Rheological behaviour of wheat glutens at small and large deformations. Comparison of two glutens differing in bread making potential

The rheological characteristics of hydrated cv. Obelisk and Katepwa glutens, with poor and good baking potential, respectively, were studied at small and large deformations. Dynamic (oscillatory) measurements at small deformations over a frequency range of 0.03 to 3 rad/s showed that cv. Katepwa gluten had a higher dynamic modulus and a lower loss tangent than cv. Obelisk gluten. Overmixing resulted in increases in the dynamic moduli of both glutens. Measurements at different water contents indicated that the lower dynamic moduli at higher water contents resulted mainly from a concentration effect and were not due to water acting as a plasticiser. The apparent biaxial extensional viscosities of the glutens were determined by uniaxial compression of cylindrically shaped test pieces at various cross-head speeds. This proved to be a very useful method of providing information about the rheological behaviour of glutens at large deformations as a function of different strain rates. At every biaxial strain rate tested, the apparent biaxial extensional viscosity of cv. Katepwa gluten was higher than that of cv. Obelisk gluten. A thin layer of biaxially extended gluten showed a higher resistance to further biaxial extension than a less biaxially extended, thicker laver. Cv. Katepwa gluten exhibited this strain hardening behaviour to a greater extent than cv. Obelisk gluten. Possible consequences for baking performance are discussed. (C) 1996 Academic Press Limited