James F. Steffe

Rheological behavior of undeveloped and developed wheat dough

ABSTRACT Undeveloped wheat dough is essentially wheat flour that has become fully hydrated without being deformed. The rheological properties of this material were compared to dough (developed dough) made using the standard method involving a farinograph. Flow behavior of undeveloped and developed dough samples made from hard and soft wheat flours were tested using creep tests, frequency sweep oscillatory tests, and temperature sweep oscillatory tests. All experiments showed that the undeveloped dough requires less resistance for deformation than developed dough. The differences are due to the energy input received by the developed dough and the influence of this factor in forming the protein matrix associated with developed dough. To attain a comparable state as the dough made in the farinograph, an energy input must be applied to the undeveloped dough material. Understanding the differences between undeveloped and developed dough may lead to new products, equipment, and processes in the bakery industry.

Relationship Between Rheological Properties and Microstructural Characteristics of Nondeveloped, Partially Developed, and Developed Doughs

ABSTRACT Farinography and mixography are two commonly used procedures for evaluating dough properties. These procedures, however, cannot separate hydration and energy input during dough development, both of which are critically important for understanding fundamental rheological properties of dough. A rheometer and laser scanning confocal microscopy (LSCM) were used to study the relationship between rheological properties and microstructural characteristics of developed (by farinograph with both shear and extensional deformations), of partially developed (by rheometer with either shear or extensional deformation), and of nondeveloped (no deformation) dough samples of wheat flours. Rheological data revealed that developed dough had the highest G* (most elastic or strong), followed by doughs partially developed with extensional deformation, and then shear deformation, and finally by nondeveloped dough. The LSCM z-sectioning (scanning of different layers of the sample) and the analysis of amount of protein m...

Effects of Transglutaminase Enzyme on Fundamental Rheological Properties of Sound and Bug-Damaged Wheat Flour Doughs

ABSTRACT Transglutaminase (TG) catalyzes the formation of nondisulfide covalent crosslinks between peptide-bound glutaminyl residues and e-amino groups of lysine residues in proteins. Crosslinks among wheat gluten proteins by TG are of particular interest because of their high glutamine content. Depolymerization of wheat gluten proteins by proteolytic enzymes associated with bug damage causes rapid deterioration of dough properties and bread quality. The aim of the present study was to investigate the possibility of using TG to regain gluten strength adversely affected by wheat bug proteases. A heavily bug-damaged (Eurygaster spp.) wheat flour was blended with sound cv. Augusta or cv. Sharpshooter flours. Dynamic rheological measurements, involving a frequency sweep at a fixed shear stress, were performed after 0, 30, and 60 min of incubation on doughs made from sound or blended flour samples. The complex moduli (G* values) of Augusta and Sharpshooter doughs blended with 10% bug-damaged flour decreased si...

Average Shear Rates in the Rapid Visco Analyser (RVA) Mixing System

ABSTRACT The principle of mixer viscometry was utilized to determine the average shear rate in the mixing system (impeller-cup combination) of the Rapid Visco Analyser (RVA). A relationship between the impeller Reynolds number and the power number was established with Newtonian standards. Using the matching viscosity technique and non-Newtonian fluids consisting of various aqueous solutions of guar gum and methylcellulose, the average value of the mixer viscometer constant (k′) was 20.1/rev over speeds of 1.0–3.5 rev/sec (60–210 rpm). Hence, the average shear rate in the RVA can be estimated as 20.1 multiplied by the angular velocity given in revolutions per second. Results show the RVA system has very good potential for characterizing the rheological properties of various non-Newtonian fluid foods.

Flow profiles in a tube rheometer using magnetic resonance imaging

The velocity profiles of non-Newtonian fluids have been measured in a tube rheometer using magnetic resonance imaging (MRI). This experimental method of flow visualization is a non-invasive and non-destructive means to characterize flow behavior. The fluids examined in this paper are carboxymethylcellulose solution (CMC) and tomato juice. The velocity profiles obtained experimentally for the CMC solution by MRI were in good agreement with the analytical predictions. Velocity profiles obtained by imaging for tomato juice showed much greater dispersion of velocity than expected in the laminar flow regime

Biochemical Studies of Proteins in Nondeveloped, Partially Developed, and Developed Doughs

ABSTRACT Nondeveloped, partially developed with shear and extensional deformations, and developed doughs represent different stages of dough development. To understand the relationship between gluten proteins and dough rheology, this study used disulfide-sulfhydryl analyses, gel filtration chromatography, SDS-PAGE, acid polyacrylamide gel electrophoresis (A-PAGE), and densitometry to examine proteins in the four types of doughs mentioned. Free sulfhydryl content was the lowest in native flour and nondeveloped dough, and the highest in partially developed doughs, while a reverse trend was observed for disulfide content. For each flour sample, the protein elution profile from gel filtration chromatography shifted with the level of dough development. With respect to the smallest sized molecules, native flour had the most, followed by nondeveloped, partially developed, and then developed doughs. SDS-PAGE and A-PAGE exhibited similar protein patterns among the same chromatographed protein fractions of each nat...

Characterization of the swelling of starch doughs during extrusion

Abstract A simple but practical model has been presented for assessing the die swell of extruded food doughs for a given process history and in the absence of puffing, as a function of die geometry, shear rate and dough rheology. Since there are no simple yet effective models which account for these different phenomena, a phenomenological approach was adopted by combining parts of several models to achieve the objective of the study. The method offers two important advantages to die swell analysis. First, all predictions are made solely on the basis of die geometry, die temperature, pressure drop across the die, and dough rheological properties, thereby correlating die swell pressure to key operating conditions. Secondly, it provides a basis for developing die swell criteria that may be useful for incorporation in process control algorithms.

Statistical method to evaluate the critical Reynolds number for pseudoplastic fluids in tubes

Abstract An experimental, non-intrusive tube system with appropriate instrumentation for measuring pressure drop and mass flow rate was developed to investigate the departure from laminar flow of pseudoplastic fluids (aqueous solutions of sodium carboxymethylcellulose). A critical Reynolds number was selected to correspond to the intersection of the two lines joining the laminar and turbulent flow data on the pressure drop versus Reynolds number plots. The standard deviation of pressure drop increased at these critical points. Results also indicated large spikes at these points in the plots of variance ratio of pressure drop versus the critical Reynolds number. This phenomenon could form the statistical basis for establishing the departure from laminar flow. In the laminar region, standard deviations were low, suggesting calm, stable flow of the fluids, a well known characteristic of laminar flow.

Vibration induced settling of a sphere in a Herschel-Bulkley fluid

Abstract Settling of spheres suspended in a Herschel-Bulkley fluid with a yield stress under the influence of vibrations is of great practical significance while transporting liquid food systems such as soups, sauces and jams. A dimensionless equation has been developed to predict the settling time of a sphere in a Herschel-Bulkley fluid subjected to sinusoidal vibration. The model was used to determine the effect of random vibrations as induced in a shipping environment. A separation criterion has been developed to determine whether a particle will settle. Methods described in this paper can also be used to characterize non-Newtonian fluids.

Some observations on the use of slit rheometry for characterizing the primary normal stress difference of extrudates

Abstract Experimental evidence is presented to demonstrate that the standard procedure of linearly extrapolating pressure profiles through the exit of slit rheometers as a means of characterizing extrudate elastic properties is inappropriate. This widely used procedure, based on the assumption that the pressure gradient is constant over the entire instrument, is erroneous because the flow does not remain fully developed through the exit of the rheometer.