Keisuke Matsumoto

Recent progress on research and applications of non-digestible galacto-oligosaccharides

Galacto-oligosaccharides (GOS) are non-digestible carbohydrates, which are resistant to gastrointestinal digestive enzymes, but are fermented by specific colonic bacteria. After the discovery of bifidogenic activity of GOS and the development of an industrial production process by transgalactosidase activity of β-galactosidases, GOS have been extensively studied for their physiological roles on the intestinal flora and functions. GOS are selectively utilized by bifidobacteria in vitro, and show a bifidogenic effect at a daily intake of more than 2.5 g in human studies, whereas at least 5 g are needed to have effects on stool frequency. It is suggested that the products of fermentation of GOS in the colon, mainly short chain fatty acids, have a role in the improvement of the colonic environment, energy supply to the colonic epithelium, and calcium and magnesium absorption. These physiological effects in conjunction with the physicochemical characteristics of GOS enable GOS to be promising prebiotic food ingredients applicable to a variety of designed foods.

Effect of dietary deoxycholic acid and cholesterol on fecal steroid concentration and its impact on the colonic crypt cell proliferation in azoxymethane-treated rats.

To elucidate the role of fecal steroids in the malignant tumor formation of colonic epithelial cells, we examined the effects of dietary deoxycholic acid (DCA) and cholesterol (CHL) on fecal steroid concentrations and their impact on colonic crypt cell proliferation. Twenty 5-week-old male Fischer 344 rats were provided with either a control semisynthetic diet or the same diet supplemented with 0.15% DCA and 1% CHL (steroid diet) over a 5-week period. The effects of these two diets were compared among rats that were either injected with azoxymethane (AOM), a known gastrointestinal carcinogen, or saline. In a 2 x 2 factorial design, rats fed each of these diets were given two weekly subcutaneous injections of either AOM (15 mg/kg b.w.) or saline at 6 and 7 weeks of age. At 9 weeks of age, fecal samples were obtained for analysis of bile acids, CHL and its bacterial metabolites of intestinal microflora. At 10 weeks of age, animals were sacrificed and colonic proliferation was assessed as vincristine-accumulated mitotic figures per crypt. Rats fed the steroid diet had significantly elevated fecal bile acid (5x, P < 0.001) and neutral steroid (10x, P < 0.01) levels when compared to those fed the control diet. AOM treatment did not appear to influence these levels. However, rats injected with AOM had a significant increase (P < 0.001) in their rate of colonic cell proliferation as compared to saline-injected control animals on both diets. Furthermore, rats fed the steroid diet had a significantly higher (P < 0.001) cell proliferation rate than animals fed the control diet. The effects of AOM treatment and the steroid diet on cell proliferation were additive. Our results demonstrate that high concentrations of neutral and acid steroids in the colonic lumen can enhance carcinogen-induced elevated cell proliferation and thus may play a key role in the etiology of colon cancer.

Inhibitory effect of microfibril wheat bran on azoxymethane-induced colon carcinogenesis in CF1 mice.

Microfibril wheat bran (MFW), a processed dietary fiber prepared by milling of coarse wheat bran (WB), is softer and has a more pleasant taste than WB. In this study, we examined the inhibitory effect of MFW on azoxymethane (AOM)-induced colon carcinogenesis in female CF1 mice and compared its effect with that of WB and cellulose (CL). The mice were fed a modified AIN 76 A diet supplemented with either MFW, WB, or CL at a final concentration of 20% (w/w). Six weekly s.c. injections of AOM (10 mg/kg body weight) were administered per mouse commencing 1 week after the start of the feeding period. Control mice were injected with saline only. Thirty-three weeks after the initial injection, the mice were sacrificed, examined for tumors, and the cecal contents were analyzed to determine the moisture content and the concentrations of short-chain fatty acids (SCFA). The average number of total tumors per mouse in the MFW (2.9 +/- 0.6, P = 0.017) and WB (5.3 +/- 1.3, P = 0.373) diet groups was lower than that of the CL diet group (7.5 +/- 1.3), though there was no significant difference in tumor incidence (94.7%, 90.0% and 94.7%, respectively) between the groups. More than 90% of the tumors in each group were adenocarcinomas. The incidence of adenoma and that of carcinoma in situ in the MFW diet group (5.3% and 0%, respectively) were also lower than those in the CL diet group (26.3 and 26.3%, respectively; P = 0.180 and P = 0.046, respectively). Analysis of the cecal contents revealed a significantly higher moisture content and significantly higher concentrations of SCFA, butyrate in particular, in the MFW and WB diet groups. The results of this study indicate that the source and texture of dietary fiber can influence tumor development in CF1 mice, and more specifically that MFW is a promising and useful dietary supplement with properties serving to protect against the development of colon cancer.

Comparison of the water-holding capacity of wheat bran products prepared by wet and dry smashing methods in vitro and effect on the gastrointestinal retention time in rats in vivo.

Microfibril wheat bran (MFW) prepared by wet smashing of wheat bran using a colloidal mill has the advantages of being more palatable than other wheat bran and easier to apply to various foods. In this study, we investigated water-holding capacity (WHC) and physiological effects of a novel food material, MFW, focusing on shortening of the retention time of the gastrointestinal contents compared to those of dry smashing of wheat bran (DWB) prepared by conventional method, and wheat bran (WB), which is the raw materials. The mean particle size of MFW was 35 microns, and WHC was 5.1 g/g. In contrast, those of DWB were 61 microns and 3.0 g/g, respectively. Those of WB were 420 microns and 5.0 g/g, respectively. The WHC of MFW was 1.7 times greater than that of DWB and comparable to that of WB. The dietary fiber content in MFW, DWB, and WB were 73.5, 66.9 and 70.2%, respectively. Six-week-old Fisher rats were divided into three groups, and fed for 20 days with AIN-76 chow supplemented with MFW, DWB, or WB to a dietary fiber content of 10%. On days 14-16 of the experimental period, the mean retention time (MRT) of gastrointestinal content and fecal weight were measured using solid phase and liquid phase markers. On day 20 of the experimental period, animals were killed, and the water content, pH, composition of short chain fatty acids (SCFAs) in the cecal content and total amounts of SCFAs in the cecum were investigated. MRT in the MFW group was 15.2 +/- 0.8 h in the solid phase, which was significantly shorter than that in the DWB group (18.0 +/- 0.9 h) (p < 0.05), and comparable to that in the WB (15.5 +/- 2.4 h). MRT in the liquid phase was almost the same as that in the solid phase: 14.7 +/- 1.0, 18.4 +/- 0.8, and 16.0 +/- 2.5 h in the MFW, DWB, and WB groups, respectively. The fecal weight, pH, the concentration of SCFA in the cecal content and total amounts of SCFAs in the cecum did not differ among the groups, but the cecal water content was in the order of MFW > WB > DWB, showing a significant difference between each group (p < 0.05). The above finding suggested that MFW is a novel food material with a greater WHC and the ability of shortening the retention time of the gastrointestinal contents compared to DWB.