The viscosity curve calculated from Eq. (4) will superimpose
with that obtained from Eq. (3) if a is equal to 1. In this work,
the frequency sweep experiment was performed in a stress-controlled
mode. Therefore, the strain amplitude of oscillation was
not constant. Consequently, the extended Cox–Merz rule was not
applicable to the obtained data. However, the curve shifting along
angular frequency axis of complex viscosity was carried out to obtain
the fitting value of amplitude of oscillation, cm, fitting. Goodness
of fit in terms of residue of sum square (RSS) was analysed with the
shear viscosity in the shear rate range of 0.1–100 1/s.
Values of the constants k and a of the generalised Cox–Merz
rule are shown in Table 5 for all studied chili sauces. The cm, fitting
obtained from the best fit of complex viscosity curve, were also
shown in the table. It can be seen that the complex viscosity of
all chili sauces were greater than the shear viscosity as k values
were greater than unity. In addition, values of a for sauce H, K
and A were higher than one while that of sauce F was close to 1.
This indicates that the extended Cox–Merz rule was not applicable
for most of the studied sauces. Differences in structure arrangement
or particle orientation at small amplitude oscillation and
continuous flow of sauce H, K and A may have caused the value
of a to be more than 1. Furthermore, the best fitting of extended
Cox-Merz rule by shifting angular frequency with cm, fitting cannot
be obtained as RSS was quite large.