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Utilization and Excretion of a New Sweetener, Fructooligosaccharide (Neosugar), in Rats

Department of Nutrition, Faculty of Medicine, University of Tokyo, Hongo, Bunkyo, Tokyo, Japan 113

In order to study the digestibility of the fructooligosaccharide "Neosugar," [U-¹⁴C]Neosugar or [U-¹⁴C]sucrose was orally administered to germfree, conventional and antibiotic-treated rats and the radioactivities of expired ¹⁴CO₂, urine and feces were determined 24 h later. More than 50% of the Neosugar was expired as CO₂ in conventional rats. This was the same as for sucrose, but the time course was delayed by about 2 h. In germfree rats, no ¹⁴CO₂ was released for the first 8 h, and ¹⁴CO₂ released after 8 h probably reflected bacterial colonization of the gut. The radioactivity of the urine was about 3–4% in all groups, but that of the feces from germfree rats was about eight times higher than the level in conventional rats. When [U-¹⁴C]Neosugar was anaerobically incubated with the cecal contents of conventional rats, more than 10% of the added Neosugar was metabolized to CO₂, about 66% to volatile fatty acids and about 7% to microbes. More than 58% of 1-¹⁴C-volatile fatty acids such as acetic acid, propionic acid or butyric acid injected directly into the cecum of conventional rats was excreted as CO₂ within 24 h. These results indicate that Neosugar given orally to rats is metabolized mainly to volatile fatty acids and CO₂ by intestinal microorganisms, and the volatile fatty acids produced are absorbed and further converted to CO₂ in the body. Thus, the data indicate that Neosugar is partially utilized as an energy source.

KEY WORDS: • sweetener • fructooligosaccharide • Neosugar • conventional rats • germfree rats • microorganism • volatile fatty acids

¹ Present address: Bioscience Laboratories, Meiji Seika Kaisha Ltd., 5-3-1, Chiyoda, Sakado-shi, Saitama 350-02.

² Present address: The Research Foundation for Sugar Metabolism, K. I. Building #1001, 2-2-14, Hamamatsu-cho, Minato, Tokyo 105.

Manuscript received 22 June 1988. Revision accepted 6 January 1989.