Comparison of Small and Large Deformation Measurements of Whole Meal Rye Doughs

The rheological properties of rye flour-water-salt doughs prepared from different flour types (different falling number and coarseness) at different water levels were studied after mixing and after 90 min of incubation (30°C and 80% rh). Both the effect of water and the coarseness of the flour had significant effects on storage modulus (G′) measured by oscillatory test in the linear viscoelastic region and on compressional force measured at large deformation. The results of the two rheological methods correlated very well with each other (correlation coefficients varied in the different doughs at r = 0.975–0.999). Dough rheological measurements suggested that falling number did not have a statistically significant effect on dough rheology after mixing or incubation. Although the two rheological methods correlated well, the responses for incubation were different. In the small deformation method, the storage modulus of all doughs, independent of the falling number, decreased during incubation, whereas in the large deformation method, only the hardness of doughs made from flours with lower falling number decreased during incubation. The rheological measurements of doughs after mixing and the viscosity measurements of flourwater suspension at 30 and 40°C did not correlate with each other. Total pentosans have great effect on viscosity measurements of flour-water suspensions, whereas flour particle size and soluble pentosans correlated more with rheological properties of doughs (r = 0.851 between G′ and soluble pentosans).     

Effect of Gaseous Acetic Acid on Dough Rheological and Breadmaking Properties

Breads baked from wheat flours (protein contents 14.1–16.5% at 14.0% mb) that were pretreated with 2–3 mL of gaseous acetic acid per kg of wheat flour, showed maximum bread height and specific volume (cm³/g). Flour-water suspension and the crumb pH values were gradually decreased with increased amounts of acetic acid. Gas generation and dough expansion tests with bread dough showed that the addition of the same amount of acetic acid, which achieved maximum specific volume, also showed the highest rate of gas generation and dough expansion. However, increasing acetic acid decreased these values. Scanning electron microscope (Cryo-SEM) observation showed that the bread dough made from the same acetic acid-treated flour indicated continuum and no cracks in the dough matrix. Evaluation of mixograms showed the decrease of mixing stability with increased acetic acid levels. Viscosity and water binding capacity of flour-water suspensions were sharply increased by the addition of acetic acid at pH 5.0–3.5.     

Effect of Oxidation on the Dynamic Rheological Properties of Wheat Flour-Water Doughs

Oxidation increased the strength of the dough. Addition of ascorbic acid or azodicabonamide (ADA) to dough increased both elastic modulus (G′) and viscous modulus (G″), while addition of cysteine decreased both values. Hydrogen peroxide, from either calcium peroxide or glucose oxidase, increased G′ and G″ and decreased tan δ (G″/G′) values. In addition to strengthening the dough, hydrogen peroxide dried the dough, but ADA did not. The absorption of doughs containing 20 GU of glucose oxidase (source of hydrogen peroxide) could be increased by ≈5% without altering the rheological properties. Presumably, the mobility of water in the gel formed by oxidative gelation decreased, thereby causing a drying of the dough.     

Effect of Exogenous Lipase on Dough Lipids During Mixing of Wheat Flours

In control dough, endogenous wheat lipase was inactive, because the triacylglycerol (TAG), 1,2-diacylglycerol (DAG_1,2), and 1,3-diacylglycerol (DAG_1,3) fractions of nonpolar lipids were not affected by mixing. Conversely, the free fatty acid (FFA) and monoacylglycerol (MAG) fractions decreased, mainly due to the oxidation of polyunsaturated fatty acids (PUFA) catalyzed by wheat lipoxygenase. Addition of exogenous lipase to flour (15 lipase units [LU] per gram of dry matter) resulted in substantial modification of nonpolar lipids during dough mixing. Due to the 1,3 specificity of the lipase used in this experiment, the TAG and DAG_1,3 fractions decreased, whereas the MAG and FFA fractions increased. The DAG_1,2 fraction increased at the beginning of mixing and decreased after 40 min of mixing. Moreover, part of the PUFA released by lipase activity was oxidized by wheat lipoxygenase, resulting in major losses of PUFA. Conversely, the net content of the saturated and monounsaturated fatty acids (SMUFA) remained constant, because the free SMUFA content increased primarily at the expense of the esterified forms. For a constant mixing time of 20 min, increasing the amount of lipase added to dough (from 2.5 to 25 LU/g of dry matter) resulted in a linear decrease in the TAG fraction and a linear increase in the SMUFA content in the FFA fraction. At the same time, the PUFA content of the FFA fraction increased only for additions of lipase to flour of >5 LU/g of dry matter, due to partial oxidation by wheat lipoxygenase.     

