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The effect of lactulose, pectin, arabinogalactan and cellulose on the production of organic acids and metabolism of ammonia by intestinal bacteria in a faecal incubation system

Published online by Cambridge University Press:  09 March 2007

A. J. Vince ,
N. I. Mcneil ,
J. D. Wager  and
O. M. Wrong
A. J. Vince
Affiliation:
Department of Medicine, The Rayne Institute, University College and Middlesex School of Medicine, University Street, London WCIE 6JJ
N. I. Mcneil
Affiliation:
Department of Medicine, The Rayne Institute, University College and Middlesex School of Medicine, University Street, London WCIE 6JJ
J. D. Wager
Affiliation:
Department of Medicine, The Rayne Institute, University College and Middlesex School of Medicine, University Street, London WCIE 6JJ
O. M. Wrong
Affiliation:
Department of Medicine, The Rayne Institute, University College and Middlesex School of Medicine, University Street, London WCIE 6JJ
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Abstract

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An in vitro faecal incubation system was used to study the metabolism of complex carbohydrates by intestinal bacteria. Homogenates of human faeces were incubated anaerobically with added lactulose, pectin, the hemicellulose arabinogalactan, and cellulose, both before and after subjects had been pre-fed each carbohydrate. Fermentation of added substrate was assessed by the production of short-chain fatty acids (SCFA) and suppression of net ammonia generation over 48 h of incubation. Control faecal homogenates to which carbohydrate was not added yielded an average increment of SCFA of 43 mmol/l, equivalent to 172 mmol/kg in the original stool. The addition of lactulose, pectin and arabinogalactan each increased the yield of SCFA by a similar amount, averaging 6·5 mmol/g carbohydrate or 1·05 mol/mol hexose equivalent; organic acid yield was not increased by pre-feeding these substances for up to 2 weeks. Acetate was the major SCFA in all samples at all times and, after pre-feeding with extra carbohydrate, butyrate concentrations exceeded propionate in all samples. Faecal homogenates incubated with cellulose showed no greater SCFA production than controls over the first 48 h, but there was a slight increase when samples from two subjects pre-fed cellulose were incubated for 14 d. Net ammonia generation was markedly suppressed by addition of lactulose to faecal incubates with an initial period of net bacterial uptake of ammonia. Pectin and arabinogalactan also decreased ammonia generation, but the reductions were not significant unless subjects were pre-fed these materials; cellulose had no effect on ammonia generation.

Keywords

AmmoniaCarbohydratesFaecal incubationShort-chain fatty acids
Type
Carbohydrate Digestion by Colonic Microflora
Information
British Journal of Nutrition , Volume 63 , Issue 1 , January 1990 , pp. 17 - 26
Copyright
Copyright © The Nutrition Society 1990

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