EFEITO DA ADIÇÃO DE GOMA XANTANA NAS PROPRIEDADES REOLÓGICAS DE POLPA DE UMBU

In this study, the rheological properties of an umbu pulp suspension containing a food hydrocolloid (xanthan gum) at many concentrations (0.25, 0.50, 0.75 and 1.00%) and temperatures (10, 20, 30, 40 and 50oC), were evaluated by means of shear flow, and at 30oC for the oscillatory shear tests. The experiments were conducted in a Haake RS 600 rheometer. The tests for steady shear were conducted in the shear rate range between 0.1 – 1000 s-1. In the dynamic shear tests, frequency sweeps between 0.01 and 100 Hz were used to characterize the viscoelastic behavior of the material. The storage moduli (G’), loss moduli (G”) and tangents (tan δ) were determined. Suspensions containing the biopolymer xanthan exhibited shear-thinning behavior, characterized by yield stress, and hence the rheograms were fitted to the Herschel-Bulkley model. An exponential model was used to evaluate the effect of concentration on the apparent viscosity and the Arrhenius model was used to describe the temperature effect. The umbu pulp suspension behaved like a weak gel, with the storage greater than loss moduli. Both elastic (G’) and viscous (G”) moduli increased with increase in frequency (ω).