Competition for Oxygen Among Oxidative Systems During Bread Dough Mixing: Consequences of Addition of Glucose Oxidase and Lipoxygenase on Yeasted Dough Rheology

The effect on O₂ uptake during the mixing of yeasted dough, either unsupplemented or supplemented with glucose oxidase (GOX), horsebean flour (HB), soybean flour (SB), or combinations thereof, was studied using an airtight mixer. Two wheat flours with a low (flour A) and a high (flour B) content of free polyunsaturated fatty acids were used. Addition of HB or SB provokes a similar increase of O₂ uptake for both wheat flours, whereas addition of GOX causes a larger increase for flour A than for flour B. When the wheat flours were supplemented with HB or SB, addition of GOX caused a small but significant increase of O₂ uptake for flour A. This increase was not observed for flour B. The mixing tolerance of dough A, determined with the Chopin Consistograph, is increased by GOX addition. However, this effect is less pronounced when flour A is supplemented with HB or SB. Similarly, the relaxation index of dough B is decreased by GOX addition, but the decrease is less distinct in the presence of HB or SB. These results can be explained by a competition among yeast, GOX, and lipoxygenases (present in wheat, HB, and SB flours) for the O₂ uptake by dough, which likely decreases the amount of hydrogen peroxide produced by GOX during dough mixing. This competition for O₂ consequently also modifies the rheological properties of dough.     

Determination of secondary structural changes in gluten proteins during mixing using Fourier transform horizontal attenuated total reflectance spectroscopy

Fourier transform horizontal attenuated total reflectance (FT-HATR) was used to examine changes in the secondary structure of gluten proteins in a flour-water dough system during mixing. Midinfrared spectra of mixed dough revealed changes in four bands in the amide III region associated with secondary structure in proteins: 1317 (alpha-helix), 1285 (beta-turn), 1265 (random coil), and 1242 cm (-1) (beta-sheet). The largest band, which also showed the greatest change in second derivative band area (SDBA) during mixing, was located at 1242 cm (-1). The bands at 1317 and 1285 cm (-1) also showed an increase in SDBA over time. Conversely, the band at 1265 cm (-1) showed a corresponding decrease over time as the doughs were mixed. All bands reached an optimum corresponding to the minimum mobility of the dough as determined by the mixograph. Increases in alpha-helix, beta-turn, and beta-sheet secondary structures during mixing suggest that the dough proteins assume a more ordered conformation. These results demonstrate that it is possible, using infrared spectroscopic techniques, to relate the rheological behavior of developing dough in a mixograph directly to changes in the structure of the gluten protein system.     

Effects of Mixing Conditions and Wheat Flour Dough Composition on Lipid Hydrolysis and Oxidation Levels in the Presence of Exogenous Lipase

