VISCOELASTIC PROPERTIES OF WHEAT FLOUR DOUGHS: VARIATION OF DYNAMIC MODULI WITH WATER AND PROTEIN CONTENT1

The elastic and loss moduli of fiue types of wheat flour doughs were measured in an eccentric rotating disc (ERD) rheometer. G’ and G”, determined from the linear portions of the response curve, were very sensitive to water content, decreasing as water content increased. Differentiation among samples was greatest at the highest water content. Results also depended on protein level, with higher moduli being observed at higher protein level. Samples mixed in a Farino-graph to constant consistency showed differing values of both storage and loss moduli. The ERD geometry thus appears suited to characterization of doughs and to study of component interactions in such systems.     

DETECTION OF PEA FLOUR IN FLOUR OF CHICKPEA BY LACTATE POLYACRYLAMIDE GEL ELECTROPHORESIS1

Polyacrylamide gel electrophoresis was applied to detect adulteration of chickpea flour with pea flour by the presence of extra bands in the unique electro-phoregram of chickpea. Protein extracts prepared by a single extraction with 5M acetic acid produced patterns which were used to differentiate pea and chickpea samples. Using the described procedure, 10 varieties of chickpea did not show intervarietal variation in their electrophoregrams, whereas 11 varieties of pea showed intervarietal differences in their protein composition. However, six of the 25–30 protein bands present in electrophoregrams of most pea varieties can be used as markers for detection of pea flour in chickpea flour. Band 37, present both in chickpea and pea samples, can be used as an internal reference for inter gel comparisons.     

APPLICATION OF A VISCOMETRIC METHOD TO THE STUDY OF WHEAT FLOUR DOUGHS*

The cone and plate viscosimeter was found applicable to studying the effect of experimental variables on the behaviour of flour doughs. A simple method of analysis based on the use of a power law is proposed. The variables studied were: type of flour, water content, mixing time, temperature and the presence of certain chemical compounds. Based on the results obtained, hypotheses were advanced on the importance of non-covalent bonds in influencing the rheological properties of doughs.     

EFFECT OF GUM ARABIC ON THE RHEOLOGY OF CORN FLOUR DOUGHS AND FRIED PRODUCT QUALITY

Small deformation stress relaxation studies were performed on corn flour dough at 48–62%, wet basis moisture and 0–2% gum Arabic contents. Corn doughs were sensitive to moisture contents that were reflected by the values of the elastic and viscous components. The instrumental stickiness of the dough increased markedly when the moisture content was increased. The stress decay curves were modeled by using 3-element spring-dashpot models as evidenced by low values of root mean square error. Sensory assessment of the dough as well as fried products were conducted to relate the parameters obtained from stress relaxation studies.     

EFFECT OF HEATING RATE ON VISCOSITY OF WHEAT FLOUR DOUGHS1

Doughs were sheared at a constant rate and heated in a cone-and-plate viscometer. As the temperature increased, the apparent viscosity first decreased, passed a minimum, and then increased rapidly presumably due to the swelling of starch granules. If the dough was heated more rapidly, the viscosity had its minimum value at a higher temperature. This is explained by the swelling of starch granules being a rate process. The present experiments explain why in previous work with heating prior to shearing, the minima in the viscosity versus temperature curves were found at unexpectedly low temperatures. The temperature at which in a standard amylograph experiment the viscosity begins to rise is a fairly good estimate of the temperature at which viscosity has its minimum value during baking. The agreement is due to compensating effects of the rate of heating and of the starch concentration.     

EXTENSIONAL FLOW STUDIES ON WHEAT FLOUR DOUGHS WITH DIFFERENT PROTEIN CONTENT1

Uniaxial compression technique was used to relate the rheological behavior of dough to wheat quality for bread. Dough of nine flours of the cultivar Rayon, grown in three different regions of Sonora, Mexico, and with a protein content from 10% to 12.8%, were studied using the lubricated squeezing‐flow test connected to a texturometer. Wheat flour quality determinations were protein, moisture and ash content, dry gluten, falling number, and sedimentation volume. Traditional dough rheological evaluations were made with the farinograph and alveograph. The baking test was also done. The extensional viscosity was measured at three crosshead speeds (0.2, 0.5, and 1.0 mm/min). Extensional viscosity, measured at the lowest speed, significantly (P < 0.05) and negatively correlated with protein content (r = ‐0.63) and bread volume (r = ‐0.72). The rheological behavior of wheat doughs during lubricated uniaxial compression showed dependence on the strain rate as demonstrated by the patterns of the extensional viscosity curves.     

