Influence of concentration on the steady and oscillatory shear behavior of umbu pulp

Abstract

In this experimental work the rheological behavior of umbu pulp has been studied by shear flow (pseudoplasticity, apparent viscosity) and in oscillatory mode (dynamic modules) in the linear domain of viscoelasticity. The studies were carried out with the use of a controlled stress Rheometer Haake RS 100, at different soluble solid concentrations (10, 15, 20 and 25 °Brix), measured at 30 °C. Tests in steady shear were conducted over a shear rate range of 0.1 - 300 s-1 and oscillatory measurements over a frequency range of 0.01 - 100 Hz. The results indicated that umbu pulp behaves as a non-Newtonian fluid, with pseudoplastic characteristics and yield stress appearance and exhibits tixotropic properties. Rheograms were fitted to the Herschel-Bulkey model. From the dynamic test the umbu pulp showed storage modulus (G') values that were always higher than loss modulus (G"), indicating weak gel-like behavior. Storage and loss modulus increased with increase in the concentration.

Rheological behavior of mixed drink of annona and milk

“…It is noted from Table 3, a decrease in apparent viscosity with increasing temperature, at all concentrations and an increase in the apparent viscosity with increasing pulp concentration in the sample. The same behavior was observed by Oliveira et al (2011) to study the rheological behavior of strawberry pulp; PEREIRA et al (2008), working with umbu.…”

“…The values for the fluid behavior index (n and n H ), for Ostwald-de-Waelle and Hershel and Bulkley models, respectively, are below 1.0, characterizing the behavior of fluid mixtures as nonNewtonian and pseudoplastic, as it was expected, since such behavior is common in pulp and fruit juice, as reported by numerous authors as PEREIRA et al (2008) in a study of the rheological behavior of umbu. BEZERRA et al (2009) to analyze the model parameters for Hershel Bulkley rheological behavior of strawberry pulp found that all the n H values were also below 1.0, with values of at most 0.24.…”

“…It is also noted that inasmuch as the increase in the temperature, a decrease of the shear tension. OLIVEIRA et al (2011) working with strawberry pulp and Pereira et al (2008), working with umbu observed the same behavior. PICTURE 2.…”

“…Perhaps the high water content of the milk with the fat can occasion dilution, with consequent loss of consistency. Food materials are complex rheological structure consisting of a mixture of solids, liquids and structural components and any change in the content of these constituents may lead to changes sometimes unpredictable in its structure (OLIVEIRA et al, 2009;PEREIRA et al, 2008). For the Herschel-Bulkley model, the results obtained for consistency index (K H ) showed oscillations and without tendency defined in relation to concentration and temperature.…”

Estudo Da Estabilidade, Comportamento Reológico E Efeito Da Temperatura Da Polpa De Cupuaçu (Theobroma Grandinflorum) Em Diferentes Concentrações

“…As energias de ativação mostraram tendência de redução com o aumento dos sólidos solúveis totais como mostrado na Tabela (2). Os valores de energia de ativação encontrados nesse estudo foram similares aos encontrados por Alexandre (2002), que ao analisar o comportamento reológico da polpa de açaí integral, encontrou o valor igual a 6,28 kJ/mol, Ferreira et al (2002), que estudou o comportamento reológico da polpa de goiaba integral (6,11 kJ/mol) e Pereira et al (2008) que analisou a polpa de umbu (6,15 kJ/mol). …”