Evaluation of partial-vacuum baking for gluten-free bread: Effects on quality attributes and storage properties

The purpose of this study was to evaluate the impact of partial-vacuum baking on the quality and storage properties of gluten-free bread (GFB). Conventional (180°C-30 min at atmospheric pressure) and partial-vacuum (180°C-15 min at atmospheric pressure and at 180°C-15 min at 60 kPa vacuum pressure) methods were conducted to bake GFB. Quality attributes (specific volume, colour, texture, total water loss) were assessed, DSC and SEM analyses were carried out to understand the effect on the bread's microstructure when using vacuum during baking. No significant differences (p > 0.05) were observed in the hardness and specific volume of the partial-vacuum baked GFB; however, changes in the total water loss and in the total colour change were statistically significant (p < 0.05). The DSC, SEM and XRD results showed that more crystalline structure and different starch crystal types formed after partial-vacuum baking. Storage properties were also investigated over a 3-day period. Partial-vacuum baking significantly affected the total water loss and the texture parameters (p < 0.05) during storage. Partial-vacuum baked samples were softer and had a tendency to become stale more slowly than the control. The findings indicate that the partial-vacuum baking method increases the shelf life of gluten-free products by modifying the microstructure of the bread.     

Effect of barley flour addition on the physico-chemical properties of dough and structure of bread

The effects of different percentages of barley flour (i.e. 0–25%) in wheat flours on the physico-chemical properties and structure of dough and bread were investigated. As the percentage of barley flour in mixed flour was increased, its protein and gluten contents decreased whereas the ash content and enzyme activity increased. The rheological characteristics of the four dough mixes were studied using Farinograph, Extensograph and Alveograph. The water absorption (p < 0.01) and stability (p < 0.05) decreased significantly as the percentage of barley flour increased, while no changes were observed in the extensibility and maximum heights. Significant differences were observed in the structural and physical properties as well as in the image analysis of breads. With the increase in the percentage of barley flour, the crumb apparent density decreased (p < 0.1) whereas the porosity (i.e., fraction to total volume) increased (p < 0.1). Overall, the shape and pore structure at 10% barley flour (W90B10) were similar to the pure wheat flour bread, while addition at 15 and 25% of barley flour (W85B15 and W75B25) showed more non-uniform and larger pores.     

面筋蛋白对小麦粉理化性质及面包烘焙品质的影响

为明确不同类型小麦的面粉改良方案,为我国优质面包专用粉的生产提供理论与技术支持,以三个筋力不同的小麦品种宁麦13、扬麦16和郑麦9023为材料,通过洗面筋法提取各供试材料的湿面筋,将其冷冻干燥后按照7%、8%、9%、10%、11%的添加比例与各自面粉进行配比,对配粉的面包烘焙品质、面粉理化性质和面团流变学特性进行了测定分析。结果发现,随着面筋蛋白添加量的提高,配粉的蛋白质、湿面筋、谷蛋白大聚体(GMP)含量和沉降值逐步上升;粘度参数和面团弱化度有所下降;糊化温度和糊化时间呈上升趋势。在同一添加量下,强筋小麦的烘焙品质和面粉理化性质始终优于中筋小麦和弱筋小麦。随着面筋蛋白添加量的提高,面包体积、弹性、回复性、内聚力增大,而硬度、咀嚼性减小,感官品质得到改善。面筋蛋白添加量超过一定范围(宁麦13、扬麦16添加9%,郑麦9023添加8%),面包品质改良效果变缓,且色泽不断加深。综上所述,适量添加面筋蛋白可改变面粉的理化性质,提高其面包烘焙品质;配粉的蛋白质含量为18%左右是最经济的面包烘焙品质改良方案。     

Effect of extrusion cooking of sorghum flour on rheology,morphology and heating rate of sorghum–wheat composite dough

