Retrogradation of Rice Flour Gel and Dough: Plasticization Effects of Some Food Additives

Certain food additives commonly used in flour products also have a plasticization effect on product shelf life regarding retrogradation. Sucrose, sorbitol, glycerol, citric acid, and acetic acid at 25, 25, 25, 0.5, and 0.5%, respectively, were added to two different starch gel systems: slurry (high‐amylose rice flour gel) and dough (waxy rice flour dough). All plasticizers increased gelatinization temperature, decreased enthalpy (ΔH), and promoted a more homogeneous system. Sucrose had the greatest effect on gelatinization increase. Rice dough was more susceptible to plasticizers, resulting in higher moisture content and a more amorphous structure. Retrogradation was highly positively correlated with amylose content, moisture retention, ratio of protons of water/starch, and previous occurrence of retrogradation. Moisture retention was increased in plasticizer‐added samples, especially waxy rice dough. Over a longer storage period, sucrose and sorbitol showed an antiplasticization effect in waxy rice flour dough, but glycerol and acid caused higher retrogradation in high‐amylose rice flour gel.     

Physicochemical and Rheological Characterization of Wheat Flour Dough

Rheological and structural behavior of dough prepared with two Argentinean flours (FI and FII) of different dough extensibilities were studied. Flours were analyzed by composition and rheological assays. Structural properties of dough prepared at different mixing times were analyzed by scanning electron microscopy, free sulfhydryls quantification, and yield of different protein fractions, as well as their protein surface hydrophobicity. Size of high molecular weight glutelin soluble aggregates was analyzed through multistacking gel electrophoresis. Dynamic viscoelasticity of dough was also studied. Flours FI and FII presented similar physicochemical properties but different rheological properties. Structural properties of both flour components were different. Starch from FI flour generated a more viscous paste than that of FII. FI presented a higher glutenin‐to‐gliadin ratio and a higher content of free sulfhydryls than FII. The resulting dough of FI showed a high development time and was more stable than FII. FI contained a high proportion of soluble HMW glutenins and formed dough with a more depolymerized insoluble protein residue containing a lower amount of gliadin in its matrix than FII. FI also formed a more elastic and stable dough with higher development time than FII. The specific structural characteristic of FI turns this flour into suitable raw material for the preparation of different bakery products in which elasticity of dough would be an important functional property.     

Effects of Leavening Acids and Dough Temperature in Wheat Flour Tortillas

Functionality of four leavening acids (sodium aluminum phosphate [SALP], sodium aluminum sulfate [SAS], monocalcium phosphate [MCP] and sodium acid pyrophosphate [SAPP‐28]) was evaluated during processing of wheat flour tortillas. Formulas were optimized to yield opaque, large‐diameter tortillas with pH 5.9–6.1. Each leavening acid and sodium bicarbonate was first evaluated at 38°C and then evaluated in combination with fumaric acid at 34 and 38°C. Ionic and pH interactions of leavening salts adversely affected dough properties and resting time. Opacity and pH of tortillas prepared with MCP was lower than for other treatments. Higher dough temperature required more leavening acid and base to compensate for some of the loss of CO₂ incurred during dough mixing and resting at 38°C. The addition of fumaric acid decreased the amount of leavening acid, the dough‐resting time and tortilla pH, and improved storage stability. Combinations of MCP, SALP (or SAS), and fumaric acid produced dough and tortillas with good qualities. Tortillas prepared using SALP (or SAS) and fumaric acid tended to be of better quality.     

Genotypic and Environmental Effects on Color and Discoloration Potential of Barley in Food Products

Twelve genotypes of barley, including hulled and hulless proanthocyanidin‐containing and hulled proanthocyanidin‐free types, were grown in five environments (location‐year combination) to determine the relative contribution of genotype and environment on quality traits associated with discoloration potential of barley. Barley grains were abraded and milled into flour. Protein, ash, total polyphenol content, and polyphenol oxidase (PPO) activity were determined. Brightness (L*) of abraded kernels, cooked kernels, gels, and dough sheets were determined and used as indicators of discoloration potential. Genetic factors were more important in determining total polyphenol content, PPO activity, and brightness of dough sheets and as important as environmental factors for protein and ash content. Across environments, L* of dough sheets was consistently higher in proanthocyanidin‐free barley (73–76) than in proanthocyanidin‐containing barley (59–70). Total polyphenol content of abraded grains was highest in barley grown in a dry area at 0.18%, lower in high rainfall areas at 0.13%, and lowest in irrigated areas at 0.12%. Genotype (G) by environment (E) interactions were significant for all traits, except for brightness of cooked kernels. However, the effects of the G × E interactions were generally small compared with either the genetic or the environmental effect alone and primarily due to changes in magnitude rather than in rank. Stability analyses confirmed the nature of the G × E interactions.     

