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Solid-state cultivation (SSC) is microbial growth on solid supports under limited water conditions. Citric acid, one of the products obtained by SSC, is a microbial aerobic metabolic product with various industrial applications. Several wastes from agro-industries are used in SSC, such as sugarcane bagasse and vinasse. As xylanolytic enzymes of inoculum breakdown the lignocellulosic material (bagasse), mixed fungal cultures or co-cultures are used in these SSC. Thus, this study aims to evaluate the effect of inoculum (Aspergillus niger and Trichoderma reesei consortium) in the production of citric acid from sugarcane bagasse impregnated with vinasse using bench packed bed reactors (PBR). The results show the importance of T. reesei in inoculum with A. niger at a ratio of 50:50 and 25:75, suggesting the use of solid support due to the complementation of the hydrolytic enzymes. The highest concentration of approximately 1000 mg L− 1 of citric acid yield for 100 mm of bed height in 48 and 72 h, with the maximum yield from glucose to citric acid (2.2 mg citric acid mg glucose−1). kLa indicates that maintaining solid moisture and liquid film thickness is important to keep the oxygen transfer in SSC.

Fungal pigments, including melanin, are recognized as promising materials for biomedical, environmental, and technological applications. In previous studies, we have demonstrated that the DOPA-melanin produced by the MEL1 mutant of Aspergillus nidulans exhibits antioxidant, anti-inflammatory, and antimicrobial activities without any cytotoxic or mutagenic effects, suggesting its potential use in pharmaceuticals. In order to increase the yield of this pigment and reduce the costs of its large-scale production, the present study aimed to evaluate agro-industrial by-products, sugarcane molasses, vinasse, and corn steep liquor as inexpensive substrates for fungal growth using experimental design methodology. According to the results obtained, the optimal composition of the culture medium was 0.81% (v/v) vinasse and 1.62% (w/v) glucose, which promoted a greater production of melanin (225.39 ± 4.52 mg g−1 of biomass), representing a 2.25-fold increase compared with the condition before optimization (100.32 mg.g−1 of biomass). Considering the amount of biomass obtained in the optimized condition, it was possible to obtain a total melanin production of 1 g L−1. Therefore, this formulation of a less complex and low-cost culture medium composition makes the large-scale process economically viable for future biotechnological applications of melanin produced by A. nidulans.

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