EFFECT OF XANTHAN GUM ADDITION ON THE RHEOLOGICAL PROPERTIES OF UMBU FRUIT PULP

Abstract

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).