In Vitro Bile Acid Binding Capacity of Wheat Bran Extruded at Five Specific Mechanical Energy Levels

Cereal Chem. 83(2):157-160 The in vitro binding of bile acids of extruded wheat bran (EWB) at five specific mechanical energy (SME) levels of 120 (EWB-120), 177 (EWB177), 234 (EWB-234), 291 (EWB-291), and 358 (EWB-358) Wh/kg on a dry weight basis, was determined using a mixture of bile acids secreted in human bile at a duodenal physiological pH 6.3. Experiments were conducted using six treatments and two blank incubations to test Unextruded and extruded wheat bran samples on an equal dry matter (DM) basis. Relative to cholestyramine (bile acid binding, cholesterol-lowering drug), in vitro bile acid binding ability of unextruded and extruded wheat bran treatments on an equal DM basis was 14-23%. The bile acid binding ability of the total dietary fiber (TDF) was 28-51% and insoluble dietary fiber (JDF) was 29-53%. Bile acid binding on DM, TDF, and IDF bases for EWB-177 was significantly (P !^ 0.05) higher, and EWB-358 was significantly lower than UWB, EWB-l20, EWB-234, and EWB-291. Bile acid binding for EWB-120 was significantly higher than that for UWB, EWB-234, and EWB-291. These results demonstrate the relative health promoting potential of EWB-177 > EWB-120 > UWB = WB-234 = EWB-291 >EWB-358 as indicated by bile acid binding ability on DM, TDF, and 11)F bases. The variability in bile acid binding of wheat bran treatments may be due to fragmenting of particles or macromolecules, creating new linkages in proteins, starches, and nonstarch polysaccharides, changes in physical and chemical characteristics, and binding sites. World wheat production is z585 million metric tons per year, resulting in l40 million metric tons of wheat bran. Health benefits associated with the consumption of wheat bran include fecal bulking and improved regularity (Marlett et at 2002). Extrusion processing is used in the production of many popular foods including ready-to-eat cereals, snacks, and pasta. The extrudates have physical and chemical characteristics different from those of the original food (Harper and Clark 1979; Linko and Mercier 1981). These differences depend on the extrusion parameters (e.g., energy input, residence time, and the type of extruder used) and the chemical composition (e.g., moisture, fat, and fiber content) of the raw material. Extrusion cooking modifies the starch, protein, fat, and fiber components of the raw material used by forming physical and chemical complexes in the extrudate that may have cholesterol-lowering properties. Extruded wheat bran and other foods have lowered blood cholesterol in humans (Meshcheriakova et at 1995). Extruded wheat bran (EWB) at low specific mechanical energy (SME) of 221 Whlkg, significantly lowered cholesterol in hamsters compared with unextruded wheat bran (UWB), whereas, wheat bran extruded at high energy (442 Wh/kg) resulted in cholesterol values similar to those of unextruded and low energy (221 Whlkg) extruded wheat bran (Kahlon et at 1998). Bile acids are acidic steroids synthesized in the liver from cholesterol. After conjugation with glycine or taurine, they are secreted into the duodenum. Bile acids are actively reabsorbed by the terminal ileum and undergo an enterohepatic circulation (Hofmann 1977). Binding of bile acids and increasing fecal excretion has been hypothesized as a possible mechanism for lowering cholesterol by dietary fiber (Trowell 1975; Lund et al 1989; Anderson and Siesel 1990). By binding bile acids, cereal fibers prevent reabsorption and stimulate plasma and liver cholesterol conversion to additional bile acids (Eastwood and Hamilton 1968; Balmer and Zilversmit 1974; Kritchevsky and Story 1974). Toxic metabolites in the gut and secondary bile acids increase the risk of colorectal cancer Western Regional Research Center, USDA, Agricultural Research Service. 800 Buchanan Street, Albany, CA 94710. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. 2 Corresponding author, Phone: 510-559-5665. Fax: 510-559-5777. E-mail: