TAUROCHOLIC ACID ADSORPTION DURING NONSTARCH POLYSACCHARIDE FERMENTATION - AN IN-VITRO STUDY

The association of radiolabelled taurocholic acid with the solid fract ion of a faecal fermentation mixture was measured. A human faecal inoc ulum was incubated with [24-C-14]taurocholic acid and several nonstarc h polysaccharide sources (pectin, wheat bran, ispaghula (Plantago ovat a) husk acid seed), glucose or a substrate-free control. Portions of f ermentation mixture were taken at 0, 3, 6, 21 and 24 h and centrifuged to acquire a supernatant fraction and a pellet containing the ferment ation residue. C-14 was measured in supernatant fractions and pellets at all time points. Volatile fatty acids (VFA) were measured at 0 and 24 h to confirm bacterial growth. Radioactivity in the pellet increase d over time for all substrates. Glucose resulted in the greatest incor poration of taurocholic acid into the pellet, followed by pectin. At 2 4 h the proportion of the total radioactivity found in the pellet was 92% for glucose, 79% for pectin, 60% for wheat bran, 59% for ispaghula seed, 53% for ispaghula husk and 26% for the control (mean of duplica tes). Glucose and pectin produced the greatest quantity of VFA at 24 h . VFA production was highly correlated with radioactivity in the pelle t (r0.976, P < 0.005). These results suggest that the bile acid bindin g capacity of a faecal culture mixture may be strongly influenced by t he fermentability of the available substrate and hence related to bact erial metabolic activity.