Propriedades reológicas da polpa e néctar de cacau e suas interações com gomas xantana, guar e locusta.

Abstract

The objective of this work was to evaluate the rheological behavior of whole cocoa pulp and cocoa pulp with guar and xanthan gums in different concentrations (0.3, 0.7 and 1.0% w/w), and cocoa nectars with xanthan gums, guar and locust at different concentrations (0, 0.08, 0.17, 0.25, 0.5 and 0.33% w/w). The rheological properties of whole cocoa pulp and pulp with xanthan gum and guar gum in the temperatures of 10-50 °C were performed on a rheometer (TA instruments AR 2000), steady-state and dynamic. The measures cocoa nectars with addition of xanthan gums, guar and locust were performed on a Brookfield viscometer (DV- II + Pro) to the steady state rheometer (Bohlin Instruments Advanced) for the dynamic state in the temperatures from 20 to 60 ºC. The whole cocoa pulp, and the pulp with xanthan gum and guar gum have been characterized as pseudoplastic fluids. The Ostwald-de-Waelle model can be used to more accurately estimate the rheograms of these samples. The temperature influenced on the apparent viscosity. The increase of the concentration of xanthan gum or guar gum resulted in the increased of consistency index of cocoa pulp. The whole cocoa pulp showed dependence with time, with the Hahn and Figoni and Shoemaker models best represent this characteristic. In dynamic for all samples with cocoa pulp tests the storage modules were larger than the loss modules, characterized as weak gel structures. Nectars were also classified as pseudoplastic fluids and their rheograms can be more accurately described by the Ostwald-de-Waelle model. There were also those samples effect of temperature on the apparent viscosity; nectar cocoa with 0.25% xanthan gum and locust bean gum 0.25% was the one who showed thixotropy, or saddle, change in viscosity with time. For all samples the elastic character predominated over the viscous, the modules being superior to the loss modules featuring as storage structures gels, being confirmed in creep and creep tests. The Cox-Merz rule the complex viscosity occurred was higher than the apparent viscosity for all samples, confirming the formation of weak gels.