Avaliação das propriedades gelificantes e emulsionantes de ...

Thus, in contrast to firmness, it seems to have no relationship between PE percentage in
mixtures and adhesivity of gels.
The rheological studies revealed that a gel network was rapidly formed upon heating from 20 to
90 ºC, and when cooling down to 5 ºC, the gel structure was reinforced as interactions between
the proteins were strengthened. Mechanical spectra obtained for gels with different mixtures
showed typical patterns of weak gels. Storage modulus (G’) and loss modulus (G’’) are higher
for higher concentrations of PRP which corresponds to more structured systems. Gels prepared
with different mixtures showed a thermo-reversible behaviour with G´ obtained after the 2 nd
heating/cooling cycle very similar to that after the 1 st heating/cooling cycle. Nevertheless, the
gel prepared with 100PRP showed a typical pattern of myofibrillar protein networks with a clear
thermo-reversible behaviour.
Emulsions prepared with different protein mixtures at pH 7,0 and 3,8 showed high W values.
The stress sweep tests of the emulsions prepared at pH 7,0 and 3,8 indicated that G´ and G´´ are
stress independent (linear viscoelasticity region) in the range of 0,5-10 Pa.
The linear viscoelastic behaviour shown by the emulsions prepared with protein mixtures at pH
7,0 and 3,8 is typical of protein-stabilized emulsions in which an elastic network develops due
to the occurrence of an extensive flocculation process. G´ is higher than G´´ in the frequency
range studied and the evolution of G´ with increased frequency shows a tendency to the
development of a plateau region, followed by a minimum G´´. The Plateau modulus (G 0 N) was
studied as a characteristic parameter of the plateau region and has been related to the formation
of a structural network in oil-in-water emulsions due to the extension of entanglements among
protein molecules located at the oil-in-water interface. At pH 7,0 there was no relation between
the percentage of PE and G 0 N, but at pH 3,8, a markedly increase of G 0 N with percentage of PE
(0-50 %) was observed. From mechanical spectra it can be also underline that the shape of
frequency dependence of G´ and G´´ is slightly different for the emulsions studied.
Steady-state flow curves, and the respective zero-shear-rate limiting viscosity, 0 , for the
emulsions with different protein mixtures, were studied. For all emulsions a clear shear-thinning
behaviour was noticed. The emulsion that presents a higher 0 at pH 7,0 was the emulsion
prepared with the mixture 20PE+80PRP and at pH 3,8 the higher 0 was obtained with the
mixture 100PRP.
Another objective of this work was the development of a product with the protein mixtures
evaluated. Thus, 2 salad dressings with mixtures 50PE+50PRP and 20PE+80PRP were
prepared with herbs and vinegar. The overall assessment of these two salad dressings was quite
satisfactory. 58,3 % of the panelists preferred the salad dressing prepared with protein mixture
20PE+80 PRP and 16 % the one prepared with 50PE+50 PRP.
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