Isolation and Identification of a Wheat Flour Compound Causing Sticky Dough

Fractionation and reconstitution studies of a flour from 1B/1R wheat showed that the factor causing sticky dough was water soluble. In addition, these studies showed that enzymes and lipids in the flour were not responsible for producing sticky dough. Dialysis experiments showed that the active component was nondialyzable. Gel-filtration chromatography of the retentate fraction showed that the substance causing sticky dough contained both a carbohydrate and a UV-absorbing material. Treatment of the active fraction with base caused the fraction to lose its ability to cause stickiness. The UV-absorbing material and the carbohydrate fraction had to be covalently linked for the compound to be active. Gas chromatography-mass spectrometry and HPLC analysis showed that the UV-absorbing moiety was predominantly trans-ferulic acid, and the carbohydrate part was a glucose polymer. The glucose polymer was not degraded by α-amylase but was degraded by lichenase, suggesting that the glucose polymer was a mixed-linkage β-glucan.     

Thermomechanically Induced Protein Aggregation and Starch Structural Changes in Wheat Flour Dough

Various studies have been carried out on wheat flour to understand protein and starch changes when subjected to mixing and temperature constraints, but structural changes of proteins and starch at the typical moisture levels of a dough system are not fully understood. The aim of this research was to improve our understanding of (micro)structural changes at the mesoscopic level, through empirical rheology, microscopy (light and scanning electron microscopy), sequential protein extractions, and glutenin macropolymer wet weight along the mixing, heating, and cooling stages of the Mixolab assay. Studies were performed on three wheat flours with different protein contents. The rheological analysis allowed identifying the role of the proteins and the relationship between the protein content and different primary and secondary parameters obtained from the recorded curves. The progressive heating and mixing stages during the Mixolab assay resulted in a dynamic de‐ and restructuring of proteins involving interactions between the flour proteins from water soluble to SDS soluble to SDS insoluble and vice versa. The microstructure analysis with light, polarized, and scanning electron microscopy revealed the changes that proteins and starch molecules underwent during mixing, heating, and cooling. Qualitatively, the starch structural changes, swelling, and gelatinization observed by microscopic techniques showed some parallels with protein (and glutenin) content of the respective flour. Nevertheless, this tentative finding needs further confirmation by studying flour samples with large differences in glutenin content.     

1H Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) Studies of Water Mobility in Dough Systems Containing Barley Flour

This study used ¹H nuclear magnetic resonance (NMR) spin‐spin relaxation time (T₂) and differential scanning calorimetric (DSC) measurements of unfreezable water content (UFW), to assess water behavior in freshly prepared (25°C), refrigerator‐stored (4°C, one day), or freezer‐stored (–35°C, one day) doughs containing 5, 10, or 30% whole grain, air‐classified β‐glucan‐diminished, and air‐classified β‐glucan‐enriched (BGB‐E) barley flours. Three populations of water were detected by NMR, depending on moisture content of dough, namely, tightly (T₂₁, 2–5 msec), less tightly (T₂₂, 20–50 msec), and weakly (T₂₃, 100–200 msec) bound water. T₂₂ peak was always detectable, and T₂₂ peak time linearly correlated to moisture content of dough in a range of 0.7–2.0 g/g db (r = 0.99, P < 0.05). Freezer storage showed less effect on water mobility in dough compared with refrigerator storage, whereas cooking and cool storage of cooked dough significantly decreased the water mobility (P < 0.05). Adding barley flour steadily decreased the water mobility in dough, and the reduction was more significant with adding BGB‐E (P < 0.05). Immobile water content was calculated by extrapolating T₂₂ peak time versus total moisture content in dough and significantly correlated to the UFW content measured by DSC (r = 0.72, P < 0.05).     

