*3.2.1. Empirical test*

Table 2 shows the mean values for water absorption, stability and developing time each flour. Salamanca had the highest values of water absorption and developing time, while cultivar Barcenas had the greatest stability. Values for water absorption, stability and developing time are directly proportional with protein content. In addition, water absorption is directly proportional to the diameter of the cookie (Bloksma, 1990; Bloksma & Bushuk, 1988; Farrand, 1969; Yamamoto et al., 1996).

Table 2 shows also the alveographic parameters for flours from the soft wheat cultivars. Cultivar Salamanca showed the highest values of W, P and P/L. These high values probably were due to its protein content, a factor that also results in high water absorption (Unbehend et al., 2004; Yamamoto et al., 1996).

Use of the Stress-Relaxation and Dynamic Tests to Evaluate the Viscoelastic Properties of Dough from Soft Wheat Cultivars 265

This indicates that in soft wheat cultivars dough prevailed the viscous behavior over the

Figures 1 and 2 show the dependence of G´ and G´´ with frequency (Hibber & Wallace, 1966). In both figures, values of G´ and G´´ are increasing, which could indicate that dough hardness increase, and it could be due to content of gluten (Chiotelli et al., 2004) and protein quality, resulting in the gluten of wheat dough not as weak as expected (since soft wheat flour contains a weak gluten). Several authors (Huebner et al., 1999; Yamamoto et al., 1996) agreed that content and quality of protein and gluten content are factors affecting positively

In Figure 3 is presented the behavior of Tan δ with frequency for dough from all soft wheat cultivars. Initially, Tan δ shows a slight decrease; at intermediate levels (1-10 rad/s) values at a given frequency are similar; and at high frequencies this parameter shows the same initial phenomenon that at low frequency values. Tan δ for all the soft wheat cultivars is higher than 0.5, which indicates that viscous behavior is higher than the elastic

Stress-relaxation test. Dough was subjected to a deformations much greater than that in the dynamic test (>1%). The parameters evaluated from this test were the initial (maximum) stress at 15% strain (G0), and the relaxation time (τ). This last parameter is related to the process of flow occurring when dough is relaxed, and is defined as the time required for the

> Frequency (rad/s) 0,1 1 10 100

**Figure 1.** Storage modulus (G´) evaluated with the dynamic test for dough made of soft wheat

Barcenas Cortazar Salamanca Saturno

force to fall 1/e times, or by 36.8% of its original value (Smith et al., 1970).

elastic behavior.

behavior.

G´ (Pa)

cultivars.

1e+3

1e+4

1e+5

these viscoelastic parameters.


a Dry basis b Standard Deviation



**Table 2.** Rheological characteristics of flour from soft wheat cultivars

#### *3.2.2. Fundamental test*

Two techniques were used to characterize the viscoelasticity of dough from soft wheat cultivars: a) the dynamic method; and b) the stress-relaxation test, which were performed in a rheometer.

Dynamich method. The viscoelastic properties of dough obtained from the soft wheat cultivars were the storage modulus (G´), loss modulus (G´´) and tangent of angle phase (Tan δ) (Figures 1, 2 y 3, respectively). To evaluate if there were statistically differences among the viscoelastic properties of dough from the different wheat cultivars, an analysis of variance was performed on the G´, G´´ and Tan δ values at a frequency of 5 rad/s, where the dough viscoelasticity was in the linear viscoelastic domain (Figures 1, 2 and 3). According to the ANOVA, G´, G´´ and Tan δ obtained with the dynamic test at a frequency of 5 rad/s had similar values (p>0.05), indicating that dough from the soft wheat cultivars were in the same values of viscoelasticity (Table 3). For all the soft wheat cultivars, the G´ values were greater than those for G´´, and Tan δ was greater than 0.50. This indicates that in soft wheat cultivars dough prevailed the viscous behavior over the elastic behavior.

264 Viscoelasticity – From Theory to Biological Applications

et al., 2004; Yamamoto et al., 1996).

