Glass Transition Behavior and Rheological Properties of Surfactants and Gluten‐Surfactant Mixtures

Diacetyltartaric acid esters of monoglycerides (DATEM) and sodium stearoyl lactylate (SSL) displayed thermal events corresponding to glass transition temperature (T_g) and melting of crystalline domains, while monoglycerides (MG) exhibited an endothermic peak corresponding to melting of crystalline structures when heated in a differential scanning calorimeter. The plasticizing effect of water on T_g of gluten exhibited little apparent change in the presence of DATEM, MG, or SSL (glutensurfactant 10:1), in the moisture range of 6.5–21.3% as shown by mechanical spectrometry and differential scanning calorimetry. Glutensurfactant mixtures showed higher G′ and apart from gluten‐SSL, which displayed higher tan δ (G″/G′) at ≤2.51 rad/sec, lower tan δ values than gluten in the frequency range of 0.1–100 rad/sec. DATEM and SSL softened the gluten network before cross‐linking reactions, while MG shifted the onset of cross‐linking reactions to higher temperatures at moisture contents of 30–40%. Complete vitrification of the gluten network occurred at higher temperatures, at the indicated moisture contents, in the presence of surfactants. Softening of the matrix and the delay in cross‐linking of gluten, in the presence of surfactants, might allow for greater expansion of doughs during baking with concomitant increase in loaf volumes.     

Effect of l‐Cysteine on the Rheological Properties of Wheat Flour

Extrudate expansion of cereal‐based products is largely dependent on the molecular interactions and structural transformations that proteins undergo during extrusion processing. Such changes strongly influence the characteristic rheological properties of the melt. It is possible to modify rheological properties of wheat flour during extrusion processing, in particular shear viscosity, with cysteine. The objective of this work was to further develop an understanding of the molecular interactions and structural transformations of wheat flour from dynamic oscillatory rheological measurements. Temperature and frequency sweeps were conducted in the linear viscoelastic range of the material. Changes in the storage modulus (G′), the loss modulus (G″) and the loss tangent (tan δ) of 25% moisture wheat flour disks as a function of cysteine concentration (0–0.75%) were monitored. Molecular weight between cross‐links (M_c) and the number of cross‐links (N_c) per glutenin molecule were determined from frequency sweep data. Increasing cysteine concentration broke cross‐links by decreasing G′ maximum and increasing tan δ values. Molecular weight between cross‐links increased and the number of cross‐links decreased. G′ values from temperature sweeps showed a similar trend. This information leads to a better understanding of the viscoelastic behavior of wheat flour doughs during extrusion cooking and elucidation of protein‐protein reaction mechanisms and other interactions in extruded cereal‐based snack foods.     

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.     

Relationships Between Gluten Rheological Properties and Hearth Loaf Characteristics

The rheological properties of fresh gluten in small amplitude oscillation in shear (SAOS) and creep recovery after short application of stress was related to the hearth breadbaking performance of wheat flours using the multivariate statistics partial least squares (PLS) regression. The picture was completed by dough mixing and extensional properties, flour protein size distribution determined by SE‐HPLC, and high molecular weight glutenin subunit (HMW‐GS) composition. The sample set comprised 20 wheat cultivars grown at two different levels of nitrogen fertilizer in one location. Flours yielding stiffer and more elastic glutens, with higher elastic and viscous moduli (G′ and G″) and lower tan δ values in SAOS, gave doughs that were better able to retain their shape during proving and baking, resulting in breads of high form ratios. Creep recovery measurements after short application of stress showed that glutens from flours of good breadmaking quality had high relative elastic recovery. The nitrogen fertilizer level affected the protein size distribution by an increase in monomeric proteins (gliadins), which gave glutens of higher tan δ and flatter bread loaves (lower form ratio).     

