Milled wheat bran contains substantial amounts of residual starchy endosperm that may interfere with the analyses that are used to determine a bran's composition and physicochemical properties. In addition, it is possible that during extrusion cooking, this residual starchy endosperm may undergo certain chemical modifications that may affect composition, physicochemical properties, and functionality of wheat bran. Therefore, the objectives of the present study were: (1) to develop a method that removes most of the residual starchy endosperm still adherent to milled wheat bran, (2) to investigate the effects of particle size of non-washed and washed wheat bran coupled with extrusion processing conditions on total dietary fiber, insoluble dietary fiber, and soluble dietary fiber contents of non-washed and washed bran, (3) to investigate the effects of extrusion cooking variables on the physicochemical properties of extruded wheat bran, and (4) to evaluate the effects of treated wheat bran on the baking properties of bread and cookies. The washing method developed in the present study reduced starch adherent to milled wheat bran by 76% (w/w), changed insoluble dietary fiber content in the bran from 39% to 69% (w/w), and decreased soluble fiber content from 4.93% in NWB to 1.68% (w/w). The water binding capacity was higher for washed bran and was not affected by bran particle size. To investigate the effects of particle size coupled with extrusion processing conditions, non-washed bran (NWB), ground to pass through 1000 μm (NWB1000) and 425 μm (NWB425) screens, and washed bran (WB), ground to pass through 1000 μm (WB1000) and 425 μm (WB425) screens, were extruded through a co-rotating and inter-meshing twin-screw extruder under conditions of varying screw configurations (low and high shear), feed moisture (25 and 35%), screw speed (100 and 400 rpm), and die temperature (100 and 150oC). Extrusion increased soluble dietary fiber in both NWB1000 and NWB425 but decreased insoluble dietary fiber. Certain extrusion conditions increased or decreased the contents of insoluble and soluble fiber in WB425. The insoluble dietary fiber contents were lower in extrudates made from WB1000 than in non-extruded WB1000. Extrusion conditions increased or decreased soluble dietary fiber in WB1000. The effects of extrusion processing on the physicochemical properties of wheat bran samples were studied. Extrusion increased the water binding capacity (WBC) of NWB samples. Washing and extrusion decreased weight average molecular weight of soluble dietary fibers extracted from NWB and WB samples. Differential Scanning Calorimetry results indicated that thermal decomposition properties of extrudates made from NWB and WB samples were not affected by extrusion. In vitro binding of bile acids was highest in extrudates made from WB1000, whereas the lowest binding of bile acids was in extrudates made from NWB425. Baking studies indicated that bread formulations containing wheat bran resulted in breads with decreased loaf volumes. Substituting soft wheat flour with 5% or 15% of the prepared bran samples significantly decreased cookie spread. The contents of insoluble dietary fiber in the crumb and crusts of breads baked from hard wheat flour and hard wheat flour substituted with bran were higher than those in the unbaked flours. The contents of soluble dietary fiber were not significantly different from each other in the crumb and crusts of breads baked from flour samples substituted with bran.
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