Impact of redox agents on the extractability of gluten proteins during bread making

The gluten proteins gliadin and glutenin are important for dough and bread characteristics. In the present work, redox agents were used to impact gluten properties and to study gliadin-glutenin interactions in bread making. In control bread making, mixing increased the extractability of glutenin. The level of SDS-extractable glutenin decreased during fermentation and then further in the oven. The levels of extractable alpha- and gamma-gliadin also decreased during bread baking due to gliadin-glutenin polymerization. Neither oxidizing nor reducing agents had an impact on glutenin extractabilities after mixing. The redox additives did not affect omega-gliadin extractabilities during bread making due to their lack of cysteine residues. Potassium iodate (0.82-2.47 micromol/g of protein) and potassium bromate (1.07-3.17 micromol/g of protein) increased both alpha- and gamma-gliadin extractabilities during baking. Increasing concentrations of glutathione (1.15-3.45 micromol/g of protein) decreased levels of extractable alpha- and gamma-gliadins during baking. The work not only demonstrated that, during baking, glutenin and gliadin polymerize through heat-induced sulfhydryl-disulfide exchange reactions, but also demonstrated for the first time that oxidizing agents, besides their effect on dough rheology and hence bread volume, hinder gliadin-glutenin linking during baking, while glutathione increases the degree of covalent gliadin to glutenin linking.     

Microbial Transglutaminase as a Tool to Restore the Functionality of Gluten from Insect‐Damaged Wheat

In some wheat‐growing countries, considerable quantities of commercial wheat are rendered unusable in standard baking because of preharvest damage of the grain by protease‐injecting bugs. In the present study, we studied the ability of transglutaminase (TG) treatment of damaged wheat flour to return the functionality of the gluten network. To confirm the TG cross‐linking, the degree of protein hydrolysis, the amount of free thiol groups, and the electrophoresis properties of glutenin subunits were determined. The effectiveness of the TG treatment on insect‐damaged wheat was analyzed by measuring the dough mixing behavior and the gluten quality. A decrease in the degree of hydrolysis (or free amino groups), a reduction in thiol group concentration, and a decrease of extractable high molecular weight glutenin subunits (HMW‐GS) (measured by high‐performance capillary electrophoresis) confirmed the protein cross‐linking catalyzed by TG, the simultaneous formation of disulfide bonds by the proximity of the cross‐linked polypeptide chains, and the formation of aggregates of high molecular weight. The TG treatment of the damaged wheat flour led to a recovery of the consistograph parameters and gluten index value, and the covalent nature of the bonds ensured the stability of the protein changes.     

Tyrosine cross-links: molecular basis of gluten structure and function

The formation of the large protein structure known as "gluten" during dough-mixing and bread-making processes is extremely complex. It has been established that a specific subset of the proteins comprising gluten, the glutenin subunits, directly affects dough formation and breadmaking quality. Glutenin subunits have no definitive structural differences that can be directly correlated to their ability to form gluten and affect dough formation or breadmaking quality. Many protein structural studies, as well as mixing and baking studies, have postulated that disulfide bonds are present in the gluten structure and contribute to the process of dough formation through the process of disulfide-sulfhydryl exchange. Evidence presented here indicates that tyrosine bonds form in wheat doughs during the processes of mixing and baking, contributing to the structure of the gluten network. The relative contributions of tyrosine bonds and disulfide--sulfhydryl interchange are discussed.     

Concentrations of low and high molecular weight thiols in wheat dough as affected by different concentrations of ascorbic acid

Different amounts of ascorbic acid (AA) were added to flour, and the concentrations of low and high molecular weight thiols in the dough were determined. For the determination of the low molecular weight thiols, glutathione, cysteine, and the corresponding disulfides, an isotope dilution assay with a (14)C-labeled internal standard was used. For the determination of the high molecular weight thiols, a method was developed that involved derivatization of dough with Ellman's reagent, removal of excess reagent by dialysis, micro-Osborne fractionation, release of the label by reduction, and determination of reduced Ellman's reagent by reversed-phase high-performance liquid chromatography. Mixing of flour without AA led to a decrease of the glutathione and an increase of the cysteine concentration. Addition of AA reduced the concentration of both thiols to a minimum when 125 mg of AA/kg of flour was applied. Furthermore, the concentrations of high molecular weight thiols in the glutenins of flours from different wheat cultivars were determined. The values ranged from 5.6 to 8.2 micromol/kg of protein and showed a correlation between flour quality and SH concentration. On addition of AA and mixing of a dough, the concentrations of the protein thiols in the glutenins isolated from the dough increased to a maximum when 100 mg of AA/kg of flour was added. Higher concentrations of AA led to a decrease of the SH concentration. The last results are not in accordance with previously published data or with current hypotheses about the mechanism of the AA improver action.     

