A Modified Extensigraph Method for Evaluating Dough Properties of Hard Wheat Breeding Lines

Cereal Chem. 86(5):582–589 A modified extensigraph method reduced sample quantity to 100 g from 300 g and testing time by half with easy dough preparation compared to the AACC standard extensigraph method, which challenges wheat breeding programs where the sample size is small and evaluations of large numbers of samples are demanded. Correlation coefficients (r) for 93 pairs of each of six extensigraph dough characteristics of 31 different tested wheat samples were r = 0.95 for resistance-to-extension, r = 0.80 for extensibility, r = 0.93 for ratio of resistance-to-extension to extensibility, r = 0.92 for ratio of maximum resistance-to-extension to extensibility, and r = 0.81 for area under the curve (energy). Correlation coefficients for the measurements of extensigraph dough characteristics at each of three rest-time tests between the modified and standard methods were significant. Some dough mixing characteristics and bake tests correlated better with dough extension characteristics when determined by the modified method. Repeatability of the modified method test was good. The modified extensigraph method can be a useful alternative to the standard method for the milling and baking industries, crop quality surveys, and wheat quality research. Rheological characteristics of wheat flour dough with explicit, nonlinear shear thinning (pseudoplastic), and thixotropic behaviors (Weipert 1990) are complex and very important parameters for wheat quality evaluation and determination of end product quality. The complex and important rheological parameters, stress vs. strain, resistance-to-extension vs. extensibility, elasticity vs. viscosity, and maximum pressure vs. time taken for bubble to burst, can be measured with fundamental or empirical techniques. Fundamental measurements are not suited for establishing the possible relationship between the rheological properties of wheat flour dough and its baking behavior because the small deformations involved are completely different from the large deformations during fermentation and baking (Kokelaar et al 1996). However, rheological tests developed using either small or large strain levels give information that can be related to the structural characteristics of dough (Davidou et al 2008). The empirical tests have proven to be useful in practical industrial applications and continue to be used in research on wheat flour dough (Janssen et al 1996) because they generally correlate well with breadmaking performance (Tronsmo et al 2003). The Brabender extensigraph is one of several empirical rheological instruments that offer a measurement of stress-strain relationship in dough after defined rest periods (Preston and Hoseney 1991). The extensigraph test can specifically determine dough extension characteristics that predict breadmaking quality or other end product qualities of wheat flour, estimate gluten quality, standardize optimum dough properties for baked goods, evaluate specific effects of dough ingredients and additives, differentiate qualities of breeding lines, improve the rapid screening of wheat cultivars, and control the flour quality for both the milling and baking industries (Bloksma 1990a,b; Hoseney 1994; Kokelaar et al 1996; Anderssen et al 2004; Mirsaeedghazi et al 2008). Although the standard extensigraph method has been widely used for many years, it requires a large sample size (300 g), which does not include amount of flour for determination of flour water absorption and mix time using the 50-g farinograph and a lengthy testing time with complicated dough preparation. Other instruments that are used for evaluation of dough extension characteristics include the Chopin alveograph and the TA-XT2i texture analyzer with a modified-geometry Kieffer rig used as a smallscale method (Kieffer et al 1998; Mann et al 2005). The alveograph method also requires a large sample size (250 g) and relies on identical water absorption and mix time for dough preparation. Large sample size and time requirements for both standard extensigraph and alveograph tests have precluded their general use for breeding programs in the United States (Nash et al 2006). Although a small flour sample was used for the TA-XT2i texture analyzer with a Kieffer rig, the data did not correlate with the standard extensigraph method, making the data interpretation difficult. In addition, very little information was reported about the reproducibility of the small-scale extension test (Dunnewind et al 2004). Thus, the standard extensigraph test has more advantages and benefits than other extension tests, but with some significant limitations such as requiring large amounts of flour, long testing times, and inconvenient dough preparation. Such limitations do not allow the standard extensigraph test to be used for evaluation of wheat samples in wheat breeding programs where sample size is small and evaluation is demanded of large number of samples. U.S. hard winter wheat breeders are interested in the dough extension tests for their breeding programs if the test requires small sample size (personal conversations). The USDA-ARS Hard Winter Wheat Quality Lab in Manhattan, KS, has conducted the standard extensigraph or alveograph tests on composite hard winter wheat breeding lines for some of hard winter wheat breeding programs in the Great Plains. Composite breeding lines were used for the dough extension tests because of lack of seeds in one location. Therefore, developing or modifying a method that requires a small amount of flour, cuts testing time, allows easy dough preparation, generates satisfying results, and has good repeatability for the dough extension tests on the extensigraph instrument could help avoid many limitations of the standard extensigraph and other tests and bring about a more efficient and effective evaluation of dough extension characteristics. Our objective was to modify the standard extensigraph method and minimize its limitations by reducing sample size and decreasing dough preparation time. A modified method that offered convenient dough preparation and required small sample size and less testing time would be available to evaluate flour samples in wheat breeding programs and available as an alternative to the standard extensigraph method for the milling and baking industries, wheat crop quality surveys, and wheat quality research. 1 USDA, ARS, Hard Winter Wheat Quality Laboratory, 1515 College Ave., Manhattan, KS 66502. 2 Corresponding author. Phone: 785-776-2750. Fax: 785-537-5534. E-mail address: [email protected] 3 Kansas State University, Department of Grain Science and Industry, Manhattan,