Application of electron spin resonance spectroscopy and spin probes to investigate the effect of ingredients on changes in wheat dough during heating

The change in microviscosity of the aqueous and lipid phases of wheat flour dough, during heating and subsequent cooling, has been measured using novel spin probes based on the isoindolin-yloxyl structure. The spin probes, water and/or lipid soluble, were used with combinations of dough ingredients: diacetyl tartaric acid ester of monoglycerides (DATEM), salt, yeast, and sodium ascorbate. The lipid soluble probe showed that DATEM does not produce a homogeneous phase with endogenous lipids but is found in a separate, less mobile phase. Also, the lipids were shown not to be involved in the baking process, although DATEM may be incorporated into the gelled starch matrix. The water soluble probe enabled starch gelatinization to be investigated in detail and showed that gelatinization produces a reduction of dielectric constant. The technique is appropriate for the detailed examination of the behavior of different ingredients during baking and also potentially to examine interactions between ingredients and flour components in dough.     

Influence of Added Starch on Mixing of Dough Made with Three Wheat Flours Differing in High Molecular Weight Subunit Composition: Rheological Behavior

The effect of mixing time (6 and 20 min) and starch content were studied on doughs prepared with three wheat flours differing in high molecular weight subunit composition. Rheological measurements were performed in dynamic oscillation: frequency and strain sweeps, stress relaxation, and in large deformation viscosity measurements. The flours were diluted with starch to cover flour protein contents of 10–15%. Water was added to keep the starch‐water ratio constant when doughs were prepared with different protein contents. By increasing the starch content of the doughs, the rheological properties approached those of a starch‐water mixture prepared with the same starch‐water ratio as in the dough. The effect of the starch granules was reinforced by prolonged mixing. This may explain the higher values of the storage modulus and relaxation times observed after 20 min of mixing. Qualities related to gluten properties, appeared more clearly in large deformation viscosity measurements.     

ESR/spin probe study of ice cream

Spin probes based on the 1,1,3,3-tetramethylisoindolin-2-yl structure have been used, in conjunction with electron spin resonance spectroscopy (ESR), to study the physical changes occurring in ice cream during freezing and melting. The ESR measurements allowed the rotational correlation times, tau(B), of the spin probes to be determined. Two probes were used together in a given sample of ice cream, namely, 1,1,3,3-tetramethylisoindolin-2-yl (TMIO), which samples the fat phase, and the sodium salt of 1,1,3,3-tetramethylisoindolin-2-yloxyl-5-sulfonate (NaTMIOS), which samples the aqueous phase. Data from the TMIO probe showed that when ice cream is cooled, the fat phase is a mixture of solid and liquid fat until a temperature of approximately -60 degrees C is reached. The water-soluble probe NaTMIOS showed that the aqueous phase changes completely from liquid to solid within 1 degrees C of -18 degrees C. On cooling further to -24.7 degrees C and then allowing it to warm to +25.0 degrees C, the rotational correlation times of the NaTMIOS were slow to recover to their previous values. For the lipid phase, tau(B)(298) was found to be 65.7 +/- 2.0 ps and the corresponding activation enthalpy, DeltaH, was 32.5 +/- 0.9 kJ mol(-)(1): These values are typical of those expected to be found in the type of fat used to make ice cream. The water phase gave corresponding values of 32.2 +/- 0.5 ps and 24.5 +/- 0.4 kJ mol(-)(1) values, which are those expected for a sucrose concentration of 24%.     

Effect of Germination and Water Content on the Microstructure and Rheological Properties of Two Rye Doughs

Two rye cultivars, Marder and Motto, with falling numbers 314 and 309, respectively, were germinated in vitro. Relative to the native grains, germination induced minor local changes in the microstructure of cell walls and proteins in the kernels. Kernels of germinated and native grains were milled, and doughs were prepared from the flours, with water content and incubation time varied according to experimental design. The viscoelastic properties of the doughs were measured just after mixing and after various incubation times. The area of blue fluorescence, a measure of intact cell walls, was quantified by computer-assisted image analysis in thin sections of rye dough after mixing and incubation, and the starch structure was studied under the microscope after iodine staining. The water content of the doughs was explained well by the rheological behavior. Doughs made from flours of germinated grains were always softer than doughs made from flours of native grains, and Marder doughs were always more rigid than Motto doughs. The higher the water content, and the longer the incubation time, the greater the rheological changes during incubation. Microstructural studies showed that germination and incubation caused changes in the cell wall structures of dough that might explain the softening of the doughs.     