Alkylation of Free Thiol Groups During Extraction: Effects on the Osborne Fractions of Wheat Flour

Wheat proteins are classified according to solubility into the so‐called Osborne fractions. Because wheat flour contains both free thiol and disulfide groups, thiol–disulfide interchange reactions are possible during extraction. Osborne fractionation of 12 different wheat flour samples was performed in the presence of N‐ethylmaleinimide (NEMI) to alkylate free thiol groups and without addition of NEMI (control). The addition of NEMI during extraction tended to decrease the content of gliadins (predominantly α‐gliadins) and caused an increase of the content of glutenins in most flour samples. Thus, alkylation of free thiol groups during extraction led to a decline of the gliadin/glutenin ratio from 2 (control) to approximately 1.5 (NEMI). NEMI and control gliadins were separated by gel‐permeation HPLC into an oligomeric subfraction (high‐molecular‐weight [HMW] gliadins) and two monomeric subfractions. In most flours (8 of 12), the addition of NEMI led to a significant increase of the content of HMW gliadins. HMW gliadins from cultivar Akteur wheat were preparatively isolated from NEMI and control gliadins and characterized by HPLC, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and N‐terminal sequencing. HMW gliadin isolated in the presence of NEMI had a significantly higher content of low‐molecular‐weight glutenin subunits and disulfide‐bound cysteine as well as a lower content of α‐gliadins and disulfide‐bound glutathione compared with the control.     

Immunocytochemical Localization of Gluten Proteins Uncovers Structural Organization of Glutenin Macropolymer

The content and composition of the disulfide‐bonded glutenin macropolymer has been shown to influence dough properties, although its structural organization is poorly characterized. The structure of the glutenin macropolymer in dough was studied using an immunolocalization transmission electron microscopy (TEM) technique by localizing gliadins, low molecular weight glutenin subunits (LMW‐GS), and high molecular weight glutenin subunits (HMW‐GS) in sections of dough using antibody probes selective for each of the three classes of gluten polypeptides. Distinct differences in the distribution patterns of gliadins, LMW‐GS, and HMW‐GS were observed, which suggests that proteins have different roles in the structural organization of the gluten matrix. On the basis of the observed distribution of the proteins in dough, it is speculated that gliadins, which are randomly distributed as individual particles, fill space within the glutenin macropolymer; LMW‐GS, which are present as clusters, are speculated to form aggregated branch structures; and HMW‐GS, which are present as chains, are speculated to form a network from which the LMW‐GS branches are formed. Changes in the distribution of gliadins, LMW‐GS, and HMW‐GS in dough during mixing were also noted. Such an arrangement supports previous biochemical evidence which has established that gliadins, LMW‐GS, and HMW‐GS have specific roles in the structural organization of the glutenin macropolymer in doughs.     

Depolymerization of the Glutenin Macropolymer During Dough Mixing: I. Changes in Levels,Molecular Weight Distribution,and Overall Composition

Changes in the amounts, molecular weight distributions, and levels of major groups of subunits in the glutenin macropolymer (GMP) of doughs during mixing were investigated. The GMP (gel protein) is the unreduced fraction of gluten protein that remains as a layer on top of the starch after extraction of SDS-soluble proteins and centrifugation. Experiments involved doughs prepared from flours derived from one weak and one strong cultivar and lines derived from cv. Olympic that were null for specific high molecular weight glutenin subunits (HMW-GS). During mixing, the amount of GMP decreased; the major changes occurred before peak mixing time (MT, achievement of peak resistance). In addition, the average apparent molecular weight of GMP (determined by both size-exclusion HPLC and multilayer gel electrophoresis) decreased during mixing, but in this case, the major changes were seen later in the mixing process, during dough breakdown. Even after extensive mixing, polymers and oligomers were released, not free glutenin subunits. During dough breakdown, the composition of GMP also changed, such that the proportion of HMW-GS decreased but β-amylases/D low molecular weight glutenin subunits (LMW-GS) increased. Changes in the total amounts of other LMW-GS typically were smaller with a decrease in the proportion of B subunits and an increase in the proportion of C subunits. The major changes in GMP composition were observed after peak MT (peak resistance) occurring earlier and to a greater extent in the weaker dough. Our results suggest that dough breakdown during mixing may be triggered by loss of HMW-GS, leading to changes in the molecular weight distribution and composition of the disulfide-bonded GMP.     

