Correlation between water-holding capacity of different types of cellulose in vitro and gastrointestinal retention time in vivo of rats

Rats were assigned to a fibre-free basal diet or one of three indigestible and poorly fermentable food components (cellulose powder, microfibril cellulose prepared from cellulose by milling, and plastic particles) incorporated in the basal diet at a level of 7%. The mean retention time (MRT) of the indigestible food components in the whole gut were measured with solid and liquid markers. Further, caecal weight and content of organic acids as well as faecal moisture were determined. The weight of the caecal digesta in the rats fed the basal diet was lower than that in rats fed a diet incorporated with indigestible food components. The faecal moisture differed between the different groups and decreased in the following order: microfibril cellulose, cellulose, and plastic particles; ie the same order as for the settling volume in water. The MRTs of the solid phase in microfibril cellulose (MFC), cellulose (CEL), plastic particles (PLS) and fibre-free basal (BD) groups were 9.4, 11.1, 13.6 and 17.8 h respectively. The MRTs of the liquids in the MFC, CEL, PLS and BD groups were 12.9, 15.0, 14.2 and 13.9 h, respectively. Thus, there was an inverse relationship (r = 0.74, P < 0.01) between the MRT of the solid phase and the settling volume, whereas the MRT of the liquid phase was not significantly affected by the diets. Any effect on the concentration of organic acid and the pH of the caecal contents could not be detected with any of the diets. Although the significance of the differences in the total amount of organic acids produced in the caecum between diets could not be detected, the relationship between (r = 0.61, P < 0.01) the amount of organic acids and the settling volume was found. These results suggest that the settling volume in water, which closely parallels the water-holding capacity of indigestible food components, affected the gastrointestinal retention time of solid phase of digesta in different types of cellulose.