Human colonic bacterial degradability of dietary fibres from sea-lettuce (Ulva sp)
1997
Bobin-Dubigeon, C. | Lahaye, M. | Barry, J.L.
Sea-lettuce (Ulva sp) is one of the commonly consumed seaweeds which contains 16.5% of water-soluble and 13.3% insoluble dietary fibres. Since physiological effects of fibres are partly related to their colonic bacteria fermentability, Ulva sp and its constitutive soluble and insoluble 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 constitutive sugars, respectively, were degraded. Consequently, Ulva and its soluble fibre, ulvan, are poorly fermented by colonic bacteria. The constitutive sugars, rhamnose and glucuronate and the aldobiouronate beta-D-glucuronosyluronate-(1,4)-L-rhamnose of the glucuronoxylorhamnan sulphate present in the soluble fibre are highly fermented. Chemical desulphation and/or carboxyl group reduction did not modify this fermentation behaviour. Thus, the particular chemical structure of ulvan is responsible for the resistance of this polysaccharide and of Ulva to colonic bacterial fermentation. As a physiological consequence of this particular behaviour, consumption of dietary fibres from sea-lettuce could be expected to act mainly as bulking agents with little effect on nutrient metabolism due to colonic bacterial fermentation products (short-chain fatty acids).
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