Evaluation of the potential prebiotic effect of Himanthalia elongata, an Atlantic brown seaweed, in an in vitro model of the human distal colon

Until now, although different studies have shown the potential prebiotic effect of seaweed carbohydrates, no studies with the whole seaweeds have been carried out. In addition, the prebiotic effect throughput sequencing remains poorly investigated since most of the published works used qPCR or FISH to estimate bacterial changes. In this work, an in vitro model of the human distal colon was used to determine, for the first time, the potential prebiotic effect of a brown whole seaweed Himanthalia elongata. The whole seaweed was characterized in basis of its nutritional and mineral composition and submitted to the entire gastrointestinal digestion. The prebiotic effect was evaluated by the microbial modulation through 16S rRNA amplicon sequencing , qPC R and short-chain fatty acid analysis. The obtained results indicated that the colonic fraction of H. elongata was used selectively by the Bacteroides genus, more specifically by the specie Bacteoides ovatus, whereas inulin was used mainly by the Parabacteroides genus, being Parabacteroides distasonis the most abundant identified specie. Selective use of inulin by P. distasonis is, therefore, reported by the first time. qPCR analysis shown no significative differences in Bifidobacterium population and a decrease in Lactobacillus along the fermentation assays with both substrates. Regarding to the short-fatty acid production, maximal concentration, 56.11 +/- 20.48 mM, was achieved for H. elongata, at 24 h of fermentation whereas for inulin total acid production was 93.66 +/- 21.82 mM at 48 h of assay. The metabolic pathways associated with bacterial genera were not significantly different between the two tested substrates. Although more studies are necessa r y to elucidate the prebiotic character of H. elongata, the results presented in this work are promissor y and could open new opportunities of research and application in the area of Nutrition and Food Chemistry.