Effect of Polarity of Complexing Agents on Thermal and Rheological Properties of Rice Starch Gels

The ability of rice starch to complex with ligands of various polarities was studied to examine the mechanism of complex formation in an aqueous solution. Differential scanning calorimetry (DSC) showed that TNuS19 rice starch (27.9% amylose) formed inclusion complexes with all 12-C complexing agents. The onset melting temperatures (T_o) of the complexes were ≈93–96°C. The saturation concentrations of added ligands with high polarity, lauric acid (LA), and lauryl alcohol (LOH), had a range of 2–4% (w/w) of the starch, and both of the corresponding melting enthalpies (ΔH) were ≈3.0 J/g. In contrast, the saturation concentrations of ligands with low polarity, methyl laurate (ML) and dodecane (DO), were ≈1–2% (w/w), and the ΔH were 1.87 and 1.80 J/g, respectively. This implied that solubility of ligands had a significant effect on the extent of complexation. The T_o and ΔH increased with an increase of annealing time at 85°C, and the optima for the partially reversible complex formation were 2 hr of annealing in all cases. When measured by a dynamic rheometer, the TNuS19 rice starch gel with added LA or LOH showed a higher storage modulus (G′) than that with no complexing agent added during heating. The G′ and tan δ of the complexed gel were further increased during 12 hr of storage. The increase of G′ indicated that the elastic structure of the concentrated rice starch gels could be improved by complex formation and annealing, whereas the increase of tan δ suggested incompatibility of starch components during storage.     

Viscoelastic Properties of Gelatinized Dispersions of Maize Starch Modified by Solid‐State Milling

Solid‐state milling is an effective physical modification method applied to improve functional properties of starch. In this work the effect of solid‐state milling on the viscoelastic characteristics of maize starch gelatinized dispersions (gels) was investigated by using oscillatory squeeze film rheometry. The relaxation spectrum of the samples under study was calculated from the data obtained. It was found that solid‐state milling resulted in a decrease of the storage (G′) and loss (G″) moduli; meanwhile, loss tangent (tan δ) increased. At a starch milling time more than 10 h, G″ > G′ and the gelatinized starch dispersions behaved as liquid‐like systems. The relaxation maxima shifted to shorter relaxation times, and the heights of the maxima decreased with increasing milling time. The relationship between the complex viscosity η* and steady‐shear viscosity η gradually altered from η* > η to η* < η as the milling time increased. The results can be used to determine the processing conditions of milled starch.     

Predicting Baking Performance from Rheological and Adhesive Properties of Rye Meal Suspensions During Heating

Rheological methods were used to study the behavior of rye meal suspensions during a time‐temperature treatment corresponding to the initial baking conditions (<70°C). Eight different rye cultivars were investigated, with four of the cultivars grown during two different years. Baking experiments included pan bread and hearth bread. Viscosity, falling number, and the amount of adhesive material present during heating were measured. The storage (G′) and loss (G″) moduli increased during a temperature sweep from 45°C, reaching a maximum at 62.1–67.1°C. At the same time, the amount of adhesive material increased. A further increase in temperature caused a decrease in G′ and G″, whereas the amount of adhesive material continued to increase. The mechanical spectra (G′ or G″ vs. frequency) showed that the rye meal suspensions had gel‐like behavior at 45°C which turned into behavior typical of a strong gel at 70°C. The rye meals performing the best in hearth bread baking gave intermediate values of G′ and G″ and high values of the phase shift (δ) at 45°C. During the temperature sweep, the G′ values of these rye meal suspensions increased slowly to a maximum of 62.1–67.1°C.     

Effects of Flour Particle Size and Starch Damage on Processing and Quality of White Salted Noodles

Several reduction grinding conditions were used on a Canadian Western Red Spring (CWRS) farina to yield flours of comparable protein content within three specific particle size ranges (132–193, 110–132, 85–110 μm) at three starch damage levels (3.0, 3.9, 7.0 Megazyme units). White salted noodles (1% w/w NaCl) were initially processed at a fixed absorption (32%). Dynamic oscillatory and large deformation creep measurements indicated that doughs with lower starch damage, thick or thin, exhibited lower G′ (storage modulus), higher tan δ (G″ [loss modulus]/G′) values, and greater maximum strain during creep than doughs with higher starch damage. There were no clear trends between work input during sheeting and either starch damage or particle size. Instrumental texture analysis of raw noodles showed no significant differences due to either starch damage or flour particle size. Flours with fine particle size gave cooked noodles with the best textural attributes, whereas starch damage exhibited no consistent relationship with cooked noodle texture. Cooking loss was greatest in samples with highest starch damage and coarsest particle size; water uptake was inversely related to starch damage and particle size. Experiments were repeated at adjusted water absorptions (32–36.5%) for fine and coarse flours with highest and lowest starch damage. Differences in raw noodle dough rheological properties were largely eliminated, confirming that differences noted at constant absorption were primarily due to flour water absorption. Work input during sheeting was inversely related to starch damage and was higher for fine particle size. Cooking losses were highest for higher starch damage and fine particle size. Water uptake was highest for fine particle size, but in contrast to cooking loss, was higher at lower starch damage. Textural parameters indicated superior cooking quality when particle size was finer and starch damage was lower. Flour particle size and starch damage (as indicated by water absorption) are both primary quality determinants of white salted noodle properties and, to some extent, exert their influence independently.     

