VERY ACIDIC FERMENTATIONS IN THE RAT CECUM DURING ADAPTATION TO A DIET RICH IN AMYLASE-RESISTANT STARCH (CRUDE POTATO STARCH)

The effects of very acidic fermentation on the production of organic acid by the cecal microflora has been investigated in rats fed a 40% crude potato starch (CPS) diet. The rats were adapted first to a fiber-free diet for 8 days before receiving the CPS diet. The diet elicited a dramatic enlargement of the cecum, especially during the first 5 days' adaptation, along with an almost immediate drop of cecal pH down to about 5. Lactic fermentations developed during the first days' adaptations (up to 120 mmol/L D + L-lactate), then lactate concentrations progressively declined whereas volatile fatty acids (VFA) concentrations rose. VFA concentrations also exhibited an evolution, with low butyrate fermentations up to 15 days' adaptation, then a rise of butyrate to values higher than those of propionate. Even during the period of maximal lactic fermentations, lactic acid absorption was relatively limited since its efficiency was about 5-8 fold lower than that of VFA. The CPS diet led to very high concentrations of calcium (up to 80 mmol/L) and phosphate in cecal contents. The activity of ornithine decarboxylase (ODC) increased rapidly at the beginning of adaptation to the CPS diet and reached a very high value after 30 days' adaptation. Thus, it appears that diets rich in CPS may elicit various types of fermentation profile during the period of adaptation to the diet, which is particularly long. These fermentations elicit a sustained hyperactivity of ODC in the cecal mucosa.