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Bread: Dough Mixing and Testing Operations
Bread: Dough Mixing and Testing Operations S To¨mo¨sko¨zi, Budapest University of Technology and Economics, Budapest, Hungary F Be´ke´s, FBFD PTY LTD, Sydney, NSW, Australia ã 2016 Elsevier Ltd. All rights reserved.
Introduction
Mixing and Dough Making
The fundamental basis of utilizing wheat flour as one of the most important food source around the world is its unique property of forming dough and developing gluten when it is mixed with water. Wheat gluten is a protein–lipid–carbohydrate complex formed as a result of specific covalent and noncovalent interactions from flour components during dough making as the components are hydrated and energy from mechanical input from the mixing process is provided. Wheat varieties at the same protein level were found to differ in their bread-making quality, giving the first indication of protein quality. Protein content and its composition are important determinants of good bread-baking quality. Gluten-forming proteins contribute 80–85% of the total wheat protein and are the major storage proteins of wheat. They belong to the prolamin class of seed storage proteins. Gluten proteins are largely insoluble in water or dilute salt solutions. Two functionally distinct groups of gluten proteins can be distinguished: monomeric gliadins and polymeric (extractable and unextractable) glutenins. Gliadins and glutenins are usually found in more or less equal amounts in wheat. Large level of polymorphism of wheat prolamins results in a special effect in relation to the overall functional properties of wheat dough. During dough formation when prolamin proteins are hydrated and form the gluten network, the numerous structurally similar but slightly different proteins produce a mass in which several characteristics (such as size, polarity, charge distribution, solubility, and viscosity) show a continuous distribution in a relatively large interval. This structural feature provides a unique characteristic of gluten proteins among any other protein systems.
Dough mixing is a very important stage in the bread-making process. The extent of mixing has a critical impact on final bread quality. The mixing process promotes different physical, chemical, and physicochemical modifications that contribute to the dough development.
Phases of Bread-Making Process The bread-making process has several functions, accomplished at different stages in the preparation and baking of dough: (a) mixing of flour and water, together with yeast, salt, and other ingredients in specified ratios to form the dough; (b) developing the gluten structure of hydrated proteins through application of energy during mixing (a stage often termed ‘kneading’); (c) incorporating air bubbles within the dough during mixing; (d) continuing the development of the gluten structure after kneading to improve its ability to expand when gas pressures increase (a stage termed ‘ripening’ or ‘maturing’); (e) creating or modifying flavor compounds in the dough; (f) subdividing the dough mass into unit pieces; (g) modifying the shape of the divided dough pieces; (h) resting to allow further modification of the dough pieces’ physical and rheological properties; (i) shaping to achieve required configuration; (j) proofing (fermenting and expanding) the dough; and (k) expanding and fixing the dough into its final shape by baking.
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Chemical, Physical, and Physicochemical Alterations during Dough Mixing Stages Dough chemistry involves a series of interactions between carbohydrates, lipids, and proteins. The principal physical science involved with dough making is rheology (see in the succeeding text). Good baking quality depends on several rheological properties such as extensibility exceeding a minimum level, viscosity, strain hardening, and optimal resistance to deformation. Dough is viscoelastic, combining properties of a Hookean solid with those of a non-Newtonian viscous fluid. Dough is essentially foam, which becomes sponge after baking. The transformation from the closed cell structure of a foam to the open cells of a sponge is one of the many changes that occur during dough processing. Individual dough-property parameters describe only certain essential elements of dough properties. Depending on the final product, different levels of these attributes are required to get superior processing quality. For example, the balance of dough strength and extensibility is believed to be the most important factor governing the suitability of a flour to make good bread. However, for different types of breads and even for different types of processing technologies, a diversity of dough strength and extensibility values may provide the optimum balances needed in each case. The complexity of relating protein composition to quality derives from the fact that the question can (and has to) be investigated on different levels of protein composition, namely, protein content, the ratio of polymeric proteins to monomeric proteins, the ratio of high-molecular-weight (HMW) glutenin subunits to low-molecular-weight glutenin subunits, and the proportions of x-type and y-type HMW glutenin subunits. These various parameters can be determined for a specific flour sample to see if there is a ‘good balance’ between the various components in the sample, thereby to satisfy quality-related criteria. The polymeric glutenin is mostly responsible for the elasticity of the dough, whereas the monomeric gliadins are the extensibility-related characters in the system. Thus, the ratio of polymeric proteins to monomeric proteins (the glutenin-to-gliadin ratio) can be directly related to the balance of dough strength and extensibility of the sample. Two preconditions must be met for the production of dough with the right properties: (a) appropriate proportioning
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Bread: Dough Mixing and Testing Operations
of the individual ingredients as established in a well-balanced dough formulation and (b) homogenous distribution of these ingredients throughout the dough mass. In its essentials, dough mixing involves the combining and blending of the formula ingredients and then applying sufficient physical work to the mixture to transform it into a cohesive mass with the requisite viscoelastic properties. In large-scale commercial bakery production, the major ingredients (flour and dry sweeteners) are normally weighed by automatic scales that feed directly into the mixers, while water, liquid shortener, and liquid sweeteners are piped into the mixer through meters that can be preset to deliver specified volumes. In addition to achieving a thorough dispersion of the ingredients into a homogeneous mixture, the dough mixing process in bread making has the further important objective of physically developing the gluten proteins into a coherent threedimensional structure that will impart to the dough the desired degree of plasticity, elasticity, and viscosity. The initial mixing phase must physically hydrate the flour particles and incorporate air to nucleate gas cells responsible for leavening. In other words, mixing has three functions: (a) creating a homogenous mass from ingredients of differing characteristics, (b) developing (kneading) the dough sufficiently to ready for subsequent processing, and (c) occluding air into the mass to form the cell structure necessary for finished crumb quality. At the beginning of the mixing, blending action leads to an even distribution of the dough ingredients and ensures hydration and swelling of flour particles. Wheat flour dough or batter may appear to be uniform and well mixed, but actually, it is multiphasic: starch, gluten proteins, lipids, and water representing the principal phases. Furthermore, the form of these phases changes during periods of mixing that prepare them for separation or food uses. Microscopic changes begin with the instant formation of protein fibrils at first contact of water and flour particles. Slow mechanical development induces these fibrils to coalesce into fibrous bands or tendons and segregates the starch into clusters. When flooded with a displacing fluid, this open, spongelike structure readily releases the entrained starch. Additional development disbands the protein into relatively fine, uniformly distributed, and networked or webbed filaments that entrap the starch and gas bubbles formed when the dough is fermented and baked. The physical properties of hydrated wheat proteins are the result of covalent and noncovalent interactions of wheat gluten proteins. These interactions are altered by the repeated extension, tearing, and compression during mixing or development. Specific chemical effects include (1) disulfide bond disruption, (2) chain disentanglement and rupture, (3) disulfide–sulfhydryl interchange, (4) formation of dityrosine cross-links, (5) formation of new disulfide cross-links, (6) free radical interactions, and especially (6) reorientation leading to enhanced hydrogen bonding. Mixing produces a homogeneous gluten film regularly distributed around the starch granules. The dough must be mixed for a specific time (referred to as optimum dough development) to ensure optimal loaf volume and bread texture. Stopping mixing before the optimal point results in undermixed dough that gives bread of inferior volume and crumb quality. The optimal mixing requirement is a specific characteristic of each wheat flour. Beyond optimum dough development time,
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overmixing induces dough stickiness, decreases dough consistency (due to degradation by shearing effects), and negatively affects bread quality. Stability of the gluten–starch matrix – the primary stabilizing factor for expanding gas cells against disproportionateness and coalescence – depends on its tendency to strain harden. The phenomenon of strain hardening appears to depend on the balance between strength and extensibility of the entangled network of polymeric proteins of wheat flour. Extensibility ensures slippage of the maximum number of statistical segments between entanglements, whereas strength prevents disruption of the entangled network of polymeric proteins. Thus, to ensure stability of gas cells, the dough needs to be not only sufficiently extensible to respond to gas pressure but also strong enough to resist collapse. A good gas-holding capacity of dough is necessary for producing a loaf of bread with light and even crumb. The strain hardening properties of gluten are vital to avoid early rupture of gas ‘cell wall’ during proofing. The gas phase of bread, which makes up more than 70% of the final volume of a loaf, has a major influence on its textural and sensory attributes. Controlling the gas phase volume is a major challenge as during proving and early stages of baking gas must be captured within bread dough, only being released at the end of baking. The main factors, important in determining the gas cell structure, include (1) the formation of the initial foam structure during mixing and (2) stabilization of the foam structure, including those factors governing bubble disproportionateness and coalescence. There is particular focus on the role that the thin film lining the bubbles may play in stabilizing the foam structure of a risen dough. The surface properties of components have been suggested to be the important factor to the stability of gas cells. Recently, proteomic methods have been used to identify foam-forming soluble proteins from dough that may play an important role in stabilizing gas bubbles in dough and hence influence the crumb structure of bread. Proteins from a soluble fraction of dough (dough liquor) or dough liquor foam have been separated and identified. Major polypeptide components included b-amylase, tricitin, and serpins, with members of the a-amylase/trypsin inhibitor family being particularly abundant. Neither prolamin seed storage proteins nor the surfaceactive protein puroindoline was found. Differences in gluten quality can significantly affect the bread-making potential. Strength is conferred by the fraction of polymeric proteins having molecular weight greater or equivalent to a critical size, MT, (250 000 kDa), and the fraction of gluten protein smaller than MT may counter the strength by acting as diluents. The optimum balance seems to exist when the relative proportions of polymeric proteins greater and smaller than MT are roughly 60:40. Shift in the balance to either side will decrease loaf volume. Increase in smaller proteins (less than MT) may decrease stability of the gluten–starch matrix due to a lesser number of entanglements per chain. On the other hand, increase in strength conferring proteins may prevent sufficient expansion of the gluten–starch matrix required to increase loaf volume due to reduced slippage of gluten polymers through entanglement nodes as a result of increase in number of entanglements per chain. The secondary stabilizing mechanism involves thin liquid lamellae stabilized by adsorbed surface-active compounds (lipids and
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proteins) at the gas–liquid interface. Liquid lamellae prevent coalescence and disproportionateness of gas cells when they come in close contact with each other during the late proving and early baking stages of bread making, that is, when discontinuities begin to appear in the gluten–starch matrix. Flour lipids at their natural levels do not influence rheological properties of the gluten–starch matrix surrounding the gas cells, as measured by the dough inflation system. Nevertheless, the small amounts in which these lipids are naturally present are sufficient to influence surface properties. This short and simplified description of well-accepted observation-based hypothesis of dough behavior underlines the essential importance of size distribution of gluten proteins in relation to their role in determining dough properties. As a consequence of this, a combination of reducing agents, oxidizers, and proteolytic enzymes is frequently used in the baking process to alter dough properties through their effects on the disulfide bonds in the gluten structure. Functional additives play a big role in modern bread making. Among the improvers, ascorbic acid is the most important in modern bread formulation to oxidize flour proteins to improve gluten strength. Other such ingredients (and their functions) include azodicarbonamide (oxidizing agent), cysteine (reducing agent), mono- and diglycerides (emulsifiers and antistaling agents), calcium propionate (mold inhibitor), stearoyl lactylate (dough strengthener), soy flour (crumb whitener), Table 1
dextrose (fermentable sugar source for the yeast), ammonium chloride (nitrogen source for yeast), enzymes (starch and protein adjustment), and, occasionally, gluten (strengthener).
