Improving enzyme production by solid-state cultivation in packed-bed bioreactors by changing bed porosity and airflow distribution.

Enzymes production by solid-state cultivation in packed-bed bioreactor needs to be improved by mathematical modeling and also by experimentation. In this work, a mixture of sugarcane bagasse and wheat bran was used for the growth of the fungus Myceliophthora thermophila I-1D3b, able to secrete endoglucanase and xylanase, enzymes of interest in the second-generation ethanol production. Bench and pilot-scale bioreactors were used for the experiments, while critical parameters as bed porosity and airflow distribution were evaluated. Results showed enzymes with higher activities for the most porous medium, even though the less substrate amount to be cultivated. For the pilot-scale bioreactor, only the most porous medium was evaluated using different airflow distribution techniques. Using an inner tube for air supply resulted in more homogeneous enzyme production, with higher activities. The results here presented will be helpful for the scale-up of this class of bioreactor into industrial apparatuses.

Production of conidia of the entomopathogenic fungus Metarhizium anisopliae ICB 425 in a tray bioreactor.

The use of Metarhizium anisopliae as a bioinsecticide is steeply increasing worldwide. However, to reduce the production costs, it is necessary to develop sophisticated techniques for conidia production. This work aimed to use a tray bioreactor to produce conidia of M. anisopliae ICB-425 in long rice and find the limiting bed depth in which the production is still viable. Experiments have been carried out to assess the influence of the air temperature and relative humidity on the spore concentration in order to determine the limiting temperature. Two scales of bioreactors in plastic packages have been used, containing 10 and 500 g of rice, and the results were similar. In the tray bioreactor, the bed depths of 2, 4 and 6 cm have been used, corresponding to the dry rice weights of 1, 2 and 3 kg, respectively, and the results were similar to the ones in plastic packages. A one-phase heat transfer model has been used to foresee the maximum temperature within the bed and the results agreed fairly well with the experimental ones. Using the model, a bed depth of 7 cm was found to be the limit for the tray bioreactor. The results obtained are very promising for the mass production of conidia of M. anisopliae at lower costs and with more effective control.

Synthesis, characterization and antifungal activity of quaternary derivatives of chitosan on Aspergillus flavus.

Two series of new chitosan derivatives were synthesized by reaction of deacetylated chitosan (CH) with propyl (CH-Propyl) and pentyl (CH-Pentyl) trimethylammonium bromides to obtain derivatives with increasing degrees of substitution (DS). The derivatives were characterized by (1)H NMR and potentiometric titration techniques and their antifungal activities on the mycelial growth of Aspergillus flavus were investigated in vitro. The antifungal activities increase with DS and the more substituted derivatives of both series, CH-Propyl and CH-Pentyl, exhibited antifungal activities respectively three and six times higher than those obtained with commercial and deacetylated chitosan. The minimum inhibitory concentrations (MIC) were evaluated at 24, 48 and 72 h by varying the polymer concentration from 0.5 to 16 g/L and the results showed that the quaternary derivatives inhibited the fungus growth at polymer concentrations four times lower than that obtained with deacetylated chitosan (CH). The chitosans modified with pentyltrimethylammonium bromide exhibited higher activity and results are discussed taking into account the degree of substitution (DS).