Bread Quality Relationship with Rheological Measurements of Wheat Flour Dough

The rheological properties of wheat doughs prepared from different flour types, water contents, and mixing times for a total of 20 dough systems were studied. The results were compared with the results of standard baking tests with the same factors. Water and flour type had a significant effect on storage modulus (G′) or phase angle measured by an oscillatory test both in the linear viscoelastic region and as a function of stress, and on compressional force measured as a function of time. The correlation of maximum force of dough in compression and G′ of dough measured within the linear viscoelastic region was r = 0.80. Correlation between the compression and oscillation test improved when all measuring points of the G′ stress curve were included (r = 0.88). The baking performance of the different doughs varied greatly; loaf volumes ranged from 2.9 to 4.7 mL/g. Although the water content of the dough correlated with the rheological measurements, the correlation of G′measured in the linear viscoelastic region or maximum force from stress‐time curve during compression was poor for bread loaf volumes. Mixing time from 4.5 to 15.5 min did not affect the rheological measurements. No correlation was observed with the maximum force of compression or G′ of dough measured in the linear viscoelastic region and baking performance. Good correlation of rheological measurements of doughs and baking performance was obtained when all the data points from force‐time curve and whole stress sweep (G′ as a function of stress) were evaluated with multivariate partial least squares regression. Correlation of all data points with loaf volume was r = 0.81 and 0.72, respectively, in compression and shear oscillation.     

Rheological Properties of Fermented Rice Flour Gel

To clarify the rheological properties of fermented rice noodle (sour mifen) produced in South China, we studied the mechanical properties of gels made from fermented and nonfermented (control) rice flours using static tensile testing, two-bite testing, and dynamic viscoelastic measurement. Rheological measurement under large deformation showed that retrogradation in fermented rice gel proceeded more slowly than in nonfermented rice gel. Lower hardness and brittleness and higher cohesiveness and resilience (degree of recovery) for gels made from fermented rice flour demonstrated that the gel was less firm but more elastic and flexible. Storage moduli of both types of gel increased with time, but the starch retrogradation was suppressed for fermented rice gel. Fermented rice gel exhibited higher resilience and lower rigidity than nonfermented gel, thus the gel stability improved. The chemical analysis of both starches suggests that the partial hydrolysis of amylopectin occurred during the fermentation process.     

Dough Properties and Bread Quality of Wheat–Barley Composite Flour as Affected by β‐Glucanase

Barley is rich in nutritionally positive compounds, but the quality of bread made of wheat–barley composite flours is impaired when a high percentage of barley is used in the mixture. A number of enzymes have been reported to be useful additives in breadmaking. However, the effect of β‐glucanase on breadmaking has scarcely been investigated. In this paper, the influence of different levels (0.02, 0.04, 0.06, and 0.08%, based on composite flour) of β‐glucanase (100,000 U/g) on the properties of dough and bread from 70% wheat, 30% barley composite flour were studied. Although dough development time, dough stability, and protein weakening value decreased after β‐glucanase addition, dough properties such as softness and elasticity as well as bread microstructure were improved compared with the control dough. β‐Glucanase also significantly improved the volume, texture, and shelf life of wheat–barley composite breads. The use of an optimal enzyme concentration (0.04%) increased specific volume (57.5%) and springiness (21%), and it reduced crumb firmness (74%) and staling rate. Bread with added β‐glucanase had a better taste, softness, and overall acceptability of sensory characteristics compared with the control bread. Moreover, the quality of wheat–barley composite bread after addition of 0.04% β‐glucanase was nearly equal to the quality of pure wheat bread. These results indicate that dough rheological characteristics and bread quality of wheat–barley composite flour can be improved by adding a distinct level of β‐glucanase.     