Dough Preparation Systems No single standard method for mixing ingredients to create dough is followed by all bakers; instead, more than a halfdozen different procedures can be used. The detailed characterization of these methods is shown in Table 1. Baker preference, product type, and plant practice determine the choice of method. Preparation of the dough can be done in batches or continuously, and fermentation times vary from none to several hours. Today, most commercial bakers prepare dough as separate batches, sized sufficiently to permit an uninterrupted production schedule but not too large to risk overaging the dough as it waits in the divider hopper. The continuous mix method was developed during the 1950s to automate dough preparation. At one time, it was used by the majority of bakeries producing white pan bread, but this method fell out of favor when consumer demand for variety bread increased starting in the late 1970s. Technologies that grew up around continuous mix such as water brews and liquid sponge, however, remain in wide use for lines dedicated to baking long runs of fast-food buns and similar products.
Overview of the most generally used dough preparation systems
Dough system
Bread and related product produces
Advantages
Disadvantages
Straight dough
Lean formula hearth bread, pita bread, 100% whole wheat
Sponge and dough
Sponge and dough bread and rolls
Liquid sponge
Sponge and dough bread and rolls
Continuous mix
White pan bread, hamburger/hotdog buns
Good flavor Medium process time Good mixing tolerance Good fermentation tolerance Superior product score Good dough handling Longer product shelf life Uniformity of product Medium process time Good flavor with high amount of flour in the sponge Same advantages as liquid sponge if fermented Less equipment, labor, and space used
Difficult dough handling Long mixing time Poor fermentation tolerance Poor mixing tolerance Long process time High-cost equipment Larger space equipment High-cost equipment Limited to 50–60% of flour in sponge Lack of flavor and shelf life with low flour in sponge Limited to 50–60% of flour in sponge
No-time dough
Frozen dough, bagels, hard rolls, pizza crusts, dinner rolls, variety pan bread, English muffins
Chorleywood process
Hamburger/hotdog buns, variety pan bread, rye bread
Authentic sourdough process
Source: O’Donell (1996).
Authentic sourdough breads and buns
Lack of crumb strength
Short production time Greater flexibility Less equipment and space Superior yeast survival in freezing Tolerant to low-protein flours
Lack of flavor and shelf life with less fermentation Lack of flavor Lack of shelf life Higher ingredient costs Problem with floor time High equipment cost
Short production time Greater flexibility No floor time problems Sourdough flavor Increased shelf life ‘Blistered’ appearance Chewy, resilient texture
High energy cost Lack of flavor Lack of product shelf life Very long process times Nurturing of sponge Less consistency Increased space requirement
Bread: Dough Mixing and Testing Operations
Among mixing methods being practiced commercially, the most prevalent is the sponge-and-dough process that involves two mixing stages, namely, one of the sponge and the other of the dough. The sponge mixing stage aims at homogeneous ingredient dispersion and flour hydration and is normally of relatively brief duration, whereas the more critical phase of dough development is reserved for the more extensive mixing of the final dough. In the straight-dough method, as well as in those systems that employ various forms of liquid preferment, there is but one mixing stage in which complete dough development must be achieved. White pan bread is highly standardized, has wellrecognized quality characteristics, and represents the main product style in many parts of the world. Some countries, notably France, take the baguette as the standard product. Table 1 shows the advantages and limitations of the most important methodologies based on the excellent review of Mihalos.
Testing Operations Introduction Dough testing methodologies are essential tools through the whole wheat chain from basic research, prebreeding, selection for quality attributes during breeding, characterizing source material, quality control, process, and product development in the wheat-based food industry. Testing operations can be classified as direct dough testing methods and indirect methods where dough properties are estimated from chemical, physicochemical (spectral), or physical (sedimentation) characteristics. Dough properties, directly related to the bread-making quality of the sample, describe certain viscosimetric or rheological properties of the dough, so the dough testing investigations apply viscosimetric and rheological principles. In general, viscosimetric methods show strong relationships to the starch composition of the samples, while the rheological properties are directly related to both qualitative and quantitative aspects of gluten protein composition. Some basic information on the direct dough testing methods is given here, with special emphases on the small-scale and microscale testing methods, which revolutionized our understanding about structure–function relationships in wheat dough in the last 30 years. Only some key references are given about the principles, solutions, and achievements of indirect methods in the paragraphs summarizing future trends in the area.
Basic and Empirical Rheology Rheology is the science of the deformation and flow of materials as a response to physical stresses. The deformation can be classified as elastic or inelastic, while the flow properties of a material can be described as plastic or viscous behavior. Ideal elastic bodies undergo reversible elastic strain when anisotropic forces are applied. In this case, the applied energy is partly stored. In case of ideal viscous body, irreversible changes can be observed, where the exerted energy is
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transformed. Viscous fluids generally exhibit viscosity, while solids exhibit elasticity. The aim of fundamental rheology is trying to describe and model the physical behavior of materials by studying the relationships between molecular composition and the observed deformation. Widely applicable instruments (viscometers, rheometers, etc.) and/or specific, often purpose-built methods are used for this purpose. The resulting information, however – despite its scientific merit – does not satisfy the demands dictated by the practice: Fundamental rheology methods often do not differentiate enough among samples and, most importantly, they are not suitable for high-throughput, reasonably cheap routine application in selecting for quality in plant breeding or in case of quality control in the food industry. During the first quarter of the last century, several empirical rheological equipments and methodologies have been developed, and the last 100 years proved that these standardized methodologies can be applied fruitfully for the comparison/ rating of samples derived from the breeding or industrial operations. The collected/archived data derived from these analyses form an invaluable knowledge base based on which the new wheat cultivars and new wheat products of the future can be developed.
Traditional empiric rheological methods and instruments As it was mentioned earlier, when wheat flour, water, and other related ingredients are mixed, the whole system undergoes a number of chemical reactions and physicochemical and physical changes during dough formation. The type and the rate of these changes highly depend on the composition of wheat flour, on the ingredients, and on the parameters of dough mixing like length mixing, energy input, and temperature. Molecular processes related to the aforementioned changes can be monitored by the continuous measurement of physical (rheological) properties of dough from the starting stage of homogenization through the formation of protein–carbohydrate–lipid–water complex (gluten) until its certain break caused by overmixing. Wheat dough has both elastic and flowing properties; therefore, it shows a complex viscoelastic behavior. Therefore, the main challenge in the development of empiric rheological methods and instruments has been how one can apply adequate external forces on the dough to measure both elastic strain and viscous flow in one system. Two principally different empiric rheological methodologies have been developed: mixing methods to monitor dough formation and stretching methods for the determination of dough strength and extensibility. In case of the latter process, dough is mixed to its optimum consistency in a separate process followed by a relaxation step before stretching. So, the two methods together mimic the industrial bread-making technology with one important exception: instead of a full formulation of the dough, including yeast, dough is mixed here with either water or salt solution. Mixing methods: The traditional simple solution for detecting the physical changes in a dough is the utilization of standardized (laboratory) mixers with the recording of torque on the mixing arm(s) and/or bowl. The first recording laboratory mixers – regarded as the forerunners of the first commercial machines developed later on, the Swanson–Working
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Bread: Dough Mixing and Testing Operations
mixograph and Brabender farinograph – have been developed by the Hungarian inventor Jeno˝ Hanko´czy. The working principle of the farinograph is to monitor the torque (energy requirement) during the continuous but relatively gentle mixing of wheat flour – added water system at constant speed and temperature (at 30 C). The sigmoid (or Z-type) shape of the mixing blades is very unique, which is able to knead and extend the dough, periodically. The torque that arises from dough resistance against mixing was originally measured using a special balance system and replaced later with electronic recording systems. Basically, dough resistance, detected in this equipment, is determined by the rheological properties of dough, particularly viscosity, but the surface properties of the dough, sticking to the bowl walls and blades, also contribute to the measured values. The comparability of different dough behaviors (or flour quality) is ensured with the standardization of maximum dough resistance. Beyond the mixing parameters such as mixing speed and resistance measured with this system, there is the function of the flour behavior and the amount of water added to the flour. The huge success of the farinograph spreading all around the wheat chain as early as the 1930s derived from the idea of using this direct relationship between the amount of water in the system and resistance for the determination of the most
important quality attribute of the flour, water absorption, which is the amount of water needed to be added to the flour to reach the constant consistence (500 or 600 farinograph or Brabender units, BU) of dough. The routine investigation on the farinograph is a two-step process: water absorption of the flour is determined through a ‘titration-like’ process, followed by the main mixing experiment using this amount of water to characterize the rheological properties of the dough such as dough development time, stability, and degree of softening (Figure 1). The detailed description of the farinograph method including the evaluation of curves is summarized in different standard methods (ICC, AACCI, ISO, etc.). The second traditional type of recording dough mixer is the mixograph. The main difference between these two mixers is the mixing action. The mixograph equipped with pin mixers, where a pull–fold–repull type of movement is applied causing much greater mechanical stress on dough than that in the farinograph or other Z-arm-type mixers. In case of mixing with mixograph, there is no predetermined optimum consistency of dough; therefore, other methods have to be used for measuring the optimal water absorption. Two methods are used in practice: (a) Samples are compared with a uniform amount of water added and
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Mixing Tolerance Index
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300 200 Peak time
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Figure 1 Important farinograph parameters.
