Extensional rheological properties in mixed and fermented/rested dough and relationships with steamed bread quality

In this study, sixteen wheat varieties for cultivation in China were examined for the flour characteristics using the farinograph, extensograph and rheofermentometer, uniaxial extensional rheology employing the extensograph and the Kieffer extensibility rig and biaxial extension by uniaxial compression of mixed dough with and without yeast, rested and fermented dough, and steamed bread quality including specific volume and texture properties. Three statistical analysis methods including Pearson correlation, principle component and stepwise multiple regression analysis were carried out to correlate dough properties with steamed bread quality. Biaxial extension viscosity was positively correlated with texture properties (hardness and chewiness) of steamed bread (r = 0.521–0.685, p < 0.05). Based on the correlation coefficients and the model (r² = 0.852, p = 0.003) obtained using stepwise multiple regression analysis, the best predictors for specific volume of steamed bread were the maximum resistance to extension of rested dough (r = 0.664, p < 0.01) and total work for breakage of fermented dough (r = 0.662, p < 0.01). Principal component analysis of rheological properties of fermented dough and flour characteristics provided more useful information for discriminating wheat flour quality and help breeders to select most convenient wheat flour for the steamed bread making.     

Rheological Behaviour of Wheat Glutens at Small and Large Deformations. Comparison of Two Glutens Differing in Bread Making Potential

The rheological characteristics of hydrated cv. Obelisk and Katepwa glutens, with poor and good baking potential, respectively, were studied at small and large deformations. Dynamic (oscillatory) measurements at small deformations over a frequency range of 0·03 to 3 rad/s showed that cv. Katepwa gluten had a higher dynamic modulus and a lower loss tangent than cv. Obelisk gluten. Overmixing resulted in increases in the dynamic moduli of both glutens. Measurements at different water contents indicated that the lower dynamic moduli at higher water contents resulted mainly from a concentration effect and were not due to water acting as a plasticiser. The apparent biaxial extensional viscosities of the glutens were determined by uniaxial compression of cylindrically shaped test pieces at various cross-head speeds. This proved to be a very useful method of providing information about the rheological behaviour of glutens at large deformations as a function of different strain rates. At every biaxial strain rate tested, the apparent biaxial extensional viscosity of cv. Katepwa gluten was higher than that of cv. Obelisk gluten. A thin layer of biaxially extended gluten showed a higher resistance to further biaxial extension than a less biaxially extended, thicker layer. Cv. Katepwa gluten exhibited this strain hardening behaviour to a greater extent than cv. Obelisk gluten. Possible consequences for baking performance are discussed.     

On the relationship between large-deformation properties of wheat flour dough and baking quality

Baking performance for bread and puff pastry was tested for Six European and two Canadian wheat cultivars and related to the rheological and fracture properties in uniaxial extension of optimally mixed flour–water doughs and doughs to which a mix of bakery additives was added. Extensive baking tests were performed as a function of water addition for puff pastry and as a function of water addition and mixing time for bread. For optimum baking performance, puff pastry doughs required lower water additions than bread doughs. Baking performance of the flours differed for the two products. For puff pastry, higher volumes were obtained per gram of flour than for bread. Puff pastry volume was positively correlated with optimum bread dough mixing time, while bread volume was not. Instead, bread volume was positively correlated with gluten protein content.All doughs exhibited strain hardening, a more than proportional increase of the stress with the strain. For all doughs fracture, stress and strain increased with increasing displacement speed of the hook and decreasing temperature. Large differences were observed between the cultivars regarding stress, strain hardening, strain rate-dependency of the stress, fracture stress and fracture strain. At both 25 and 45 °C, addition of a mix of bakery additives resulted in a decrease of the stress at relatively small strains and a significant increase of the strain hardening coefficient. Fracture strains remained the same or increased as a result of addition of the mix. Differences between flours regarding the strain rate and temperature-dependency of the fracture strain remained. The weaker the dough, the stronger the strain rate and temperature-dependency of the fracture strain.Puff pastry volume was positively correlated with strain hardening and negatively with the strain rate-dependency of the stress. In short, the stronger the dough, the higher the puff pastry volume. For bread, it were not the strongest doughs that gave the highest loaf volumes, but those with intermediate dough strength. Low volumes for puff pastry and bread were found for doughs having a low fracture stress and low strain hardening coefficients. Loaf volumes of flours with high dough strength (i.e. high stress-level and high strain hardening) gave intermediate loaf volumes. We concluded that a high stress can hamper the extensibility of dough films between gas cells, thus limiting the expansion of gas cells during fermentation and baking and hence the loaf volume that can be obtained.     

