Textural Comparisons of Gluten‐Free and Wheat‐Based Doughs,Batters, and Breads

Studies were conducted with two newly developed gluten‐free bread recipes. One was based on corn starch (relative amount 54), brown rice (25), soya (12.5), and buckwheat flour (8.5), while the other contained brown rice flour (50), skim milk powder (37.5), whole egg (30), potato (25), and corn starch (12.5), and soya flour (12.5). The hydrocolloids used were xanthan gum (1.25) and xanthan (0.9) plus konjac gum (1.5), respectively. Wheat bread and gluten‐free bread made from commercial flour mix were included for comparison. Baking tests showed that wheat and the bread made from the commercial flour mix yielded significantly higher loaf volumes (P < 0.01). All the gluten‐free breads were brittle after two days of storage, detectable by the occurrence of fracture, and the decrease in springiness (P < 0.01), cohesiveness (P < 0.01), and resilience (P < 0.01) derived from texture profile analysis. However, these changes were generally less pronounced for the dairy‐based gluten‐free bread, indicating a better keeping quality. Confocal laser‐scanning microscopy showed that the dairy‐based gluten‐free bread crumb contained network‐like structures resembling the gluten network in wheat bread crumb. It was concluded that the formation of a continuous protein phase is critical for an improved keeping quality of gluten‐free bread.     

Application of Response Surface Methodology in the Development of Gluten‐Free Bread

The formulation of gluten‐free (GF) bread of high quality presents a formidable challenge as it is the gluten fraction of flour that is responsible for an extensible dough with good gas‐holding properties and baked bread with good crumb structure. As the use of wheat starch in GF formulations remains a controversial issue, naturally GF ingredients were utilized in this study. Response surface methodology was used to optimize a GF bread formulation primarily based on rice flour, potato starch, and skim milk powder. Hydroxypropylmethylcellulose (HPMC) and water were the predictor variables. Analyses of the treatments from the design were made 24 hr after baking. Specific volume and loaf height increased as water addition increased (P < 0.01). Crumb firmness decreased as water levels increased (P < 0.01). Significant interactions (P < 0.01) between HPMC and water were found for the number of cells/cm². The number of large cells (>4 mm²) decreased with increasing levels of HPMC and water. Optimal ingredient levels were determined from the data obtained. The optimized formulation contained 2.2% HPMC and 79% water flour/starch base (fsb) and measured responses compared favorably to predicted values. Shelf‐life analysis of the optimized formulation over seven days revealed that, as crumb firmness increased, crust firmness and crumb moisture decreased.     

Levels of Protein and Protein Composition in Hard Winter Wheat Flours and the Relationship to Breadmaking

Protein and protein fractions were measured in 49 hard winter wheat flours to investigate their relationship to breadmaking properties, particularly loaf volume, which varied from 760 to 1,055 cm³ and crumb grain score of 1.0–5.0 from 100 g of flour straight‐dough bread. Protein composition varied with flour protein content because total soluble protein (SP) and gliadin levels increased proportionally to increased protein content, but albumins and globulins (AG), soluble polymeric proteins (SPP), and insoluble polymeric protein (IPP) levels did not. Flour protein content was positively correlated with loaf volume and bake water absorption (r = 0.80, P < 0.0001 and r = 0.45, P < 0.01, respectively). The percent SP based on flour showed the highest correlation with loaf volume (r = 0.85) and low but significant correlation with crumb grain score (r = 0.35, P < 0.05). Percent gliadins based on flour and on protein content were positively correlated to loaf volume (r = 0.73, P < 0.0001 and r = 0.46, P < 0.001, respectively). The percent IPP based on flour was the only protein fraction that was highly correlated (r = 0.62, P < 0.0001) with bake water absorption followed by AG in flour (r = 0.30, P < 0.05). Bake mix time was correlated positively with percent IPP based on protein (r = 0.86) but negatively with percent SPP based on protein (r = ‐0.56, P < 0.0001).     

Starch–Hydrocolloid Interaction in Chemically Leavened Gluten‐Free Sorghum Bread

A satisfactory chemically leavened gluten‐free sorghum bread method was developed by using a blend of 90% commercially milled sorghum flour and 10% rice, tapioca, or potato starch as the “flour.” The most effective starch/hydrocolloid combinations in the formula were potato starch with 4% xanthan, tapioca starch with 3% hydroxypropyl methylcellulose, and rice starch with 3% xanthan. Overall, there was not a significant difference in the quality of loaves made with each starch/hydrocolloid combination. Rapid visco analysis showed that batter viscosity did not have a significant impact on loaf volume index but did affect crumb grain properties. Batters with lower viscosity produced loaves with better crumb grain.     

