Human Colonic Bacterial Degradability of Dietary Fibres from Sea-Lettuce (Ulva sp)*

Human Colonic Bacterial Degradability of Dietary Fibres from Sea-Lettuce (Ulva sp)*

Human Colonic Bacterial Degradability of Dietary Fibres from Sea-Lettuce (Ulva sp)*

Abstract

Sea-lettuce (Ulva sp) is one of the commonly consumed seaweeds which
contains 16É5% of water-soluble and 13É3% insoluble dietary Ðbres. Since
physiological e†ects of Ðbres are partly related to their colonic bacteria fermentability, Ulva sp and its constitutive soluble and insoluble Ðbres were incubated
with faecal bacteria in an in vitro batch fermenter system. After 24 h of incubation, 32É0^0É4%, 25É9^0É4% and 50É9^7É4% of Ulva, soluble and insoluble Ðbres constitutive sugars, respectively, were degraded. Consequently, Ulva
and its soluble Ðbre, ulvan, are poorly fermented by colonic bacteria. The constitutive sugars, rhamnose and glucuronate and the aldobiouronate b-Dglucuronosyluronate-(1,4)-L-rhamnose of the glucuronoxylorhamnan sulphate
present in the soluble Ðbre 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 Ðbres from sealettuce could be expected to act mainly as bulking agents with little e†ect on
nutrient metabolism due to colonic bacterial fermentation products (short-chain
fatty acids).

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