Síntese e recuperação de ácido xilônico e sorbitol obtidos via ação do sistema enzimático de Zymomonas mobilis

Abstract

Xylonic acid is characterized by being a polyhydroxylated acid derived from xylose, which comes from hemicellulose. Xylonic acid and its salts (xylonates) have stood out for their distinct applications in the food, pharmaceutical and chemical fields in general. This organic acid is obtained in association with sorbitol via the action of the enzyme complex glucose-fructose oxidoreductase (GFOR) and glycono-δ-lactonase (GL), from Zymomonas mobilis cells. This study evaluated the production profile and subsequent recovery of xylonic acid and its salts - sodium xylonate and calcium xylonate - from purified xylose, in relation to cell/enzyme concentration (0.05 to 0.5 g/L), substrate concentration (0.03 to 0.7 mol/L), pH (5.8 to 7.6) and temperature (34 to 53 °C), using a free biocatalyst or one immobilized in calcium alginate. Considering the enzymatic activity in relation to pH and temperature with free cells and with the use of xylose and fructose, the best results were obtained between pH 6.4 and 7.2 and 39 and 47 °C, respectively. In the bioconversion with free cells, the best result in terms of yield, 90.13%, was achieved at 39 °C and pH 6.4, with the production of 578.81 mmol/L of xylonic acid. In the bioconversion with immobilized cells, 566.99 mmol/L of xylonic acid was obtained in a process carried out at pH 6.4 and 39 ºC, with a product yield of 87%. However, superior production with the system immobilized at 43 °C and pH 6.4 was achieved with a yield of 572.90 mmol/L of xylonic acid. In the case of calcium xylonate bioproduction, 678.82 mmol/L was achieved and with a yield of 96.97%. For the recovery process, the best results were obtained using ethanol (70% v/v) at 22 ± 2 °C, although the separation and purification process needs to be improved. These results indicate that, considering the versatility of action of the GFOR/GL enzyme system of Z. mobilis against the substrates xylose and fructose and within specific process conditions, the production of xylonic acid and xylonate salts was maximized. [resumo fornecido pelo autor]