Size Distribution and Properties of Wheat Starch Granules in Relation to Crumb Grain Score of Pup‐Loaf Bread

Twelve hard winter wheat flours with protein contents of 11.8–13.6% (14% mb) were selected to investigate starch properties associated with the crumb grain score of experimentally baked pup‐loaf bread. The 12 flours were classified in four groups depending on the crumb grain scores, which ranged from 1 (questionable‐unsatisfactory) to 4 (satisfactory). Flours in groups 1, 2, 3, and 4 produced breads with pup‐loaf volumes of 910–1,035, 1,000–1,005, 950–1,025, and 955–1,010 cm³, respectively. Starches were isolated by a dough handwashing method and purified by washing to give 75–79% combined yield (dry flour basis) of prime (62–71%) and tailing (7–16%) starches. The prime starch was fractionated further into large A‐granules and small B‐granules by repeated sedimentation in aqueous slurry. All starches were assayed for weight percentage of B‐granules, swelling power (92.5°C), amylose content, and granular size distribution by quantitative digital image analysis. A positive linear correlation was found between the crumb grain scores and the A‐granule sizes (r = 0.65, P < 0.05), and a polynomial relationship (R² = 0.45, P < 0.05) occurred between the score and the weight percentage of B‐granule starch. The best crumb grain score was obtained when a flour had a weight percentage of B‐granules of 19.8–22.5%, shown by varietal effects.     

Network Formation in Gluten‐Free Bread with Application of Transglutaminase

One of the main problems associated with gluten‐free bread is obtaining a good structure. Transglutaminase (TGase), an enzyme that catalyzes acyl‐transfer reactions through which proteins can be cross‐linked could be a way to improve the structure of gluten‐free breads. The objective of this study was to evaluate the impact of TGase at different levels (0, 0.1, 1, and 10 U of TGase/g of protein) on the quality of gluten‐free bread. The recipe consisted of white rice flour (relative amount: 35), potato starch (30), corn flour (22.5), xanthan gum (1), and various protein sources (skim milk powder [SMP] [12.5], soya flour, and egg powder). The influence of the various proteins in combination with the different addition levels of TGase on bread quality (% bake loss, specific volume, color, texture, image characteristics, and total moisture) was determined. Confocal laser‐scanning microscopy (CLSM) was used to evaluate the influence of TGase on the microstructure of the bread. Baking tests showed that TGase had an effect on the specific volume of the bread. For instance, the SMP bread with 10 U of enzyme contained the most compact structure, which was reflected in the crumb texture profile analysis results (highest values) (P < 0.05), digital image analysis (highest level of cells/cm²) (P < 0.05), and CLSM micrographs (network formation). Finally, it can be concluded that it is possible to form a protein network in gluten‐free bread with the addition of TGase. However the efficiency of the enzyme is dependent on both the protein source and the level of enzyme concentration.     

Fermented Sorghum as a Functional Ingredient in Composite Breads

Whole sorghum flour was fermented (a five‐day natural lactic acid fermentation) and dried under forced draught at 60°C, and evaluated for its effect on sorghum and wheat composite bread quality. In comparison with unfermented sorghum flour, fermentation decreased the flour pH from 6.2 to 3.4, decreased total starch and water‐soluble proteins, and increased enzyme‐susceptible starch, total protein, and the in vitro protein digestibility (IVPD). Fermentation and drying did not decrease the pasting temperature of sorghum flour, but slightly increased its peak and final viscosity. In comparison with composite bread dough containing unfermented sorghum flour, fermented and dried sorghum flour decreased the pH of the dough from 5.8 to 4.9, increased bread volume by ≈4%, improved crumb structure, and slightly decreased crumb firmness. IVPD of the composite bread was also improved. Mixing wet fermented sorghum flour directly with wheat flour (sourdough‐type process) further increased loaf volume and weight and reduced crumb firmness, and simplified the breadmaking process. It appears that the low pH of fermented sorghum flour inactivated amylases and increased the viscosity of sorghum flour, thus improving the gas‐holding capacity of sorghum and wheat composite dough. Fermentation of sorghum flour, particularly in a sourdough breadmaking process, appears to have considerable potential for increasing sorghum utilization in bread.     