Addition of a gluten-free flour such as sorghum has negative impact on the quality of wheat dough for bread making. One of the methods which can be used to promote the quality of sorghum-wheat composite dough is to extrude the sorghum flour before incorporation. In this regard, to produce a dough with appropriate bakery properties sorghum flour was extruded at 110 °C and 160 °C die temperature with 10%, 14% and 18% feed moisture. The effect of extruded sorghum flour incorporation (10%) on rheological (farinography and stress relaxation behavior), morphological and temperature profile of sorghum-wheat composite dough were evaluated. Extrusion cooking altered the sorghum-wheat composite dough properties through partial gelatinization of starch granules. Addition of extruded sorghum flour increased the water absorption and dough development time but it decreased the dough stability. Native sorghum-wheat composite dough showed viscoelastic liquid-like behavior whereas addition of sorghum flour extrudate changed dough to a more viscoelastic solid-like structure. Maxwell model was more appropriate than Peleg model to describe the viscoelasticity of the sorghum-wheat composite dough. Extrusion cooking decreased composite dough elasticity and viscosity. Sorghum extrudate increased the heating rate of composite dough crumb during baking. Addition of extruded sorghum flour formed a non-uniform and less compact dough structure. As a result, dough containing extruded sorghum flour had a good potential for producing a high-yielding bread in a short time of baking.     

Surface rheological properties of bread dough components in relation to gas bubble stability

The surface rheological properties of dough (components) were determined in order to estimate the effect of these properties on disproportionation and coalescence of gas bubbles in bread dough. Three different systems were studied as a model for the gas-dough interface: a diluted aqueous dough dispersion, gluten and wheat lipids spread on water. The surface dilational modulus, E, and tanϑ of these systems were determined as a function of frequency using a modified Langmuir trough. Values of E and tanϑ found were: 35–100 mN/m and 0·7–0–2, resp., for dough dispersions, 20–45 mN/m and 0·4–0·15, resp., for gluten, and 20–90 mN/m and 1·3–0·1, resp., for lipids in the frequency range tested at room temperature. On the assumption that the gas-dough interface is comparable either to the surface of the dough dispersions tested or to a water surface with spread gluten, it was shown that disproportionation of gas bubbles in dough can be retarded but not prevented. Wheat lipids present in the right concentration in the surface can prevent this foam stabilising mechanism to a larger extent. The surface dilational modulus as well as the surface tension during continuous expansion of dough dispersions were also determined at 45°C. The surface dilational modulus of a dough dispersion at 45°C was 7–25 mN/m, which was approximately 5 times smaller than at room temperature. Results of surface tension measurements during continuous expansion in a Langmuir trough showed that values for surface tension were only slightly higher than at equilibrium (ca. 2 mN/m) at 45°C and at deformation rates of the surface comparable to those at oven rise. These results suggest that thin dough films at higher temperatures will be less stable than at room temperature. Implications in relation with coalescence in dough are discussed. No significant differences in surface rheological properties of dough dispersions of wheats with different bread-making qualities were found in the sinusoidal oscillation tests nor in the continuous expansion tests. Surface rheological properties, therefore, appear not to be the main factor responsible for differences in baking quality amongst different wheats.     

Influence of cultivar and environment on quality of Latin American wheats

Wheat consumption is growing, with processors asking for wheat-based products showing better and more consistent quality. Genotype, environment and their interaction (G × E) play an important role in the final expression of quality attributes. An international research consortium was developed in order to evaluate the magnitude of genotype, environment and G × E effects on wheat quality of cultivars developed for different agro-ecological zones in Latin America. Genotypes released in Argentina, Brazil, Chile, Mexico, Paraguay and Uruguay, were cultivated in twenty different environments within the participating countries. Each environment was characterized for cultural practices, soil type and climatic conditions. Grain yield and analyses of test weight, protein, ash, gluten, Alveograph, Farinograph, Falling Number, SDS sedimentation and flour color were determined. Allelic variations of puroindolines and glutenins were determined in all the genotypes evaluated. Both puroindoline and gluten protein alleles corresponded to genotypes possessing medium to very good bread making quality. Large variability for most quality attributes evaluated was observed, with wider ranges in quality parameters across environments than among genotypes; even for parameters known to be largely determined by genotype. The importance of growing environment on grain quality was proved, suggesting that breeders’ quality objectives should be adapted to the targeted environments.     