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Bread: Dough Mixing and Testing Operations
(b) the water used in the mixing experiments is calculated based on the protein content of the investigated flours. The parameters generally determined by the evaluation of the recorded mixogram (Figure 2) are as follows: peak time (similarly to the dough development time), maximum peak height, the height of the curve at a specified time after peak (characterizing the tolerance against overmixing, similarly to the farinographic stability), the angle between the ascending and descending portions of the curve (tolerance angle, T ), the weakening angle (W), and the area under the curve are defined. High-speed recordings obtained with a 35 g mixograph equipped with a strain gage allowed the high-resolution monitoring of the mixing action. These recordings provided data essential for developing a mathematical model of dough mixing: dough mixing on pin mixers can be interpreted as a complex, periodic series of pushing and stretching the dough around the pins. Each individual peak represents one of these circles, and so, their size and shape are characteristic to the stage of dough development, and they can be used to determine dough strength and elasticity of the dough (details (a), (b), and (c) of Figure 2 illustrate three regions of the highresolution mixing curve ((a), (b), and (c)), illustrating the hydration, dough development, and overmixing phases of the mixing). Bandwidth parameters (BWPR, BWBD, and TMBW), directly related to elasticity, in the mathematical model are also shown. Some other instruments developed by different producers (valorigraph, doughLAB, etc.) work on the same or similar principle as described earlier, with different sizes of mixing bowls and arms for mixing 10–300 g of flour. Stretching methods: Elasticity is the most unique property of wheat dough, and it mostly depends on the protein–wheat gluten composition and quality. Extensibility of wheat dough
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is responsible for the extent of expansion during leavening; therefore, it basically determines the baking performance and the quality of final products. In all stretching tests, to determine extensibility, the dough produced by one of the standardized mixing methods is then submitted to large deformations until rupture occurs and the resistance against stretching strain is recorded. Two types of extension methods are used: in uniaxial extension test, the dough is stretched in one direction, while in case of biaxial method, the dough is extended in two opposing direction. The most traditional and commonly used equipment is the Brabender Extensograph, introduced in 1936. The operation of this instrument is based on the principle of mechanical stretching in simple tension. The investigated dough samples are prepared in the farinograph mixer with optimum water absorption, and then, aliquot pieces of the dough are molded with special tools. During the measurement, the resistance of formed dough pieces to stretching and the distance the dough stretches before breaking are recorded on the extensogram (Figure 3). The following parameters are determined/calculated: the maximum resistance (Rmax), the resistance at a constant extension (generally at 50 mm, Rx), extensibility (the maximum length of extension before rupture, E), the ratio of maximum resistance to extension (as an indicator of the balance between elastic and viscous behaviors, Rmax/E), and the area under the curve (as extensional work, A). In some cases, the applied methods can differ in some parameters, like constant extension and resting time of dough before measurement. The desired quality of dough means a good combination of dough resistance and extensibility. The first device for measuring the biaxial extension character of wheat dough was also developed by Hanko´czy, while the principle of dough inflation test was developed by Marcel
b
MT
Resistance
RBD BWPR c a
BWBD
PR
0 TMBW a - Hydration
200
400
600
800
MBW b – Dough development
c – Dough overmixing
Figure 2 The most important parameters determined from the mixograph curve. MT, mixing time; PR, peak resistance; RBD, resistance breakdown; BWPR, bandwidth at peak; MBW, maximum bandwidth; TMBW, time to maximum bandwidth. High-resolution data recording of regions a, b, and c show the stages of hydration, dough development, and overmixing, respectively.
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EU
Maximum Resistance (Rmax)
Resistance
5 cm Energy (cm2)
mm Extensibility Figure 3 The determination of dough strength (Rmax) and extensibility from the extensograph curve (extensogram).
Dough tenacity
P Deformation energy W
Dough extensibility L Figure 4 The determination of dough tenacity (P), configuration ratio(P/L), and deformation energy (W) and from the alveograph curve (alveogram).
Chopin in 1927. Today, the most widely known and standardized biaxial extension test is the alveograph method, which is based on the principle of dough inflation or bubble expansion technique. This procedure mimics the microprocesses occurring in dough during fermentation in macroscale, namely, the formation of thin membranes around the CO2 bubbles. The Chopin Alveograph consists of a special thermostated, onescrew mixer for mixing and extrusion of dough, a bubble blowing apparatus, and the recording manometer. During the measuring procedure, dough disks are prepared, rested, and then inflated by constant air flow. The pressure inside the dough bubble until rupture is measured and recorded on the alveogram (Figure 4). The most generally read or calculated parameters are the maximum overpressure (an indicator of the dough tenacity, P), the average abscissa at rupture (characterizes the extensibility, L), configuration ratio (P/L), and the area under the curve (as deformation energy, W). The extension tests are also used for investigating the effects of natural or artificial modifying agents, like bugs, enzymes, oxidants or reducing components, and lubricants. The results, recorded curves, and determined parameters of the two methods are very similar. However, because of the different mixing procedures and measuring principle, the comparability of the results is limited and depends also on the type and variety of the samples.
Viscometry as a tool for investigation of the hot phase of the bread-making process The conventional dough rheology is mainly connected to the protein-dependent dough properties in the first, not heated phase of bread making. Starch as the main component of wheat flour also affects the quality-related properties, even the rheological properties of the dough, mostly as diluent of
the proteins and as a consequence of altered hydration during gelatinization in the oven. Additionally, starch is exposed to enzymatic breakdown, depending on the a-amylase activity of the flour and physical braking during the milling process resulting in damaged starch. An optimal level of enzymatic activity and amount of damaged starch are necessary for the optimal fermentation processes in baking. However, high enzyme activity or a high ratio of hydrolyzed starch results in a weaker water-holding capacity, resulting in serious drop in the end-product quality. Therefore, starch-related viscosity-based characterization of samples is an essential part of source material quality control in the baking industry, and the balanced amylolytic activity is part of the selection criteria during breeding. Starch properties are usually studied at high temperatures – similar to conditions of the baking process. Generally, the starch characterization is performed by different viscometers, carrying out measurements on temperatures appearing in the technology. The most frequently used standardized method for investigation of a-amylase activity of the grain/ flour is the determination of falling number on a special falling viscometer. While the falling number is a one-point measurement, rotational viscometers are suitable for continuous measures and therefore for more complex characterization of pasting properties of cereal flours and also isolated and modified starch products. The viscometers are heated with constant heating rate, or protocols with optional heating programs are applied depending on the sample types and the goals of measurement. In the first case, Brabender Amylograph® or similar apparatuses are used, and at the beginning of gelatinization ( C), maximum viscosity value and gelatinization temperature ( C) are determined from the registered viscosity curves
Bread: Dough Mixing and Testing Operations
according to international standards. In case of instruments working with programmable heating rates (e.g., Rapid Visco Analyser® (RVA), by Perten Instruments, or Micro ViscoAmylo-Graph® by Brabender GmbH), the pasting properties are followed continuously during heat increasing, constant heating, and heat decreasing periods. Next to the already mentioned parameters, viscosity breakdown during cooling, holding strength, and final viscosity are determined. The interpretation of the measured parameters is shown in Figure 5. These partly standardized methods allow to characterize the effects of enzymes and the hydration and viscosity development of hydrocolloids, predicting the quality of starch–protein matrices after cooling (i.e., bread crumb quality), and are applied on much wider areas than the characterization of wheat quality. The applied conditions model better the bread-baking processes in hot phases, but in all cases, the pasting properties are measured in dilute flow-water suspension. Therefore, the adaptation of the measured parameters to the real dough/bread system is not unambiguous.
GmbH) is able to measure the proving and baking quality of dough, including the changes of elasticity during the whole process.
Small-scale and microscale testing The development of very small-scale dough testing equipment and the associated automated interpretation of the resulting mixing curves has provided better reproducibility and removed operator bias, resulting in more objective assessment of the experimental variables. Several small-scale mixographs have been developed and used in different laboratories requiring 2 and 10 g of flour. The 2 g mixograph test procedure was originally designed to mimic the traditional scale methods: development of equipment and procedures included validation against the large-scale standard methods. A 10 g mixing bowl farinograph has been available since the early 1980s, while its 4 g analogous machine has been developed and its commercially available version, the micro-doughLAB, recently produced by Perten. Similar scaling-down processes have happened also in relation to the extension measurements, developing a prototype of microextension tester or the Kiefer-rig and the microdough inflation system for the TA-XT2 Texture Analyzer (Stable Micro Systems). The microextension tester has proved practical to use dough from the 2 g mixograph with micro baking facilities scaled to employ 2.4 g of dough per loaf. The traditional and small-scale dough testing methods have been found to be highly related. Essential member of the microscale machinery is the METEFEM Laboratory micro mill for supplying flour for the micro methodology. This mill is able to make flour even from one single grain and provides milling yield results from 20 g of grain, comparable to those from traditional milling tests. Beyond applying the microscale and small-scale methodology in breeding for selection to quality in much earlier stages, these developments have facilitated a wide range of research in which either only limited amounts of test material have been available or the more objective, precise assessment of data offered extra benefits. The spin-off of the developments of small-scale dough testing methodology has been that parallel with the development of small-scale machinery, the electronic data handling
Simplified dough rheometers serve very useful parameters, but their applicability for prediction of baking quality is limited mainly because the fermentation processes, the presence and distribution of the gas (CO2) phase, and the heating effects significantly modify the rheological behavior of the dough system. The frequently used laboratory test for overall characterization of baking quality of wheat flour is the baking test. It is ‘the ultimate’ method, being the real baking process, simulating the industrial conditions in laboratory environment. However, these trials are time-consuming and labor-intensive, and the interpretation of measured parameters (volume, sensory, and texture properties) is partly subjective. Because of some critical phases of fermented dough processing (like proofing and heating), continuous and better reproducible measurements are required. The Rheofermentometer (Chopin Technologies) is suitable for measuring the dough development and tolerance, the intensity of gas production, and the rate of gas retention. The similar but more complex Maturograph® combined with Oven Rise Recorder (Brabender
Viscosity
Peak viscosity
Final viscosity Re-association of molecules (retrogradation) Setback
Breakdown
Complete dispersion Holding strength
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Figure 5 Characterization of the states of starch with rotational viscometers.