Effect of Physical State of Nonpolar Lipids on Rheology and Microstructure of Gluten‐Starch and Wheat Flour Doughs

To clarify the effects of solid fat and liquid oil on dough in more detail in a simpler system, gluten‐starch doughs with different gluten contents were investigated. The results from rheological measurements indicate that dough with a higher starch content has less resistance to strain and dough with a lower starch content has a rubber‐like structure. The effects of the physical state of nonpolar lipids such as fat and oil on gluten‐starch doughs and wheat flour doughs were investigated using rheological measurements and scanning electron microscopy. Fat‐containing dough had more gas cells and a very smooth gluten gel surface with few holes, which may provide higher tolerance to strain. Moreover, the fat seemed to uniformly distribute the gluten gel between the starch granules in the dough, which reduced the friction between starch granules and led to a lower storage modulus. A mechanism governing the effect of fats on loaf volume is proposed based on the phenomena observed in the fat‐containing dough.     

Water Distribution in Frozen Lean Wheat Doughs

Frozen storage increased the amount of liquid phase and decreased the storage modulus of water-flour mixtures. The liquid phase was studied by ultracentrifugation. The most significant change occurred during the first week of storage. The negative effects of ice crystals could be controlled by reducing the water content, which was seen as smaller amounts of liquid phase and higher dough rigidity after frozen storage (G′ values). Reduced water content also prevented an increase in the self-diffusion coefficient during frozen storage (¹H NMR studies). Prefermented frozen doughs were examined under different conditions: with and without Skimo (additive from Puratos, Belgium), prefermentation time of 25 or 40 min, and reduced water content. The results obtained with autoradiographic method correlated best with the baking results and showed that S-kimo and shorter prefermentation time improve the water distribution of frozen prefermented doughs. Doughs contained small ice crystals after frozen storage and there were no large water patches in thawed doughs. Reduced water content and exclusion of S-kimo decreased the liquid phase of fermented doughs and increased dough rigidity. The baking properties of frozen prefermented doughs were better predicted by large deformation rheology (expansion potential of samples during oscillation). In general, flour quality had an obvious effect on the parameters. There was no correlation between the rheological properties and the values of liquid phase, but in most cases a high correlation between the total water content and rheological properties was observed.     

Effects of Prolonged Storage at Freezing Temperatures on Starch and Baking Quality of Frozen Doughs

The effects of prolonged frozen storage on the starch, rheological, and baking properties of doughs were investigated. Four hard red spring (HRS) wheat cultivars exhibiting consistently different gluten characteristics were used. Gelatinization properties of starches isolated from fresh and thawed frozen doughs over 16 weeks of frozen storage were examined using differential scanning calorimetry (DSC). Significance of results varied with cultivar, but all cultivars showed a significant increase in ΔH with increased frozen storage time, indicating water migration and ice crystallization. The amount of freezable water in frozen doughs increased for all cultivars with frozen storage, but the rate of increase varied. Glupro showed a consistent increase in freezable water during frozen storage (41.6%), which may be associated with its high protein content and strong gluten characteristics. Rheological strength of the frozen doughs which was determined by decreases in extensigraph resistance and storage modulus (G′), declined throughout frozen dough storage. Proofing time increased from 45 min for fresh doughs to an average of 342 min for frozen doughs stored 16 weeks. Concomitantly, loaf volumes decreased from an average of 912 cm³ for fresh doughs to an average of 738 cm³ for the frozen doughs. Longer proof times and greater loaf volume loss were obtained for the cultivars exhibiting greater gluten strength characteristics.     