Relationship Between Gliadin Alleles and Dough Strength in Italian Bread Wheat Cultivars

Dough strength, as determined by Alveograph W, was studied in Italian bread wheat cultivars grown at several locations over 21 years of testing. Broad sense heritability of Alveograph W was found to range between 0·40 and 0·82, variation in this parameter being affected by genotype×year interactions. Standardised Alveograph W values (Wst) across 40 environments (location–year combinations) were computed for 54 cultivars with reference to the long-term control (cv. Mec), and a quality score based on the Wst value was given to each gliadin allele occurring in at least four of the 54 cultivars analysed. Significant differences in Wst values were observed at theGli-B1,Gli-B2andGli-A2loci. AllelesGli-B1b,Gli-B2candGli-A2bwere significantly related to high gluten strength. An overall quality score based on allelic composition at these loci explained 41% of the observed Wst variation in the 54 cultivars used for the score definition, and 23% to 48% of W value variation in three sets of independent data. The combination of this score with a quality score based onGlu-1alleles coding for highM_rglutenin subunits could explain, on average, about 50% of gluten strength variation.     

Prediction of bread wheat baking quality using an optimized GlutoPeak®-Test method

The GlutoPeak^®-Test (GPT) as a rapid small-scale technique was optimized to evaluate the gluten aggregation properties and to predict the loaf volume, on the basis of a multiyear and multilocation analysis of wheat samples, using different solvents. 5 % lactic acid and 1 % sodium chloride displayed significant GPT responses. Relationships between protein content, sedimentation value, GPT parameters and loaf volume were investigated. With 1 % sodium chloride, the torque 15 s before maximum torque (AM) presented the highest correlation with loaf volume of samples from 2013 to 2014 (r = 0.77, r = 0.63, p < 0.001, respectively). A multiple regression analysis indicated that the best prediction of loaf volume was a linear function of protein content and AM, explaining the variation in loaf volume by 63 % and providing an uncertainty of ±39 ml. The accuracy of the validation of the linear function leads to 64 % correct and to 36 % incorrect predictions of the loaf volume. This emphasizes that the application of the linear function of protein content and AM cannot replace the actual measurement of loaf volume, but it could be a useful rapid screening test in breeding for improved baking quality in bread wheat.     

Improvement bread characteristics of high level sunn pest (Eurygaster integriceps) damaged wheat by using transglutaminase and some additives

The purpose of this study was to improve the baking quality of high level sunn pest damaged wheat (HLSPDW; 20.6%) sample by using at varying levels transglutaminase, and fixed additive combination (diacetyl tartaric acid esters of mono and diglycerides + citric acid + L-ascorbic acid) with or without transglutaminase. It was observed that transglutaminase plays an important role in baking quality of HLSPDW. The increase in transglutaminase caused very clear increase on bread characteristics of wheat. Bread yield, height, pore structure, and crumb softness values increased sharply; weight loss and wideness of bread samples decreased accurately depending on increasing transglutaminase level. This increase did not affect obviously on bread quality at a certain proportion (0.3%). However, when the transglutaminase was more than 0.3% and depend on increase of percentage, bread characteristics showed significant increase. It was determined that, in the absence of transglutaminase; other additives could not improve the bread qualities examined. The unique application of using transglutaminase was found to be considerably to improve the bread quality of the HLSPDW. Overall results indicate that the properties of the bread from HLSPDW can be restored by the addition of transglutaminase. The highly disrupted protein structure present in the HLSPDW gluten requires higher transglutaminase concentrations.     