Temperature
Investigation of dough fermentation and real baking process
Pasting temperature
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dough against mixing is decreasing. The time to maximum resistance and the value of peak maximum are the two most informative parameters, determined from the recorded GlutoPeak diagrams. The Mixolab System (Chopin Technologies) monitors the resistance of a dough during the dough formation phase and then through a heating/cooling/heating process (Figure 6) in a spiral mixer, mimicking the whole bread-making process. Phase 1 of the curve is equivalent to that of the farinograph, while information derived from phases 2–5 is similar to those of RVA. So, the Mixolab System enables the determination of the contribution of both protein and starch components of the dough in its rheological properties in a single test. Therefore, it is able to perform continuous measurement throughout a simulated baking process, which means that one can use the same instrument for several applications.
and processing and the specific software for calculating the mixing parameters and/or their analogous versions have been adapted for the traditional instruments; even, ‘mobile’ PCbased versions have been made to attach them onto industrial mixers.
New Developments Modern bakeries employ high-energy and low-temperature mixing in the production of raw and frozen dough products. However, batch variation in mixed dough quality remains a problem. Traditional instruments used to study the mixing characteristics of doughs were unable to mimic this low-temperature mixing process. The doughLAB and the Mixolab equipments have the capabilities to alter thermal and mechanical energy inputs during mixing. As it was mentioned earlier, different mixing procedures (straight, continuous, high-speed mixing, etc.) are applied in the baking industry. The amount and the intensity of energy input also affect the rheological properties of dough and so the final quality of baking products. In the case of the mentioned methods and instruments, constant mixing speeds are used. The recently developed doughLAB® (Perten Instruments) is a flexible recording rheometer, which can be used with both conventional z-arm and high-speed mixing actions. The latest one is able to emulate the high rates of mechanical energy input, applied in modern rapid baking systems. A newly developed small-scale and rapid instrument is the GlutoPeak (Brabender GmbH), where a high-speed mixing action is applied in a thermostated flour–water slurry. The gluten proteins are separated and aggregated by the highspeed sharing effects; the gluten network is formed resulting to an increase in the measured torque. Further intensive mixing destroys the gluten structure; therefore, the resistance of the
Trends and Future Recent achievements in fundamental rheology to develop new rheological tests applying the knowledge base of modern polymer rheology principles such as the measurement of extensional strain hardening provide the basis to future developments of novel, practical equipments and methodology, suitable for routine evaluation of wheat-based end products. Cumulative demand of the consumer for healthier, more nutritive bread is a challenge in the whole wheat chain: new quality attributes have to be considered and monitored. The best example for this trend is the effects of applying whole wheat meal and/or ingredients with higher fiber content as source materials. Besides their direct involvement in the development of protein–carbohydrate–lipid complex, altered fiber content alters drastically the water intake of the flour, changing
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Time (min) Figure 6 Mixolab parameters to characterize the mixing and heating/cooling related attributes of the dough.
Bread: Dough Mixing and Testing Operations
the usual hydration process and therefore altering the physical and physicochemical conditions during dough mixing. With the appearance of wheats with much more variation in starch composition (waxy wheat and high-amylase wheat), starch-related quality evaluation, largely using viscosimetric techniques, will get significantly more emphases in quality evaluation. Similarly to milling, where the application of NIR technique to monitor the composition of source material and end products is widespread, there is a strengthening trend to utilize the advantages of spectroscopic analytic and monitoring techniques also in the baking industry, especially continuously monitoring the process of dough development in the mixer. The NIR technology has the potential to provide an invasive or noninvasive mean of probing chemical changes that occur during dough development because the absorbances in the spectra can be directly related to the chemical dough components (water, starch, protein, and fat). Further spread of the application of indirect, highthroughput relatively cheap methods is expected in the future in prebreeding and breeding, applying small and micro methods such as the Micro Zeleny Tester, NIR, and Raman spectrophotometric techniques to estimate quality attributes and methods predicting important dough properties such as dough strength and extensibility or water absorption based on the genetic and chemical composition of the flour. In the breeding process to select for quality, the application of traditional dough testing methodologies (farinograph and extensograph) will be the key process also in the future, because of the archived, invaluable data of previous generations of breeding material, determined on these equipments for decades. It is therefore essential to fully understand and characterize the relationships between quality attributes determined by means of traditional methods and those derived from new generation test equipments applied by the industry for process and product development and quality control. Breeding and industrial objectives are aimed to be achieved through monitoring end-product quality rather than a set of dough parameters – a trend, appearing in the last decade that will fundamentally alter the quality control in the future. A recently developed equipment extensively used already in both basic research and developmental activities is the C-cell digital image analysis for the objective investigation of crumb structure of bread loaves, providing incomparably more insight about bread-making quality than traditional baking test determining loaf volume.
See also: Bread: Breadmaking Processes; Bread: Chemistry of Baking; Bread: Types of Bread; Cakes: Types of Cakes; Cereals: Types and Composition; Food Fraud; Pasta: Manufacture and Composition; Rheological Properties of Food Materials; Starch: Structure, Property, and Determination; Wheat: Grain Structure of Wheat and Wheat-based Products; Wheat: The Crop.
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Further Reading Anderssen RS, Gras PW, and MacRitchie F (1996) Modelling the mixing of wheat flour dough. In: Wrigley CW (ed.) Gluten 96. Proceedings of 6th international gluten workshop, pp. 249–252. Melbourne, Australia: RACI. Be´ke´s F (2012) New aspects in quality related wheat research (Review, I and II). Cereal Research Communications 40: 159–184, pp. 307–333. Be´ke´s F, Lukow O, Uthayakumaran S, and Mann G (2000) Small-scale dough testing methods. In: Shewry PR and Lookhart G (eds.) Wheat gluten protein analysis, pp. 173–198. St Paul, MN: AACC. Cauvain SP (1998) Breadmaking processes. In: Cauvin SP and Young LS (eds.) Technology of breadmaking, pp. 18–44. London: Blackie. Cornish GB, Be´ke´s F, Eagles HA, and Payne PI (2006) Prediction of dough properties for bread wheats. In: Wrigley CW, Be´ke´s F, and Bushuk W (eds.) Gliadin and glutenin. Chapter 8. The unique balance of wheat quality, pp. 243–280. St Paul, MN: AACCI Press. Dobraszczyk BJ and Morgenstern MP (2003) Rheology and the breadmaking process. Journal of Cereal Science 38: 229–245. Gorton LA (2009) Fundamental bakery dough processes. In: Pyler EJ and Gorton LA (eds.) Baking science and technology, vol. 2; 4th ed., pp. 1–136. Kansas City, MO: Sosland, Chapter 6. Gras PW, Anderssen RS, Keentok M, Be´ke´s F, and Appels R (2001) Gluten protein functionality in wheat flour processing. Australian Journal of Agricultural Research 52: 1311–1323. Hadnadev DT, Pojic M, Hadnađev M, and Torbica A (2011) The role of empirical rheology in flour quality control. In: Akyar I (ed.) Wide spectra of quality control, pp. 335–360. New York: InTech, Chapter 18. Kaddur AA and Cuq B (2011) Dynamic NIR spectroscopy to monitor bread dough mixing: A short review. American Journal of Food Technology 6: 173–185. Koksel H, Kahraman K, Sanal T, Sivri D, and Dubat A (2009) Potential utilization of mixolab for quality evaluation of bread wheat genotypes. Cereal Chemistry 86: 522–526. MacRitchie F, Simsek S, and Brookfield D (2014) Rheology. Cereal Foods World 59(5): 254. Mihalos MM (2009) Mixers. In: Pyler EJ and Gorton LA (eds.) Baking science and technology, vol. 2, 4th ed., pp. 403–421. Kansas City, MO: Sosland. Shewry PR, Ovidio RD, Lafiandra D, Jenkins JA, Mills ENC, and Be´ke´s F (2009) Wheat grain proteins. In: Khan K and Shewry PR (eds.) Wheat chemistry and technology, 4th ed., pp. 223–298. St Paul, MN: AACC Press. Sluimer P (2005) Principles of breadmaking: Functionality of raw materials and process steps. St Paul, MN: AACC International. To¨mo¨sko¨zi S, Szendi Sz, Bagdi A, et al. (2012) New possibilities in micro-scale wheat quality characterisation: micro-gluten determination and starch isolation. In: He Z and Wangm D (eds.) Proceedings of 11th international gluten workshop, Beijing, pp. 123–126. Mexico City: CIMMYT. Weipert D (2006) Fundamentals of rheology and spectroscopy. In: Popper L, Schafer W, and Freund W (eds.) Future of flour – a compendium of flour improvement, pp. 117–168. Bergen, Germany: AgriMedia. Wesley IJ, Larsen N, Osborne BG, and Skerritt JH (1998) Non-invasive monitoring of dough mixing by NIR. Journal of Cereal Science 27: 61–69.