Strain Hardening Properties and Extensibility of Flour and Gluten Doughs in Relation to Breadmaking Performance

The mechanical properties of flour–water doughs and hydrated gluten of different wheat cultivars were determined. Measurements were performed at small deformations (dynamic measurements) as well as at large deformations (biaxial extension measurements). Results of dynamic measurements of flour doughs related poorly to breadmaking quality. For hydrated gluten doughs, all having the same water content, it was found that glutens from wheat cultivars with good baking quality had higher values for the storage modulus,G, and lower values for the loss tangent. The relevant type of deformation around an expanding gas bubble is biaxial extension. Wheats with a good baking performance exhibited greater strain hardening and greater extensibility. The differences in strain hardening observed at 20 °C were also present at 55 °C. No clear effects of NaCl or emulsifiers on the biaxial extension properties of flour dough were found. Extensograms as well as Alveograms from the flour doughs showed that, in general, good baking flours exhibited stronger resistance to extension and a greater extensibility, but differences found were not directly related to the results of the baking tests. The results indicate that the baking performance of dough is related to a combination of at least three different rheological characteristics.     

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     

Correlations of the Breadmaking Performance of Wheat Flour with Rheological Measurements on a Micro-scale

For the characterization of wheat quality, micro-extension tests for dough and gluten and a micro-baking test were developed using comparable dough compositions, the same mixing temperature and cultivar-specific mixing times. By means of these methods, the flours of 26 wheat samples were studied for dough development time, maximum resistance and extensibility of dough and gluten and loaf volume of the baked products. Standard methods (rapid-mix-test, gluten index determination) were used for comparison. The results indicated that the rheological properties of dough and gluten as well as the gluten index are correlated higher with the optimised micro-baking test than with the standard baking test. If flour protein or wet gluten content is included in the correlations, the extension test of gluten, which can be performed easily and reproducibly, allows a reliable prediction of the loaf volume obtained by the micro-baking test.     

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。     

Mechanism of gas cell stabilization in bread making. I. The primary gluten–starch matrix

Expansion of dough and hence bread making performance is postulated to depend on a dual mechanism for stabilization of inflating gas bubbles. Two flours were used in this study, one from the wheat variety Jagger (Jagger) and the other from a composite of soft wheat varieties (Soft). Thin liquid lamellae (films), stabilized by adsorbed surface active compounds, act as an auxiliary to the primary gluten–starch matrix in stabilizing expanding gas cells and this mechanism operates when discontinuities begin to appear in the gluten–starch matrix during later proving and early baking stages. Contributions of the liquid lamellae stability to dough expansion were assessed using flours varying in their lipid content. Incremental addition of natural lipids back into defatted flour caused bread volume to decrease, and, after reaching a minimum, to increase. Strain hardening is a key rheological property responsible for stabilizing the primary gluten–starch matrix. Jagger gave higher test-bake loaf volume than Soft and higher strain hardening index for dough. The different lipid treatments were found to have negligible effects on strain hardening index. Image analysis of crumb grain revealed that differences in number of gas cells and average cell elongation with different lipid treatments were insignificant. The evidence agrees with a dual mechanism to stabilize the gas cells in bread dough. To understand dough rheology at a molecular level, rheological properties of doughs were varied by addition of flour protein fractions prepared by pH fractionation. Fractions were characterized by SE-HPLC and MALLS. The molecular weight distribution (MWD) of fractions progressively shifted to higher values as the pH of fractionation decreased. Mixograph dough development time paralleled the MWD. However, the strain hardening index and the test-bake loaf volume increased with increasing MWD up to a point (optimum), after which they declined. At a given strain rate, the behavior at the optimum is thought to result from slippage of the maximum number of statistical segments between entanglements, without disrupting the entangled network of polymeric proteins. Shift of MWD to molecular weight higher than the optimum results in a stronger network with reduced slippage through entanglement nodes, whereas a shift to lower molecular weights will decrease the strength of the network due to a lesser number of entanglements per chain.     