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

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

Solvent Retention Capacity Values in Relation to Hard Winter Wheat and Flour Properties and Straight‐Dough Breadmaking Quality

Solvent retention capacity (SRC) was investigated in assessing the end use quality of hard winter wheat (HWW). The four SRC values of 116 HWW flours were determined using 5% lactic acid, 50% sucrose, 5% sodium carbonate, and distilled water. The SRC values were greatly affected by wheat and flour protein contents, and showed significant linear correlations with 1,000‐kernel weight and single kernel weight, size, and hardness. The 5% lactic acid SRC value showed the highest correlation (r = 0.83, P < 0.0001) with straight‐dough bread volume, followed by 50% sucrose, and least by distilled water. We found that the 5% lactic acid SRC value differentiated the quality of protein relating to loaf volume. When we selected a set of flours that had a narrow range of protein content of 12–13% (n = 37) from the 116 flours, flour protein content was not significantly correlated with loaf volume. The 5% lactic acid SRC value, however, showed a significant correlation (r = 0.84, P < 0.0001) with loaf volume. The 5% lactic acid SRC value was significantly correlated with SDS‐sedimentation volume (r = 0.83, P < 0.0001). The SDS‐sedimentation test showed a similar capability to 5% lactic acid SRC, correlating significantly with loaf volume for flours with similar protein content (r = 0.72, P < 0.0001). Prediction models for loaf volume were derived from a series of wheat and flour quality parameters. The inclusion of 5% lactic acid SRC values in the prediction model improved R² = 0.778 and root mean square error (RMSE) of 57.2 from R² = 0.609 and RMSE = 75.6, respectively, from the prediction model developed with the single kernel characterization system (SKCS) and near‐infrared reflectance (NIR) spectroscopy data. The prediction models were tested with three validation sets with different protein ranges and confirmed that the 5% lactic acid SRC test is valuable in predicting the loaf volume of bread from a HWW flour, especially for flours with similar protein contents.     

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.     

Effects of Additives and Storage Temperature on Staling Properties of Bagels

The effects of xanthan gum, Novamyl (a type II α‐amylase), Instant Tender‐Jel C starch (a modified starch), and GMS‐90‐SSK (a hydrated monoglyceride) on the staling properties of bagels stored at 4 and 22°C from 0–7 days were studied. Texture analysis and moisture determination were conducted on the bagels before lyophilization. Analysis of percent soluble starch, crumb pasting (Rapid Visco Analyser) and degree of amylopectin recrystallization (differential scanning calorimeter) were conducted on lyophilized bagel crumb. Novamyl‐treated bagels appeared to be the most resistant to staling over time at both storage temperatures in relation to the enthalpy of gelatinization (ΔH). Bagels containing xanthan gum, Instant Tender‐Jel C starch, and GMS‐90‐SSK showed some improvements over the control bagels, although the effects of the additives on the characteristics of the bagels varied. Bagels made with xanthan gum or monoglyceride retained slightly higher crumb moisture percentages over most days of storage. The monoglyceride‐treated bagels had higher enthalpy values, lower percentages of soluble starch, and a higher pasting profile but had the softest texture. The apparent onset of increased staling of the monoglyceride‐ treated bagels was attributed to complexes formed with the starch fractions.     

Model approach to starch functionality in bread making

We used modified wheat starches in gluten-starch flour models to study the role of starch in bread making. Incorporation of hydroxypropylated starch in the recipe reduced loaf volume and initial crumb firmness and increased crumb gas cell size. Firming rate and firmness after storage increased for loaves containing the least hydroxypropylated starch. Inclusion of cross-linked starch had little effect on loaf volume or crumb structure but increased crumb firmness. The firming rate was mostly similar to that of control samples. Presumably, the moment and extent of starch gelatinization and the concomitant water migration influence the structure formation during baking. Initial bread firmness seems determined by the rigidity of the gelatinized granules and leached amylose. Amylopectin retrogradation and strengthening of a long-range network by intensifying the inter- and intramolecular starch-starch and possibly also starch-gluten interactions (presumably because of water incorporation in retrograded amylopectin crystallites) play an important role in firming.     

