Structure and properties of dough

Flour + water + air + energy dough (for aerated products) 

These four ingredients show a resemblance to the four elements of the medieval philosophers earth (from which flour is derived), water, air, and fire (corresponding to energy). When energy is imparted to a system comprising a solid (flour), a liquid (water), and a gas (air), it is converted into a material (dough) that has properties of both a liquid and a solid. It has viscosity like a liquid and elasticity like a solid and thus is said to be viscoelastic —a property that we will pursue further in Chapter 6. 

Let us examine the events that occur when a flour-and-water mixture of optimum water content is mixed. 

Some data for the proportion and composition of the liquid phase are shown in Table 5.1 (MacRitchie 1976). If the time of centrifugation is extended at a given water content, no change in the amount of liquid phase is observed after a certain amount is separated, thus confirming that a true equilibrium has been established. 

Remainder 25.5 (mainly starch) 44 (mainly starch) 25.8 (mainly starch) 55 (mainly starch) 0.77 (mainly soluble carbohydrate) 7.0 (mainly soluble carbohydrate)  

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Levine, H. and Slade, L. (1990). Influences of the glassy and rubbery states on the thermal, mechanical, and structural properties of doughs and baked produets. In H. Faridi and J.M. Faubion (Eds.), Dough Rheology and Baked Product Texture. Van Nostrand Reinhold, New York, pp. 157-330. 

Several models for the structure of wheat glutenin have been proposed. One of the earliest molecular models was that of Ewart [62]. He subsequently modified the model. Ewart s latest model shows one disulfide bond between two adjacent polypeptide chains of glutenins, which consist of linear polymers. Ewart pointed out that the rheological properties of dough are dependent on the presence of theologically active disulfide bonds and thiol groups as well as on secondary forces in the concatenations [63]. 

Baking. Flour contains enzymes, the most important of which are amylases and proteases. However, the quantities of these enzymes are not always ideal for baking purposes, and supplementary enzymes are often added. Many potential applications of enzymes are being investigated to improve the properties of bread. Traditional applications of enzymes are for improvement of the dough, loaf volume, crumb structure, and shelf-life. The enzyme products used are free-flowing microgranulates that are easy to handle and freely mixed with flour. 

Quantitative values for total hemicelluloses, and structural information on hemicelluloses, may be of practical use when the investigator seeks to discover correlations between the hemicellulosic composition of a plantstuff, or of a material derived from it, and some quality or property it is believed to affect. There have been many investigations of possible correlations between hemicellulosic composition and the milling properties of cereals,106,228 and the quality of flours,229 doughs,230 and baked products.231 Numerous applied studies on the... 

Foods are always a multicomponent physical system, so interactions between components are more significant than the chemical and physical properties of components. Food structures are mainly arranged by noncovalent, nonspecific interactions of proteins and polysaccharides in an aqueous medium. For instance, the most studied structural food macromolecules are soybean proteins, gluten, milk proteins, and starch. But despite detailed knowledge about individual components, the control of dough and milk system functionality remains empirical (but see Chapters 19 and 20). 

It is also important to remember that wheat gluten and dough are complex materials, consisting not only of protein and water, but also starch-, lipid-, water- and salt-soluble proteins and smaller carbohydrates, and so on. The properties of these materials and their interactions with the gluten proteins are poorly understood but can be expected to also influence the viscoelastic properties. The challenge therefore is to understand gluten structure at the molecular level and how this structure interacts... 

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