**1. Introduction**

258 Viscoelasticity – From Theory to Biological Applications

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Wheat is the only cereal capable of produce strong and cohesive dough, qualities responsible for the wide variety of food products made from it. In Mexico, wheat is classified into five groups based on functionality; those wheat varieties in group three are called soft, and they are used in products such as cakes and cookies.

Wheat dough is classified as viscoelastic material (Faubion & Hoseney, 1990) which has elastic and viscous characteristics conferred by gluten. Gluten network is formed by hydrophobic interactions between water and protein polymers of the flour (mainly glutenins and gliadins). The nature of the glutenin mainly influences the functional properties of strength and elasticity, while the gliadin fraction provides extensibility and viscosity to the dough (Lu & Grant, 1999). Studies have been conducted in search of those factors that influence dough's viscoelastic properties to better understand the behavior of dough, so it can be handled and utilized properly.

Smith et al. (1970) utilized the dynamic test in a gluten-starch-water system and found that high protein content is reflected in high values of the storage module (G´) and loss module (G´´). Besides protein content, it has been found that the soluble protein fraction is a determinant factor for the rheological properties of dough by acting as a lubricating agent (Rouille et al., 2005). The importance of the total gliadin fraction in the structure of gluten was observed by Lee & Mulvaney (2003). Gupta et al. (1993) utilized an extensograph to evaluate doughs and found a high correlation between unextractable proteins and maximum resistance (Rmax), which led them to believe that a high molecular weight fraction of glutenin contributes to the resistance of the dough.

© 2012 Magaña-Barajas et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Another factor affecting the rheological properties of dough is starch. It has been seen that damage to starch and the presence of other minor components affect rheological properties (Dexter et al., 1994; Lynn & Stark, 1995). Campos et al. (1997) and Chiotelli et al. (2004) suggested that the rheological changes observed in dough subjected to low heating tests may be due to starch molecules present. Zeng et al. (1997) found that 80% of the variation in the viscosity of starch paste of 13 cultivars of wheat was due to the concentration of amylose and amylopectin, and Morris et al. (1997) observed that this variation is due to the presence of isoenzymes synthesized in relation to the starch granule. Georgopulus (2006) observed that the rheological properties of dough are affected more by the removal of the native lipids of the flour than for its gluten.

Use of the Stress-Relaxation and Dynamic Tests to Evaluate the Viscoelastic Properties of Dough from Soft Wheat Cultivars 261

The study of viscoelastic properties of flour from different wheat cultivars has been reported for different authors (Larsson & Eliasson, 1996a, 1996b; Wikström & Eliasson, 1998; Safari-Ardi & Phan-Thien, 1997, 1998; Van Bockstaele et al., 2008), nevertheless, none of them specifically study the viscoelastic characteristics of soft wheat, and this could be important for the cookies and baked industry. The purpose of this research was to evaluate the rheological properties of soft wheat dough from some cultivars in order to determine in the most appropriate manner its final use and in particular its quality. The viscoelastic properties of soft wheat dough were evaluated by applying the stress-relaxation and the dynamic test, and relate them with empirical rheological measurements and

Samples of soft wheat from four cultivars were used: Barcenas, Cortazar, Salamanca and Saturno. Samples were obtained in the Central part of Mexico (El Bajío Zone), and they were sent to the Departamento de Investigación y Posgrado en Alimentos from the University of

Wheat samples of the four cultivars were cleaned (Blount/Ferrell-Ross, model M2BC), and placed in plastic bags, which were stored at refrigeration temperature (4°C) until use. Wheat samples were conditioned based on the international approved method number 26-95 (American Asociation of Cereal Chemists, [A.A.C.C], 2000), at a moisture content of 16%, utilizing a conditioner (Chopin Instruments, Villeneuve-La-Garenne, France). Samples were allowed to stand for a period of 24 h before preparation of flours. The conditioned samples were milled using the approved method number 26-10 (A.A.C.C., 2000), and an experimental mill (Brabender, model Quadrumat Senior, South Hackensack, NJ). For