Differing Effects of Mechanical Dough Development and Sheeting Development Methods on Aggregated Glutenin Proteins

Dough development using sheeting and mechanical dough development (MDD) were compared with respect to the effect the mixing method had on the molecular size distribution and degree of protein thiol exposure of the aggregated glutenin proteins. Although sheeting imparts a lower rate of work input on doughs than does MDD mixing, changes in protein aggregation patterns during mixing were similar for both methods of dough development, indicating that protein disaggregation was important in the process of dough development. In both systems, a reduced rate of change in the protein aggregation patterns was associated with optimum dough development. The MDD mixing was characterized by increasing exposure of the thiol groups on the SDS‐insoluble glutenin during mixing while the sheeting process resulted in fewer exposed thiol groups on both SDS‐soluble and SDS‐insoluble glutenin proteins. This suggested that disulfide bond rupture may not be a required process in dough development and that high effective stresses per se may not be required to develop doughs. This is consistent with a model for dough development that does not require extensive covalent bond rupture but instead involves mainly rupture and reformation of noncovalent interactions such as hydrophobic bonds and hydrogen bonds between protein chains.     

Identification of disulfide bonds in wheat gluten proteins by means of mass spectrometry/electron transfer dissociation

Disulfide bonds within gluten proteins play a key role in the breadmaking performance of wheat flour. In the present study, disulfide bonds of wheat gluten proteins were identified by using a new liquid chromatography-mass spectrometry (LC-MS) technique with alternating electron transfer dissociation (ETD)/collision-induced dissociation (CID). Wheat flour was partially hydrolyzed with thermolysin (pH 6.5, 37 °C, 16 h), and the digest was subjected to LC-MS with alternating ETD/CID fragmentation. Whereas CID provided peptide fragments with intact disulfide bonds, cleavage of disulfide bonds was preferred over peptide backbone fragmentations in ETD. The simultaneous observation of disulfide-linked and disulfide-cleaved peptide ions in the mass spectra not only provided distinct interpretation with high confidence but also simplified the conventional approach for determination of disulfide bonds, which often requires two separate experiments with and without chemical reduction. By application of the new method 14 cystine peptides were identified. Eight peptides confirmed previously established disulfide bonds within gluten proteins, and the other six cystine peptides were identified for the first time. One of the newly identified cystine peptides represented a "head-to-tail" cross-link between high molecular weight glutenin subunits. This type of cross-link, which has been postulated as an integral part of glutenin models published previously, has now been proven experimentally for the first time. From the six remaining cystine peptides interchain disulfide bonds between α-gliadins, γ-gliadins, and low molecular weight glutenin subunits were established.     

Characterization of sulfur speciation in low molecular weight subunits of glutenin after reoxidation with potassium iodate and potassium bromate at different pH values using x-ray absorption near-edge structure (XANES) spectroscopy

Sulfur speciation in low molecular weight (LMW) subunits of glutenin after reoxidation with potassium iodate and potassium bromate at different pH values, aged subunits of glutenin as well as gluten, and gliadin have been investigated in situ by S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. XANES spectra were analyzed quantitatively using a least-squares fitting routine to provide relative percentage contribution of different sulfur species occurring in the samples. Using potassium iodate and potassium bromate for reoxidation of reduced LMW subunits of glutenin led not only to disulfide states but also to higher oxidation states (sulfoxide state, sulfonic acid state). Strongest oxidation occurred at low pH values. Higher oxidation states were also predominantly detected in the aged subunits of glutenin, whereas the disulfide state was the main sulfur species in gluten and gliadin samples. The results showed that the oxidation state of sulfur prior to oxidation (thiol, disulfide) strongly influences sulfur speciation after oxidation. The choice of the oxidizing reagent seems to be of minor importance.     

