Immune and gut microbiota responses to structurally distinct pomelo pectins and their enzymatic derivatives

This study extends our previous studies of pomelo pectins by investigating their immunomodulatory effects in relation to their molecular and microbial characteristics. Six structurally distinct pectins were evaluated for cytotoxicity, nitric oxide (NO), and cytokine responses in LPS-stimulated RAW264.7 macrophages. Citric acid-assisted subcritical-water-extracted pectin (CA-SWP) and EDTA-2Na-assisted hot-water-extracted pectin (E-HWP), selected for their contrasting molecular and fermentation characteristics, were further enzymatically modified and evaluated for morphology, particle size, rheology, and in vitro fecal fermentation. All pectins were non-cytotoxic and differentially modulated inflammatory responses. At 400 μg/mL, they reduced LPS-induced NO production by 53–67%, whereas TNF-α, IL-6, and IL-10 responses varied among fractions. Enzymatic modification altered pectin morphology and rheological properties, while fermentation revealed substrate-dependent enrichment of Bacteroides, Prevotella, and Faecalibacterium and reductions in Escherichia–Shigella and Fusobacterium. These in vitro findings reveal distinct immunomodulatory responses and associations between pectin molecular characteristics and biological activities, warranting further in vivo investigation.