The lipid profiles of wheat flour doughs containing exogenous lipase were studied under different mixing conditions using a microscale mixer. An experimental design comparing the effects of dough water content (52–68%), the speed of mixing (50–100 rpm), and the mixer temperature (18–32°C) showed that the hydrolysis levels were positively influenced by temperature and speed of mixing and negatively influenced by water content. The positive effect of temperature was enhanced both by highspeed mixing and low water content. The lipid oxidation levels were positively influenced by the speed of mixing and negatively influenced by the water content. The positive effect of temperature on the oxidation levels was less important. A series of experiments conducted with different types of industrial and semi-industrial mixers with equal concentrations of lipase added to the dough showed large differences among the rates of lipid hydrolysis and oxidation. However, the mixing conditions proposed by bakers to obtain doughs with similar handling properties led to similar dough lipid profiles. Sodium chloride did not change the lipid profile when added to dough. Conversely, calcium chloride promoted a large increase of lipid hydrolysis and oxidation due to its activation of lipase activity. Addition of yeast increased the lipid hydrolysis and slightly decreased lipid oxidation.     

Role of Hydrogen Peroxide Produced by Baker's Yeast on Dough Rheology

Baker's yeast, Saccharomyces cerevisiae, has a well-known effect on dough rheology during breadmaking. During a 3-hr fermentation, hydrogen peroxide (H₂O₂) produced by yeast (0.76%, fwb) increased from 1.09 to 2.32 μmol/g of flour. The spread test, a measure of a dough's rheological properties, showed that yeast had an effect on dough rheology similar to that of H₂O₂, an oxidant that makes flour-water dough more elastic. In additional experiments (spread test and H₂O₂ measurement), glucose oxidase, an enzyme that produces H₂O₂, gave results similar to those with yeast. The fact that catalase, an enzyme that destroys H₂O₂, reversed the rheological effect of added H₂O₂ but did not reverse the effect of either yeast or glucose oxidase suggested that either wheat flour contains an inhibitor to catalase or H₂O₂ was not the active component. A series of experiments, including use of defatted flour, remixing, and mixing dough under nitrogen, all indicated that catalase was inhibited by peroxides in the lipid fraction of flour. These results also suggested that H₂O₂ is responsible for the effects of yeast and glucose oxidase on dough.     

Effects of Laccase and Ferulic Acid on Wheat Flour Doughs

The effects of a laccase from the fungus Pycnoporus cinnabarinus on the mixing of a wheat flour dough with or without added ferulic acid (FA) were studied. Laccase reduced dough time‐to‐peak and accelerated dough breakdown in comparison with the control. Its effect was enhanced with FA. The water extractability of arabinoxylans (AX) increased during mixing of a dough free of added laccase, especially with exogenous FA. At the same time, the extractability of FA decreased during mixing. Added FA may have competed with endogenous AX feruloyl esters, inhibiting partly oxidative gelation. Laccase decreased AX extractability by chain cross‐linking through oxidative dimerization of feruloyl esters. FA and, moreover, FA plus laccase, increased the oxidation of sulfhydryl (SH) groups. FA and, even more, FA in combination with laccase, increased the rate of protein depolymerization during mixing. FA and the products of FA laccase oxidation participated in a redox reaction involving SH groups. A coupling reaction involving enzymatically generated feruloyl radicals and thiol radicals generated through the mechanical breakdown of inter‐chain disulfide bonds might explain these results.     

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.     

Effect of Adding Exogenous Oxidative Enzymes on the Activity of Three Endogenous Oxidoreductases During Mixing of Wheat Flour Dough

