On the other hand, fine emulsions prepared with heat denatured proteins showed a pronounced thixotropic
and shear thinning behaviour (Fig. 2 – B) that probably corresponded to the structure formed by the large
aggregates observed for those systems (Fig. 1- e and f). On the other hand, the shear thinning behaviour is the
most expected for food emulsions (second ramp up of shear stress in Fig 2 –B) and in such a case, it could be
related to several reasons as the alignment of dispersed phase spherical droplets or serum exudation during
shear with possible disruption of emulsion structure [8].
The values of Newtonian viscosity of serum phase of coarse emulsions increased as the temperature of heat
treatment was higher. It ranged from 2.5 ± 0.3 mPa.s for non heated proteins to 3.3 ± 0.1 mPa.s and 10.7 ±
0.5 mPa.s for treated at 70 and 90ºC, respectively. However, the effect of heat treatment on whey proteins
was less pronounced on apparent viscosity (at shear rate of 100 s-1) of the cream phase of coarse emulsions.
Table 2 shows the Newtonian viscosity of fine emulsions containing non heated whey proteins, as well as the
apparent viscosity of the other fine emulsions, measured at shear rate of 100 s-1 (η100 - Pa s). This rheological
parameter was evaluated at this shear rate because it is typical for food processes such as flow through a pipe,
stirring or mastication [7].