Lactic acid bacteria fermentation of porphyran: Compositional transformation and generation of immunomodulatory postbiotics

Abstract

Porphyran, a sulfated polysaccharide derived from Porphyra, has recently been recognized as a fermentable substrate for selected enteric lactic acid bacteria (LAB). However, the compositional transformations induced by LAB fermentation and the immunological properties of the resulting fermentates remain insufficiently characterized. In this study, we investigated the compositional change and immunomodulatory activities of porphyranderived fermentates produced by Ligilactobacillus murinus A5 and Limosilactobacillus reuteri A9. LAB fermentation led to significant increases in reducing sugar content and sulfate group exposure, indicating polysaccharide depolymerization and enhanced accessibility of functional moieties. Concurrently, notable changes in monosaccharide composition and molecular weight distribution were observed. Fourier-transform infrared spectroscopy (FT-IR) analysis revealed the presence of organic acid-related functional groups and confirmed the retention of sulfate groups. Notably, distinct substitution patterns were observed between the two LAB strains, suggesting strain-specific compositional transformations. In vitro assays demonstrated that both fermentates significantly attenuated the production of pro-inflammatory cytokines in LPS-stimulated RAW264.7 macrophages and bone marrow-derived mononuclear cells (BMMCs). In vivo, oral administration of the fermentates in a murine delayedtype hypersensitivity (DTH) model markedly reduced cutaneous inflammation and macrophage infiltration at the antigen-challenge site. Collectively, these findings demonstrate that LAB-mediated bioconversion of porphyran generates fermentates with significant immunomodulatory effects. This study highlights a promising strategy for marine polysaccharide valorization and supports the potential use of porphyran-derived fermentates as postbiotic agents for immunomodulation.