The behavior of different exogenous enzymes (soybean lipoxygenase [SLOX], horseradish peroxidase [HPOD], catalase from bovine liver [BCAT], and glucose oxidase [GOX] from Aspergillus niger) added to dough was studied during mixing. The effect of adding these exogenous oxidoreductases on the activity of three oxidative enzymes present in wheat flour (lipoxygenase [WLOX], peroxidase [WPOD], and catalase [WCAT]) was examined. Proper assay conditions were established to differentiate between added WLOX, WPOD, and WCAT and the corresponding activities present in wheat flour. For doughs with added SLOX, an immediate loss of extractable SLOX (≈40%) was observed which remained constant during further mixing. When compared with the control dough, addition of SLOX decreased the losses in WLOX and WCAT activities, whereas WPOD activity was unaffected. With doughs supplemented by HPOD, an immediate loss of 20% in the HPOD activity was observed which did not change after 20 min of mixing. Compared with control dough, addition of HPOD did not affect the behavior of WLOX and WPOD, whereas a slight decrease in the WCAT losses was observed. Addition of BCAT to the dough did not change the behavior of WLOX and WPOD, whereas the losses in WCAT were less rapid. Half of the extractable activity of BCAT was lost at the beginning of mixing with no change during further mixing. For doughs supplemented with GOX, 25% of the GOX activity was lost in the first 5 min of mixing and an additional loss of 20% was observed after 20 min of mixing. Compared with dough without GOX, addition of GOX decreased the losses in WLOX, whereas losses in WCAT and WPOD increased. Glucose and ferulic acid were also added to doughs supplemented with GOX. Added glucose decreased the losses in GOX and WLOX and did not change the behavior of WPOD and WCAT during mixing. Addition of ferulic acid promoted a slight increase of the losses in WLOX and WCAT and almost no change for GOX and WPOD.     

Improvement of Sorghum-Wheat Composite Dough Rheological Properties and Breadmaking Quality Through Zein Addition

Addition of sorghum flour to wheat flour produces marked negative effects on rheological properties of dough and loaf volume. Although there are notable differences in the chemical composition of sorghum proteins (kafirins) compared with wheat gluten that might imply poor functionality in breadmaking systems, a larger constraint may be the unavailability of kafirins due to encapsulation in protein bodies. In this study, zein, the analogous maize prolamin to kafirin, was used to determine the potential effects of protein-body-free prolamins on dough rheology and baking quality of wheat-sorghum composite flour. Mixograms run at 35°C (above the glass transition temperature of zein) were significantly (P < 0.01) improved with addition of zein. Mixogram peak heights increased while mixing time decreased uniformly with addition of zein. Dough extensibility studies showed an increase in maximum tensile stress, while baking studies showed an increase in loaf volume with increasing amounts of added zein. These data are supported by a previous study showing that, in a model system, zein mixed with starch can form viscoelastic networks, and suggest that kafirin, if made available, could contribute to dough formation.     

Thermal Expansion of Flour-Water Dough Measured with a Dynamic Mechanical Analyzer

Thermal expansion of a wheat flour-water dough was measured with a dynamic mechanical analyzer (DMA) at a temperature scan range of 25 to 160°C, in 5°C/min increments. Dough water-absorption levels were increased from 50 to 70% (14% mb) in 4% increments. A standard breadbaking method was used, and loaf volume was measured for regression analysis. The thermal expansion pattern of flour-water dough during heating included four stages with changes in the thermal expansion coefficient: gas thermal expansion (GTE) (25–60°C), starch gelatinization-gluten matrix formation (GMF) (60–100°C), vapor pressure expansion (VPE) (100–120°C), and structure fixation-crust formation (SCF) (>120°C). The onset temperature (T_o) between each stage and the thermal expansion coefficient (C_e) of each stage were affected significantly by dough water content. The onset temperature () from GTE to GMF (the starting temperature of gelatinization of starch in dough) decreased from 68 to 55°C as water absorption increased from 50 to 70%. The thermal expansion coefficient () of flour-water dough during GMF was highly correlated (r² = 0.886) to bread loaf volume. The ratio () of thermal expansion coefficient during the GMF stage to the coefficient during the GTE stage also was significantly correlated (r² = 0.882) to baking volume. Thus, DMA measurement of dough thermal expansion has the potential to be a powerful method of predicting baking quality in cultivar screenings, baking simulations, and scale-up studies.     

