Relaxation Time Spectrum of Dough and the Influence of Temperature, Rest, and Water Content

Abstract

The effect of temperature, rest period, and water content on stress relaxation in doughs held at constant extension has been studied with a relaxometer previously described. Temperature was varied from 13 to 35°C, rest period from 2 to 120 min, and water content from 74.4 percent to 86.0 percent dry basis. It is found that the shape of the relaxation curves on a log time plot does not change with temperature in the above range but that the curve is shifted laterally along the log time axis. This permits the construction of master curves valid in the temperature range and extends the time scale of observation. The long relaxation time end of the distribution of relaxation times is affected most by rest period, decreasing as rest period is increased, and the short time end increases as water content is decreased. Activation energies from 11 to 24 kcal per mole are calculated for relaxation from the shift of the curve on the log time axis. There is an indication that the activation energy depends on temperature and increases with rest period. A mathematical framework, based on the general Maxwell model, is discussed and the distribution function on the log time axis is interpreted in terms of viscosity and modulus of the relaxing mechanisms. Special reference is made to the ``box distribution'' and a viscosity is calculated.

Stress relaxation behaviour of yellow alkaline noodles: Effect of deformation history

“…Allocating fewer terms to the Prony series gave poorer fits (results to shown). The kernel function employed shared exponential terms for both the loading and the constant-strain deformation steps (i.e., Steps 1 and 2), allowing Chen's model to be regarded as an improvement over previous methods (Alfrey and Doty, 1945;Cunningham and Hlynka, 1954;Matsumoto, 1979;Peleg, 1979;Peleg and Normand, 1983;Rao et al, 2001) to model the viscoelastic foods (e.g., oriental noodles) via stress relaxation testing.…”

“…This concept was employed to evaluate the stress relaxation curves of wheat flour doughs by Rao et al (2001) and Li et al (2003) by neglecting the relaxation data falling after a time equivalent to half the loading time. Alfrey and Doty (1945) and Cunningham and Hlynka (1954) approach to this problem was to disregard an arbitrarily short period of time (comparable to the loading time) following sample loading.…”

The Viscoelastic Properties of Wheat Flour Doughs

“…Hlynka and co-workers (Hlynka and Anderson, 1952;Cunningham et ai., 1953;Cunningham and Hlynka, 1954), in a series of classic investigations, utilized a specially designed split-pin "relaxometer" operating in tension. Stress relaxation of dough was found not to be highly dependent on initial strain, and the calculated values of N (2.5 x 10° poise) and G (0.64 x 10 4 cgs) generally agreed with earlier determinations of Schofield and Scott Blair (1933a).…”

The Effect of Temperature on Some Rheological Properties of Wheat Flour Doughs

“…With increasing temperature, the rate of stress relaxation slightly increased, passed through a maximum at 40-45"C, and then decreased rapidly. It has been reported earlier that the rate of stress relaxation increases with the increasing temperature in the range up to 35°C (Cunningham and Hlynka, 1954;Kovdts and Ldsztity, 1966;Launay and Bur& 1974).…”