Effects of alginate and laminaran on the microbiota and antioxidant properties of human faecal cultures

Alginate and laminaran are water soluble dietary fibres in brown algae.In a previous study,pure cultures of Bacteroides xylanisolvens,Bacteroides uniformis,and Erysipelaclostridium ramosum increased antioxidant capacities in the broth with alginate and/or laminaran fermentation.This study was conducted to evaluate the presence of the alginate-and laminaran-responsive human gut indigenous bacteria(RIB)and their functions.Briefly,human stool samples were cultured in media without(control),or with 1%(w/v)alginate or laminaran at 37℃ for 24 h under anaerobic conditions.Results showed that during incubation,the pH of the culture reduced with the polysaccharides.Phenol production was clearly suppressed via laminaran supplementation in the faecal sample cultures.The 16S rRNA(V4)gene amplicon sequencing confirmed that B.xylanisolvens-,B.uniformis and E.ramosum-like bacteria were alginate-and/or laminaran-RIB in human gut,although their read numbers differed among individuals.Additionally,some butyrate-producers,such as Faecalibacterium and Roseburia,were also detected as the RIB in alginate and laminaran cultures,respectively.Fermentation increased 1,1-diphenyl-2-picrylhydrazyl and superoxide anion radical-scavenging capacities and the Fe-reducing power of the culture medium.Additionally,the fermented cultures increased the nitric oxide secretion in macrophage like RAW 264.7 cells culture.These results suggest that the interaction of alginate and laminaran with their RIB may have desirable effects on the host as next generation prebiotics when brown algae are ingested.