RHEOLOGICAL BEHAVIOR OF WHEAT GLUTENS AT SMALL AND LARGE DEFORMATIONS- COMPARISON OF 2 GLUTENS DIFFERING IN BREAD-MAKING POTENTIAL

The rheological characteristics of hydrated cv. Obelisk and Katepwa gl utens, with poor and good baking potential, respectively, were studied at small and large deformations. Dynamic (oscillatory) measurements a t 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 t he dynamic moduli of both glutens. Measurements at different water con tents 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 cylindrical ly shaped test pieces at various cross-head speeds. This proved to be a very useful method of providing information about the rheological be haviour of glutens at large deformations as a function of different st rain 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 h igher resistance to further biaxial extension than a less biaxially ex tended, thicker laver. Cv. Katepwa gluten exhibited this strain harden ing behaviour to a greater extent than cv. Obelisk gluten. Possible co nsequences for baking performance are discussed. (C) 1996 Academic Pre ss Limited