Structural Modifications of Gluten Proteins in Strong and Weak Wheat Dough During Mixing

The network‐forming attributes of gluten have been investigated for decades, but no study has comprehensively addressed the differences in gluten network evolution between strong and weak wheat types (hard and soft wheat). This study monitored changes in SDS protein extractability, SDS‐accessible thiols, protein surface hydrophobicity, molecular weight distribution, and secondary structural features of proteins during mixing to bring out the molecular determinants of protein network formation in hard and soft wheat dough. Soft wheat flour and dough exhibited greater protein extractability and more accessible thiols than hard wheat flour and dough. The addition of the thiol‐blocking agent N‐ethylmaleimide (NEM) resulted in similar results for protein extractability and accessible thiols in hard and soft wheat samples. Soft wheat dough had greater protein surface hydrophobicity than hard wheat and exhibited a larger decrease in surface hydrophobicity in the presence of NEM. Formation of high‐molecular‐weight (HMW) protein in soft wheat dough was primarily because of formation of disulfides among low‐molecular‐weight (LMW) proteins, as indicated by the absence of changes in protein distribution when NEM was present, whereas in hard wheat dough the LMW fraction formed disulfide interaction with the HMW fraction. Fourier transform infrared spectroscopy indicated formation of β‐sheets in dough from either wheat type at peak mixing torque. Formation of β‐sheets in soft wheat dough appears to be driven by hydrophobic interactions, whereas disulfide linkages stabilize secondary structure elements in hard wheat dough.     

Role of Gluten and Its Components in Determining Durum Semolina Dough Viscoelastic Properties

Gluten was isolated from three durum wheat cultivars with a range in strength. Gluten was further fractionated to yield gliadin, glutenin and high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits (GS). The gluten and various fractions were used to enrich a base semolina. Enriched dough samples were prepared at a fixed protein content using a 2‐g micromixograph. Mixing strength increased with addition of gluten. Dynamic and creep compliance responses of doughs enriched with added gluten ranked in order according to the strength of the gluten source. Gliadin addition to dough resulted in weaker mixing curves. Gliadin was unable to form a network structure, having essentially no effect on dough compliance, but it did demonstrate its contribution to the viscous nature of dough (increased tan δ). Source of the gliadin made no difference in response of moduli or compliance. Addition of glutenin to the base semolina increased the overall dough strength properties. Glutenin source did influence both dynamic and compliance results, indicating there were qualitative differences in glutenin among the three cultivars. Enrichment with both HMW‐GS and LMW‐GS increased overall dough strength. Source of HMW‐GS did not affect compliance results; source of LMW‐GS, however, did have an effect. The LMW‐2 proteins strengthened dough to a greater extent than did LMW‐1. Mechanisms responsible for dough viscoelastic properties are described in terms of reversible physical cross‐links.     

Changes in SDS Solubility of Glutenin Polymers During Dough Mixing and Resting

An online coupling of high‐performance size‐exclusion chromatography (HPSEC) combined with multiangle laser‐light scattering (MALLS) and a reverse‐phase HPLC procedure were used to characterize and reveal the polydispersity of the glutenin polymers of doughs during mixing and resting. Experiments involved doughs prepared from several samples of a common French wheat cultivar (Soissons) differing in total amount of SDS‐unextractable glutenin polymers. During dough mixing, the amounts, size distribution of protein, and glutenin subunit composition within the SDS‐unextractable polymers changed. However, the major changes in SDS‐unextractable glutenin content and size distribution occurred before the peak mixing time (MT) was reached, whereas detectable changes in subunit composition also occurred after the peak MT. Even if sonication, which was used to solubilize the total wheat glutenin, can narrow the glutenin size distribution, HPSEC‐MALLS revealed a close relationship between the SDS solubility of the glutenin polymers and size distribution, confirming a depolymerization and repolymerization hypothesis. During the depolymerization of the SDS‐unextractable polymers, glutenin subunits were released in nonrandom order, which indicated that the polymers have a hierarchical structure. Some HMW glutenin subunits (HMW‐GS), especially 1D×5, were particularly resistant to the depolymerization mechanism. This suggested that the subunit plays a major role in forming the backbone of the SDS‐unextractable polymers, consistent with the potential to form branched structure. These studies suggest that the SDS‐unextrac‐table polymers in flours have a well‐ordered structure that can be modified by dough mixing and resting.     