Extensional Flow Studies of Wheat Flour Dough. II. Experimental Method for Measurements in Constant Extension Rate Squeezing Flow and Application to Flours Varying in Breadmaking Performance

An experimental method for biaxial extensional measurements on wheat flour doughs in a squeezing flow geometry is reported, in which the speed is controlled so as to be proportional to the gap between the disks, resulting in a constant extensional strain rate in the sample. In such measurements, the stress was obtained directly as a function of Hencky strain at constant pre-set strain rate. This allowed a straightforward evaluation of the strain hardening phenomenon, its onset and strength. Measurements were made at three strain rates and at Hencky strains varying from 0 to 3 for 15 winter wheat cultivars, five of high (H), five of intermediate (M) and five of low (L) protein content and baking performance. It was concluded that all three groups showed strain hardening, which started before a Hencky strain value of 1 was reached. All three groups, at all three strain rates satisfied the stability criterion n>_Hat all values of Hencky strain (n is the strain hardening index in the power-law representation σ=K_Hⁿwhere σ is the stress, _His the Hencky strain, and K is a constant). Differences between the groups were seen most clearly at the lowest strain rate: (i) the onset occurred at a lower Hencky strain, the higher the protein content and baking quality; (ii) the strain hardening index reached a maximum just before a Hencky strain of 2, where the H group had a 25% higher value than the M and L groups.     

The relationship between rheological characteristics of gluten-free dough and the quality of biologically leavened bread

The rheological characteristics of gluten-free doughs and their effect on the quality of biologically leavened bread were studied in amaranth, chickpea, corn, millet, quinoa and rice flour. The rheological characteristics (resistance to extension R, extensibility E, R/E modulus, extension area, stress at the moment of dough rupture) were obtained by uniaxial dough deformation. Specific loaf volume of laboratory prepared gluten-free breads was in significant positive correlation with dough resistance (r = 0.86), dough extensibility (r = 0.98) and peak stress at the moment of dough rupture (r = 0.96). Even if the correlation between R/E modulus and the characteristics of loaf quality were not significant, the breads with the highest specific loaf volume were prepared from flours with R/E closer to the wheat check sample (18 N?mm-1). The results showed, in general, good baking flours exhibited stronger resistance to extension and greater extensibility, but differences found were not directly related to the results of baking tests.     

面包烘焙品质与小麦品质性状的相关性

为了了解适宜的面包小麦的品质指标范围，对58个小麦品种(系)的面包烘焙品质与小麦品质性状的相关性进行了分析与研究，将58个品种(系)的面包总评分分为三个梯度与小麦品质性状进行比较，结果表明，面包总评分和面包体积与蛋白质含量、湿面筋含量、沉淀值、吸水率、延伸性呈显著正相关，与抗延阻力相关不显著；面包芯平滑度与蛋白质含量、湿面筋含量、沉淀值、形成时间呈显著正相关；纹理结构与蛋白质含量、湿面筋含量、沉淀值、延伸性呈显著正相关；面包弹柔性与蛋白质含量呈显著正相关；与其它指标相关性不显著．     

Dough mixing characteristics measured by Mixsmart software as possible predictors of bread making quality in three production regions of South Africa

South Africa has three wheat production regions, the winter rainfall region where spring wheat is planted; the summer rainfall where winter and intermediate wheat is cultivated; and the irrigation region where spring wheat is grown. The aim of this study was to determine dough mixing characteristics as measured by Mixsmart^® software in these three regions over seasons and locations, and to relate this to important quality characteristics. In the winter rainfall area Mixsmart characteristics were very poor predictors of baking quality, especially of loaf volume, flour protein content and wet gluten content. The best predictors of loaf volume in this region were flour protein content and wet gluten content, which were highly interrelated. In the irrigation area, midline peak value and midline right value were very good predictors of flour protein content, gluten content and loaf volume. Midline peak value was highly correlated with protein content in both the irrigation and summer rainfall areas and was a better predictor than peak time of baking quality. The ideal would be to select several parameters from the mixograph and use them in a multivariate statistical analysis to obtain a more accurate prediction of loaf volume in the irrigation and summer rainfall areas.     