Capillary Electrophoresis of Gliadins as a Tool in the Discrimination and Characterization of Hulled Wheats (Triticum dicoccon Schrank and T. spelta L.)

Twenty‐two lines of emmer (T. dicoccon Schrank) and 10 of spelt (T. spelta L.) were analyzed using capillary electrophoresis for their gliadins. These proteins were separated on an uncoated fused‐silica capillary (30 cm long, 22 cm to detector, 50 μm i.d.) using the isoelectric buffer 40 mM aspartic acid, 4M urea, 0.5% (w/v) HEC, and 20% (v/v) acetonitrile. Samples were run for 20 min at 22kV and 42°C. By using these conditions, gliadins were separated into 21–30 components (peaks and shoulders). The major peaks eluted between 4.5 and 8.5 min. Electrophoregrams of tested lines showed qualitative and quantitative differences, including number of peaks, presence or absence of some major peaks, and areas of peaks. Lines belonging to the same species can be discriminated mainly on the basis of β‐ and ω‐gliadin patterns. The γ‐and ω‐gliadins seem to be more useful in the differentiation of emmer from spelt. The comparison of electrophoregrams relative to hulled and unhulled species evidenced the high similarity between species with the same genome composition (durum wheat‐emmer, and common wheat‐spelt).     

Rheological Properties of Vital Wheat Gluten Suspensions

Flour and doughs represent rheologically complex materials whose properties are dependent on many factors including processing conditions. To avoid some of the problems associated with the rheological characterization of dough, we have initiated a study focused on the rheological properties of one of the major components of dough, vital wheat gluten. Suspensions of vital wheat gluten were prepared with concentrations of 225–325 mg/mL.The moduli of the gluten suspensions was 0.2 Pa at 225 mg/mL to 37 Pa at 325 mg/mL. At <250 mg/mL, the gluten suspensions exhibited fluidlike behavior. The crossover frequency, (G′[ω] = G″[ω]) shifted slightly from 0.5 rad/sec at 225 mg/mL to 0.9 rad/sec at 250 mg/mL. At >300 mg/mL, the gluten suspensions exhibited solidlike behavior. The crossover frequencies were independent of concentration and equal to 100 rad/sec. At <250 mg/mL, the high‐frequency behavior of moduli were proportional to ω^3/4, as expected for a semiflexible coil. At >300 mg/mL, the high‐frequency behavior of moduli were proportional to ω^1/2, indicating a flexible coil. These results suggest vital wheat gluten suspensions undergo a structural change between 250 and 300 mg/mL.     

