New insights in the hydration properties of wheat bran as function of particle size were gained based on a novel water retention capacity test. Upon milling coarse bran with an average particle size of 1687 μm down to 77 μm, the specific surface increases by twofold, structural integrity was lost and water extractable arabinoxylan and damaged starch content were practically unaffected. A standard centrifugation-based water retention capacity, swelling capacity and Enslin-Neff absorption test showed up to threefold higher water absorption for large particles. During these hydration tests, bran is not (continuously) subjected to external forces which allows larger particles to hold more water in between bran particles and probably in micropores. In contrast, the water retention capacity as determined by a novel drainage centrifugation method, and Farinograph absorption were not affected by particle size. In these methods, continuous exposure of bran to external forces causes bran to retain only strongly bound water which is most likely bound in cell wall nanopores and through hydrogen bonding. These insights reconcile contradicting observations in literature with regard to this matter.
Keywords: Capillaries; Hydration; Hydrogen bonds; Micropores; Nanopores; Stacking water; Wheat bran matrix.
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