Accelerated ageing of wheat grains: Part II-influence on thermal characteristics of wheat starch and FTIR spectroscopy of gluten

Wheat quality characteristics are influenced by different factors such as moisture content, storage time and temperature. In this study accelerated ageing of wheat grains was carried out by increasing moisture content (16, 18 and 20%) and keeping the samples in different temperatures (30, 40 and 50 °C) for different periods (2, 5 and 8 days). After milling, the thermal properties of starch and structure of gluten were investigated using Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR); respectively. The experimental set up was designed using response surface methodology and the three distinct factors were combined by central composite design. Results showed that increasing moisture content caused a decrease in onset, peak and end set temperatures of gelatinization while increasing storage time and temperature increased these parameters. By progressing storage time the band intensity of thiol groups decreased while that of disulfide groups of gluten increased indicating an improvement in gluten quality. Increasing moisture content from 16 to 20% and higher storage temperature (50 °C) decreased intensity of disulfide bands.     

Effect of thermal packaging temperature on Chinese steamed bread quality during room temperature storage

In order to investigate the influence of different packaging temperature on thermal-vacuum packaged Chinese steamed bread (CSB) quality under room temperature storage, the packaging temperatures of 50 °C, 70 °C and 90 °C were set respectively to study the effect on the packaging vacuum degree (VD) and starch retrogradation properties. The VD and moisture content of thermal-vacuum packaged CSB significantly increased with the increase of the packaging temperature from 50 °C to 90 °C, while the hardness of CSB decreased, and there was no significant difference in moisture migration during room temperature storage. The results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and small angle X-ray scattering (SAXS) indicated that CSB packaged at different temperatures formed B-type crystals, leading to an enhanced the ordered and dense state of starch structure, and the semi-crystalline growth ring structure disappeared during storage. The influence of different packaging temperatures on VD of CSB could effectively hinder the formation of ordered and dense state of CSB starch, consequently delaying the crystallization of amylopectin and inhibiting the progress of staling. The result of this study is of great significance for improving the quality of starchy foods and guiding the industrial development of Chinese steamed bread.     

Impact of different baking processes on bread firmness and starch properties in breadcrumb

The influence the quality and shelf life of baked product has previously been reported to be effected by the time and temperature of the baking process. In this study, dough was baked at 219 °C by using different ovens (conventional, impingement or hybrid) or with doughs of different sizes (large or small) for varying times. During baking the temperature profile at the dough center was recorded. Texture, thermal properties and pasting characteristics of baked product with reference to baking conditions were investigated. Small breads baked in the hybrid oven had the highest heating rate (25.1 °C/min) while large breads baked in conventional oven had the lowest heating rate (6.0 °C/min). When the data are viewed as a function of heating rate in this study, the enthalpy of amylopectin recrystallization, rate of bread firmness and the amount of soluble amylose were all-lower at the slower heating rate. The differences observed in product firmness following storage are potentially a consequence of the extent of starch granule hydration, swelling, dispersion and extent of reassociation; all of which are affected by the heating rate during baking.     

Effect of structured lipid on alveograph characteristics, baking and textural qualities of soft wheat flour

The effect of substituting canola oil/caprylic acid structured lipid (SL) for partially hydrogenated shortening (at 0, 25, 50, 75, and 100% levels) on the rheology of soft wheat flour dough (28.4% total lipid on flour weight basis, 43% moisture) was determined using the Alveograph. The effect of SL substitution on baking and textural qualities of sugar-snap cookies was also investigated. Addition of shortening to soft wheat flour dough resulted in a significant (P<0.05) decrease in dough resistance to deformation (P), dough extensibility (L), and dough baking strength (W), suggesting a less developed gluten network. SL substitution for shortening did not affect P and W. The cookies incorporating SL (50 and 75% SL substitution) were similar (P<0.05) to the shortening control cookies in both baking and textural qualities, but exhibited some baking and textural quality differences at the 25 and 100% SL substitution levels. Correlations (P<0.05) were found between some Alveograph characteristics, and baking and textural qualities.     