Simple Determination of Gluten Protein Types in Wheat Flour by Turbidimetry

A simple method based on turbidimetry has been developed for the quantitative determination of total gliadins, glutenin subunits, and high and low molecular weight (HMW and LMW) subunits of glutenin. The standard procedure includes the subsequent extraction of wheat flour (100 mg) with a salt solution, with 50% 2‐propanol (gliadins), and with 50% propanol under reducing conditions and increased temperature (glutenin subunits). Aliquots of the gliadin and the glutenin extracts are mixed with 2‐propanol to a final concentration of 83%, and the turbidity of the precipitates is measured photometrically at 450 nm and 20°C after 40 min. Another aliquot of the glutenin extract is mixed with acetone to a final concentration of 40% acetone, and precipitated HMW subunits are determined turbidimetrically after 30 min. The sample is then filtered, and an aliquot of the filtrate is mixed with 2‐propanol to a final concentration of 77% to determine the precipitated LMW subunits. Control analyses with reversed‐phase HPLC on C₈ silica gel indicate that the precipitation of the different protein types is quantitative and specific, and studies of 16 different wheat flours demonstrate the strong correlation between quantification by HPLC and turbidimetry. The turbidimetric measurements are reproducible, linear over a wide absorbance range (0.2–1.7), and sufficiently sensitive to analyze 40 μg of protein or 20 mg of flour. The absolute amounts of protein types in flour can be determined by means of calibration curves with protein standards (gliadins, HMW, and LMW subunits). Altogether, the developed method is simple, accurate, sensitive, and specific for the different protein types. The total procedure takes ≈6 hr for the analysis of six flour samples in parallel or ≈4 hr for three samples in overlapping extraction steps. The chemicals used are inexpensive, scarcely toxic, and easy to dispose.     

Glucose Oxidase in Breadmaking Systems

The mechanism of glucose oxidase action in breadmaking was investigated by studying the baking performance of glucose oxidase, the active ingredient that it produced, and its effect on the rheological properties of dough. Glucose oxidase improved the loaf volume of bread made by 45-, 70-, and 90-min fermentation processes. Although the increase in loaf volume was significant, it was less than that obtained with an optimum level of KBrO₃. With the 90-min fermentation process, the crumb grain of bread was similar for loaves oxidized with optimum levels of glucose oxidase or KBrO₃. The rheological properties of doughs containing glucose oxidase and doughs containing no oxidant were compared. Doughs made with glucose oxidase had higher G′ and G″ and lower tan δ values than doughs made without an oxidant. Hydrogen peroxide was responsible for a drying effect in doughs. This drying effect of glucose oxidase was reduced significantly by incorporation of free radical scavengers into the dough.     

Effects of Salt and Alkaline Reagents on Dynamic Rheological Properties of Raw Oriental Wheat Noodles

To gain further understanding of the functionality of ingredients in oriental wheat noodles, the rheological properties of raw noodles made using high protein (Red Bicycle) or low protein (Sandow) wheat flours and various additives (salt or alkaline reagents at concentrations of 0, 0.1, 0.5, 1.0, 2.0, 3.0, and 4.0%) were investigated using frequency sweep and temperature sweep oscillatory tests. Generally, both the elastic modulus(G′) and viscous modulus (G″) of raw noodles increased when various levels of salt or alkaline (kansui and NaOH) reagents were included in the formulation, with the exception of Red Bicycle noodles where the G″ was not significantly affected by the salt. The G′was significantly decreased in the presence of sodium chloride at concentrations ≤4.0% and kansui at <0.5%. The change in rheological properties of raw noodles was related to the wheat flour quality, type, level of additive, and frequency. The G′, G″, phase angle, and complex viscosity changed in a similar pattern when raw noodles were heated from 25 to 100°C. These parameters decreased initially with increasing temperature until they reached a valley and then increased either to a plateau or continuously in noodles containing kansui. The appearance of valley points at 75.5 and 77.2°C during heating of Sandow and Red Bicycle noodles containing salt, and 89.4, and 83.2°C during heating of Sandow and Red Bicycle noodles containing kansui, respectively, was not associated with starch gelatinization as determined using differential scanning calorimetry. The continuous increase in G′, G″, and complex viscosity observed with noodles containing kansui during the hold period at 100°C was attributed to the high pH environment and not to the inactivation of α‐amylase.     

