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The rheological properties of acid hydrolyzed corn stover at high solids concentration (20-35 wt.%) were investigated using torque rheometry. These materials are yield stress fluids whose rheological properties can be well represented by the Bingham model. Yield stresses increase with increasing solids concentration and decrease with increasing hydrolysis reaction temperature, acid concentration, and rheometer temperature. Plastic viscosities increase with increasing solids concentration and tend to decrease with increasing reaction temperature and acid concentration. The solids concentration dependence of the yield stress is consistent with that reported for other fibrous systems. The changes in yield stress with reaction conditions are consistent with observed changes in particle size. This study illustrates that torque rheometry can be used effectively to measure rheological properties of concentrated biomass.

The aim of this work was to elucidate the underlying physical mechanism(s) by which bran influences whole grain dough properties by monitoring the state of water and gluten secondary structure in wheat flour and bran doughs containing 35–50% moisture and 0–10% added bran. The system was studied with attenuated total reflectance (ATR) FTIR spectroscopy. Comparison of the OH stretch band of water in flour dough with that in H2O‐D2O mixtures having the same water content revealed the formation of two distinct water populations in flour dough corresponding to IR absorption frequencies at 3,600 and 3,200 cm–1. The band intensity at 3,200 cm–1, which is related to water bound to the dough matrix, decreased and shifted to lower frequencies with increasing moisture content of the dough. Addition of bran to the dough caused redistribution of water in the flour and bran dough system, as evidenced by shifts in OH stretch frequency in the 3,200 cm–1 region to higher frequencies and a reduction in monomeric water (free water). This water redistribution affected the secondary structure of gluten in the dough, as evidenced by changes in the second‐derivative ATR‐FTIR difference spectra in the amide I region. Bran addition caused an increase in β‐sheet content and a decrease in β‐turn (β‐spiral) content. However, this bran‐induced transconformational change in gluten was more significant in the 2137 flour dough than in Overley flour dough. This study revealed that when bran is added to flour dough, water redistribution among dough components promotes partial dehydration of gluten and collapse of β‐spirals into β‐sheet structures. This transconformational change may be the physical basis for the poor quality of bread containing added bran.

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ABSTRACT:The flow and mixing in a 3D geometrically accurate representation of a twin sigma blade mixer is simulated using the finite element method (FEM) combined with the mesh superimposition technique as implemented by Polyflow (Fluent, Inc.) to calculate the velocity, velocity gradients, shear rates, and mixing index. The mixing conditions and material models are based on those used in the laser-Doppler anemometry (LDA) experiments of Prakash and Kokini. The simulation results are analyzed to determine the effect of increasing shear thinning on the flow and mixing, and are also compared with the experimental results of Prakash and Kokini for the This is publication no. NJAES D10544-3-05 of the New Jersey Agricultural Experiment Station.