods and results: Immunostimulatory activity of fermentation digesta was investigated using bone marrow derived dendritic cells (BMDCs) from toll-like receptor 2/4 (TLR2/4) knockout mice, which were unresponsive to microbe-associated molecular patterns. Cytokine responses were elicited to dietary fibers and not to the SCFA and microbiota. The fermentation digesta were analyzed for their SCFA profiles and glycan metabolites over time. During fermentation the amount of insoluble precipitating fibers increased and induced as well as soluble molecules of lower molecular mass greater amounts of cytokines in BMDCs than the parental fiber. Additionally, high amounts of cytokines can be attributed to soluble galactose-rich beet pectin molecules.

Conclusions: The fermentation of the two fibers led to fiber-specific amounts of SCFA, glycosidic metabolites, and different immunomodulatory properties. BMDC from TLR2/4 knockout mice did not respond to the digest microbiota and SCFA, making it a useful approach to study temporal effects of fermentation on the immunomodulatory effects of fibers.

Keywords: Batch fermentation; Dendritic cells; Digesta; Human fecal inocula; Immunomodulation.