For proximate chemical analysis of flours, the official methods of the A.A.C.C. International (2000) were used, and the following determinations were made: protein content (approved method number 46-13) using a nitrogen analyzer (LECO, model FP-528, MI, USA), and the protein factor was N x 5.7; ash content (approved method number 08-03); and moisture

Wet gluten content was determined utilizing the approved method number 38-11 (A.A.C.C., 2000) and the apparatus Glutomatic (Falling Number, model 2100, Huddinge, Sweden). Sedimentation volume was determined using the approved method number 56-61A (A.A.C.C., 2000). The falling number was measured utilizing approved method number 56- 81b (A.A.C.C., 2000) and the apparatus Falling Number (model 1400, Huddinge, Sweden).

Sonora at Hermosillo Sonora, México, where was carried out this study.

maturation, flours were allowed to stand for a period of 15 days.

physicochemical characteristics.

**2. Experimental procedure** 

**2.1. Raw material** 

**2.2. Flours elaboration** 

**2.3. Flours quality analysis** 

content (approved method number 44-40).

Rheological properties of wheat flour are determinants of the desired characteristics in the final product, as well as for the design of equipment and processes. Therefore, it is necessary to find reliable rheological tests that are a useful tool for characterizing dough of wheat flours (Safari-Ardi & Phan-Thien, 1998). Rheology of wheat dough is broad, and the tests utilized are diverse. Initially, empirical tests were more used than the fundamental tests, but disadvantages were seen such as: dependence on the instrument, the form and quantity of the sample utilized and lack of theoretical basis (Faubion & Hoseney, 1990), which led to the development of fundamental tests. The most important fundamental viscoelastic tests utilized for wheat dough are the force-deformation ratio, creep test, the dynamic test and stress-relaxation test (Mohsenin, 1978).

Recently, the dynamic test and the stress relaxation test have been used to characterize the dough viscoelasticity. Safari-Ardi & Phan-Thien (1998), utilizing the dynamic test observed that there were no differences among dough elaborated with different flours, probably due to the small deformation used (<1%). Therefore, it was decided to evaluate viscoelastic properties of dough applying a stress-relaxation test. In this technique, the dough is rapidly deformed at a predetermined level and the stress is measured over time, where deformations are >1% (Faubion & Hoseney, 1990; Mohsenin, 1978; Rao et al., 2000).

Several researches have utilized and recommended the stress-relaxation test (Lee and Mulvaney, 2003; Rao et al., 2000; Uthayakumuran et al., 2002; Wikström & Eliasson,, 1998; Yadav et al., 2005). Safari-Ardi et al. (1997) found when using the stress-relaxation test, it was possible to differentiate dough from distinct wheat flours, and demonstrated that besides the method being consistent, the data of the stress-relaxation test obtained at high amplitudes (1-15% deformation in 3x103 s) were very precise (Safari-Ardi & Phan-Thien, 1998). Utilizing the stress-relaxation test, it has been found that the distribution of the quantity of protein (high molecular weight glutenin) and its molecular weights are related to the relaxation time (Rao et al., 2000; Uthayakumaran et al., 2002). In addition, it has been shown that moisture content and strain affect the relaxation characteristics of dough by doing them no linear (Yadav et al., 2005). Similarly, Smith et al. (1970) observed that the relaxation time increases with mixing, and Rao et al., (2000) concluded that this parameter is less for strong dough than that moderately strong.

The study of viscoelastic properties of flour from different wheat cultivars has been reported for different authors (Larsson & Eliasson, 1996a, 1996b; Wikström & Eliasson, 1998; Safari-Ardi & Phan-Thien, 1997, 1998; Van Bockstaele et al., 2008), nevertheless, none of them specifically study the viscoelastic characteristics of soft wheat, and this could be important for the cookies and baked industry. The purpose of this research was to evaluate the rheological properties of soft wheat dough from some cultivars in order to determine in the most appropriate manner its final use and in particular its quality. The viscoelastic properties of soft wheat dough were evaluated by applying the stress-relaxation and the dynamic test, and relate them with empirical rheological measurements and physicochemical characteristics.