Oat malt as a baking ingredient – A comparative study of the impact of oat,barley and wheat malts on bread and dough properties

Oat malt is a nutritionally rich ingredient mainly used in a small number of speciality products. The aim of this study was to evaluate the suitability of oat malt in wheat baking. The effect of oat malt on bread and dough properties at levels ranging from 0.5% to 5% was studied and compared with barley and wheat malts. The addition of all malts increased loaf specific volumes. Barley and wheat malts at levels above 2.5% led to a sticky and coarse crumb, but the effect of oat malt on the crumb grain was negligible. Rheological characterisation could not explain the superior baking performance of oat malt, as it increased extensibility and decreased resistance extensively indicating weakening of the extensional properties of the gluten network. The high lipolytic activity may have compensated for the loss of dough strength by improving the surface properties of gas cells. The results show that oat malt can be used in wheat baking to improve the loaf volume and nutritional quality without the detrimental effects associated with the excess amylolytic activity of barley and wheat malts.     

Oat malt as a baking ingredient – A comparative study of the impact of oat,barley and wheat malts on bread and dough properties

Oat malt is a nutritionally rich ingredient mainly used in a small number of speciality products. The aim of this study was to evaluate the suitability of oat malt in wheat baking. The effect of oat malt on bread and dough properties at levels ranging from 0.5% to 5% was studied and compared with barley and wheat malts. The addition of all malts increased loaf specific volumes. Barley and wheat malts at levels above 2.5% led to a sticky and coarse crumb, but the effect of oat malt on the crumb grain was negligible. Rheological characterisation could not explain the superior baking performance of oat malt, as it increased extensibility and decreased resistance extensively indicating weakening of the extensional properties of the gluten network. The high lipolytic activity may have compensated for the loss of dough strength by improving the surface properties of gas cells. The results show that oat malt can be used in wheat baking to improve the loaf volume and nutritional quality without the detrimental effects associated with the excess amylolytic activity of barley and wheat malts.     

Effects of Wheat Variety and Processing Conditions in Experimental Bread Baking Studied by Univariate and Multivariate Analyses

The effects of variety, mixing conditions and fermentation time on bread loaf characteristics were studied by univariate and multivariate statistical methods. Nearly all the measured bread loaf characteristics were significantly affected by variety, fermentation time, and mixing conditions. Significant interactions were also found. Multivariate analysis (principal component analysis; PCA), was used to find the main variation among the bread samples and to identify the bread loaf characteristics that contributed to describe this variation. The characteristics loaf volume and weight described a large part of the main variation among the loaves and these characteristics were studied in more detail by response surface methodology. The loaf volume and weight response surfaces for varieties, which by multivariate analysis were found to have common properties, followed similar general patterns. It was shown that the experimental design used provided information about the baking performance of wheat flours over a wide range of experimental conditions and, thus, can be a useful supplement to standardised and optimised baking tests.     

Rheological properties of kafirin and zein prolamins

The possibility of forming dough from kafirin was investigated and laboratory prepared kafirin was formed into a viscoelastic dough system. Measurements with Contraction Flow showed that dough systems prepared from kafirin and from commercial zein had the required extensional rheological properties for baking of leavened bread. The extensional viscosity and strain hardening of the kafirin and zein dough systems were similar to those of gluten and wheat flour doughs. The kafirin dough system, however, unlike the zein dough system rapidly became very stiff. The stiffening behaviour of the kafirin dough system was presumed to be caused by cross-linking of kafirin monomers. SDS-PAGE showed that the kafirin essentially only contained α- and γ-kafirin, whereas the zein essentially only contained α-zein. Since γ-kafirin contains more cysteine residues than the α-prolamin it is more likely to form disulphide cross-links, which probably caused the differences in stiffening behaviour between kafirin and zein dough systems. Overall the kafirin dough system displayed rheological properties sufficient for baking of porous bread. Kafirin like zein appears to have promising properties for making non-gluten leavened doughs.     