Wheat Flour Exposed to Ethanol Yields Dough with Unexpected Properties

Exposure of wheat flour to ethanol solutions followed by slow drying of the ethanol in situ alters the subsequent transformation of the flour into dough. Several types of wheat flour were exposed to small amounts of ethanol solutions so as to be “wetted” but without the appearance of a separate liquid phase. The wet sample was then dried in air. Dough was formed from the treated flour, and its rheological parameters were assessed, including time to peak strength (mixograph and farinograph) and gluten index (glutomatic). Untreated and treated flour and the dough prepared therefrom were assayed using 1D SDS‐PAGE (reducing and unreducing conditions), capillary zone electrophoresis (CZE) applied to 70% leachates with and without sonication, and differential scanning calorimetry. Both gluten index and time to peak increased as a result of the treatment, and the increase was greater for flour or enriched vital gluten with an initially low gluten index than for flour with a relatively high initial index. Endosperm fragmentation following milling of the treated flour was improved by the treatment. Thermal transitions were at lower temperatures following treatment, indicating less structural order and reduced thermal stability. No compositional differences were evident when studied with robust analytical methods. CZE of leached samples (no sonication) revealed lower amounts of accessible or detected proteins following treatment. Conformational changes and new secondary interactions, therefore, appear to cause the effect.     

Effects of Ferulic Acid and Transglutaminase on Hard Wheat Flour Dough and Bread

The effects of ferulic acid and transglutaminase (TG) on the properties of wheat flour dough and bread were investigated. Ferulic acid and TG were blended with hard wheat flour at levels of 250 and 2,000 ppm of flour weight, respectively. The addition of ferulic acid reduced the mixing time and mixing tolerance. The addition of TG did not obviously affect the mixing properties. Significant effects of ferulic acid plus TG on the rested dough texture were observed for overmixed dough. The maximum resistance (Rmax) of the dough was significantly reduced with the addition of ferulic acid but increased with the addition of TG. The addition of TG with ferulic acid restored the Rmax reduced by ferulic acid alone. The proportion of SDS‐soluble high molecular weight proteins in the dough increased with the addition of ferulic acid and decreased with TG, when assessed with size‐exclusion HPLC fractionation. Although the addition of TG improved the handling properties of the dough made sticky with added ferulic acid, it did not improve the quality of the bread with added ferulic acid as measured by loaf volume and firmness.     

Relationship of Bread Quality to Kernel,Flour, and Dough Properties

This study measured the relationship between bread quality and 49 hard red spring (HRS) or 48 hard red winter (HRW) grain, flour, and dough quality characteristics. The estimated bread quality attributes included loaf volume, bake mix time, bake water absorption, and crumb grain score. The best‐fit models for loaf volume, bake mix time, and water absorption had R² values of 0.78–0.93 with five to eight variables. Crumb grain score was not well estimated, and had R² values ≈0.60. For loaf volume models, grain or flour protein content was the most important parameter included. Bake water absorption was best estimated when using mixograph water absorption, and flour or grain protein content. Bake water absorption models could generally be improved by including farinograph, mixograph, or alveograph measurements. Bake mix time was estimated best when using mixograph mix time, and models could be improved by including glutenin data. When the data set was divided into calibration and prediction sets, the loaf volume and bake mix time models still looked promising for screening samples. When including only variables that could be rapidly measured (protein content, test weight, single kernel moisture content, single kernel diameter, single kernel hardness, bulk moisture content, and dark hard and vitreous kernels), only loaf volume could be predicted with accuracies adequate for screening samples.     

Modified Dough Preparation for Alveograph Analysis with Limited Flour Sample Size

Dough rheological characteristics obtained by alveograph testing, such as extensibility and resistance to extension, are important traits for determination of wheat and flour quality. A challenging issue that faces wheat breeding programs and some wheat research projects is the relatively large flour sample size of 250 g required for the standard alveograph method (AACCI Approved Method 54‐30.02). A modified dough preparation procedure for a small flour sample size was developed for the alveograph test method. A dough was prepared by mixing 80 g of flour with 60% water absorption (2.5% salt solution) for 4 min in a 100 g pin mixer; it was then sheeted and cut into three patties of defined thickness. Data generated by the modified dough preparation method were significantly correlated with the results from the approved alveograph method. The correlation coefficients (r) for each of six alveograph dough characteristics of 40 different advanced breeding lines and wheat varieties were 0.92 for P (mm H₂O), 0.73 for L (mm), 0.83 for W (10^–4 J), 0.90 for P/L, 0.90 for le (%), and 0.76 for G. The modified dough preparation was easier and more convenient than the approved method, and test time for the modified dough preparation was shorter by 20–25 min. This modified dough preparation procedure for the alveograph may be useful for wheat breeding programs as well as an alternative to the approved alveograph method for milling and baking industries and wheat quality research.     