**Moisture Content** 

**Water Absorption (%)** 

dP/L= Curve configuration ratio, extensibility

*3.2.2. Fundamental test* 

a rheometer.

a Dry basis b Standard Deviation

**Protein Contenta**

**Table 1.** Physicochemical characteristics of flour from soft wheat cultivars

**Stability (min)** 

**Table 2.** Rheological characteristics of flour from soft wheat cultivars

**Cultivar** 

**Cultivar** 

were due to its protein content, a factor that also results in high water absorption (Unbehend

**Wet Glutena**

**(%) (%) (%) (%) (mL) (s)** 

**Farinograph Alveograph**

**Wb (10-4J)**  **Sedimentati on Volumea**

**Pc** 

**(mm H20) P/Ld**

**Falling Number** 

**Ash Contenta** 

Barcenas 14.08 ± 0.33b 11.81 ± 0.50 0.84 ± 0.18 34.87 ± 4.82 32.03 ± 1.62 476.60 ± 31.73 Cortazar 14.06 ± 0.23 10.58 ± 0.31 0.69 ± 0.21 31.77 ± 2.47 22.04 ± 1.18 422.51 ± 9.51 Salamanca 14.10 ± 0.45 11.27 ± 0.49 0.76 ± 0.18 33.00 ± 1.02 28.92 ± 8.66 449.67 ± 27.54 Saturno 14.05 ± 0.61 10.32 ± 0.41 0.55 ± 0.04 30.86 ± 2.46 25.46 ± 1.94 409.98 ± 13.85

> **Developing Time (min)**

Barcenas 54.04 ± 3.84a 4.28 ± 2.01 3.70 ± 0.66 114.75 ± 14.25 49.76 ± 5.04 0.46 ± 0.11 Cortazar 56.16 ± 1.48 1.96 ± 0.59 3.39 ± 0.39 85.50 ± 10.22 52.63 ± 7.54 0.57 ± 0.05 Salamanca 56.39 ± 1.70 3.75 ± 2.14 4.54 ± 1.67 139.62 ± 66.88 67.01 ± 16.41 0.70 ± 0.15 Saturno 53.28 ± 1.51 3.51 ± 0.68 3.14 ± 0.54 106.33 ± 17.58 48.69 ± 4.13 0.52 ± 0.10 a Standard Deviation; bW= Deformation energy of dough; cP= Maximum overpressure, tenacity;

Two techniques were used to characterize the viscoelasticity of dough from soft wheat cultivars: a) the dynamic method; and b) the stress-relaxation test, which were performed in

Dynamich method. The viscoelastic properties of dough obtained from the soft wheat cultivars were the storage modulus (G´), loss modulus (G´´) and tangent of angle phase (Tan δ) (Figures 1, 2 y 3, respectively). To evaluate if there were statistically differences among the viscoelastic properties of dough from the different wheat cultivars, an analysis of variance was performed on the G´, G´´ and Tan δ values at a frequency of 5 rad/s, where the dough viscoelasticity was in the linear viscoelastic domain (Figures 1, 2 and 3). According to the ANOVA, G´, G´´ and Tan δ obtained with the dynamic test at a frequency of 5 rad/s had similar values (p>0.05), indicating that dough from the soft wheat cultivars were in the same values of viscoelasticity (Table 3). For all the soft wheat cultivars, the G´ values were greater than those for G´´, and Tan δ was greater than 0.50. Figures 1 and 2 show the dependence of G´ and G´´ with frequency (Hibber & Wallace, 1966). In both figures, values of G´ and G´´ are increasing, which could indicate that dough hardness increase, and it could be due to content of gluten (Chiotelli et al., 2004) and protein quality, resulting in the gluten of wheat dough not as weak as expected (since soft wheat flour contains a weak gluten). Several authors (Huebner et al., 1999; Yamamoto et al., 1996) agreed that content and quality of protein and gluten content are factors affecting positively these viscoelastic parameters.

In Figure 3 is presented the behavior of Tan δ with frequency for dough from all soft wheat cultivars. Initially, Tan δ shows a slight decrease; at intermediate levels (1-10 rad/s) values at a given frequency are similar; and at high frequencies this parameter shows the same initial phenomenon that at low frequency values. Tan δ for all the soft wheat cultivars is higher than 0.5, which indicates that viscous behavior is higher than the elastic behavior.

