Implementação de reator de leito fixo empacotado com biomassa catalítica de Aspergillus oryzae IPT-301 para a produção de frutooligossacarídeos

Abstract

Fructooligosaccharides (FOS) are low-calorie prebiotic sugars that have several benefits to human health. They are commercially available through synthetic production, by transfrutosylation reaction, using microbial enzymes such as fructosyltransferase (FTase, E.C.2.4.1.9) and sucrose as substrate. Among the microorganisms potentially producers of this enzymes, Aspergillus oryzae IPT-301 stands out, synthesizing mycelial FTase (enzyme adhered to microbial biomass) with high transfrutosylation activity (At). Currently, the production of FOS is carried out in batch bioreactors, a slow and costly process. Therefore, it is necessary to implement continuous reaction systems, in fixed bed reactors (FBR), which increase the volume of FOS production and decrease its production costs. For this, the use of biocatalysts in the form of whole cells (catalytic biomass) for the production of sugar becomes advantageous because they exhibit natural support for the enzyme itself. In this context, this work proposed to implement a continuous reaction system in a FBR reactor, packed with catalytic biomass of Aspergillus oryzae IPT-301, aiming at obtaining high transfrutosylation activity for the production of FOS. To this end, we initially sought to obtain the best design conditions (diameter of the biomass spheres and height of the catalytic bed) through studies and characterization of the Residence Time Distribution (RTD). However, since it is a porous bed, it was necessary to saturate the catalytic biomass with methylene blue (AM) to reduce the errors associated with the adsorption of the dye in the catalytic bed. Subsequently, the influence of operational parameters on the transfrutosylation activity profiles was studied, evaluating the effect of the temperature of the reaction medium (40 ºC, 50 ºC and 60 ºC), of the sucrose concentration (173 g L-1 at 573 g L-1) and the volumetric flow rate of substrate feed (5.0 mL min-1 to 20.0 mL min-1) in order to obtain the best reaction conditions. The kinetic parameters were also obtained by adjusting the Michaelis-Menten and Hill models to the experimental data and, finally, internal (TMI) and external (TME) mass transfer studies were carried out, as well as operational stability tests with and without recycling in the PBR reactor. For the saturation of the catalytic biomass in situ, two cycles of adsorption/purge were necessary and, as the best design condition, a catalytic bed of 13.0 cm in height was made up of spheres of biomass of 6.0 ± 0,4 mm in diameter. The best profiles of enzymatic activity were obtained operating the PBR reactor at 50 ºC, fed with sucrose solution of 473 g L-1, pH 5.5 and a volumetric flow rate of 11.5 mL min-1. A kinetic enzyme was better fitted to the Michaelis-Menten model. Under these conditions, it is possible to observe that the reaction was not limited by the effects of TMI and TME. The stability tests showed, in the first 420 minutes of reaction, a 25% reduction in enzyme activity, remain stable after this period. Compared to the batch process, under the same operational conditions, it was found that the continuous process presented the best results for the activity of transfrutosylation and operational stability. In view of the results obtained, it can be concluded that the implementation of the continuous process, for the production of FOS, has shown promise when reaching high profiles of enzymatic activities in a PBR reactor filled with microbial catalytic biomass.