Protein insolubilization and thiol oxidation in sulfite-treated wheat gluten films during aging at various temperatures and relative humidities

Gluten films were prepared by casting an acidic and ethanolic solution of gluten previously treated with sodium sulfite. The effects of sulfitolysis on proteins were investigated by SE-HPLC and thiol/disulfide content measurements. During sulfitolysis, insoluble glutenin macropolymer was converted into its constitutive subunits. About 10% of gluten disulfide bonds were cleaved, of which three-fourths originated from interchain disulfide bonds. Oxidation of thiol groups released during sulfitolysis was followed for various temperatures (T) and relative humidities. Oxidation was shown to be a second-order rate process occurring below the glass transition temperature (T(g)) and related to T - T(g). Thiol oxidation ensured the formation of interchain bonds between specific classes of gluten proteins according to an ordered process. Intrachain bonds were also formed and through thiol/disulfide-exchange reactions were finally converted to interchain bonds. Thus, fully oxidized gluten films had more insoluble glutenin macropolymers than native gluten.     

Quantitative Determination of High Molecular Weight Glutenin Subunits of Hard Red Spring Wheat by SDS-PAGE. I. Quantitative Effects of Total Amounts on Breadmaking Quality Characteristics

Thirteen hard red spring wheat genotypes in which seven genotypes had the same high molecular weight (HMW) glutenin subunits (2*, 7+9, 5+10) were compared for their physical-chemical and breadmaking properties. These samples were categorized into three groups based on their dough mixing and baking performances as follows: the strong dough (SD) group (six genotypes), characterized by the strongest dough mixing (average stability, 35 min); the good loaf (GL) group (four genotypes), characterized by the largest loaf volume; and the poor loaf (PL) group (three genotypes), characterized by the smallest loaf volume. Total flour proteins were fractionated into 0.5M salt-soluble proteins, 2% SDS-soluble proteins, and residue proteins (insoluble in SDS buffer). SDS-soluble proteins, residue proteins, and total flour proteins were analyzed by SDS-PAGE and densitometry procedures to determine the proportions of HMW glutenin subunits, medium molecular weight proteins, and low molecular weight proteins in relation to the total amount of proteins. No differences in the amount of salt-soluble proteins were found among the different groups of samples. Solubilities of gluten proteins (total proteins minus salt-soluble proteins) in SDS buffer were related to the differences in dough strength and baking quality among the three groups. The SD group had the lowest solubility and the PL group had the highest. SDS-PAGE analysis showed that SDS-soluble proteins of the SD group contained a smaller amount of HMW glutenin subunits than those of the GL and PL groups. The highest proportions of HMW glutenin subunits in total flour proteins were found in the SD group, while the PL group had the lowest percentage of HMW glutenin subunits in their total flour proteins. These results showed that the total quantities of HMW glutenin subunits played an important role in determining the dough mixing strength and breadmaking performance of hard red spring wheats.     

Relationship between endogenous protein disulfide isomerase family proteins and glutenin macropolymer

The effects of endogenous protein disulfide isomerase (PDI) family proteins on the properties of gluten proteins in dough during breadmaking were determined using bacitracin, an inhibitor of PDI. Bread loaf volume in the presence of bacitracin was increased to 118% of that in the absence of bacitracin. The addition of bacitracin caused a decrease in the extension tolerance of the dough. The amount of sodium dodecyl sulfate (SDS)-insoluble glutenin macropolymer (GMP) in dough decreased to approximately 70% of that in flour during the 20 min of mixing for doughmaking. The addition of bacitracin to dough caused a dramatic GMP decrease, corresponding to ～20-30% of that in flour during the 20 min of mixing. The decrease in GMP was compensated by an increase in SDS-soluble glutenin polymer. Taken together, these results suggest that the endogenous PDI family proteins in flour suppress the depolymerization of GMP during dough mixing.     

Prolamin aggregation, gluten viscoelasticity, and mixing properties of transgenic wheat lines expressing 1Ax and 1Dx high molecular weight glutenin subunit transgenes

The composition of high molecular weight (HMW) subunits of glutenin determines the gluten strength and influences the baking quality of bread wheat. Here, the effect of transgenes coding for subunits 1Ax1 and 1Dx5 was studied in two near-isogenic wheat lines differing in their HMW subunit compositions and mixing properties. The subunits encoded by the transgenes were overexpressed in the transformed lines and accounted for 50-70% of HMW subunits. Overexpression of 1Ax1 and 1Dx5 subunits modified glutenin aggregation, but glutenin properties were much more affected by expression of the 1Dx5 transgene. This resulted in increased cross-linking of glutenin polymers. In dynamic assay, the storage and loss moduli of hydrated glutens containing 1Dx5 transgene subunits were considerably enhanced, whereas expression of the 1Ax1 transgene had a limited effect. The very high strength of 1Dx5 transformed glutens resulted in abnormal mixing properties of dough. These results are discussed with regard to glutenin subunit and glutenin polymer structures.     

