Influence of long-term feeding of different purified dietary fibers on the volatile fatty acid (VFA) profile, pH and fiber-degrading activity of the cecal contents in rats

The aim of this study was to investigate the effect of four weeks ingestion of 10% fiber diets (cellulose, lignocellulose, pectin or guar gum) and fiber free diets on volatile fatty acid (VFA) concentration, pH, and in vitro fiber-degrading activity of the cecal contents of female Sprague Dawley rats. The pH was significantly lower (p<0.05) on guar gum (6.1) and pectin (6.4) than on the other diets (7.2–7.6). The cecal concentration of VFAs was similar among groups, ranging from 62.5±12 for cellulose to 93.8±12 μg/g for pectin. Guar gum produced significantly more propionic acid than all the other groups, with a relative acetic-propionic-butyric-other acids ratio of 53-29-9-9, compared with 57-22-13-8 for pectin, 50-20-12-18 for cellulose, 51-21-15-13 for lignocellulose and 61-19-9-11 for fiber free. The in vitro fermentation showed a marked increase in guar (+210%) and pectin (+90%) fermentability when incubated with inocula from adapted rats, supporting the hypothesis of a change in the in vivo metabolic activity of the fecal microflora after long term feeding of these fibers.