Comparison of predictions of baking volume using large deformation rheological properties

Three large deformation rheological tests, the Kieffer dough extensibility system, the D/R dough inflation system and the 2 g mixograph test, were carried out on doughs made from a large number of winter wheat lines and cultivars grown in Poland. These lines and cultivars represented a broad spread in baking performance in order to assess their suitability as predictors of baking volume. The parameters most closely associated with baking volume were strain hardening index, bubble failure strain, and mixograph bandwidth at 10 min. Simple correlations with baking volume indicate that bubble failure strain and strain hardening index give the highest correlations, whilst the use of best subsets regression, which selects the best combination of parameters, gave increased correlations with R²=0.865 for dough inflation parameters, R²=0.842 for Kieffer parameters and R²=0.760 for mixograph parameters.     

黄淮冬麦区强筋小麦品种的产量及品质分析

为了解当前黄淮冬麦区强筋小麦品种的产量和品质表现,选用9个近年来黄淮麦区育成、在河南省大面积推广种植的强筋小麦品种,种植于河南的郑州和泛区,按AACC或国标的方法对其蛋白质和淀粉品质进行分析。结果表明,供试强筋小麦品种的产量显著低于高产对照品种周麦18;有5个品种的有效穗数显著高于周麦18,有3个品种与周麦18差异不显著;分别有1个品种的穗粒数、千粒重与周麦18差异不显著,其余品种均显著低于周麦18。说明黄淮冬麦区强筋小麦品种的穗粒数和千粒重有待提高。分析各品种的品质指标,对于湿面筋含量,有5个品种在两个试点均达国标,有2个品种在一个试点达国标;弱化度、面包体积、面包评分等反映面筋质量的品质指标均表现为郑州点优于泛区点;弱化度、面包体积在2个试点的差异达极显著水平;面包评分在2个试点的差异达显著水平。含5+10亚基的品种中,非1BL/1RS易位品种的烘焙品质显著优于1BL/1RS易位品种。郑麦366、师栾02-1、新麦26的麦谷蛋白亚基构成和面包烘焙品质均较优。郑麦366、矮抗58的峰值黏度较高,淀粉糊化特性较好,适合制作优质面条。     

不同品质类型小麦阿拉伯木聚糖流变性质的研究

为了解阿拉伯木聚糖流变性质及其与小麦品质的关系,对不同品质类型的小麦（强筋、弱筋）阿拉伯木聚糖(简称WEAX)的零剪切黏度（η0）及酶促氧化胶凝能力等指标进行了研究。结果表明,不同品质类型小麦间WEAX溶液的黏度特性存在一定差异,零剪切黏度值（η0）变幅为0.20～56.50 Pa·s,大部分集中在0.20～2.43 Pa·s,个别品种（中优206、烟农19）数值偏差较大。在过氧化物酶体系(POX/H2O2)作用下,WEAX凝胶特性（G′、G″值）差异显著,强筋与弱筋小麦中均存在胶凝能力或强或弱的品种,说明WEAX的上述流变特性与小麦筋力（或硬度）无直接关系。     

不同糯小麦品种(系)品质及其烘烤制品研究

为推动糯小麦的品质改良及开发利用,以国内不同育种单位育成的多个糯小麦为试验材料,以普通强筋、中筋及弱筋小麦作为对照,分析其淀粉组分、糊化特性、面团流变学特性,并对其制作的酥条进行比较。结果表明,糯小麦的淀粉含量及直链淀粉含量显著低于普通小麦;在淀粉糊化特性上,糯小麦的低谷黏度、最终黏度、回生值显著低于普通小麦,峰值温度高于普通小麦;在粉质仪参数上,糯小麦的吸水率显著高于普通小麦,形成时间、稳定时间及粉质质量指数均显著低于师栾02-1,糯小麦弱化度较高,显著高于师栾02-1和扬麦158;糯小麦制作的酥条体积、酥性显著高于普通小麦,硬度显著低于普通小麦,气孔大且均匀,横截面积明显大于普通小麦。不同糯小麦品种(系)间比较,扬17G76、天糯158、扬14-282及扬糯麦1号在面团流变特性和制作酥条上表现较为优异,表明通过提高糯小麦筋力有助于改善糯小麦面团流变学特性及烘烤食品品质。本研究结果可为糯小麦育种及品质改良提供理论依据。