Effect of Hydrophilic Gums on the Quality of Frozen Dough: Electron Microscopy,Protein Solubility,and Electrophoresis Studies

Hydrophilic gums have been shown to improve the shelf‐life stability of frozen doughs during long periods of frozen storage. The objective of this research was to determine the effect of gums on starch and protein characteristics of frozen doughs using electron microscopy and electrophoresis studies. Frozen doughs, supplemented with three levels of gum arabic, carboxy methyl cellulose (CMC), kappa (κ) carrageenan, and locust bean gum, were studied after day 1 and after 4, 8, 12, and 16 weeks of frozen storage. Changes in the ultra structure of the frozen doughs were investigated, as well as the solubilities and composition of dough proteins by SDS‐PAGE. Scanning electron micrographs of doughs evaluated on day 0 (unfrozen) showed starch granules securely embedded in the gluten matrix. However, after 8 and 16 weeks of frozen storage, the frozen control dough without the gum additives clearly showed damage to the gluten network, and the starch granules appeared to be separated from the gluten. Doughs with locust bean gum and gum arabic showed better retention of the gluten network compared with the frozen control evaluated after different periods of storage. The SDS‐soluble protein content increased while residue protein content decreased as the frozen storage time increased. After each frozen storage period, the control dough without the gum additive had the highest amount of SDS‐soluble proteins and the lowest amount of residue proteins when compared with the doughs treated with gums. κ‐Carrageenan and locust bean gum had the lowest amount of SDS‐soluble proteins compared with doughs with CMC and gum arabic. The frozen control had the lowest amount of residue proteins at any particular time of frozen storage. κ‐Carrageenan treated doughs had the highest amount of residue proteins, followed by doughs with locust bean gum. Doughs with gum arabic and CMC had the lowest amount of residue proteins but still higher than the control doughs.     

Frozen Bread Dough Properties Modified by Thermostable Ice Structuring Proteins Extract from Chinese Privet (Ligustrum vulgare) Leaves

Thermostable ice structuring proteins (TSISPs) extracted from Chinese privet (Ligustrum vulgare) leaves were used in frozen dough. TSISPs extract thermal hysteresis activity ranged from 0 to 0.27°C based on different ice fractions in solution. The effects of the TSISPs extract on melting enthalpy of ice (ΔH), water molecular state, microstructure, rheofermentation capacity, and baking properties of doughs during frozen storage were investigated by differential scanning calorimetry, thermal gravimetric analysis, scanning electron microscopy, rheofermentometer, and texture analyzer. The addition of TSISPs in frozen dough caused a decrease in freedom of water molecules and ΔH, which resulted in improved microstructure, fermentation capacity, and baking properties of frozen doughs. Residual gluten fibril increased, exposed starch granules decreased, and gas production and retention of frozen doughs was enhanced. These effects resulted in an increase in specific volume and a decrease in crumb hardness of baked frozen dough.     

Stress Relaxation Behavior of Wheat Dough,Gluten, and Gluten Protein Fractions

Relaxation behavior was measured for dough, gluten and gluten protein fractions obtained from the U.K. biscuitmaking flour, Riband, and the U.K. breadmaking flour, Hereward. The relaxation spectrum, in which relaxation times (τ) are related to polymer molecular size, for dough showed a broad molecular size distribution, with two relaxation processes: a major peak at short times and a second peak at times longer than 10 sec, which is thought to correspond to network structure, and which may be attributed to entanglements and physical cross‐links of polymers. Relaxation spectra of glutens were similar to those for the corresponding doughs from both flours. Hereward gluten clearly showed a much more pronounced second peak in relaxation spectrum and higher relaxation modulus than Riband gluten at the same water content. In the gluten protein fractions, gliadin and acetic acid soluble glutenin only showed the first relaxation process, but gel protein clearly showed both the first and second relaxation processes. The results show that the relaxation properties of dough depend on its gluten protein and that gel protein is responsible for the network structure for dough and gluten.     

