Avaliação comparativa das propriedades hidrodinâmicas de xantanas produzidas pelo pv Pruni e Clairana

Abstract

The knowledge on the biopolymers properties are important to predict his future industrial applications because reflects his chemical primary structure. Besides, the physical and chemical characteristics of the biopolymers are a consequence of the process used in his synthesis. The aim of this work was the study of the hydrodynamic properties of solution of biopolymers xanthan synthesized by Xanthomonas arboricola pv pruni, strains 06 and 82, and clairana FL, synthesized by Beijerinckia sp. strain 7070, in 7L fermentation volume. The results from rheological analysis, acetyl and piruvate content, ion content and thermal stability were compared with the ones obtained for commercial xanthan. The commercial xanthan is more efficient in the rheological properties due to divalent ion in their composition. The results for acetyl and piruvate content were in accordance with the literature. Thermal analysis showed presence of protein in the pv pruni xanthan´s and in clairana, but not in commercial xanthan. Hydrodynamic properties behavior of xanthan (Xc06), clairana and tara gum, in various concentrations, was examined using dynamic light scattering. Concentration regimes were determined by critical concentrations c* and c**, applying two methods. The first method was based on diffusional coefficient behavior of a range of biopolymers concentrations. A theoretical curve was proposed for results evaluation. With this method, c* and c** were determined for xanthan and tara gum , but nor for clairana due to its non-regular behavior. Distribution curves of relaxation times (DTR) were the second method applied. Distribution curves for xanthan and tara gum presented different number of relaxation modes. The concentrations where the number of modes did change corresponds to the c* and c**, determined using the first method. So, the distribution curves of relaxation times were obtained for clairana and the critical concentrations determined. Size distribution, hydrodynamic radii and polydispersity index for different concentrations were obtained from the respective correlation curves. The parameters showed dependence with solution concentration. The size distribution changed from monomodal to bimodal and to trimodal due to the increase in solution concentration. This behavior was attributed to the slow motion in diffusion due to particle aggregation formation. This aggregation causes hydrodynamic radii variation because their radii are higher than the particle radius in dilute solution. The polydispersity index increases with concentration increment, due to the appearing new peaks, while the width of the peaks of size distribution decreases.