Frequency Dependence of Viscoelastic Properties of Bread Crumb and Relation to Bread Staling

The viscoelastic behavior of bread crumb was studied using dynamic mechanical analysis (DMA) in the compression mode with the frequency sweep. The dynamic storage modulus (E′), loss modulus (E″), and tanδ (E″/E′) were measured for bread crumb aged up to three days at ambient temperature. The viscoelastic properties of bread crumb showed a characteristic frequency dependence similar to that of a soft rubberlike solid. Typical behavior of bread crumb involved a transition from rubberlike to glasslike consistency with increasing frequency. At a low frequency region, the E′ and E″ values were relatively small and nearly constant, showing characteristics of the rubbery plateau. Then, they increased rapidly with increasing frequencies and approached a glasslike state. Tanδ was low and almost constant at low frequencies before the transition, then went through a prominent peak with increasing frequency. The frequency at which the tanδ of bread crumb started to rapidly increase was defined as the onset frequency (ƒ_o) of the transition. The ƒ_o values increased with the aging of bread crumb samples, which correlated highly to bread staling (r = 0.942). Both dynamic moduli E′ and E″ at ƒ_o also increased with the aging of bread, which correlated highly to firmness obtained using a texture analyzer in a static compression mode (r = 0.941 and 0.943, respectively). DMA measurements could be helpful in characterizing bread staling.     

Effects of Granular Structures on the Pasting Behaviors of Starches

Japonica (Tainung 67 [TNu67]) and waxy (Taichung 70 [TCW70]) rice, normal and waxy corn, and cross-linked waxy rice and corn starches were used in an investigation of the influence of the granular structure on the pasting behavior of starch, using small amplitude oscillatory rheometry. Both normal corn and normal rice (TNu67) starches had the highest storage moduli (G′), followed by their cross-linked versions; native waxy corn and rice starches had the lowest. Native waxy starches showed paste characteristics (G′ < 500 Pa; tan δ > 0.2) at concentrations of up to 35%. However, cross-linked waxy starches exhibited gel behavior at 10% concentration (cross-linked TCW70) or higher (cross-linked waxy corn starch). The degrees of swelling power were in the order: TCW70 > native waxy corn > TNu67 ≅ cross-linked TCW70 ≅ normal corn ≅ cross-linked waxy corn starches. Solubilities were in the order: normal corn > TNu67 > native waxy > cross-linked waxy starches. The addition of 2% purified amylose from indica rice (Kaohsiung Sen 7) did not induce gelation of waxy corn starch. Swelling powers of normal corn, TNu67, and crosslinked waxy starches were similar, but normal corn and TNu67 had much higher G′ value. Such results implied that the formation of gel structure was governed by the rigidity of swollen granules and that the hot-water soluble component could strengthen the elasticity of the starch gel or paste.     

Comparison of Physical Properties of Wheat Starch Gels with Different Amylose Content

The effects of amylose content and other starch properties on concentrated starch gel properties were evaluated using 10 wheat cultivars with different amylose content. Starches were isolated from grains of two waxy and eight nonwaxy wheat lines. The amylose content of waxy wheat lines was 1.4–1.7% and that of nonwaxy lines was 18.5–28.6%. Starch gels were prepared from a concentrated starch suspension (30 and 40%). Gelatinized starch was cooled and stored at 5°C for 1, 8, 16, 24, and 48 hr. The rheological properties of starch gels were studied by measuring dynamic viscoelasticity with parallel plate geometry. The low‐amylose starch showed a significantly lower storage shear modulus (G′) than starches with higher amylose content during storage. Waxy starch gel had a higher frequency dependence of G′ and properties clearly different from nonwaxy starches. In 40% starch gels, the starch with lower amylose showed a faster increase in G′ during 48 hr of storage, and waxy starch showed an extremely steep increase in G′. The amylose content and concentration of starch suspension markedly affected starch gel properties.     

