Algal oligosaccharides as functional foods: In vitro study of their cellular and fermentative effects

Algal polysaccharides are indigestible and exhibit unusual biochemical and fermentative characteristics from which stem interesting biological effects such as antitumoral, immunostimulating and/or prebiotic effects. In this s tudy, we aimed to determine whether oligosaccharides obtained from alginate s and laminarans also have such biological activities and can thus be consi dered as functional foods. The chemical structures of the oligosaccharides were determined using NMR. Both the fermentation and the effects on microbi al populations of oligo-alginates and oligo-laminarans were investigated us ing batch incubations with, and continuous culture of, human faecal bacteri a. The kinetic and intensity of fermentation were measured by continuous mo nitoring of gas production and determination of final pH value, respectivel y. Effects on intestinal flora activity and composition were determined via metabolite quantification and main bacterial genera enumeration. Cytotoxic , proliferative and differentiating effects were estimated after exposure o f epithelial (Caco-2), monocytic (THP1) and lymphocytic T (Jurkat) cell lin es. Despite very different biochemical structures, the two oligo-alginates exhibited similar fermentation patterns. As with native alginates, they req uired adaptation prior to their metabolism. However, this adaptation did no t result in any change in the global bacterial composition. No noticeable b iological effect was detected for oligo-alginates, In contrast to native la minarans, oligo-laminarans did not require adaptation prior to their fermen tation. Propionate production was stimulated but no significant modificatio n of the balance between the main bacterial genera was observed during cont inuous culture of human fecal flora. Oligo-laminarans exhibited slightly in hibitory effects on Caco-2 cells, inhibited mononuclear cell proliferation and stimulated the expression of ICAM-1 by monocytic cells. This last prope rty appears promising, and may allow algal oligosides to be used as functio nal foods and/or components.