Rheological Properties of Soft Wheat Flour Doughs: Effect of Salt and Triglycerides

The small deformation rheological properties of wheat flour doughs in relation to their structure and hydration were studied by dynamic mechanical thermal analysis, differential scanning calorimetry, and electron spin resonance. The effect of salt and triglycerides was also examined and compared with results we obtained previously on starch dispersions. Moisture content was adjusted to 48 or 60% (w/w, wb). Samples contained 0–16% NaCl (g/100 g of flour‐water) and 0–18% triolein or lard (g/100 g of flour‐water). The obtained results suggested that starch has an active role in determining the evolution of dough rheological characteristics during heating. The main factors controlling rheological behavior during thermal treatment are the volume fraction and deformability of starch granules. Gluten changes the viscoelasticity of the continuous phase and competes with starch for water. The addition of sodium chloride to flour dispersions shifted the structural disorganization and rigidity increased during heating to higher temperatures. At >7% NaCl, the reverse effect was observed. The mechanism controlling the effect of salt on dough rheological behavior was explained in terms of effect on water properties and on starch structure and hydration. Triglycerides had a lubricant effect (i.e., lowering G′ modulus) on the wheat flour dough system. These effects are of great importance for production and quality of bakery products.     

Determination of the total antioxidant activity of fruits and vegetables by a liposome assay

The effects of mixtures of antioxidants on the oxidation of phospholipids have been investigated in large unilamellar liposomes following initiation by 2,2'-azobis(2-aminopropane) dihydrochloride. The lag phase increased linearly with antioxidant concentration. The lag phases of mixtures containing alpha-tocopherol with ascorbic acid showed synergy between the antioxidants, but mixtures of beta-carotene with alpha-tocopherol or ascorbic acid were not synergistic. The liposome system was used to investigate the total antioxidant activity of lipid- and water-soluble extracts from 16 samples of fruits, vegetables, and related food products. The water-soluble extracts caused greater increases in lag phase than the lipid-soluble extracts. The lag phase of liposomes containing the water-soluble extracts from fruits and vegetables increased linearly with the total phenolic concentration, with the continental salad extract having the longest lag phase. The lipid-soluble extract from apples caused the largest increase in lag phase of the lipid-soluble extracts. The lag phases of the lipid-soluble and water-soluble extracts of all fruits and vegetables studied were additive, but no synergy was detected. The lag phase of the liposomes containing both the water-soluble and lipid-soluble extracts varied from 611.5 min for the continental salad extracts to 47.5 min for the cauliflower extracts.     

Demixing in Wheat Doughs—Its Influence on Dough and Gluten Rheology

Reshaping of relaxed wheat doughs leads to an increase in firmness that significantly changes the results of rheological measurements involving large uniaxial deformations of the dough, whereas the gluten properties remain unaffected. Microscopic investigations reveal that directly after kneading, starch and gluten are thoroughly mixed. However, the shaping procedure of a relaxed dough or shear-flow during rheological measurements cause a separation of gluten and starch. The dilatant behavior of the starch granules and the capacity of gluten to aggregate account for the observed dough-hardening.     

Creep‐Recovery of Wheat Flour Doughs and Relationship to Other Physical Dough Tests and Breadmaking Performance

Measurements of creep‐recovery of flour‐water doughs were made using a dynamic mechanical analyzer (DMA) in a compression mode with an applied probe force of 50 mN. A series of wheat flour and blend samples with various breadmaking potentials were tested at a fixed water absorption of 54% and farinograph optimum water absorption, respectively. The flour‐water doughs exhibited a typical creep‐recovery behavior of a noncross‐linked viscoelastic material varying in some parameters with flour properties. The maximum recovery strain of doughs with a fixed water absorption of 54% was highly correlated (r = 0.939) to bread loaf volume. Wheat flours with a large bread volume exhibited greater dough recovery strain. However, there was no correlation (r = 0.122) between maximum creep strain and baking volume. The maximum recovery strain of flour‐water doughs also was correlated to some of the parameters provided by mixograph, farinograph, and TA‐XT2 extension.     

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.     

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.     