Pilot scale production of a non-immunogenic soluble gluten by wheat flour transamidation with applications in food processing for celiac-susceptible people

Celiac disease (CD) is an immune-mediated disease triggered by wheat gluten and related prolamins. A lifelong gluten-free (GF) diet is mandatory to normalize the intestinal mucosa. We previously found that transamidation by microbial transglutaminase of gluten was effective in suppressing the gliadin-specific inflammatory response in CD patients without influencing the main technological properties of wheat flour or semolina. In this study, we produced on a pilot scale a soluble form of transamidated gluten (soluble protein fraction, spf), characterised by a high protein content (88 mg/ml), while native gluten was dramatically reduced (32 ± 2 ppm; R5-ELISA). Using HLA-DQ8 transgenic mice as a CD model, we found suppression of interferon-γ secretion in gliadin-specific CD4⁺ T cells challenged with spf-primed dendritic cells. In terms of functional properties, spf showed both solubility and emulsifying activity values within the range of commercial soluble glutens. Notably, dough prepared by mixing rice flour with spf could leaven. After baking, blended rice bread had a higher specific volume (2.9 ± 0.1) than control rice bread (2.0 ± 0.1) and acquired wheat-like sensory features. Taken together, our results highlighted the technological value of transamidated soluble gluten to improve both nutritional and sensory parameters of GF food.     

Storage changes in the quality of sound and sprouted flour

Sound and sprouted flours (24 and 48 hr) from bread wheat (WL-1562), durum wheat (PBW-34) and triticale (TL-1210) were stored at room temperature (34.8°C) and relative humidity (66.7%) for 0, 45, 90 and 135 days to assess the changes in physico-chemical and baking properties. Protein, gluten, sedimentation value, starch and crude fat decreased during storage in all the samples; however, the decrease was more in sprouted flours. Free amino acids, proteolytic activity, diastatic activity and damaged starch decreased with increase in storage period. Total sugars and free fatty acids increased more rapidly in the flours of sprouted wheats during 135 days of storage. Loaf volume of breads decreased during storage in both sound and sprouted flour but the mean percent decrease in loaf volume was more in stored sound flours. Aging of sprouted flour for 45 days improved the cookie and cake making properties but further storage was of no value for these baked products.Chapati making properties of stored sound and sprouted flour were inferior to that of fresh counterparts.     

Improving the baking quality of bread wheat using rapid tests and genomics: The prediction of dough rheological parameters by gluten peak indices and genomic selection models

The measurement of baking quality by dough mixing and viscoelastic tests is often labor-intensive and time-consuming, thus the possibility to predict these rheological parameters either by rapid tests or genomic selection models based on molecular markers was investigated in this study. A winter wheat breeding population of 128 genotypes was measured for its rheological parameters, gluten peak indices and other rapid test variables in multiple environments. The prediction accuracy of the rheological parameters was assessed in different cross-validation schemes, reflecting scenarios encountered either in food-processing or by plant breeders. Predictions based on gluten peak indices (r = 0.41–0.82) outperformed the other investigated rapid tests in the food-processing scenario. The combination of gluten peak indices with sedimentation value and protein content gave furthermore the overall highest prediction accuracy (r = 0.70). Cross-validation results from the plant breeding scenario revealed that the prediction accuracy of genomic selection models was merely slightly lower (r = 0.42) than using a combination of sedimentation value and protein content (r = 0.44). Merging gluten peak indices with genomic estimated breeding values resulted in a higher accuracy than either method alone (r = 0.52), and was a promising strategy to select for baking quality in wheat breeding.     

Properties of whole grain wheat flour and performance in bakery products as a function of particle size

The aim of this study was to evaluate the effect of particle size distribution on composition, properties rheological, pasting, microstructural and baking properties of whole grain wheat flour (WGWF) of three different particles sizes (194.9 μm, 609.4 μm and 830.0 μm). The quantification of free sulfhydryl groups (-SH) of WGWF samples, together with the effects observed in the behavior of the dough and bread showed that particle size influences the functionality of the gluten network in a differentiated way. Firmer and lower breads volume compared to refined wheat flour (RF) were correlated with the quality of the gluten network. In the sample of finer particles, more pronounced adverse effects in quality (dough rheology, bread volume and texture) compared to the medium and coarse particle size sample suggests that the larger contact surface and the increased release of reactive compounds due to cell rupture interact with the gluten-forming proteins changing their functionality.     