Macromolecular Features of Amaranth Starch

High-performance size-exclusion chromatography (HPSEC), static light scattering (SLS) and dynamic light scattering (DLS) techniques were used for the structural characterization of amaranth starch, solubilized in water by microwave heating in a high-pressure vessel. Apparent average molar mass (M _w) gyration radius (R _G), and hydrodynamic radius (R _H) values were obtained from Berry and Zimm treatment of light-scattering data. When heating time increased from 35 to 90 sec, the M _w, R _G, and R _H decreased, demonstrating a possible polymer degradation due to temperature. Apparent M _r values from HPSEC at 35 sec (27 ± 2 × 10⁷ g/mol) and 50 sec (20 ± 2 × 10⁷ g/mol) were lower than those determined by SLS (35 sec = 69 × 10⁷ g/mol, 50 sec = 56 × 10⁷ g/mol). However, at 70 and 90 sec, the inverse pattern was obtained. The fractal dimensions (d′_f) from HPSEC study for samples dissolved for 35 (3.26), 50 (3.24), and 70 sec (3.14) are characteristic of a particle that has the internal structure of hard sphere, and for samples dissolved for 90 sec (2.19), are characteristic of a fully swollen, randomly branched macromolecule. From SLS, d′_f decreased with increasing treatment time (d′_f = 2.44, 2.18, 1.50, and 1.03 for 35, 50, 70, and 90 sec, respectively). The particle-scattering factors and Kratky plots, well-suited for studying the internal structure of a macromolecule, showed a sample degradation when treatment time increased. Results from DLS showed bimodal distributions with differences in the peak locations when treatment time increased. The ratio of R _G to R _H (ρ) for samples analyzed were between 0.88 and 1.3; these values are characteristic of a sphere or globular structure.     

HMW-glutenin and gliadin variations in Tibetan weedrace, Xinjiang rice wheat and Yunnan hulled wheat

Nine Tibetan weedrace, 9 Xingjiang rice wheat and 14 Yunnan hulled wheat accessions were evaluated for the variability of HMW-glutenins and gliadins. Higher variability was observed for both HMW-glutenins and gliadins in Tibetan weedrace and Xingjiang rice wheat, while lower variability was observed in Yunan hulled wheat. There were 4 HMW-glutenin and 9 gliadin patterns in 9 Tibetan weedrace accessions, 5 HMW-glutenin and 8 gliadin patterns in 9 Xingjiang rice wheat accessions, and 3 HMW-glutenin and 8 gliadin patterns in 14 Yunnan hulled wheat accessions. In Xinjiang rice wheat, one accession (i.e. Daomai 2) carried subunits 2.1 + 10.1 encoded by Glu-D1, which is very rare in common wheat.     

Combined use of gliadins and SSRs to analyse the genetic variability of the Spanish collection of cultivated diploid wheat (Triticum monococcum L. ssp. monococcum)

This work studied the combined use of gliadins and SSRs to analyse inter- and intra-accession variability of the Spanish collection of cultivated einkorn (Triticum monococcum L. ssp. monococcum) maintained at the CRF-INIA. In general, gliadin loci presented higher discrimination power than SSRs, reflecting the high variability of the gliadins. The loci on chromosome 6A were the most polymorphic with similar PIC values for both marker systems, showing that these markers are very useful for genetic variability studies in wheat. The gliadin results indicated that the Spanish einkorn collection possessed high genetic diversity, being the differentiation large between varieties and small within them. Some associations between gliadin alleles and geographical and agro-morphological data were found. Agro-morphological relations were also observed in the clusters of the SSRs dendrogram. A high concordance was found between gliadins and SSRs for genotype identification. In addition, both systems provide complementary information to resolve the different cases of intra-accession variability not detected at the agro-morphological level, and to identify separately all the genotypes analysed. The combined use of both genetic markers is an excellent tool for genetic resource evaluation in addition to agro-morphological evaluation.     

Effect of Added Fat on the Rheological Properties of Wheat Flour Doughs

The effect of added fat content on the rheological properties of wheat flour doughs was determined for three different added fat contents (2.5, 5.0, and 7.5%) at 25°C using dynamic mechanical analysis (DMA) and stress relaxation (SR) tests. Frequency sweeps indicated that added fat had a plasticizing effect on G′ and G″ in the rubbery region. SR results were parameterized using a Maxwell model and a Williams-Watts (WW) model. The WW model indicated that each dough could be characterized by just two major relaxation modes, while four elements were needed for the Maxwell model. The average relaxation time for the shorter process was <1 sec and was not affected by added fat. However, the average relaxation time for the longer WW process actually increased from 107 to 261 sec with added fat up to 5%, and then decreased again. Taken together, these results suggest that added fat actually delayed the onset of viscous flow, while simultaneously attenuating the short-time elastic properties of the gluten fraction of the dough. Furthermore, rheological testing over a wide time (frequency) scale was needed to observe the effect of added fat on both the short-time elastic and longer-time viscous behavior of these doughs.