Relationships of Free Lipids with Quality Factors in Hard Winter Wheat Flours

Hard winter wheat (Triticum aestivum L.) flours (n = 72) were analyzed for free lipids (FL) and their relationships with quality parameters. The two main glycolipid (GL) classes showed contrary simple linear correlations (r) with quality parameters. Specifically, kernel hardness parameters, flour yields, and water absorptions had significant negative correlations with monogalactosyldiglycerides (MGDG) but positive correlations with digalactosyldiglycerides (DGDG). MGDG showed negative correlations with gluten content but positive correlations with gluten index. The percentages of DGDG in FL had significant positive correlations among cultivars (n = 12) with mixograph and bake mix times (r = 0.71, P < 0.01 and r = 0.67, P < 0.05, respectively), mixing tolerance (r = 0.67, P < 0.05), and bread crumb grain score (r = 0.71, P < 0.01). These results suggest that increasing DGDG in FL could contribute to enhancing wheat quality attributes including milling, dough mixing, and breadmaking quality characteristics. FL content and composition (ratio of MGDG or DGDG to GL) supplement flour protein content to develop prediction equations of mixograph mix time (R² = 0.89), bake mix time (R² = 0.76), and loaf volume (R² = 0.72).     

Pyranose Oxidase from Trametes multicolor Impacts Dough and Bread Microstructure

Pyranose oxidase (P₂O) improves wheat flour dough stability and bread quality. We related its effect on dough spread behavior to that on dough and bread crumb structure. Increasing P₂O addition levels gradually reduced dough flow. High P₂O addition levels further increased dough strength, significantly increased dough cell wall thickness, and decreased bread loaf volume. Taken together, affecting dough spread behavior impacts dough and bread (crumb) structure, and dough structure largely determines bread crumb structure.     

Evaluation of Nebraska Waxy Sorghum Hybrids for Ethanol Production

To evaluate the ethanol production performance of waxy sorghum hybrids and the effects of location and harvest year on ethanol yield, samples of four waxy sorghum hybrids collected from two Nebraska locations (Mead and Lincoln) in both 2009 and 2010 were tested for ethanol production in a dry‐grind process. No significant difference (P = 0.216) in starch contents was observed among the four hybrids, but starch contents of the hybrids were significantly affected by growth location (P = 0.0001) and harvest year (P = 0.0258). Location, hybrid, and harvest year all had significant effects on ethanol fermentation efficiency in the dry‐grind process. Lincoln sorghum samples showed higher (P = 0.022) ethanol fermentation efficiency (90.4%) than did Mead sorghum samples (90.0%). Sorghums harvested in 2010 had higher (P < 0.001) ethanol fermentation efficiency (91.1%) than those harvested in 2009 (89.3%). The 2009 sorghum flours had more amylose‐lipid complexes than the 2010 samples did, and amylose‐lipid complexes as previously reported had adverse effects on ethanol fermentation. Residual starch contents in distillers dried grains with solubles (DDGS) were significantly affected by hybrid and harvest year (P < 0.0001), but we observed no difference in protein content in DDGS from the four hybrids.     

Physicochemical Properties of Flours that Relate to Sorghum Couscous Quality

Flours from eight sorghum cultivars were evaluated for their couscous-making ability with the objective of finding predictive relationships between flour physicochemical properties and couscous quality. Chemical composition, physical characteristics, and pasting and gelatinization properties of the flours were determined. A laboratory procedure was used to prepare couscous. Couscous properties were evaluated and compared to a laboratory-prepared and a commercial durum wheat couscous. Hard grain produced flours containing a high proportion of coarse particles with low ash and high damaged starch content and yielded a higher proportion of desirable sorghum couscous granules. A variety of colors ranging from brown to yellow were obtained when flours were processed into couscous. Cooked sorghum couscous stickiness was positively correlated (r = 0.89, P < 0.01) with the amount of damaged starch in flour. Cooked couscous hardness correlated positively (r = 0.79, P < 0.05) with apparent amylose content of flour and correlated negatively (r = -0.75, P < 0.05) with flour peak viscosity. Durum wheat couscous was lighter and had more yellow color than sorghum couscous. Sorghum couscous was stickier and harder than durum wheat couscous. Addition of 2% oil to the cooking water considerably improved the texture of some sorghum couscous to a level comparable to that of durum wheat couscous.     

