Stress Relaxation of Wheat Kernels and Their Relationship with Milling, Rheological, and Breadmaking Quality of Wheat

The stress relaxation behaviors of soft and bread-type wheat kernels were studied using the generalized Maxwell model. The data showed two phases, a fast phase at short times of about 1.52-16.88 sec (tau(1) and tau(2)) and a slow phase with longer times of about 81.28-793.81 sec (tau(3) and tau(4)). The shorter decay of sigma(1) can be explained by very weak forces that affect mainly the rheological properties. The slow decay (sigma(4)) located at longer relaxation times resulted from strong forces. The first derivative obtained from the stress relaxation curve of intact wheat kernels was quite similar in shape to the dough farinograms. The stress relaxation parameters showed differences in springs, relaxation times, and viscosities of bread wheat compared with soft-type wheat kernels. The stresses sigma(1) and sigma(4) were correlated with wheat kernel, flour, rheological, and breadmaking properties; so especially were the elasticity of the spring (sigma(0)) and viscosity of the fourth Maxwell element (eta(4)), which were significantly correlated with all the quality properties, whereas sigma(2), sigma(3), eta(1), and eta(2) did not show correlation at all, except that eta(2) was correlated with falling number and volume of CO2.