Otimização da Produção e Caracterização de Goma Xantana Empregando Caldo de Cana

Abstract

Xanthan gum production and its structural characterization under the conditions optimized by experimental design were the main objectives of this study. Several reports point to the sugar cane broth as an excellent raw material for the production of fermentable media, under the microbial species different action (bacteria, yeasts, fungi) in the products biosynthesis of commercial interest. In this context, the forward supply of sugarcane cultivars in Brazil, this research was motivated the development of xanthan gum by Xanthomonas campestris pv. campestris NRRL B-1459 using diluted sugar cane broth for experiments with during 24 h, through a sequence defined by two design, built from the Statistica Software. The first one selected to evaluate the effects of sucrose (12.13 to 37.87 g.L-1), yeast extract (until 6.0 g.L-1) and ammonium nitrate (until 1.714 g.L-1) concentrations in the responses that indicate the process performance (gum concentration, conversion of substrate to product (P/S), and apparent viscosity of xanthan solution). The second design complementary to the first consolidated the interactions due the agitation speed (500 to 1000 rpm) and aeration rate (0.25 to 0.75 vvm) in non-Newtonian behavior of the system. After interpretation of responses, considering the contour curves generated by the adjusted models, the costs involved in the biotransformation was selected this set of variables (27.0 g.L-1 sucrose, 1.8 g.L-1 yeast extract, 0.8 g.L-1 NH4NO3, 750 rpm and 0.35 vvm) to proceed the kinetic parameters prediction of the Weiss & Ollis (1980) model, by adjusting the experimental data (cell growth, substrate consumption and product formation) and, the structural characterization of xanthan gum. This test has reached 16.40 g.L-1 of gum, conversion YP/S equal to 0.61 g.g-1 and viscosity of 1% (w/v) 23000.0 cP at 0.75 s-1. The molecular weight (MW) and total sugar content obtained for the gum, considering the polymerization carried out at the optimum point were 4.172*106 Da and 85.3%, respectively, distributed in 43% glucose, 32% mannose and glucuronic acid 24% in the 1.79:1.33:1 proportion. The infrared spectrum recorded remarkable groups in the elucidation of the compound and, when the samples, commercial and optimized, subject to comparison, sent their bands in the regions of wavelength equivalent to the gum similarity has been confirmed. The gum also was evaluated using the Nuclear Magnetic Resonance Proton (1H NMR) technique and, therefore, identified in the last stage by common chemical shifts ( ppm) the hydrogen nucleus and the presence proton at α-anomeric and proton at β carbon of hexoses or pentoses, proton of carbon connected to oxygen, proton H6 of rhamnose and proton of glucuronic and uronic acid. Additionally to the main purposes of this study, an complementary fermentation using sugarcane broth hydrolyzate at 40 g.L-1 sucrose by invertase action, had its performance to the cell growth (7.57 g.L-1) over the biosynthesis (13.70 g.L-1) usually reported.