Studies on Effects of Microbial Transglutaminase on Gluten Proteins of Wheat. I. Biochemical Analysis

The enzyme transglutaminase (TG) is known to have beneficial effects on breadmaking. However, only limited information is available on the structural changes of gluten proteins caused by TG treatment. The effect of TG has, therefore, been systematically studied by means of model peptides, suspensions of wheat flours and doughs. The treatment of synthetic peptides mimicking amino acid sequences of HMW subunits of glutenin with TG results in isopeptide bonds between glutamine and lysine residues. To study the effect on gluten proteins, different amounts of TG (0 to 900 mg enzyme protein per kg) were dissolved in a buffer and added to wheat flour. The flour suspensions were incubated and centrifuged and the residues were successively extracted with water, a salt solution, 60% aqueous ethanol (gliadin fraction) and SDS solution including a reducing agent (glutenin fraction). The characterization of the fractions by amino acid analysis, SDS‐PAGE, gel permeation HPLC and reversed‐phase HPLC has indicated that the quantity of extractable gliadins decreases by increasing TG amounts. Among gliadins, the ω5‐type was affected to the greatest extent by the reduction of extractability, followed by the ω1,2‐, α‐ and γ‐types. The oligomeric portion of the gliadin fractions (HMW gliadin) was strongly reduced when flour was treated with 450 and 900 mg TG per kg of flour, respectively. In the first instance, the quantity of the glutenin fractions increased by the treatment of flour with 90 and 450 mg TG per kg of flour, and significantly decreased by the treatment of flour with 900 mg TG per kg of flour. Parallel to an increase in TG concentration, the amounts of glutenin‐bound ω‐gliadins and HMW subunits were strongly reduced, whereas the LMW subunits reached a maximal amount after treatment with 450 mg TG per kg of flour. The insoluble residue was almost free of protein when flour was treated with lower amounts of TG. Higher amounts led to a great increase of protein in the residues. The effects of TG on doughs were similar to those of flour suspensions, but less strongly pronounced probably due to the lower water content of the dough system. Sequence analysis of peptides from a thermolytic digest of the insoluble residue revealed that HMW subunits of glutenin and α‐gliadins were predominantly involved in cross‐links formed by TG treatment.     

Identification of isopeptide bonds in heat-treated wheat gluten peptides

Results in this paper confirm heat-induced isopeptide bond formation in wheat gluten. Heating (24 h, 130 °C) of wheat gluten [moisture content 7.4%] decreased its extractability in sodium dodecyl sulfate containing buffer (pH 6.8), even after reduction of disulfide (SS) bonds. Thus, both SS bonds and non-SS bonds were responsible for the extractability loss. Cross-links of the lysinoalanine and lanthionine type were not present in the heated samples, but heat treatment reduced levels of available amino groups. Heating of purified and alkylated high molecular weight glutenin subunits (HMW-GS) under similar conditions also resulted in extractability loss, demonstrating that cross-linking did not solely depend on the availability of cysteine or cystine. These observations indicated that heat treatment had induced isopeptide bond formation, resulting in larger and unextractable molecules. Heating HMW-GS lysine- and glutamine-containing peptides induced the formation of isopeptide bonds, thereby supporting the above hypothesis. The level of isopeptide bond formation increased with heating time.     

Influence of Vacuum Mixing on Structural Characteristics and Physical Properties of Noodle Dough

The effects of vacuum mixing on the structural characteristics and physical properties of noodle dough were investigated using three leading Chinese wheat cultivars. Texture profile analysis showed that vacuum mixed doughs when sheeted all gave significantly higher levels of adhesiveness, elasticity, and chewiness than doughs from nonvacuum mixing. The cross section of sheeted dough mixed at 0.06 MPa had a more continuous and compact microstructure with fewer holes and gaps, as well as more even protein distribution at the surface, as evidenced by scanning electron microscopy and Fourier transform infrared microimaging. However, a higher degree of vacuum was detrimental to the developed network for weak dough. Dough mixed at 0.06 MPa had higher glutenin macropolymer content and lower free thiol group concentration compared with nonvacuum mixed doughs, which may largely relate to the improvement of dough texture. The development of the gluten network for weak gluten flour was more sensitive to the degree of vacuum.