Seaweed (Saccharina latissima) modulates the microbiome composition during fecal fermentation with limited effect of common processing methods

Seaweed fibers show promising effects on gut health, but it is unclear if processing of whole seaweed changes the nutrient accessibility for gut microbiota. This study investigated the effects of processed Saccharina latissima on the fecal microbiome composition and metabolic activity. Seaweed was blanched, oven-dried or fermented by Lactiplantibacillus plantarum , and subjected to static simulated digestion (INFOGEST 2.0) and in vitro fecal fermentation. Seaweed-supplemented media changed the microbiome composition, increasing the relative abundances of Bacteroides, Escherichia/Shigella and the Lachnospiraceae family, while Bifidobacteria decreased, compared to the high-fiber control. Meanwhile, alpha and beta diversity were similar between processing methods, indicating limited effects of processing on the microbiome. SCFA concentrations were higher in seaweed media than in the high-fiber control, but were not significantly different from the low-fiber control. Overall, seaweed changed the microbiome composition with minimal impact of processing. Further studies could explore alternative processing methods and co-formulations to improve seaweed fermentability.