Stress–Relaxation Properties of Mixograph Semolina–Water Doughs from Durum Wheat Cultivars of Variable Strength in Relation to Mixing Characteristics,Bread- and Pasta-making Performance

Stress–relaxation behaviours of Mixograph semolina–water doughs prepared from Canadian durum wheat cultivars with diverse gluten strength were investigated and related to mixing characteristics, large deformation properties, and bread- and pasta-making quality. Semolina from «strong» (S) and «moderately strong» (MS) durum wheat cultivars required a longer Mixograph mixing time (4–5 min) and higher work input (140–196 Arbitrary Units) to mix to peak dough resistance (PDR) than «weak» (W) and «very weak» (VW) durum cultivars (2–3 min and 80–117 AU). Extensigraph maximum resistance to extension (R_max/E ratio) and Alveograph P/L (tenacity to length ratio) values were higher for doughs from S cultivars than for MS, W, and VW cultivars. Doughs from S cultivars exhibited higher storage modulus (G′) and lower tan δ values at all frequencies, and slower rates of stress relaxation as compared to MS, W, and VW cultivars. Stress relaxation (times to relax 50% (t₅₀) and 75% (t₇₅) of initial stress) indicated that stronger doughs, which had higher proportions of glutenins, took longer to reach these iso-relaxation states, regardless of their initial relaxation modulus value. The parameters t₅₀and t₇₅were also strongly correlated with dough mixing properties, Extensigraph R_max/E, Alveograph P/L, mixing energy, mixing time and loaf volume obtained by a long and a short bread-making process. However, for S cultivars loaf volume was 10 to 20% lower than that expected of bread wheat of comparable protein content. Stress relaxation data demonstrated no simple correlation to pasta cooking quality indicating that stronger gluten did not translate into a superior pasta cooking quality. Results are interpreted in the context of multimodal networks and transient networks with reversible crosslinks.     

Simulating the formation of bread crust in a DMTA rheometer

Water evaporates very fast from the surface layers of dough, enhanced by high heating rates at the beginning of baking. The rheological properties of the surface layers play an important role during the baking process, especially in local and overall expansion and water loss. The aim of this study was to determine the rheological properties of bread dough in the heat-moisture dynamics of the baking process, especially in surface drying and delayed drying conditions. The DMTA method was used in tensile mode in order to expose the samples to fast dehydration to simulate real bread crust. The degree of starch gelatinization was demonstrated by the disappearance of the “Maltese cross” (polarized light microscopy). Temperature and water content were monitored during baking. The modulus evolution depended on both the heat and moisture evolution (i.e. immediate or delayed in the present study). In contrast to reports in the literature, starch gelatinization was observed even under drying conditions. Nevertheless, comparison between samples under drying and under delayed drying conditions suggested that water content prevailed in the rheological changes.     

我国春麦区部分小麦品种品质状况分析

1999年将 38份春小麦品种 (品系 )种植于内蒙古呼和浩特 ,对其磨粉品质和面包烘烤品质进行了评价。结果表明 ,我国春小麦品种的面包烘烤品质较差 ,不同地区品种间品质差异较大 ,辽宁和内蒙品种的磨粉品质和面包烘烤品质优于其它地区的品种。回归分析表明 ,蛋白质含量和单位蛋白质含量的面包体积决定了面包体积总变异的 99.9% ,硬度、沉淀值和吸水率对面包总分有重要作用。品种的出粉率主要取决于 1心槽路出粉率 ,2心和 1皮槽路出粉率对出粉率贡献也较大。高分子量麦谷蛋白亚基 (HMW GS)Glu A1和Glu D1位点的等位变异与品质性状密切相关。面包烘烤品质的改良应在分析HMW GS的基础上 ,将硬度作为选择指标之一 ,适当提高蛋白质含量 ,重点加强对沉淀值的选择