THE EFFECT OF TEMPERATURE ON SOME RHEOLOGICAL PROPERTIES OF WHEAT FLOUR DOUGHS

Abstract. Doughs from three flours were sheared between a cone and plate at constant rates in the range 6 times 10^-4-2 times 10^-2 s^-1.
At temperatures between 25 and 40C, the apparent viscosity decreased with increasing temperature and with increasing rate of shear. The effects of the temperature and of the rate of shear were independent one of another, and can be described by an Arrhenius type equation and a power equation, respectively. At temperatures between 45 and 60C, the apparent viscosity increased rapidly with increasing temperature; this is ascribed to starch gelatinization. In this temperature range, the apparent viscosity decreased more rapidly with increasing rate of shear than at lower temperatures.
At temperatures between 25 and 45C, the shear modulus decreased with increasing temperature and slightly increased with increasing rate of shear. From the former fact it is concluded that the elasticity of dough has an origin different from rubber elasticity. In this temperature range, the shear modulus can be described by an equation similar to that for the apparent viscosity. At temperatures between 45 and 65C, the modulus increased with increasing temperature, though to a lesser extent than the apparent viscosity.
Changes in the rate of stress relaxation are in accordance with the effects of temperature and rate of shear on the apparent viscosity and the modulus.     

TEXTUROMETER AS A TOOL FOR STUDYING VARIETAL DIFFERENCES IN WHEAT FLOUR DOUGHS AND GLUTEN PROTEINS

The General Food's Texturometer has been used for studying the differences in wheat flour doughs prepared from 11 Indian wheat varieties of known gluten composition. The quantities of residue proteins in these varieties and the ratios of residue proteins over gliadins and glutenins were found to show high positive correlation with texturometer hardness and areas of first and second peaks. Adhesiveness was found to show high negative correlations. Of the gluten proteins only glutenins showed varietal differences i.e., the hardness and the areas of the first and the second peaks were found to increase from weak to strong varieties. The gliadins and the residue proteins of the varieties studied were found to be similar. Only gliadins were found to have adhesive character.     

UNIAXIAL COMPRESSIBILITY OF BLACKGRAM DOUGHS BLENDED WITH CEREAL FLOURS

The uniaxial compression characteristics of papad dough (moisture content 62%, dry basis), made from blackgram flour as well as after incorporation of different types of cereal (rice, sorghum and wheat) flours at different levels (20 and 40%), were determined. The stress-strain data can be interrelated by a power law type equation. The sensory attributes (stickiness, firmness, elasticity and ease of flattening/rolling) were correlated with the energy for compression, deformability modulus and apparent biaxial elongational viscosity. Inelastic doughs resulted from the blackgram dough; doughs with 20% rice or wheat blends were also inelastic but sorghum samples were elastic. The deformability modulus for sorghum doughs were extremely high. The blackgram dough as well as the wheat blended doughs were the easiest doughs to roll/flatten. Blended dough consisting of wheat flour (at 20 and 40% level) or rice flour up to 20% level was suitable for making cereal-blended papad doughs.     

EFFECTS OF MIXING SOYBEAN FLOUR DOUGHS ON THEIR DYNAMIC MODULI MEASURED IN AN ORTHOGONAL RHEOMETER

An orthogonal rheometer was used to determine the dynamic loss moduli and storage moduli of defatted soybean flour doughs. Doughs of 30 to 50% moisture were prepared by mixing for 1 to 10 min in a Brabender laboratory mixing head. Both moduli decreased as dough moisture increased. Moduli increased as mixing time increased. Moduli were initially constant as percent strain increased. After 1 1/2% strain, moduli decreased with increasing strain. No effect of resting time was found.     

INSTRUMENTAL MEASUREMENT OF STICKINESS OF DOUGHS AND OTHER FOODS

Stickiness is a difficult attribute to measure. It can be defined as simply the force of adhesion when two surfaces are contacted with each other. In most food systems, the adhesion force is a combination of an adhesive force and a cohesive force. It is when the adhesive force is high and the cohesive force is low that material is perceived as being sticky. Cohesive properties can be measured by rheological techniques. To measure adhesive properties it is imperative to have a clean separation at the probe-material interface.     

SENSORY AND PHYSICAL PROPERTIES OF MUFFINS MADE WITH WAXY WHOLE WHEAT FLOUR

ABSTRACT

The quality of muffins made with different amounts (0, 15, 30, 45 and 60%) of waxy whole wheat flour (WWWF) blended with conventional whole wheat flour were characterized. High amounts of WWWF blends produced darker but acceptable crust color. WWWF formulations had a softer crumb on day 0 and day 4, but greater firmness after 16 days storage. Samples did not differ in springiness on day 0, but a slight decrease occurred in all samples, and WWWF samples were slightly less springy after 16 days. Proton (¹H) NMR showed two distinct relaxation times, indicative of water migration from the crumb of the muffin to the crust. Sensory evaluation showed high overall likability, except for muffins made with 60% WWWF. The 60% muffins had lower volume than all other formulations. Results show that 15–30% WWWF produces a softer, moister muffin, but this advantage is lost after 8–16 days storage.

PRACTICAL APPLICATIONS

This study shows that 15–30% waxy whole wheat flour blended with conventional whole wheat flour produces softer and moisture whole wheat muffins, with good consumer acceptability. Muffins with WWWF remained softer for 4–8 days, but were firmer than control after 16 days storage. Waxy whole wheat flour also adds additional fiber, so its inclusion in blends with conventional whole wheat may help in the development of higher fiber products with a softer and moister crumb.