Relevant Websites http://www.aaccnet.org/Pages/default.aspx. http://www.brabender.com/english/food/products/quality-control/rheology/doughproperties-gluten. http://www.chopin.fr/fr/. http://www.foodequipment.com.au/v1/mixers.html. https://www.icc.or.at/. http://www.perten.com/products/.
Introduction
Mixing and Dough Making
The fundamental basis of utilizing wheat flour as one of the most important food source around the world is its unique property of forming dough and developing gluten when it is mixed with water. Wheat gluten is a protein–lipid–carbohydrate complex formed as a result of specific covalent and noncovalent interactions from flour components during dough making as the components are hydrated and energy from mechanical input from the mixing process is provided. Wheat varieties at the same protein level were found to differ in their bread-making quality, giving the first indication of protein quality. Protein content and its composition are important determinants of good bread-baking quality. Gluten-forming proteins contribute 80–85% of the total wheat protein and are the major storage proteins of wheat. They belong to the prolamin class of seed storage proteins. Gluten proteins are largely insoluble in water or dilute salt solutions. Two functionally distinct groups of gluten proteins can be distinguished: monomeric gliadins and polymeric (extractable and unextractable) glutenins. Gliadins and glutenins are usually found in more or less equal amounts in wheat. Large level of polymorphism of wheat prolamins results in a special effect in relation to the overall functional properties of wheat dough. During dough formation when prolamin proteins are hydrated and form the gluten network, the numerous structurally similar but slightly different proteins produce a mass in which several characteristics (such as size, polarity, charge distribution, solubility, and viscosity) show a continuous distribution in a relatively large interval. This structural feature provides a unique characteristic of gluten proteins among any other protein systems.
Dough mixing is a very important stage in the bread-making process. The extent of mixing has a critical impact on final bread quality. The mixing process promotes different physical, chemical, and physicochemical modifications that contribute to the dough development.
Phases of Bread-Making Process The bread-making process has several functions, accomplished at different stages in the preparation and baking of dough: (a) mixing of flour and water, together with yeast, salt, and other ingredients in specified ratios to form the dough; (b) developing the gluten structure of hydrated proteins through application of energy during mixing (a stage often termed ‘kneading’); (c) incorporating air bubbles within the dough during mixing; (d) continuing the development of the gluten structure after kneading to improve its ability to expand when gas pressures increase (a stage termed ‘ripening’ or ‘maturing’); (e) creating or modifying flavor compounds in the dough; (f) subdividing the dough mass into unit pieces; (g) modifying the shape of the divided dough pieces; (h) resting to allow further modification of the dough pieces’ physical and rheological properties; (i) shaping to achieve required configuration; (j) proofing (fermenting and expanding) the dough; and (k) expanding and fixing the dough into its final shape by baking.
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Chemical, Physical, and Physicochemical Alterations during Dough Mixing Stages Dough chemistry involves a series of interactions between carbohydrates, lipids, and proteins. The principal physical science involved with dough making is rheology (see in the succeeding text). Good baking quality depends on several rheological properties such as extensibility exceeding a minimum level, viscosity, strain hardening, and optimal resistance to deformation. Dough is viscoelastic, combining properties of a Hookean solid with those of a non-Newtonian viscous fluid. Dough is essentially foam, which becomes sponge after baking. The transformation from the closed cell structure of a foam to the open cells of a sponge is one of the many changes that occur during dough processing. Individual dough-property parameters describe only certain essential elements of dough properties. Depending on the final product, different levels of these attributes are required to get superior processing quality. For example, the balance of dough strength and extensibility is believed to be the most important factor governing the suitability of a flour to make good bread. However, for different types of breads and even for different types of processing technologies, a diversity of dough strength and extensibility values may provide the optimum balances needed in each case. The complexity of relating protein composition to quality derives from the fact that the question can (and has to) be investigated on different levels of protein composition, namely, protein content, the ratio of polymeric proteins to monomeric proteins, the ratio of high-molecular-weight (HMW) glutenin subunits to low-molecular-weight glutenin subunits, and the proportions of x-type and y-type HMW glutenin subunits. These various parameters can be determined for a specific flour sample to see if there is a ‘good balance’ between the various components in the sample, thereby to satisfy quality-related criteria. The polymeric glutenin is mostly responsible for the elasticity of the dough, whereas the monomeric gliadins are the extensibility-related characters in the system. Thus, the ratio of polymeric proteins to monomeric proteins (the glutenin-to-gliadin ratio) can be directly related to the balance of dough strength and extensibility of the sample. Two preconditions must be met for the production of dough with the right properties: (a) appropriate proportioning
Encyclopedia of Food and Health
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Bread: Dough Mixing and Testing Operations
of the individual ingredients as established in a well-balanced dough formulation and (b) homogenous distribution of these ingredients throughout the dough mass. In its essentials, dough mixing involves the combining and blending of the formula ingredients and then applying sufficient physical work to the mixture to transform it into a cohesive mass with the requisite viscoelastic properties. In large-scale commercial bakery production, the major ingredients (flour and dry sweeteners) are normally weighed by automatic scales that feed directly into the mixers, while water, liquid shortener, and liquid sweeteners are piped into the mixer through meters that can be preset to deliver specified volumes. In addition to achieving a thorough dispersion of the ingredients into a homogeneous mixture, the dough mixing process in bread making has the further important objective of physically developing the gluten proteins into a coherent threedimensional structure that will impart to the dough the desired degree of plasticity, elasticity, and viscosity. The initial mixing phase must physically hydrate the flour particles and incorporate air to nucleate gas cells responsible for leavening. In other words, mixing has three functions: (a) creating a homogenous mass from ingredients of differing characteristics, (b) developing (kneading) the dough sufficiently to ready for subsequent processing, and (c) occluding air into the mass to form the cell structure necessary for finished crumb quality. At the beginning of the mixing, blending action leads to an even distribution of the dough ingredients and ensures hydration and swelling of flour particles. Wheat flour dough or batter may appear to be uniform and well mixed, but actually, it is multiphasic: starch, gluten proteins, lipids, and water representing the principal phases. Furthermore, the form of these phases changes during periods of mixing that prepare them for separation or food uses. Microscopic changes begin with the instant formation of protein fibrils at first contact of water and flour particles. Slow mechanical development induces these fibrils to coalesce into fibrous bands or tendons and segregates the starch into clusters. When flooded with a displacing fluid, this open, spongelike structure readily releases the entrained starch. Additional development disbands the protein into relatively fine, uniformly distributed, and networked or webbed filaments that entrap the starch and gas bubbles formed when the dough is fermented and baked. The physical properties of hydrated wheat proteins are the result of covalent and noncovalent interactions of wheat gluten proteins. These interactions are altered by the repeated extension, tearing, and compression during mixing or development. Specific chemical effects include (1) disulfide bond disruption, (2) chain disentanglement and rupture, (3) disulfide–sulfhydryl interchange, (4) formation of dityrosine cross-links, (5) formation of new disulfide cross-links, (6) free radical interactions, and especially (6) reorientation leading to enhanced hydrogen bonding. Mixing produces a homogeneous gluten film regularly distributed around the starch granules. The dough must be mixed for a specific time (referred to as optimum dough development) to ensure optimal loaf volume and bread texture. Stopping mixing before the optimal point results in undermixed dough that gives bread of inferior volume and crumb quality. The optimal mixing requirement is a specific characteristic of each wheat flour. Beyond optimum dough development time,
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overmixing induces dough stickiness, decreases dough consistency (due to degradation by shearing effects), and negatively affects bread quality. Stability of the gluten–starch matrix – the primary stabilizing factor for expanding gas cells against disproportionateness and coalescence – depends on its tendency to strain harden. The phenomenon of strain hardening appears to depend on the balance between strength and extensibility of the entangled network of polymeric proteins of wheat flour. Extensibility ensures slippage of the maximum number of statistical segments between entanglements, whereas strength prevents disruption of the entangled network of polymeric proteins. Thus, to ensure stability of gas cells, the dough needs to be not only sufficiently extensible to respond to gas pressure but also strong enough to resist collapse. A good gas-holding capacity of dough is necessary for producing a loaf of bread with light and even crumb. The strain hardening properties of gluten are vital to avoid early rupture of gas ‘cell wall’ during proofing. The gas phase of bread, which makes up more than 70% of the final volume of a loaf, has a major influence on its textural and sensory attributes. Controlling the gas phase volume is a major challenge as during proving and early stages of baking gas must be captured within bread dough, only being released at the end of baking. The main factors, important in determining the gas cell structure, include (1) the formation of the initial foam structure during mixing and (2) stabilization of the foam structure, including those factors governing bubble disproportionateness and coalescence. There is particular focus on the role that the thin film lining the bubbles may play in stabilizing the foam structure of a risen dough. The surface properties of components have been suggested to be the important factor to the stability of gas cells. Recently, proteomic methods have been used to identify foam-forming soluble proteins from dough that may play an important role in stabilizing gas bubbles in dough and hence influence the crumb structure of bread. Proteins from a soluble fraction of dough (dough liquor) or dough liquor foam have been separated and identified. Major polypeptide components included b-amylase, tricitin, and serpins, with members of the a-amylase/trypsin inhibitor family being particularly abundant. Neither prolamin seed storage proteins nor the surfaceactive protein puroindoline was found. Differences in gluten quality can significantly affect the bread-making potential. Strength is conferred by the fraction of polymeric proteins having molecular weight greater or equivalent to a critical size, MT, (250 000 kDa), and the fraction of gluten protein smaller than MT may counter the strength by acting as diluents. The optimum balance seems to exist when the relative proportions of polymeric proteins greater and smaller than MT are roughly 60:40. Shift in the balance to either side will decrease loaf volume. Increase in smaller proteins (less than MT) may decrease stability of the gluten–starch matrix due to a lesser number of entanglements per chain. On the other hand, increase in strength conferring proteins may prevent sufficient expansion of the gluten–starch matrix required to increase loaf volume due to reduced slippage of gluten polymers through entanglement nodes as a result of increase in number of entanglements per chain. The secondary stabilizing mechanism involves thin liquid lamellae stabilized by adsorbed surface-active compounds (lipids and
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proteins) at the gas–liquid interface. Liquid lamellae prevent coalescence and disproportionateness of gas cells when they come in close contact with each other during the late proving and early baking stages of bread making, that is, when discontinuities begin to appear in the gluten–starch matrix. Flour lipids at their natural levels do not influence rheological properties of the gluten–starch matrix surrounding the gas cells, as measured by the dough inflation system. Nevertheless, the small amounts in which these lipids are naturally present are sufficient to influence surface properties. This short and simplified description of well-accepted observation-based hypothesis of dough behavior underlines the essential importance of size distribution of gluten proteins in relation to their role in determining dough properties. As a consequence of this, a combination of reducing agents, oxidizers, and proteolytic enzymes is frequently used in the baking process to alter dough properties through their effects on the disulfide bonds in the gluten structure. Functional additives play a big role in modern bread making. Among the improvers, ascorbic acid is the most important in modern bread formulation to oxidize flour proteins to improve gluten strength. Other such ingredients (and their functions) include azodicarbonamide (oxidizing agent), cysteine (reducing agent), mono- and diglycerides (emulsifiers and antistaling agents), calcium propionate (mold inhibitor), stearoyl lactylate (dough strengthener), soy flour (crumb whitener), Table 1
dextrose (fermentable sugar source for the yeast), ammonium chloride (nitrogen source for yeast), enzymes (starch and protein adjustment), and, occasionally, gluten (strengthener).