Effect of Damaged Starch and NaCl Level on the Dough Handling Properties of a Canadian Western Red Spring Wheat

The effects of damaged starch and NaCl (1 and 2% w/w [flour weight]) on the dough handling properties of a wheat flour (Triticum asetivum L. ‘Roblin’) were investigated with rheological and textural methods. Damaged starch levels of the base flour and three remilled flours (using reduction rolls with decreasing gap sizes) were 5.42, 6.23, 7.30, and 8.43%. Rheological measurements on the dough showed that the complex modulus increased and the loss tangent (tan δ) decreased with increasing damaged starch levels in the flour, indicating that greater amounts of damaged starch produced stiffer dough. The base flour produced doughs with the highest creep compliance value (J _max), whereas the flour with the most damaged starch deformed the least. Higher levels of salt produced stiffer dough that deformed less, as evident by the higher complex modulus and lower creep compliance, compared with 1% NaCl. Damaged starch overall decreased dough stickiness (N), work of adhesion (N·s), and cohesiveness (mm). Increasing the salt content decreased the stickiness of the doughs. Increasing the damaged starch greatly increased dough extensibility at 1% NaCl. The greater amounts of damaged starch in the remilled flour mitigated some of the negative effects of reducing the salt content on the dough machinability.     

Glutenin Macropolymer in Salted and Alkaline Noodle Doughs

An attempt was made to understand the physicochemical attributes that are the basis of physical differences between alkaline and salted noodle doughs. Flour and dough properties of one soft and three hard‐grained wheat cultivars were observed. Doughs were made with either sodium chloride or sodium carbonate. Each formulation variant was tested at both high and low water additions. Samples for glutenin macropolymer (GMP) isolation were taken at selected noodle dough processing stages. When a 1.67% w/v Na₂CO₃ solution was used for mixograph testing, dough characteristics were radically altered and differences between cultivars were masked. In lubricated squeezing flow (LSF) testing, hard wheat noodle doughs had significantly (P < 0.01) longer relaxation times and higher % residual force values than soft wheat doughs in both the salted and alkaline variants. LSF maximum force and biaxial viscosity were significantly higher in alkaline doughs than salted. GMP extracted from alkaline doughs was gummy and sticky, and was more opaque than GMP from salted doughs. GMP weight decreased sequentially when extracted from samples taken in the active phase (mix, compound, sheet) of noodle dough processing and decreased more in alkaline doughs. GMP weight increased more after 24 hr of dough rest in salted doughs. GMP gel strength was noticeably higher in GMP extracted from alkaline doughs. After dough resting, alkaline GMP gel strength significantly increased, whereas it decreased in GMP from salted doughs, suggesting a role for GMP in the increased stiffness of alkaline noodle doughs.     

Stress Relaxation and Oscillatory Tests to Distinguish Between Doughs Prepared from Wheat Flours of Different Varietal Origin

The relaxation properties of flour-water-salt doughs prepared from four different flour types (weak, medium, strong, and extra strong) at different water absorption levels from 58 to 66% with protein contents of 10.0, 10.9, 13.2, and 11.8%, respectively, were studied by imposing varying strain amplitudes of 0.1–29%. Oscillatory tests in the linear viscoelastic region of the 66% absorption strong and weak dough cannot distinguish between the two types of dough. The inability to differentiate between dough types also applied to oscillatory tests on 58% absorption weak and 66% absorption strong doughs. However, the relaxation modulus of dough (extending over time) behaved quite distinctively at high strains, where dough samples experience large deformations. At strain amplitudes of ≤0.1% (i.e., in the linear viscoelastic region), different dough types behaved similarly. Likewise, the relaxation modulus completely relaxed at sufficiently long times. The magnitude of the modulus at intermediate- and high-strain amplitudes were in the order: extra strong > strong > medium > weak, indicating a higher level of elasticity in the extra strong dough samples despite its lower protein content. The relaxation times spectrum of the weak flour, extracted from the relaxation modulus data, reveals a broad relaxation process. The stress relaxation data are very reproducible at high-strain amplitudes (≈1–15% for up to 3 × 10³ sec). This work demonstrated, for the first time, the consistency in oscillatory and relaxation measurements for dough. It also clearly showed that linear viscoelastic data, although important in the characterization of time scales in dough, are largely irrelevant in differentiating between dough types. Furthermore, without proper care, a false steady-state behavior can be obtained with standard viscometric measurements due to slippage at the dough-plate interface.