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-Bulkley model. Since Vocadlo model had higher regression coefficients
and lowest error values (RMSE and c2), it was selected as
best model fitting the experimental data adequately (Table 5).
Vocadlo model estimation was in the range of 0.73e3.37 Pa for
yield stress, in the range of 0.29e0.47 for flow behavior index (n),
and in the range of 2.71e76.33 for consistency coefficient (Kv; Pa.sn)
of fermented soy milk beverages with added apple juice. Since n
values of fermented soy milk beverages with added apple juice
were lower than 1, the fermented soy milk beverages with added
apple juice were found as a pseudoplastic fluid nature. Similarly,
the rheological studies on kefir, which is a type of fermented
beverage, revealed that it behaves as a thixotropic fluid and flow
curves showed that it has shear-thinning (pseudoplastic) properties
(Glibowski & Kowalska, 2012).