Dough Preparation Systems No single standard method for mixing ingredients to create dough is followed by all bakers; instead, more than a halfdozen different procedures can be used. The detailed characterization of these methods is shown in Table 1. Baker preference, product type, and plant practice determine the choice of method. Preparation of the dough can be done in batches or continuously, and fermentation times vary from none to several hours. Today, most commercial bakers prepare dough as separate batches, sized sufficiently to permit an uninterrupted production schedule but not too large to risk overaging the dough as it waits in the divider hopper. The continuous mix method was developed during the 1950s to automate dough preparation. At one time, it was used by the majority of bakeries producing white pan bread, but this method fell out of favor when consumer demand for variety bread increased starting in the late 1970s. Technologies that grew up around continuous mix such as water brews and liquid sponge, however, remain in wide use for lines dedicated to baking long runs of fast-food buns and similar products.
Overview of the most generally used dough preparation systems
Dough system
Bread and related product produces
Advantages
Disadvantages
Straight dough
Lean formula hearth bread, pita bread, 100% whole wheat
Sponge and dough
Sponge and dough bread and rolls
Liquid sponge
Sponge and dough bread and rolls
Continuous mix
White pan bread, hamburger/hotdog buns
Good flavor Medium process time Good mixing tolerance Good fermentation tolerance Superior product score Good dough handling Longer product shelf life Uniformity of product Medium process time Good flavor with high amount of flour in the sponge Same advantages as liquid sponge if fermented Less equipment, labor, and space used
Difficult dough handling Long mixing time Poor fermentation tolerance Poor mixing tolerance Long process time High-cost equipment Larger space equipment High-cost equipment Limited to 50–60% of flour in sponge Lack of flavor and shelf life with low flour in sponge Limited to 50–60% of flour in sponge
No-time dough
Frozen dough, bagels, hard rolls, pizza crusts, dinner rolls, variety pan bread, English muffins
Chorleywood process
Hamburger/hotdog buns, variety pan bread, rye bread
Authentic sourdough process
Source: O’Donell (1996).
Authentic sourdough breads and buns
Lack of crumb strength
Short production time Greater flexibility Less equipment and space Superior yeast survival in freezing Tolerant to low-protein flours
Lack of flavor and shelf life with less fermentation Lack of flavor Lack of shelf life Higher ingredient costs Problem with floor time High equipment cost
Short production time Greater flexibility No floor time problems Sourdough flavor Increased shelf life ‘Blistered’ appearance Chewy, resilient texture
High energy cost Lack of flavor Lack of product shelf life Very long process times Nurturing of sponge Less consistency Increased space requirement
Bread: Dough Mixing and Testing Operations
Among mixing methods being practiced commercially, the most prevalent is the sponge-and-dough process that involves two mixing stages, namely, one of the sponge and the other of the dough. The sponge mixing stage aims at homogeneous ingredient dispersion and flour hydration and is normally of relatively brief duration, whereas the more critical phase of dough development is reserved for the more extensive mixing of the final dough. In the straight-dough method, as well as in those systems that employ various forms of liquid preferment, there is but one mixing stage in which complete dough development must be achieved. White pan bread is highly standardized, has wellrecognized quality characteristics, and represents the main product style in many parts of the world. Some countries, notably France, take the baguette as the standard product. Table 1 shows the advantages and limitations of the most important methodologies based on the excellent review of Mihalos.
Testing Operations Introduction Dough testing methodologies are essential tools through the whole wheat chain from basic research, prebreeding, selection for quality attributes during breeding, characterizing source material, quality control, process, and product development in the wheat-based food industry. Testing operations can be classified as direct dough testing methods and indirect methods where dough properties are estimated from chemical, physicochemical (spectral), or physical (sedimentation) characteristics. Dough properties, directly related to the bread-making quality of the sample, describe certain viscosimetric or rheological properties of the dough, so the dough testing investigations apply viscosimetric and rheological principles. In general, viscosimetric methods show strong relationships to the starch composition of the samples, while the rheological properties are directly related to both qualitative and quantitative aspects of gluten protein composition. Some basic information on the direct dough testing methods is given here, with special emphases on the small-scale and microscale testing methods, which revolutionized our understanding about structure–function relationships in wheat dough in the last 30 years. Only some key references are given about the principles, solutions, and achievements of indirect methods in the paragraphs summarizing future trends in the area.
Basic and Empirical Rheology Rheology is the science of the deformation and flow of materials as a response to physical stresses. The deformation can be classified as elastic or inelastic, while the flow properties of a material can be described as plastic or viscous behavior. Ideal elastic bodies undergo reversible elastic strain when anisotropic forces are applied. In this case, the applied energy is partly stored. In case of ideal viscous body, irreversible changes can be observed, where the exerted energy is
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transformed. Viscous fluids generally exhibit viscosity, while solids exhibit elasticity. The aim of fundamental rheology is trying to describe and model the physical behavior of materials by studying the relationships between molecular composition and the observed deformation. Widely applicable instruments (viscometers, rheometers, etc.) and/or specific, often purpose-built methods are used for this purpose. The resulting information, however – despite its scientific merit – does not satisfy the demands dictated by the practice: Fundamental rheology methods often do not differentiate enough among samples and, most importantly, they are not suitable for high-throughput, reasonably cheap routine application in selecting for quality in plant breeding or in case of quality control in the food industry. During the first quarter of the last century, several empirical rheological equipments and methodologies have been developed, and the last 100 years proved that these standardized methodologies can be applied fruitfully for the comparison/ rating of samples derived from the breeding or industrial operations. The collected/archived data derived from these analyses form an invaluable knowledge base based on which the new wheat cultivars and new wheat products of the future can be developed.
Traditional empiric rheological methods and instruments As it was mentioned earlier, when wheat flour, water, and other related ingredients are mixed, the whole system undergoes a number of chemical reactions and physicochemical and physical changes during dough formation. The type and the rate of these changes highly depend on the composition of wheat flour, on the ingredients, and on the parameters of dough mixing like length mixing, energy input, and temperature. Molecular processes related to the aforementioned changes can be monitored by the continuous measurement of physical (rheological) properties of dough from the starting stage of homogenization through the formation of protein–carbohydrate–lipid–water complex (gluten) until its certain break caused by overmixing. Wheat dough has both elastic and flowing properties; therefore, it shows a complex viscoelastic behavior. Therefore, the main challenge in the development of empiric rheological methods and instruments has been how one can apply adequate external forces on the dough to measure both elastic strain and viscous flow in one system. Two principally different empiric rheological methodologies have been developed: mixing methods to monitor dough formation and stretching methods for the determination of dough strength and extensibility. In case of the latter process, dough is mixed to its optimum consistency in a separate process followed by a relaxation step before stretching. So, the two methods together mimic the industrial bread-making technology with one important exception: instead of a full formulation of the dough, including yeast, dough is mixed here with either water or salt solution. Mixing methods: The traditional simple solution for detecting the physical changes in a dough is the utilization of standardized (laboratory) mixers with the recording of torque on the mixing arm(s) and/or bowl. The first recording laboratory mixers – regarded as the forerunners of the first commercial machines developed later on, the Swanson–Working
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mixograph and Brabender farinograph – have been developed by the Hungarian inventor Jeno˝ Hanko´czy. The working principle of the farinograph is to monitor the torque (energy requirement) during the continuous but relatively gentle mixing of wheat flour – added water system at constant speed and temperature (at 30 C). The sigmoid (or Z-type) shape of the mixing blades is very unique, which is able to knead and extend the dough, periodically. The torque that arises from dough resistance against mixing was originally measured using a special balance system and replaced later with electronic recording systems. Basically, dough resistance, detected in this equipment, is determined by the rheological properties of dough, particularly viscosity, but the surface properties of the dough, sticking to the bowl walls and blades, also contribute to the measured values. The comparability of different dough behaviors (or flour quality) is ensured with the standardization of maximum dough resistance. Beyond the mixing parameters such as mixing speed and resistance measured with this system, there is the function of the flour behavior and the amount of water added to the flour. The huge success of the farinograph spreading all around the wheat chain as early as the 1930s derived from the idea of using this direct relationship between the amount of water in the system and resistance for the determination of the most
important quality attribute of the flour, water absorption, which is the amount of water needed to be added to the flour to reach the constant consistence (500 or 600 farinograph or Brabender units, BU) of dough. The routine investigation on the farinograph is a two-step process: water absorption of the flour is determined through a ‘titration-like’ process, followed by the main mixing experiment using this amount of water to characterize the rheological properties of the dough such as dough development time, stability, and degree of softening (Figure 1). The detailed description of the farinograph method including the evaluation of curves is summarized in different standard methods (ICC, AACCI, ISO, etc.). The second traditional type of recording dough mixer is the mixograph. The main difference between these two mixers is the mixing action. The mixograph equipped with pin mixers, where a pull–fold–repull type of movement is applied causing much greater mechanical stress on dough than that in the farinograph or other Z-arm-type mixers. In case of mixing with mixograph, there is no predetermined optimum consistency of dough; therefore, other methods have to be used for measuring the optimal water absorption. Two methods are used in practice: (a) Samples are compared with a uniform amount of water added and
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Figure 1 Important farinograph parameters.
