*2.4.1. Empirical test*

The farinographic parameters of water absorption, stability and time of development were obtained based on the farinographic approved method number 54-21 (A.A.C.C., 2000), and utilizing a farinograph (Brabender Instruments, type 810143, South Hackensack, NJ).

Use of the Stress-Relaxation and Dynamic Tests to Evaluate the Viscoelastic Properties of Dough from Soft Wheat Cultivars 263

**2.5. Experimental design and statistical analysis** 

**3. Results and discussion** 

**3.1. Flours quality** 

similar for all the cultivars.

**3.2. Rheological tests** 

Bushuk, 1988; Farrand, 1969; Yamamoto et al., 1996).

*3.2.1. Empirical test* 

A completely randomized experimental design was performed, where the factor was the wheat cultivar: (Barcenas, Cortazar, Salamanca and Saturno). For the purpose of determining the effect of the factor on the different determinations, analysis of variance (ANOVA) was used with a 95% confidence interval. In addition, simple correlations (r) between different determinations were carried out. ANOVA was carried out with the

Analysis of variance showed that the wheat cultivar affected significantly (p<0.05) the proximate chemical analysis of flours. Table 1 presents mean values for protein, moisture, ash and wet gluten content, sedimentation volume, and falling number each flour from the soft wheat cultivars. Cultivar Barcenas showed the highest values of protein content, ash content, wet gluten, sedimentation volume and falling number. Moisture content was

In general, it has been observed that wheat cultivar affected the physical and chemical properties of flours (Lin & Czuchajowska, 1997). In some investigations (Carrillo et al., 1990; Chiotelli et al., 2004; Yamamoto et al., 1996), marked physicochemical differences have been observed in cultivars of soft wheat, and that falling number has been seen to influence the rheological properties of dough. Sedimentation volume indicates the quality of the proteins presents; in hard wheat the close values to 70 mL indicates high baking quality (A.A.C.C., 2000; Pomeranz, 1988). Falling number values greater than 400 s have been reported that the amylolytic activity is low. Therefore, wheat is considered that has been exposed to low rainfall during growth up to harvest time, consequently resulting in healthy grains (Carcea et al., 2006; Pomeranz, 1988). In this study, for all the flours, the Falling number was greater than 400 s, which indicate that flours were obtained from healthy soft wheat cultivars.

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 &

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

Statistical Analytical System Software (SAS Institute, Inc. Cary, NC, 2002).

To characterized flour-water dough for extensibility and resistance to extension, it was used approved method number 54-30A (A.A.C.C., 2000), and the Alveograph (Chopin Instruments, Villeneuve-La-Garenne, France).

## *2.4.2. Fundamental test*

Sample preparation. Dough was prepared with 100 g of flour of each cultivar, and adding distilled water corresponding to the absorption obtained from the farinograph. Flour was placed and mixed in a mixer with 300 g capacity (National MFG, Lincoln, NE, USA) without the distilled water. Then it was mixed for 1 min with one afterward; the dough was allowed to stand for 30 min in a proofing chamber (National MFG, Lincoln, NE, USA) with a controlled environment (30°C, 95% relative humidity). Next, samples of dough weighing individually 2.7 g were placed in plastic bag, hermetically sealed, and left at room temperature (25°C) until use in the rheometer.

Dynamic method. Oscillatory measurements were conducted at 0.1% strain within the linear viscoelastic regime (previously carried out), over a frequency range of 0.1 to 100 rad/s. Frequency sweep experiments were conducted in a Rheometer (Rheometrics Scientific, model RSF III, Piscataway, NJ, USA). The rheometer was equipped with 25-mm diameter parallel plates that were maintained at 25° C. A dough sample of 2.7 g was round by hand and placed between the plates of the rheometer. Sample was gently flattened to fit the plate geometry using a Teflon-coated spatula. The upper plate was lowered to a fixed gap between plates of 2 mm. The exposed edges of dough were trimmed, and to avoid drying, petroleum jelly was injected around the plates. Sample was allowed to rest for a period of 20 min before the test. The rheometer was run in the frequency scanning in oscillatory mode, and at a controlled temperature. The viscoelastic parameters determined were: the storage modulus (G´, Pa), the loss modulus (G´´, Pa) and tangent of phase angle (δ=G´´/G´). These parameters were obtained using the software analysis program of the rheometer (RSI Orchestrator, Rheometrics Scientific) (Magaña-Barajas et al., 2011).

Stress-relaxation test. Sample of dough was prepared and placed in the rheometer in manner similar to that utilized in the dynamic test. After placing the sample in the rheometer, it was allowed to rest for a period of 20 min before the test. Based on preliminary tests and some researches (Li et al., 2003; Rao et al., 2000; and Safari-Ardi & Phan-Thien 1998), stress relxation was measured at intervals of 0.1 s applying a 15% shear strain for 30 min at a controlled temperature of 25ºC operating in shear stress mode. The parameters determined were maximum stress at 15% strain (G0) and the relaxation time (τ).

## **2.5. Experimental design and statistical analysis**

A completely randomized experimental design was performed, where the factor was the wheat cultivar: (Barcenas, Cortazar, Salamanca and Saturno). For the purpose of determining the effect of the factor on the different determinations, analysis of variance (ANOVA) was used with a 95% confidence interval. In addition, simple correlations (r) between different determinations were carried out. ANOVA was carried out with the Statistical Analytical System Software (SAS Institute, Inc. Cary, NC, 2002).
