Content of short-chain fatty acids in the hindgut of rats fed processed bean (Phaseolus vulgaris) flours varying in distribution and content of indigestible carbohydrates

Red kidney beans (Phaseolus vulgaris) processed to differ in distribution and content of indigestible carbohydrates were used to study hindgut fermentability and production of short-chain fatty acids (SCFA). Bean flours with low or high content of resistant starch (RS), mainly raw and physically-inaccessible starch, were obtained by milling the beans before or after boiling. Flours containing retrograded starch and with a high or low content of oligosaccharides were prepared by autoclaving followed by freeze-drying with or without the boiling water. Six diets were prepared from these flours yielding a total concentration of indigestible carbohydrates of 90 or 120 g/kg (dry weight basis). The total fermentability of the indigestible carbohydrates was high with all diets (80-87 %). Raw and physically-inaccessible starch was more readily fermented than retrograded starch (97-99 % v. 86-95 %; P<0.05). Non-starch glucans were fermented to a lesser extent than RS, but the fermentability was higher (P<0.05) in the case of autoclaved (50-54 %) than boiled beans (37-41 %). The distribution between acetic, propionic and butyric acid in the caecum was similar for all diets, with a comparatively high percentage of butyric acid (approximately 18). However, with diets containing the high amounts of RS, the butyric acid concentration was significantly higher in the distal colon than in the proximal colon (P=0.009 and P>=0.047 for the high- and low-level diets respectively), whereas it remained constant, or decreased along the colon in the case of the other diets. Furthermore, the two diets richest in RS also promoted the highest percentages of butyric acid in the distal colon (24 and 17 v. 12 and 12-16 for the high- and low-level diets respectively).