Rheological behaviour of wheat endosperm - Proposal for classification based on the rheological characteristics of endosperm test samples

A simple, rapid method for the preparation of parallelepiped-shaped samples from a grain is used in the proposal of a study of the rheological behaviour of wheat endosperm. Compression rupture, creep and relaxation tests are used. A series of compression rears on mealy and vitreous endosperm of different wheat varieties (soft, hard and durum) shows that the rheological properties are influenced by both the generic origin and grain vitreousness. The main mechanical characteristics Young's modulus, elastic and rupture stresses, rupture energy and rupture strain-were determined at moisture contents of 12 to 17%. The influence of the moisture content on rheological behaviour is demonstrated. The vitreous endosperm of some wheat varieties displays considerable ductility before rupture. The nature of this plasticity was analysed by creep and relaxation tests on hard and soft wheats. Comparison of the different endosperm rheology values clarifies the notions of vitreousness and hardness. Wheal classification based on endosperm mechanical characteristics is proposed. It seems that Young's modulus characterises hardness whereas rupture energy is related to the vitreousness of the different varieties studied. Entering the results in a Youngs modulus rupture energy system leads to a classification of wheats according to two essential factors: hardness of varietal origin and vitreousness of cultural origin. (C) 2001 Academic Press.