Produção de ácido glicônico por Aspergillus niger 10V10 em biorreator instrumentado utilizando matérias-primas alternativas

Abstract

Gluconic acid (GA) is an organic acid widely used in the construction, food, pharmaceutical, textile, metallurgical, and leather industries, being considered safe by the FDA and approved as a food additive in the European Union. Its industrial production is primarily carried out via microbiological processes, using strains of the fungus Aspergillus niger in submerged fermentation, with glucose as the carbon source. Brazil, a large agricultural producer, has residual biomass such as rice husk (RH) and sugarcane bagasse (SB), which have great potential as raw materials for obtaining sugars that can be used in the bioproduction of GA. The aim of this work is the production of GA from glucose, sucrose, and hydrolysates from residual biomass (SB and RH), through submerged cultivation of the A. niger 10V10 strain in a stirred-tank bioreactor (Biostat A Plus,Sartorius) . The submerged cultivation using glucose as a carbon source was carried out with an initial concentration of 158 g/L, while the cultivation using sucrose started with an initial concentration of 305 g/L. For cultivation with hydrolysates, different solid (raw material)/liquid (sulfuric acid solution) ratios were evaluated, and the conditions that proved most promising were selected for the formulation of the culture medium, which were used in bioreactor tests. The assays were conducted at 32°C, 550 rpm, pH 5.5, with an initial aeration of 0.8 vvm, which was later changed to 1.2 vvm after 18 hours of cultivation. Different fungal morphologies, such as pellets or dispersed forms, were observed in the assays, even though operational conditions and the culture medium were kept identical. This suggests that small variations may have influenced the fungal morphology. In the assays with an initial glucose concentration of 158 g/L, approximately 129 g/L of GA was produced, with a conversion efficiency of 92% and a volumetric productivity of 1.7 g.L⁻¹.h⁻¹. With an initial sucrose concentration of 305 g/L, approximately 138 g/L of GA was produced, with an efficiency of 76% and a volumetric productivity of 1.4 g.L⁻¹.h⁻¹. For the hydrolysates, the initial glucose concentration was 1.18 g/L for RH and 1.20 g/L for SB, with efficiencies of 1.27% and 0.38%, and volumetric productivities of 0.009 g.L⁻¹.h⁻¹ and 0.005 g.L⁻¹.h⁻¹, respectively. In the sucrose assays, it was possible to observe the accumulation of fructose, which also became a coproduct with industrial applications. In the assays conducted with RH and SB hydrolysates, GA production was not observed, but oxalic acid formation occurred. The strain demonstrated robustness in GA production when fed with pure glucose and sucrose. However, it is necessary to optimize the hydrolysis conditions to ensure the efficient and high-concentration release of substrates for GA production.