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 35mum, and WHC was 5.1 g/g. In contrast, those of DWB were 61 mum and 3.0 g/g, respectively. Those of WB were 420 mum 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.