In this study, the effect of the addition of apple juice to soy milk
on rheological behavior of the fermented beverage was investigated.
The empirical data obtained from the Brookfield viscometer
were converted into viscosity functions (apparent viscosity and
shear rate). It was found that the apparent viscosity decreased as
the rate of shear increased (Fig. 1), and this behavior continued
during storage (data not shown). It was found that the fermented
soy milk beverage with added apple juice samples had non-
Newtonian fluid (shear thinning or pseudoplastic) behavior. The
apparent viscosity of the fermented soy milk beverages increased
for the 7th days of the storage period, and then remained similar
(Fig. 2) (P < 0.05). In addition, the control group had the highest
apparent viscosity values during storage period at 4 C. As the apple
juice concentration increased the apparent viscosity of the fermented
soy milk beverage decreased, and this behavior remained
similar during storage (Fig. 2) (P < 0.05).
The relationships between shear stress and shear rate values for
fermented soy milk beverages with added apple juice during
storage were determined (Fig. 3). Rheological constants were predicted
to describe this behavior by means of fitting different
rheological models of Power law (Table 3), Herschel Bulkley
(Table 4) and Vocadlo (Table 5) to experimental data.
The regression coefficients of Power Lawmodel were lower than
those of Herschel Bulkley and Vocadlo models. Furthermore, RMSE
and c2 values of Vocadlo model were lower than those of Herschel