HUMAN COLONIC BACTERIAL DEGRADABILITY OF DIETARY-FIBERS FROM SEA-LETTUCE (ULVA SP)

Sea-lettuce (Ulva sp) is one of the commonly consumed seaweeds which c ontains 16.5% of water-soluble and 13.3% insoluble dietary fibres. Sin ce physiological effects of fibres are partly related to their colonic bacteria fermentability, Ulua sp and its constitutive soluble and ins oluble fibres were incubated with faecal bacteria in an in vitro batch fermenter system. After 24 h of incubation, 32.0 +/- 0.4%, 25.9 +/- 0 .4% and 50.9 +/- 7.4% of Ulva, soluble and insoluble fibres constituti ve sugars, respectively, were degraded. Consequently, Ulva and its sol uble fibre, ulvan, are poorly fermented by colonic bacteria The consti tutive sugars, rhamnose and glucuronate and the aldobiouronate beta-D- glucuronosyluronate-(1,4)-L-rhamnose of the glucuronoxylorhamnan sulph ate present in the soluble fibre are highly fermented. Chemical desulp hation and/or carboxyl group reduction did not modify this fermentatio n behaviour. Thus, the particular chemical structure of ulvan is respo nsible for the resistance of this polysaccharide and of Ulva to coloni c bacterial fermentation. As a physiological consequence of this parti cular behaviour, consumption of dietary fibres from sea-lettuce could be expected to act mainly as bullring agents with little effect on nut rient metabolism due to colonic bacterial fermentation products (short -chain fatty acids).