Seaweeds as a source of non-digestible complex polysaccharide components for the development of novel prebiotic ingredients for the functional food industry

Abstract

This thesis used in vitro batch culture fermentation models to investigate the fermentability and prebiotic potential of the brown seaweeds Fucus vesiculosus and Laminaria digitata, and the red seaweed Palmaria palmata. Fermentation substrates included each whole seaweed (a food matrix) and a polysaccharide-rich extract from each seaweed (a mixture of dietary fibre components). Purified seaweed polysaccharides (alginate, fucoidan and laminarin from brown seaweeds; ulvan from green seaweeds; and xylan from red seaweeds) were also evaluated as fermentation substrates to understand the effect of individual seaweed dietary fibre components on gut microbiota composition and metabolic activity. Cellulose and Synergy 1 were used as negative and positive controls, respectively. Analysis was conducted on bacterial composition (qPCR, and 16S rRNA amplicon sequencing) and bacterial metabolic activity (GC-MS to quantify short chain fatty acid (SCFA) concentration). Fermentation in the presence of the whole seaweed powders of Fucus vesiculosus and Laminaria digitata resulted in significantly higher concentrations of SCFA when compared cellulose (total SCFA: cellulose = 7214.85 µM; FVWS = 15501.80 µM; LDWS = 23465.80 µM; p < 0.05). The whole brown seaweed powders and polysaccharide extracts stimulated glycan degrading bacterial families such as Bacteroidaceae, Ruminococcaceae and Lachnospiraceae when compared to cellulose. After 24 hrs fermentation, purified alginate polysaccharides yielded significantly higher concentrations of propionic acid (cellulose = 280.64 µM; Alginate-Fv = 725.26 µM; Alginate-Lj = 613.40 µM; p < 0.05) and butyric acid (cellulose = 549.43 µM; Alginate-Fv = 944.45 µM; Alginate-Lj = 864.27 µM; p <0.05), respectively. While fermentation in the presence of laminarin also yielded significantly higher concentrations of propionic acid after 24 hrs (cellulose = 280.64µM; Laminarin-Ld = 933.57 µM; p < 0.05). Alginate and laminarin substrates also stimulated populations of Bacteroides and Lachnospiraceae, respectively, when compared to cellulose. Fermentation in the presence of the Palmaria palmata whole seaweed powder and purified xylan resulted in significantly higher concentrations of SCFA when compared to cellulose (total SCFA: cellulose = 1162.1 µM; Xylan-Pp = 4781.92 µM; p < 0.05), whereas the polysaccharide extract did not. Fermentation in the presence of the Palmaria palmata whole seaweed powder, polysaccharide-rich extract, and purified xylan elicited a bifidogenic effect. Future in vivo investigations regarding the effect of seaweed polysaccharides on the gut microbiota and host health should investigate the effects of purified alginate, laminarin and xylan, and their respective oligosaccharides. Cost-effective methods to obtain these potential food ingredients are needed.

Date of Award	Jul 2020
Original language	English
Sponsors	Department for Employment and Learning, Northern Ireland & Department of Agriculture, Food and the Marine, Ireland
Supervisor	Emeir Mc Sorley (Supervisor), Chris Gill (Supervisor) & Philip Allsopp (Supervisor)