The objective of this study was to investigate the effect of wheat bran concentrations on the mechanical properties determining the texture of extruded carbohydrate matrices. For this wheat flour was extruded under different conditions with an increasing concentration of wheat bran. The mechanical properties were assessed with a three-point bending test, the relative density and the cellular structure was determined by micro-computed X-ray tomography and the phases distribution were assessed by light microscopy. Regardless of the bran concentration, the stress at rupture of the extruded foams was positively correlated with their relative density according to the Gibson-Ashby model. At same relative densities and bran concentration, finer structures with higher density of small cells led to a higher mechanical strength of the foams. Expanded foams with added bran at an intermediate level showed increased mechanical strength. This was attributed to the finer cellular structures obtained. The effect of increasing the bran to a higher concentration on the mechanical properties was depending on the cell wall thickness and bran particle dimensions. At high relative density, the strength of the foams was further increased due to the even finer structures obtained. At low relative density, even though finer structures were also obtained, the stress at rupture of the foams was decreased. This may be explained by the lower cell wall thicknesses and low adhesion properties between bran and starch favouring rupture of the cell walls.
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