The bioactive potential of red seaweed oligosaccharides obtained using autohydrolysis: Correlation between extract composition and prebiotic activity

This study evaluated, for the first time, the prebiotic-like potential of glucooligosaccharides and galactooligosaccharides derived from five red seaweeds, produced using autohydrolysis. The non-purified oligosaccharide-rich extracts were characterized in terms of composition, glycosidic linkages, and molecular weight profiles. They were then evaluated for cytotoxicity (using a co-culture of Caco-2 and HT29-MTX cells), as well as for their ability to serve as the carbon source for the growth of pure probiotics and modulate gut microbiota in vitro (fecal fermentation using five healthy donors). Despite their structural differences, all oligosaccharide-rich extracts promoted the growth of pure probiotic strains, with the extract obtained from agar-extraction residue enhancing Lactobacillus acidophilus growth more effectively than inulin (used as a prebiotic reference for benchmarking purposes). When subjected to fecal fermentation, beta diversity metrics confirmed that a Gracilaria extract with a low (<1%) sulfation degree and constituted of 44.56 ± 0.84 mol% glucose, 34.66 ± 2.45 mol% galactose, 10.99 ± 1.24 mol% 6-anhydro-L-galactose, 5.73 ± 0.86 mol% 6-methyl-galactose, and residues of mannose and xylose, linked by (1 → 4)-Glc p (~31%), (1 → 4)-Gal p (~26%), (1 → 3)-Gal p (~15%) , terminal Gal p (~9%), terminal Glc p (~5%), and (1 → 4)-AnGal p (~1%), significantly modulated the human gut microbiota, showing effects comparable to those of inulin, and supporting increased production of short-chain fatty acids. These findings highlight the potential of red seaweed-derived oligosaccharide fractions as safe functional ingredients with potential relevance for human gut health.