Obtenção e caracterização de antioxidantes derivados de xantana

Abstract

Recent studies have demonstrated the antioxidant potential of polysaccharides, such as xanthan, a microbial thickener with exceptional rheological properties and stability. According to a new line of research the antioxidant activity of this polysaccharide can be increased by means of chemical modifications. However, the fact that there is no adequate method for the determination of the antioxidant potential of natural xanthan due to its high viscosity has been detrimental to the evaluation of the efficiency of the chemical modifications proposed for the gum. The aim of this work was to adapt the traditional methods of the radicals DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azino-bis (3-ethylbenzothiazoline) 6-sulphonic acid) to the determination of the antioxidant activity of xanthan and, by means of hydrolysis with hydrogen peroxide, to obtain derivatives of greater antioxidant activity and that, at the same time, maintain a high viscosity. Three adaptations were made from the determinations of the interferences of the xanthan sample in the methods and it was proposed ways of making the analyzes feasible; it was considered more appropriate to adapt the ABTS method for practicality and reproducibility. The Rotational Central Compound Design (DCCR) 22 was used to determine the influence of the H2O2 ratio and the reaction time on the parameters antioxidant activity, acetyl and pyruvate content and viscosity of the xanthan derivatives produced. The best studied hydrolysis condition was 1.6% H2O2 and 24h reaction at 65ºC in pH13. The basic pH of the reaction deacetylated xanthan, but did not affect the pyruvate content. It was not possible to produce an oligosaccharide with increased antioxidant potential without excessive loss of viscosity. The increase in the percentage of inhibition obtained by the hydrolysis of xanthan gum with H2O2, although significant, was not satisfactory to justify the chemical modification.