Rheological properties of bread flour at elevated temperatures
Abstract
Improvement of processes to produce cereal products requires a detailed understanding of the materials' rheological properties at the same conditions as the process. Even though rheological properties of dough have been studied in detail, little research has been performed to characterize rheological properties of dough at elevated temperatures. Heating starch-containing products, in the presence of water induces starch gelatinization, causing significant changes in rheological properties. The overall objective of this work was to measure rheological properties in shear and extension for dough at elevated temperatures while accounting for material changes due to starch gelatinization to develop a rheological constitutive model for use in modeling cereal processes. Changes in rheological properties of dough during heating were measured using small and large strain rheometry, capillary extrusion and planar extensional testing. Four moisture contents ranging from 38% to 48% (wet basis) were studied at temperatures ranging from 25°C to 90°C. Using superpositioning techniques, a relaxation time master curve describing the transient rheological properties of dough was developed from the results obtained with small strain rheometry. The results of shear and extensional tests indicate properties of dough differ greatly when measured in shear versus extension. Shear stresses of dough increased with increasing extents of gelatinization, while extensional stresses decreased with increasing extents of gelatinization. Results indicate the shear properties are indicative of the physical interactions between the gluten and starch components of the dough, while extensional deformations measure the properties of the gluten network only. A modified form of Lodge's rubberlike rheological constitutive model was used to model the rheological properties of dough with moisture contents of 38% to 48% at 25°C and 38% moisture at elevated temperatures. The constitutive model was developed from transient shear tests and its ability to predict steady shear and planar extensional properties of dough was tested. The model was found to successfully predict both steady shear and extensional properties. Parameters for the damping function were found to be dependent on moisture content for samples with 38% to 44% moisture content. The damping function parameters for samples with 38% moisture at elevated temperatures illustrated no dependency on temperature.
Degree
Ph.D.
Advisors
Okos, Purdue University.
Subject Area
Food science
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