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Bread: Dough Mixing and Testing Operations
(b) the water used in the mixing experiments is calculated based on the protein content of the investigated flours. The parameters generally determined by the evaluation of the recorded mixogram (Figure 2) are as follows: peak time (similarly to the dough development time), maximum peak height, the height of the curve at a specified time after peak (characterizing the tolerance against overmixing, similarly to the farinographic stability), the angle between the ascending and descending portions of the curve (tolerance angle, T ), the weakening angle (W), and the area under the curve are defined. High-speed recordings obtained with a 35 g mixograph equipped with a strain gage allowed the high-resolution monitoring of the mixing action. These recordings provided data essential for developing a mathematical model of dough mixing: dough mixing on pin mixers can be interpreted as a complex, periodic series of pushing and stretching the dough around the pins. Each individual peak represents one of these circles, and so, their size and shape are characteristic to the stage of dough development, and they can be used to determine dough strength and elasticity of the dough (details (a), (b), and (c) of Figure 2 illustrate three regions of the highresolution mixing curve ((a), (b), and (c)), illustrating the hydration, dough development, and overmixing phases of the mixing). Bandwidth parameters (BWPR, BWBD, and TMBW), directly related to elasticity, in the mathematical model are also shown. Some other instruments developed by different producers (valorigraph, doughLAB, etc.) work on the same or similar principle as described earlier, with different sizes of mixing bowls and arms for mixing 10–300 g of flour. Stretching methods: Elasticity is the most unique property of wheat dough, and it mostly depends on the protein–wheat gluten composition and quality. Extensibility of wheat dough
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is responsible for the extent of expansion during leavening; therefore, it basically determines the baking performance and the quality of final products. In all stretching tests, to determine extensibility, the dough produced by one of the standardized mixing methods is then submitted to large deformations until rupture occurs and the resistance against stretching strain is recorded. Two types of extension methods are used: in uniaxial extension test, the dough is stretched in one direction, while in case of biaxial method, the dough is extended in two opposing direction. The most traditional and commonly used equipment is the Brabender Extensograph, introduced in 1936. The operation of this instrument is based on the principle of mechanical stretching in simple tension. The investigated dough samples are prepared in the farinograph mixer with optimum water absorption, and then, aliquot pieces of the dough are molded with special tools. During the measurement, the resistance of formed dough pieces to stretching and the distance the dough stretches before breaking are recorded on the extensogram (Figure 3). The following parameters are determined/calculated: the maximum resistance (Rmax), the resistance at a constant extension (generally at 50 mm, Rx), extensibility (the maximum length of extension before rupture, E), the ratio of maximum resistance to extension (as an indicator of the balance between elastic and viscous behaviors, Rmax/E), and the area under the curve (as extensional work, A). In some cases, the applied methods can differ in some parameters, like constant extension and resting time of dough before measurement. The desired quality of dough means a good combination of dough resistance and extensibility. The first device for measuring the biaxial extension character of wheat dough was also developed by Hanko´czy, while the principle of dough inflation test was developed by Marcel
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Figure 2 The most important parameters determined from the mixograph curve. MT, mixing time; PR, peak resistance; RBD, resistance breakdown; BWPR, bandwidth at peak; MBW, maximum bandwidth; TMBW, time to maximum bandwidth. High-resolution data recording of regions a, b, and c show the stages of hydration, dough development, and overmixing, respectively.
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Dough extensibility L Figure 4 The determination of dough tenacity (P), configuration ratio(P/L), and deformation energy (W) and from the alveograph curve (alveogram).
Chopin in 1927. Today, the most widely known and standardized biaxial extension test is the alveograph method, which is based on the principle of dough inflation or bubble expansion technique. This procedure mimics the microprocesses occurring in dough during fermentation in macroscale, namely, the formation of thin membranes around the CO2 bubbles. The Chopin Alveograph consists of a special thermostated, onescrew mixer for mixing and extrusion of dough, a bubble blowing apparatus, and the recording manometer. During the measuring procedure, dough disks are prepared, rested, and then inflated by constant air flow. The pressure inside the dough bubble until rupture is measured and recorded on the alveogram (Figure 4). The most generally read or calculated parameters are the maximum overpressure (an indicator of the dough tenacity, P), the average abscissa at rupture (characterizes the extensibility, L), configuration ratio (P/L), and the area under the curve (as deformation energy, W). The extension tests are also used for investigating the effects of natural or artificial modifying agents, like bugs, enzymes, oxidants or reducing components, and lubricants. The results, recorded curves, and determined parameters of the two methods are very similar. However, because of the different mixing procedures and measuring principle, the comparability of the results is limited and depends also on the type and variety of the samples.
Viscometry as a tool for investigation of the hot phase of the bread-making process The conventional dough rheology is mainly connected to the protein-dependent dough properties in the first, not heated phase of bread making. Starch as the main component of wheat flour also affects the quality-related properties, even the rheological properties of the dough, mostly as diluent of
the proteins and as a consequence of altered hydration during gelatinization in the oven. Additionally, starch is exposed to enzymatic breakdown, depending on the a-amylase activity of the flour and physical braking during the milling process resulting in damaged starch. An optimal level of enzymatic activity and amount of damaged starch are necessary for the optimal fermentation processes in baking. However, high enzyme activity or a high ratio of hydrolyzed starch results in a weaker water-holding capacity, resulting in serious drop in the end-product quality. Therefore, starch-related viscosity-based characterization of samples is an essential part of source material quality control in the baking industry, and the balanced amylolytic activity is part of the selection criteria during breeding. Starch properties are usually studied at high temperatures – similar to conditions of the baking process. Generally, the starch characterization is performed by different viscometers, carrying out measurements on temperatures appearing in the technology. The most frequently used standardized method for investigation of a-amylase activity of the grain/ flour is the determination of falling number on a special falling viscometer. While the falling number is a one-point measurement, rotational viscometers are suitable for continuous measures and therefore for more complex characterization of pasting properties of cereal flours and also isolated and modified starch products. The viscometers are heated with constant heating rate, or protocols with optional heating programs are applied depending on the sample types and the goals of measurement. In the first case, Brabender Amylograph® or similar apparatuses are used, and at the beginning of gelatinization ( C), maximum viscosity value and gelatinization temperature ( C) are determined from the registered viscosity curves
Bread: Dough Mixing and Testing Operations
according to international standards. In case of instruments working with programmable heating rates (e.g., Rapid Visco Analyser® (RVA), by Perten Instruments, or Micro ViscoAmylo-Graph® by Brabender GmbH), the pasting properties are followed continuously during heat increasing, constant heating, and heat decreasing periods. Next to the already mentioned parameters, viscosity breakdown during cooling, holding strength, and final viscosity are determined. The interpretation of the measured parameters is shown in Figure 5. These partly standardized methods allow to characterize the effects of enzymes and the hydration and viscosity development of hydrocolloids, predicting the quality of starch–protein matrices after cooling (i.e., bread crumb quality), and are applied on much wider areas than the characterization of wheat quality. The applied conditions model better the bread-baking processes in hot phases, but in all cases, the pasting properties are measured in dilute flow-water suspension. Therefore, the adaptation of the measured parameters to the real dough/bread system is not unambiguous.
GmbH) is able to measure the proving and baking quality of dough, including the changes of elasticity during the whole process.
Small-scale and microscale testing The development of very small-scale dough testing equipment and the associated automated interpretation of the resulting mixing curves has provided better reproducibility and removed operator bias, resulting in more objective assessment of the experimental variables. Several small-scale mixographs have been developed and used in different laboratories requiring 2 and 10 g of flour. The 2 g mixograph test procedure was originally designed to mimic the traditional scale methods: development of equipment and procedures included validation against the large-scale standard methods. A 10 g mixing bowl farinograph has been available since the early 1980s, while its 4 g analogous machine has been developed and its commercially available version, the micro-doughLAB, recently produced by Perten. Similar scaling-down processes have happened also in relation to the extension measurements, developing a prototype of microextension tester or the Kiefer-rig and the microdough inflation system for the TA-XT2 Texture Analyzer (Stable Micro Systems). The microextension tester has proved practical to use dough from the 2 g mixograph with micro baking facilities scaled to employ 2.4 g of dough per loaf. The traditional and small-scale dough testing methods have been found to be highly related. Essential member of the microscale machinery is the METEFEM Laboratory micro mill for supplying flour for the micro methodology. This mill is able to make flour even from one single grain and provides milling yield results from 20 g of grain, comparable to those from traditional milling tests. Beyond applying the microscale and small-scale methodology in breeding for selection to quality in much earlier stages, these developments have facilitated a wide range of research in which either only limited amounts of test material have been available or the more objective, precise assessment of data offered extra benefits. The spin-off of the developments of small-scale dough testing methodology has been that parallel with the development of small-scale machinery, the electronic data handling
Simplified dough rheometers serve very useful parameters, but their applicability for prediction of baking quality is limited mainly because the fermentation processes, the presence and distribution of the gas (CO2) phase, and the heating effects significantly modify the rheological behavior of the dough system. The frequently used laboratory test for overall characterization of baking quality of wheat flour is the baking test. It is ‘the ultimate’ method, being the real baking process, simulating the industrial conditions in laboratory environment. However, these trials are time-consuming and labor-intensive, and the interpretation of measured parameters (volume, sensory, and texture properties) is partly subjective. Because of some critical phases of fermented dough processing (like proofing and heating), continuous and better reproducible measurements are required. The Rheofermentometer (Chopin Technologies) is suitable for measuring the dough development and tolerance, the intensity of gas production, and the rate of gas retention. The similar but more complex Maturograph® combined with Oven Rise Recorder (Brabender
Viscosity
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Figure 5 Characterization of the states of starch with rotational viscometers.