Interrelationships of Flour,Dough, and Bread Properties Under Reduced Salt Level Conditions

The interrelationships between flour quality and the variability in the dough physical properties and bread loaf characteristics were investigated under reduced salt conditions using partial least squares (PLS) regression analysis. Seventy‐two percent of the variability in dough physical properties was explained by the flour quality using a three‐factor PLS model. Damaged starch content (DS), protein content, and farinograph dough development time (DDT) explained the variability of dough creep‐recovery behavior along PLS‐1. Farinograph absorption (FAB), located along PLS‐2, was strongly related to dough adhesiveness, in which adhesiveness was highly correlated to dough stickiness (r = 0.91). Eighty‐nine percent of the variability in bread loaf characteristics was explained by the flour quality using a four‐factor PLS model; the first two PLS factors explained 66% of the variability. The loaf volume was related to a high number of loaf cells, whose expansion resulted in a greater loaf height. The relation between loaf volume and loaf height was expressed more in PLS‐3 than PLS‐1 and PLS‐2. Mean cell wall thickness and mean cell diameter were closely related negatively along PLS‐1, for which DS and farinograph dough stability explained much of the variability in these loaf characteristics. Along the third PLS factor, FAB explained the variability in loaf weight.     

Effects of Oat Grain Hydrothermal Treatments on Wheat-Oat Flour Dough Properties and Breadbaking Quality

Hydrothermal treatments, which are routine in oat processing, have profound effects on oat flour dough rheological properties. The influence of roasting and steam treatments of oat grain on dough mixing and breadbaking properties was investigated when hydrothermally treated oat flour was blended with wheat flour. Roasting of oat grain (105°C, 2 hr) resulted in oat flours that were highly detrimental to wheat flour dough mixing properties and breadbaking quality. Steaming (105°C, 20 min) or a combination of roasting and steaming of oat grain significantly improved the breadbaking potential of the oat flours. The addition of oat flours increased water absorption and mixing requirements of the wheat flour dough and also decreased bread loaf volume. However, at the 10% substitution level, steamed oat flours exhibited only a gluten dilution effect on bread loaf volume when wheat starch was used as a reference. Oat flour in the breadbaking system decreased the retrogradation rate of bread crumb starch. The results indicate that adequate hydrothermal treatments of oat grain are necessary for oat flour breadbaking applications. Steamed oat flours used at a 10% level retarded bread staling without adversely affecting the loaf volume.     

Improved Method for Measuring Wheat Flour Dough Pressure‐Sensitive Adhesiveness

Wheat flour dough adhesiveness was evaluated using a new instrumental method based on the extrusion of a dough strip through a specific Plexiglas cell, and the measurement of adhesiveness to a Plexiglas probe attached to a texturometer (TA.XT2‐250N). Experimental conditions for adherence measurement were based on a central composite experimental design (four parameters, five levels). Effects of both dough water content and dough strip thickness were studied. As dough water content increases, bulk stretching of the dough increases, which gives rise to a shoulder on the recorded force‐displacement curve (in addition to the formation of visible fibrils), more pronounced at higher water contents, and to an increase in the specific energy of separation ω (J/m²). Increasing dough thickness also increases ω, due to additional energy dissipation in a higher volume of dough. The new strip method was then compared with a method using a screen located between dough and probe. The former gave more reproducible and discriminant results.     

Environmental Influences on Flour Composition,Dough Rheology,and Baking Quality of Spring Wheat

The highly variable environmental conditions across the Pacific Northwest (PNW) influence the milling and baking quality of wheat grain produced in this region. This study was conducted to compare the flour composition, dough rheology, and baking quality of soft and hard spring wheat grain produced in diverse environments. Thirteen soft and five hard spring wheat cultivars were grown at Lind, WA (semiarid) and Fairfield, WA (high precipitation) for three years. Grain was evaluated for flour composition, rheology, and experimental baked product quality. Flour composition, rheological properties, and baking qualities were primarily influenced by the environment. Protein contents, microSDS values, and water absorption levels were significantly (P < 0.0001) higher for all cultivars grown at Lind compared with those from Fairfield. Cookie diameters were larger (P < 0.0001) for soft flours from Fairfield, whereas loaf volumes were higher (P < 0.0001) for hard wheat flours from Lind. Results indicate that producing soft or hard wheat outside of its optimal climatic zone reduces experimental baked product quality.