Stress-relaxation test. Dough was subjected to a deformations much greater than that in the dynamic test (>1%). The parameters evaluated from this test were the initial (maximum) stress at 15% strain (G0), and the relaxation time (τ). This last parameter is related to the process of flow occurring when dough is relaxed, and is defined as the time required for the force to fall 1/e times, or by 36.8% of its original value (Smith et al., 1970).

**Figure 1.** Storage modulus (G´) evaluated with the dynamic test for dough made of soft wheat cultivars.

Use of the Stress-Relaxation and Dynamic Tests to Evaluate the Viscoelastic Properties of Dough from Soft Wheat Cultivars 267

Figure 4 shows the behavior and mean values for the viscoelastic parameters of τ and initial maximum stress (G0) of dough from the soft wheat cultivars, obtained in the stressrelaxation test. Initially, dough was subjected a high deformation (15%) yielding in response a high initial stress, and as time progress, dough relaxed and stress diminished. It is observed that all curves present a single maximum stress coinciding with Rao et al. (2000). Li et al (2003) found that relaxation process occur in two steps: the first, correspond at the increase of distribution of protein polymers short chain (gliadin and glutenins of low molecular weight). The second peak corresponds at the protein polymers of large chain like glutenins of high molecular weight. In this case, the soft wheat cultivars evaluated had slow protein content (9.9%) and the content of protein polymers short chain (44.22% of gliandins, of total) is highest than the content of protein polymers short chain (data not showed),

**Cultivar Dynamic Testg Stress Relaxation Testh** 

Barcenas 29080 ± 3384a 16378 ± 1926 0.56 ± 0.03 510.42 ± 119.61 0.36 ± 0.07 Cortazar 28445 ± 11489 15621 ± 1114 0.54 ± 0.02 466.00 ± 55.61 0.38 ± 0.02 Salamanca 28246 ± 4174 16007 ± 2714 0.56 ± 0.01 484.28 ± 130.50 0.33 ± 0.07 Saturno 29750 ± 2967 17121 ± 1524 0.057 ± 0.02 462.45 ± 56.50 0.41 ± 0.02 a Standard Deviation; b G´: Storage modulus; cG´´: Loss modulus; dTan δ: Tangent of phase angle; eG0:

**Table 3.** Viscoelastic characteristics of dough made from soft wheat cultivars evaluated with the

In Table 3 is presented G0 and τ values for all flours. The wheat cultivar Saturno had the highest value of τ (0.41 s). The high values of τ indicates that the recovery of deformed dough structure is slow, reflecting a weak gluten. That wheat cultivar presents the lowest values of moisture, protein content, ash content, wet gluten and falling number, which probably caused a lesser strength in gluten. This could explain the strength of the dough. Dough of cultivars Salamanca and Barcenas had the lowest τ values (0.33 y 0.36 s, respectively). These varieties have high values in almost all the physicochemical properties. Low values of τ correspond at strong gluten. For this reason when dough is subject to a deformation quickly recovers its original form. In general, variation of values of τ (range 0.33 s to 0.41 s) was probably attributed at the content and type of protein, and moisture content of the wheat cultivar. This has been observed in several investigations, where it has been found that moisture and gluten properties (such as gluten strength) affect the parameters of this test (Fu et al., 1997; Larsson & Eliasson, 1996a; Li et al., 2003; Yadav et al.,

Results obtained show an inverse relationship between the values of G0 and τ. Applying a high strain to dough with three-dimensional network structure of strong gluten, values of

**G´b (Pa) G´´c (Pa) Tan δd G0e (Pa) f (s)** 

: Relaxation time; g: the viscoelastic parameters were evaluated at frequency

changing the ratio glutenins/gliadins.

Initial maximum stress; τ<sup>f</sup>

2005).

dynamic and stress relaxation tests

of 5 rad/s; h: the viscoelastic parameters were measured at 15% shear strain

G0 are obtained almost immediately after deformation.

**Figure 2.** Storage modulus (G´) evaluated with the dynamic test for dough made of soft wheat cultivars.

**Figure 3.** Tangent of angle phase (Tan δ) evaluated with the dynamic test for dough made of soft wheat cultivars.

An ANOVA was carried out to see if there were differences between the viscoelastic properties of the different soft wheat cultivars determined with the stress-relaxation test. It was shown that the soft wheat cultivar affected only to τ (p<0.05).