Relationship Between Solvent Retention Capacity and Protein Molecular Weight Distribution,Quality Characteristics,and Breadmaking Functionality of Hard Red Spring Wheat Flour

This research aims to investigate the relationship between the solvent retention capacity (SRC) test and quality assessment of hard red spring (HRS) wheat flour samples obtained from 10 HRS cultivars grown at six locations in North Dakota. The SRC values were significantly (P < 0.05) correlated with flour chemical components (protein, gluten, starch, and damaged starch contents, except arabinoxylan); with farinograph parameters (stability [FST], water absorption, peak time [FPT], and quality number); and with breadmaking parameters (baking water absorption [BWA], bread loaf volume [BLV], and symmetry). Differences in locations and cultivars contributed significantly to variation in quality parameters and SRC values. Suitability of SRC parameters for discriminatory analysis of HRS wheat flour is greatly influenced by molecular weight distribution (MWD) of SDS‐unextractable proteins. SRC parameters, except for sucrose SRC, showed significant (P < 0.01) and positive correlations with high‐molecular‐weight (HMW) polymeric proteins in SDS‐unextractable fractions, whereas only lactic acid SRC exhibited significant (P < 0.01) correlations with low‐molecular‐weight polymeric proteins. HMW polymeric proteins also exhibited positive associations with FPT, FST, BWA, and BLV. The discrepant variation in association of SRC parameters with respect to MWD of SDS‐unextractable proteins could improve segregation of HRS wheat flour samples for quality.     

Effects of Pearling on Falling Number and α‐Amylase Activity of Preharvest Sprouted Spring Wheat

Preharvest sprouted wheat is often characterized by the falling number (FN) test. FN decreases in preharvest sprouted wheat as enzymatic degradation of the starchy endosperm increases. Wheat with FN values <250–275 is often discounted at the time of sale. The intent of this investigation was to evaluate the effects of debranning or pearling on the flour quality traits of five samples of wheat rated as low, med‐low, medium, med‐high, and sound that exhibited a range in FN values of 62–425 sec. Replicates of each sample were pearled for 30, 60, and 120 sec to remove portions of the outer bran layers before milling. FN was highly correlated with α‐amylase activity (r > ‐0.97) in the med‐low, medium, and med‐high FN sample sets as pearling time increased. FN increased in the medlow, medium, and med‐high FN samples by 128, 123, and 80%, respectively, after 120 sec of pearling. Pearling had no effect on flour FN of the low FN sample but α‐amylase activity was significantly decreased. Pearling had little or no effect on FN and α‐amylase activity of the sound sample. FN was moderately to strongly correlated with Rapid Visco Analyser (RVA), alveograph, and farinograph properties, and poorly correlated with protein content, flour yield, and bread loaf volume. In subsequent breadmaking studies, bread loaf volume, and crumb characteristics of flour from pearled wheat were not significantly different from loaf volume and crumb characteristics of flour from the corresponding nonpearled wheat.     

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

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

Characteristics of French Bread Baked from Wheat Flours of Reduced Starch Amylose Content

Wheat genotypes of wild type, partial waxy, and waxy starch were used to determine the influence of starch amylose content on French bread making quality of wheat flour. Starch amylose content and protein content of flours were 25.0–25.4% and 14.3–16.9% for wild type; 21.2 and 14.9% for single null partial waxy; 15.4–17.1% and 13.2–17.6% for double null partial waxy; and 1.8 and 19.3% for waxy starch, respectively. Wheat flours of double null partial waxy starch produced smaller or comparable loaf volume of bread than wheat flours of wild type and single null partial waxy starch. Waxy wheat flour, despite its high protein content, generally produced smaller volume of bread with highly porous, glutinous, and weak crumb than wheat flours of wild type and partial waxy starch. French bread baked from a flour of double null partial waxy starch using the sponge-and-dough method maintained greater crumb moisture content for 24 hr and softer crumb texture for 48 hr of storage compared with bread baked from a flour of wild type starch. In French bread baked using the straight-dough method, double null partial waxy wheat flours with protein content >14.3% exhibited comparable or greater moisture content of bread crumb during 48 hr of storage than wheat flours of wild type starch. While the crumb firmness of bread stored for 48 hr was >11.4 N in wheat flours of wild type starch, it was <10.6 N in single or double null partial waxy flours. Wheat flours of reduced starch amylose content could be desirable for production of French bread with better retained crumb moisture and softness during storage.