Effect of initial moisture content on two Amazon rainforest Aspergillus strains cultivated on agro-industrial residues: Biomass-degrading enzymes production and characterization

Abstract

Production of biomass-degrading enzymes using inexpensive and readily available agricultural residues as substrates for solid-state fermentation (SSF) can contribute to a broader application of enzymes for the conversion of biomass into biofuels and chemicals. Among the operational parameters that affect SSF process efficiency, moisture content is one of the most important. This work evaluates the effect of initial moisture content on two Aspergillus strains (Aspergillus niger P47C3 and Aspergillus fumigatus P40M2), isolated from the Amazon rainforest and grown under SSF. Analyses were made of the biomass-degrading enzymes produced using different agro-industrial residues as carbon sources (wheat bran, sugar cane bagasse, soybean bran, and orange bagasse). The enzymatic complex produced by a selected strain of A. fumigatus was characterized in terms of optimum pH and temperature, and thermal stability. The most effective carbon sources for multienzyme production during Aspergillus cultivation were wheat and soybean bran, as well as a 1:1 mixture of sugar cane bagasse and wheat bran. Much higher activity values were achieved for β-glucosidase (105.8IU/g) and xylanase (1055.6IU/g) when wheat bran with 50% initial moisture content was used as substrate. Under this condition, endoglucanase and total cellulase activity values were 56.6IU/g and 5.0FPU/g, respectively. Characterization of the crude enzymatic complex showed that the A. fumigatus P40M2 enzymes were active in the acidic pH range, with maximal activities at the range of 50–65°C, demonstrating the potential of the organism for the production of acidophilic and thermophilic biomass-degrading enzymes.