Dose dependency of fermentation and the extent of renal excretion of palatinit (isomalt) in rats with respect to its energy value

Abstract

The impact of dose-dependent caloric salvage by microbial fermentation processes in the lower gut and the extent of renal excretion for the overall energetic availability of the alternative bulk sweetener Palatinit were investigated in rats. To evaluate the extent of dose-dependent fermentation a conventional and a germ-free rat model were used and fecal excretions of Palatinit after intragastric application were compared. Because of the lack of bacterial colonization in the gastrointestinal tract in germ-free rat the difference in fecal excretion of Palatinit between germ-free and conventional rat is mainly due to bacterial fermentation. To determine the amount of renal excretion of Palatinit the urine was collected. The experiments were conducted using different amounts of Palatinit (300 and 1,200 mg/kg body weight = mg/kg b.w.). Fecal excretions of Palatinit and its monomers (sorbitol and mannitol) were measured by high-performance liquid chromatography (HPLC) and for the determination of renal excretions a gas chromatography system was used. After the application of 300 mg/kg b.w. Palatinit only the breakdown product sorbitol could be recovered in the feces of germ-free rats (29% of the applied dose). No intact Palatinit could be found. In contrast, neither Palatinit nor the breakdown products sorbitol or mannitol could be detected in the feces of conventional rats after application of the same dose. After the application of the higher dose only small amounts of intact Palatinit were found in the feces of germ-free rats (average 12%). There was no intact measurable Palatinit in the feces of conventional rats. The fecal excretions of sorbitol and mannitol in the feces of the germ-free rats were 55% and 39%; in conventional rats only 21% sorbitol was excreted. Only traces of Palatinit, sorbitol or mannitol were found in the urine of conventional and germ-free rats after application of the low as well as the high dose. In conclusion, this study clearly shows the dose dependency of fermentation and therefore the dose dependency of the energetic (i.e., caloric) availability of this disaccharide sugar alcohol. In the calculation of the energy value of Palatinit the renal excretion of Palatinit and its monomers can be neglected.