Phase Separation of Wheat Flour Dough Studied by Ultracentrifugation and Stress Relaxation. II. Influence of Mixing Time, Ascorbic Acid, and Lipids

Cereal Chem. 73(l):25-31 Separation by ultracentrifugation provides a simple tool for studies of with increased mixing time, while the separation of spring wheats was the aqueous phases of wheat flour dough. A separation into liquid, gel, not influenced. The general effect of adding ascorbic acid to dough or gluten and starch, phases was maintained. More or less unseparated using defatted flour was improved separation. Lecithin impaired separadough was also found at the bottom of the test tube. In the present study, tion. An advantage of this technique is that the phases could be studied the separation behavior was studied for three wheat cultivars when influ- without disturbing the composite system. This resulted in valuable inenced of factors known to affect the baking behavior. The separation formation for the interpretation of rheological measurements on dough. properties differ among cultivars. Increased mixing time caused an It was possible to relate effects on the modulus to either gluten strength, approximately linear increase for incorporation of water into the gluten the liquid phase, or interactions between starch and gluten. phase. For winter wheat, the amount of unseparated dough decreased One of the unique features of wheat flour is the phase separation of two continuous aqueous phases when the flour is mixed into a dough. The bicontinuous phases are the gluten phase (water-swollen protein) and the liquid phase (containing the dispersed starch granules and soluble components) (Eliasson and Larsson 1993). In a previous study, in which ultracentrifugation was used to illustrate the phase separation of dough, it was observed that the separation of dough occurred when the water content was high enough to enable a gluten phase to separate (Larsson and Eliasson 1996). The rheological behavior at small deformations was correlated with the phase separation behavior over a wide range of water contents. However, it was not possible to establish a simple relationship between the rheological behavior and the amount or properties of the separated phases when cultivars were compared. In the present study, the influence of factors such as mixing time, ascorbic acid, defatting, and lecithin, which are known to affect both the baking behavior, and the Theological behavior at small deformations has been investigated. These factors, which may modify the properties of either or both of the bicontinuous phases, are compared for three wheat cultivars. Results from rheological measurements on dough at small deformations may appear conflicting. For example, for an increasing flour protein content, both an increase (Abdelrahman and Spies 1986) and a decrease (Hibbered 1970) in the modulus have been observed. Also, for increasing mixing time, different studies have shown both an increase (Bohlin and Carlsson 1980) and a decrease (Mani et al 1992) in the modulus measured at small deformations. The present technique demonstrates that an effect on the rheological behavior at small deformations, such as stress relaxation, may be attributed to different properties of the two aqueous phases present in dough.