The Combination of Rhizopus chinensis Lipase and Transglutaminase Affects the Rheology and Glutenin Macropolymer Properties of Frozen Dough

The combination of Rhizopus chinensis lipase (RCL) and transglutaminase (TG) was previously reported to improve the quality of frozen dough bread. In this study, the effects of RCL, TG, and their combination on the modification of glutenin macropolymer (GMP) and rheological properties of dough during frozen storage were investigated. Frozen storage changed both GMP and rheology properties of dough. TG treatment significantly decreased the ratio of high‐molecular‐weight glutenin subunits to low‐molecular‐weight glutenin subunits and GMP content in fresh dough, and GMP particle size increased. The effect of RCL on GMP properties was not significant, but its combination with TG dramatically increased the proportion of the larger particles and weighted average volume (D_4.3) in GMP. The treatment with the enzyme combination could have inhibited the depolymerization of GMP, which slowed down the decrease rate of some parameters such as GMP content, proportion of larger particles, D_4.3, and release of free amino and thiol groups during frozen storage. The modification of GMP properties by enzyme treatment weakened the effect of the freezing process on rheological properties of dough, especially TG treatment and its combination with RCL. Correlation between GMP particle size and dough properties (dough tensile force and elastic modulus) after freezing and enzyme treatment were confirmed.     

硒镉伴生对富硒土壤柑橘生长及生理代谢的影响

为保障富硒柑橘的安全生产,明确富硒土壤硒镉伴生现象对柑橘生长、硒镉吸收转运和抗氧化能力的影响,采用盆栽试验,以一年生大雅柑橘为试验材料,研究添加硒代蛋氨酸(SeMet,CK,模拟富硒土壤)和添加SeMet与镉(模拟富硒土壤硒镉伴生)对富硒土壤柑橘的生长指标、硒镉含量、叶片还原型抗坏血酸-谷胱甘肽(AsA-GSH)循环效率的影响。结果表明,与CK相比,富硒土壤中,硒镉伴生增加了柑橘叶片叶绿素a+b、叶绿素a、叶绿素b和类胡萝卜素含量,但对株高、新梢长度、新梢数量以及根茎叶的干物质量影响不显著;在富硒土壤中,硒镉伴生显著增加了大雅柑橘硒含量和硒的富集系数(BCF),降低了硒的转运系数(TF);硒和镉主要分布在根系,其次是叶片和茎;在AsA-GSH循环中,硒镉伴生使过氧化氢(H₂O₂)和还原型抗坏血酸(AsA)含量显著上升,脱氢抗坏血酸(DHA)含量上升但未达到显著水平,抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)活性和脱氢抗坏血酸还原酶(DHAR)活性显著上升,而GSH和氧化型谷胱甘肽(GSSG)含量下降,AsA/(AsA+DHA)和GSH/(GSH+GSSG)比值降低,谷胱甘肽过氧化物酶(GPX)活性显著降低。本研究为阐明镉胁迫对富硒土壤柑橘的生理影响机制提供了理论依据。     

Effects of Temperature and Mechanical Input on Semisweet Biscuit (Cookie) Quality and Dough Characteristics

The effects of specific mechanical energy (SME) and dough temperature at the end of mixing (T_f) on semisweet biscuit dough characteristics and biscuit quality were studied using an experimental mixer fitted with monitoring devices. The fluid circulating in the double jacket of the mixing bowl was regulated at variable temperatures and mixed dough samples were prepared at T_f of 23, 30, and 37°C for three levels of SME input (20, 60 and 120 kJ/kg). Correlation analysis showed that semisweet biscuit length and thickness were independent quality parameters, influenced respectively by the T_f of dough and SME. Biscuit thickness and volume increased with SME input, but SME had no significant influence on the physicochemical characteristics of the dough. Biscuit length was related to the density and stickiness of the dough and to rheological behavior as assessed by fundamental and empirical measurements. A rise in dough temperature >35°C induced a dramatic increase in viscoelastic properties, leading to biscuit shrinkage. The increase of dough density with T_f seemed to be related to the melting of solid fat in the dough recipe. Melting of fat during mixing could also be a source of viscoelastic changes in the dough at T_f.     