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Investigation of dough fermentation and real baking process
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dough against mixing is decreasing. The time to maximum resistance and the value of peak maximum are the two most informative parameters, determined from the recorded GlutoPeak diagrams. The Mixolab System (Chopin Technologies) monitors the resistance of a dough during the dough formation phase and then through a heating/cooling/heating process (Figure 6) in a spiral mixer, mimicking the whole bread-making process. Phase 1 of the curve is equivalent to that of the farinograph, while information derived from phases 2–5 is similar to those of RVA. So, the Mixolab System enables the determination of the contribution of both protein and starch components of the dough in its rheological properties in a single test. Therefore, it is able to perform continuous measurement throughout a simulated baking process, which means that one can use the same instrument for several applications.
and processing and the specific software for calculating the mixing parameters and/or their analogous versions have been adapted for the traditional instruments; even, ‘mobile’ PCbased versions have been made to attach them onto industrial mixers.
New Developments Modern bakeries employ high-energy and low-temperature mixing in the production of raw and frozen dough products. However, batch variation in mixed dough quality remains a problem. Traditional instruments used to study the mixing characteristics of doughs were unable to mimic this low-temperature mixing process. The doughLAB and the Mixolab equipments have the capabilities to alter thermal and mechanical energy inputs during mixing. As it was mentioned earlier, different mixing procedures (straight, continuous, high-speed mixing, etc.) are applied in the baking industry. The amount and the intensity of energy input also affect the rheological properties of dough and so the final quality of baking products. In the case of the mentioned methods and instruments, constant mixing speeds are used. The recently developed doughLAB® (Perten Instruments) is a flexible recording rheometer, which can be used with both conventional z-arm and high-speed mixing actions. The latest one is able to emulate the high rates of mechanical energy input, applied in modern rapid baking systems. A newly developed small-scale and rapid instrument is the GlutoPeak (Brabender GmbH), where a high-speed mixing action is applied in a thermostated flour–water slurry. The gluten proteins are separated and aggregated by the highspeed sharing effects; the gluten network is formed resulting to an increase in the measured torque. Further intensive mixing destroys the gluten structure; therefore, the resistance of the
Trends and Future Recent achievements in fundamental rheology to develop new rheological tests applying the knowledge base of modern polymer rheology principles such as the measurement of extensional strain hardening provide the basis to future developments of novel, practical equipments and methodology, suitable for routine evaluation of wheat-based end products. Cumulative demand of the consumer for healthier, more nutritive bread is a challenge in the whole wheat chain: new quality attributes have to be considered and monitored. The best example for this trend is the effects of applying whole wheat meal and/or ingredients with higher fiber content as source materials. Besides their direct involvement in the development of protein–carbohydrate–lipid complex, altered fiber content alters drastically the water intake of the flour, changing
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Time (min) Figure 6 Mixolab parameters to characterize the mixing and heating/cooling related attributes of the dough.
Bread: Dough Mixing and Testing Operations
the usual hydration process and therefore altering the physical and physicochemical conditions during dough mixing. With the appearance of wheats with much more variation in starch composition (waxy wheat and high-amylase wheat), starch-related quality evaluation, largely using viscosimetric techniques, will get significantly more emphases in quality evaluation. Similarly to milling, where the application of NIR technique to monitor the composition of source material and end products is widespread, there is a strengthening trend to utilize the advantages of spectroscopic analytic and monitoring techniques also in the baking industry, especially continuously monitoring the process of dough development in the mixer. The NIR technology has the potential to provide an invasive or noninvasive mean of probing chemical changes that occur during dough development because the absorbances in the spectra can be directly related to the chemical dough components (water, starch, protein, and fat). Further spread of the application of indirect, highthroughput relatively cheap methods is expected in the future in prebreeding and breeding, applying small and micro methods such as the Micro Zeleny Tester, NIR, and Raman spectrophotometric techniques to estimate quality attributes and methods predicting important dough properties such as dough strength and extensibility or water absorption based on the genetic and chemical composition of the flour. In the breeding process to select for quality, the application of traditional dough testing methodologies (farinograph and extensograph) will be the key process also in the future, because of the archived, invaluable data of previous generations of breeding material, determined on these equipments for decades. It is therefore essential to fully understand and characterize the relationships between quality attributes determined by means of traditional methods and those derived from new generation test equipments applied by the industry for process and product development and quality control. Breeding and industrial objectives are aimed to be achieved through monitoring end-product quality rather than a set of dough parameters – a trend, appearing in the last decade that will fundamentally alter the quality control in the future. A recently developed equipment extensively used already in both basic research and developmental activities is the C-cell digital image analysis for the objective investigation of crumb structure of bread loaves, providing incomparably more insight about bread-making quality than traditional baking test determining loaf volume.
See also: Bread: Breadmaking Processes; Bread: Chemistry of Baking; Bread: Types of Bread; Cakes: Types of Cakes; Cereals: Types and Composition; Food Fraud; Pasta: Manufacture and Composition; Rheological Properties of Food Materials; Starch: Structure, Property, and Determination; Wheat: Grain Structure of Wheat and Wheat-based Products; Wheat: The Crop.
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Further Reading Anderssen RS, Gras PW, and MacRitchie F (1996) Modelling the mixing of wheat flour dough. In: Wrigley CW (ed.) Gluten 96. Proceedings of 6th international gluten workshop, pp. 249–252. Melbourne, Australia: RACI. Be´ke´s F (2012) New aspects in quality related wheat research (Review, I and II). Cereal Research Communications 40: 159–184, pp. 307–333. Be´ke´s F, Lukow O, Uthayakumaran S, and Mann G (2000) Small-scale dough testing methods. In: Shewry PR and Lookhart G (eds.) Wheat gluten protein analysis, pp. 173–198. St Paul, MN: AACC. Cauvain SP (1998) Breadmaking processes. In: Cauvin SP and Young LS (eds.) Technology of breadmaking, pp. 18–44. London: Blackie. Cornish GB, Be´ke´s F, Eagles HA, and Payne PI (2006) Prediction of dough properties for bread wheats. In: Wrigley CW, Be´ke´s F, and Bushuk W (eds.) Gliadin and glutenin. Chapter 8. The unique balance of wheat quality, pp. 243–280. St Paul, MN: AACCI Press. Dobraszczyk BJ and Morgenstern MP (2003) Rheology and the breadmaking process. Journal of Cereal Science 38: 229–245. Gorton LA (2009) Fundamental bakery dough processes. In: Pyler EJ and Gorton LA (eds.) Baking science and technology, vol. 2; 4th ed., pp. 1–136. Kansas City, MO: Sosland, Chapter 6. Gras PW, Anderssen RS, Keentok M, Be´ke´s F, and Appels R (2001) Gluten protein functionality in wheat flour processing. Australian Journal of Agricultural Research 52: 1311–1323. Hadnadev DT, Pojic M, Hadnađev M, and Torbica A (2011) The role of empirical rheology in flour quality control. In: Akyar I (ed.) Wide spectra of quality control, pp. 335–360. New York: InTech, Chapter 18. Kaddur AA and Cuq B (2011) Dynamic NIR spectroscopy to monitor bread dough mixing: A short review. American Journal of Food Technology 6: 173–185. Koksel H, Kahraman K, Sanal T, Sivri D, and Dubat A (2009) Potential utilization of mixolab for quality evaluation of bread wheat genotypes. Cereal Chemistry 86: 522–526. MacRitchie F, Simsek S, and Brookfield D (2014) Rheology. Cereal Foods World 59(5): 254. Mihalos MM (2009) Mixers. In: Pyler EJ and Gorton LA (eds.) Baking science and technology, vol. 2, 4th ed., pp. 403–421. Kansas City, MO: Sosland. Shewry PR, Ovidio RD, Lafiandra D, Jenkins JA, Mills ENC, and Be´ke´s F (2009) Wheat grain proteins. In: Khan K and Shewry PR (eds.) Wheat chemistry and technology, 4th ed., pp. 223–298. St Paul, MN: AACC Press. Sluimer P (2005) Principles of breadmaking: Functionality of raw materials and process steps. St Paul, MN: AACC International. To¨mo¨sko¨zi S, Szendi Sz, Bagdi A, et al. (2012) New possibilities in micro-scale wheat quality characterisation: micro-gluten determination and starch isolation. In: He Z and Wangm D (eds.) Proceedings of 11th international gluten workshop, Beijing, pp. 123–126. Mexico City: CIMMYT. Weipert D (2006) Fundamentals of rheology and spectroscopy. In: Popper L, Schafer W, and Freund W (eds.) Future of flour – a compendium of flour improvement, pp. 117–168. Bergen, Germany: AgriMedia. Wesley IJ, Larsen N, Osborne BG, and Skerritt JH (1998) Non-invasive monitoring of dough mixing by NIR. Journal of Cereal Science 27: 61–69.
Relevant Websites http://www.aaccnet.org/Pages/default.aspx. http://www.brabender.com/english/food/products/quality-control/rheology/doughproperties-gluten. http://www.chopin.fr/fr/. http://www.foodequipment.com.au/v1/mixers.html. https://www.icc.or.at/. http://www.perten.com/products/.