Linear viscoelastic range strain sweep experiments

Creep-compliance studies conducted in the linear viscoelastic range also provide valuable information on the viscoelastic behavior of foods (Sherman, 1970 Rao, 1992). The existence of linear viscoelastic range may also be determined from torque-sweep dynamic rheological experiments. The creep-compliance curves obtained at all values of applied stresses in linear viscoelastic range should superimpose on each other. In a creep experiment, an undeformed sample is suddenly subjected to a constant shearing stress, Oc. As shown in Figure 3 1, the strain (y) will increase with time and approach a steady state where the strain rate is constant. The data are analyzed in terms of creep-compliance, defined by the relation ... 

An advanced rheometric expansion system (ARES) is used to determine Tg of samples. Strain sweep experiments from 0.01 to 1% strain are conducted to ensure that experiments are carried out in the linear viscoelastic region. All experiments are done at a frequency of IHz and a strain level of 0.05%, which is in the linear region. Temperature sweeps are conducted at a heating rate of 5°C/min over a temperature range which covers the glassy and rubbery regions of the soy flour samples at different water activities. The temperature at which the loss modulus (G") was at a maximum is used to estimate the T . 

The Bohhn VOR was also used for stress relaxation experiments. Experiments were carried out over a frequency range from 0.01 to 60 rad s Strain sweeps were carried out on both instruments at 6 rad s" and the viscoelastic response was linear over a range of strain of 0.25-0.65 on the Instron instrument, whereas the Bohlin VOR also showed a hnear response over the range used (i.e., 0.05-0.20). 

Oscillatory frequency sweep and strain amplimde sweep experiments were first performed in range of 0.01 -100 rad/s and 0.1% - 50%, respectively in order to establish the extent of the linear viscoelastic regime. Based on these data, all subsequent experiments were... 

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