Figure 4 shows the behavior and mean values for the viscoelastic parameters of τ and initial maximum stress (G0) of dough from the soft wheat cultivars, obtained in the stressrelaxation test. Initially, dough was subjected a high deformation (15%) yielding in response a high initial stress, and as time progress, dough relaxed and stress diminished. It is observed that all curves present a single maximum stress coinciding with Rao et al. (2000). Li et al (2003) found that relaxation process occur in two steps: the first, correspond at the increase of distribution of protein polymers short chain (gliadin and glutenins of low molecular weight). The second peak corresponds at the protein polymers of large chain like glutenins of high molecular weight. In this case, the soft wheat cultivars evaluated had slow protein content (9.9%) and the content of protein polymers short chain (44.22% of gliandins, of total) is highest than the content of protein polymers short chain (data not showed), changing the ratio glutenins/gliadins.

266 Viscoelasticity – From Theory to Biological Applications

G´´ (Pa)

cultivars.

cultivars.

Tan

0,0

0,2

0,4

0,6

0,8

1,0

1e+3

1e+4

Frequency (rad/s) 0,1 1 10 100

Frequency (rad/s) 0,1 1 10 100

**Figure 3.** Tangent of angle phase (Tan δ) evaluated with the dynamic test for dough made of soft wheat

An ANOVA was carried out to see if there were differences between the viscoelastic properties of the different soft wheat cultivars determined with the stress-relaxation test. It

was shown that the soft wheat cultivar affected only to τ (p<0.05).

**Figure 2.** Storage modulus (G´) evaluated with the dynamic test for dough made of soft wheat

Barcenas Cortazar Salamanca Saturno

Barcenas Cortazar Salamanca Saturno


Initial maximum stress; τ<sup>f</sup> : Relaxation time; g: the viscoelastic parameters were evaluated at frequency of 5 rad/s; h: the viscoelastic parameters were measured at 15% shear strain

**Table 3.** Viscoelastic characteristics of dough made from soft wheat cultivars evaluated with the dynamic and stress relaxation tests

In Table 3 is presented G0 and τ values for all flours. The wheat cultivar Saturno had the highest value of τ (0.41 s). The high values of τ indicates that the recovery of deformed dough structure is slow, reflecting a weak gluten. That wheat cultivar presents the lowest values of moisture, protein content, ash content, wet gluten and falling number, which probably caused a lesser strength in gluten. This could explain the strength of the dough. Dough of cultivars Salamanca and Barcenas had the lowest τ values (0.33 y 0.36 s, respectively). These varieties have high values in almost all the physicochemical properties. Low values of τ correspond at strong gluten. For this reason when dough is subject to a deformation quickly recovers its original form. In general, variation of values of τ (range 0.33 s to 0.41 s) was probably attributed at the content and type of protein, and moisture content of the wheat cultivar. This has been observed in several investigations, where it has been found that moisture and gluten properties (such as gluten strength) affect the parameters of this test (Fu et al., 1997; Larsson & Eliasson, 1996a; Li et al., 2003; Yadav et al., 2005).

Results obtained show an inverse relationship between the values of G0 and τ. Applying a high strain to dough with three-dimensional network structure of strong gluten, values of G0 are obtained almost immediately after deformation.

Use of the Stress-Relaxation and Dynamic Tests to Evaluate the Viscoelastic Properties of Dough from Soft Wheat Cultivars 269

with developing time (farinograph) (r=-0.959), which indicates indirectly a high protein content and strong gluten, resulting in a rapid response upon deformation, as a consequence lower τ values. G0 showed a strong correlation with protein (r=0.984), which could be reflected in the greater strength of gluten, thereby a high resistance upon deformation. A second correlation of G0 was with wet gluten (r=0.987), which probably is due to the fact that a greater amount of gluten causes greater resistance to deformation, and this is in agreement the study carried out by (Li et al., (2003). Finally, the last correlation of G0 was with falling