Effects of Oxido-Reductants on Rheological Properties of Wheat Flour Dough and Comparison with Some Characteristics of Extruded Noodles

The effects of oxido-reductants on the rheological properties of wheat flour dough were evaluated by using a capillary rheometer and an oscillatory rheometer at three temperatures. The oxidants potassium iodate (KIO₃) and l -ascorbic acid (l -AA) significantly increased the apparent viscosity and G′ and decreased loss tangent at low temperatures of 30 and 60°C due to enhanced formation of disulfide bonds. The reductant glutathione (GSH) had the opposite effect. Heating caused the gelatinization of starch, which diminished the effects of the oxido-reductants and produced doughs with similar rheological properties at 80°C. The correlation between dough rheology and characteristics of extruded noodles was also studied.     

Contribution of Hydrophobic Soluble Gluten Proteins,Fractionated by Hydrophobic Interaction Chromatography in Highly Acetylated Agarose,to Dough Rheological Properties

Hydrophobic interaction chromatography with highly acetylated agarose in 1‐mL columns was used to fractionate gliadins and acid‐soluble glutenins. Proteins were eluted in two fractions, the first with acetate buffer (pH 3.6) containing 35% propanol, and the second with Tris buffer in 8M urea. The proportion of eluted protein in the second fraction was called the surface hydrophobicity index. The study included 20 wheat samples of different baking qualities. Multiple regression analysis using the general linear model combined with the stepwise technique was used to relate the surface hydrophobicity index of soluble gluten proteins to specific dough rheological characteristics. Surface hydrophobicity index of gliadins and acetic acid soluble glutenins explained part of the variability of swelling index, extensibility, and work of deformation (dough strength) measured with the alveograph, and part of the farinograph water absorption variability, but showed no relationship to dough mixing characteristics. Hydrophobic soluble gluten proteins fractionated by hydrophobic interaction chromatography (HIC) explained a part of the variability of dough rheological properties.     

棉花幼苗AsA-GSH循环对低温胁迫的响应机制研究

为探究棉花幼苗营养器官抗坏血酸-谷胱甘肽(AsA-GSH)循环系统对低温胁迫的响应机制,以新陆早57号为试验材料,研究4℃低温胁迫不同时间(0、1和2 d)对根、茎和叶中抗氧化物质含量和酶活性的影响。结果表明,与对照(0 d)相比,随着低温胁迫时间延长,棉花幼苗根中还原型抗坏血酸(AsA)含量及单脱氢抗坏血酸还原酶(MDHAR)和谷胱甘肽还原酶(GR)活性呈上升趋势,氧化型抗坏血酸(DHA)含量先减少后增加,氧化型谷胱甘肽(GSSG)含量和脱氢抗坏血酸还原酶(DHAR)活性先升高后降低,谷胱甘肽氧化还原状态(GSH/GSSG比率)和抗坏血酸过氧化物酶(APX)活性总体呈下降趋势,抗坏血酸氧化还原状态(AsA/DHA比率)、还原型谷胱甘肽(GSH)含量和谷胱甘肽过氧化物酶(GPX)活性无显著性差异;茎和叶中AsA和GSH含量、AsA/DHA比率及APX、MDHAR和GR活性总体呈上升趋势,且茎中DHAR活性升高,DHA和GSSG含量先减少后增加,GSH/GSSG比率和GPX活性无显著性差异,而叶中DHA含量和GSH/GSSG比率先不变后增加,DHAR活性先升高后降低,GSSG含量和GPX活性无显著性差异。综合分析显示,棉花幼苗通过调节根、茎和叶中抗氧化物质含量和酶活性来清除活性氧,从而适应低温胁迫,减轻低温伤害。此外,低温对根中AsA-GSH循环影响最大。本研究结果为揭示低温胁迫对棉花幼苗AsA-GSH循环代谢机制提供了理论依据。