Flow behavior of XG aqueous samples

Flow behavior of XG aqueous samples obtained at the first step
of the shear program is shown in Fig. 2b. These samples exhibited
the characteristic non-Newtonian behavior of XG aqueous dissolutions
with the presence of a viscosity plateau at small shear rates
(0.1 or 1 s1
) and shear thinning at high shear rates (Dolz et al.,
2007; Martínez-Padilla et al., 2004). The transition from the constant
low shear rate viscosity to a power-law behavior was smooth.
All mixtures showed curves similar to those of XG aqueous samples
and were adjusted to the Carreau model (Eq. (1)) (Fig. 2c,
Fig. 2d); respective parameters are summarized in Table 1.
An increase in XG concentration resulted in greater values of g0
and viscosity, but with the same overall trend. As expected, in mixtures
g0 increased as WPC concentration increased, with values
ranging from 0.027 to 5.3 Pa s. The effects of WPC concentration
on g0 at low and high level of XG were different when comparing
to XG alone. For XG 0.05%, with WPC, lower g0 values were
obtained (dilution effect) while at XG 0.15%, higher values were
achieved (synergist effect) with WPC 15% or higher concentrations.
Lower g0 in mixtures than respective value of XG (0.05%) aqueous
systems could indicate biopolymers co-solubility and that the
microstructure of the less entangled system formed by XG was disturbed
by WPC aggregates. Higher g0 in mixtures than respective
value of XG (0.15%) imply a biopolymer segregative phase separation,
as has been reported for whey protein isolate-XG (Bryant and
McClements, 2000; Hemar et al., 2001; Li et al., 2006). In samples
with 0.15% XG, the complex structure of the weak network formed
by XG was not disturbed even with the high concentration of WPC
used. This was considered synergistic because the viscosities of the
mixture were larger than those calculated from each biopolymer
independently, as reported by Sanchez et al. (1997).
The flow behavior index for mixtures oscillated between 0.69
and 0.87. Comparing this index to that of XG dissolution alone,
an increase was observed when WPC was added, independent of