Breakdown of Mucin and Plant Polysaccharides in the Human Colon

To obtain an estimate of the extent to which complex carbohydrates are degraded by bacteria in the human colon, aqueous extracts of colon contents from four human subjects were separated into high and low molecular weight fractions by chromatography on a Sephadex G-100 column. The composition of these fractions was compared with the composition of similar fractions from ileal contents, i.e., from material entering the colon. In all four subjects, high molecular weight carbohydrate concentrations were lower in the colon than in the ileum, indicating that breakdown of complex carbohydrate occurs in the colon. The high molecular weight carbohydrate fraction contained sugars characteristic of plant polysaccharides (arabinose, xylose, mannose, rhamnose) as well as sugars characteristic of mucin (fucose, hexosamines, sialic acids). Concentrations of most of these sugars were uniformly lower in the colon than in the ileum. Since high molecular weight protein concentrations were lower in the colon than in the ileum of two of the four subjects tested, some degradation of protein may also occur in the colon.