The dynamic test only yielded a highly significant negative correlation (p<0.01) for the viscoelastic parameter of G´ (storage modulus) with water absorption (r=-0.975), which could be explained by the fact that high water absorption can give indirect evidence of a high moisture content, which in turn has a negative effect on G´ (Faubion & Hoseney, 1990). No correlations were found between the stress-relaxation test and dynamic test utilized to

The viscoelastic characterization of dough made from flours of soft wheat cultivars was achieved by fundamental tests. The soft wheat cultivar showed to be a determinant factor in all characteristics of the flour. Apparently, the strength of the gluten network is critical in the rheological and viscoelastic characteristics of dough. All the cultivars presents more viscous behavior than elastic behavior (Tan δ>0.5). Wheat varieties evaluated showed a

The stress-relaxation test was better than the dynamic test in differentiating the viscoelastic characteristics of the soft wheat dough. This is confirmed by the highest number of correlations relative to the stress relaxation test, compared with the dynamic method. In our case, τ offers more information than that of G0, making it an important parameter for characterizing dough. Parameters most affecting τ was content and quality of the protein moisture content and falling number in flours. The stress-relaxation test is a simple and rapid method to perform viscoelastic evaluations, and it is believed to be a technique suitable for the characterization and differentiation of viscoelastic characteristic among dough made from soft wheat cultivars, which is important for determining the final use.

We thank to CONACyT for financial support of the project Integral Study of the Quality of Mexican Wheat and its Potential Use, project no. G35201-B,and the project Study of Water

determine the viscoelastic properties of the dough of soft wheat cultivars.

number (r=0.986).

**4. Conclusions** 

**Author details** 

**Acknowledgement** 

Elisa Magaña-Barajas, Benjamín Ramírez-Wong, Patricia I. Torres-Chávez and I. Morales-Rosas *Universidad de Sonora, Hermosillo, Sonora, México* 

range τ of between 0.33 to 0.41 s.

**Figure 4.** Relaxation modulus, G (t) vs time of dough from soft wheat cultivars, at 15% of deformation. τ: relaxation time.

The relaxation time was the parameter showing the greatest difference among the soft wheat cultivars. However, the differences obtained in τ among dough from the soft wheat cultivars were less than estimated. This despite to the range of low protein content of the soft wheat cultivars (10 to 12%, approximately), and besides, the fraction of gliadin and glutenin were of low molecular weight and approximately similar in all the samples (70% gliadin and 30% glutenin of low molecular weight, data not shown). This could indicate that tests used to evaluate the viscoelasticity in dough were high sensibility being capable to characterize dough from different soft wheat cultivars. Characterization and differentiation of dough was better with the stress-relaxation test than with the dynamic test, coinciding with others authors (Lee and Mulvaney, 2003; Rao et al., 2000; Uthayakumuran et al., 2002; Wikström & Eliasson,, 1998; Yadav et al., 2005; Safari-Ardi et al., 1997).

#### *3.2.3. Correlations between viscoelastic characteristics and other determinations*

To determine if there were significant relations among the viscoelastic properties of dough from soft wheat cultivars, and physicochemical and rheological evaluations in flours, simple correlations *(r)* were performed.

Five significant correlations were found among the viscoelastic characteristics and physicochemical determinations. Regarding to the stress-relaxation test, there were four highly significant correlations (p<0.01). The relaxation time (τ) showed a strong correlation with developing time (farinograph) (r=-0.959), which indicates indirectly a high protein content and strong gluten, resulting in a rapid response upon deformation, as a consequence lower τ values. G0 showed a strong correlation with protein (r=0.984), which could be reflected in the greater strength of gluten, thereby a high resistance upon deformation. A second correlation of G0 was with wet gluten (r=0.987), which probably is due to the fact that a greater amount of gluten causes greater resistance to deformation, and this is in agreement the study carried out by (Li et al., (2003). Finally, the last correlation of G0 was with falling number (r=0.986).

The dynamic test only yielded a highly significant negative correlation (p<0.01) for the viscoelastic parameter of G´ (storage modulus) with water absorption (r=-0.975), which could be explained by the fact that high water absorption can give indirect evidence of a high moisture content, which in turn has a negative effect on G´ (Faubion & Hoseney, 1990). No correlations were found between the stress-relaxation test and dynamic test utilized to determine the viscoelastic properties of the dough of soft wheat cultivars.
