Production and isolation of catalase and endoglucanase from Aspergillus niger by solid fermentation using agricultural wastes

In the area where our laboratory is located agriculture is highly developed the production soybean and corn, their industrialization produces thousands tons of wastes that are highly polluting of the environment. The processing of soybean generates soy skin which has not utility. This residue represent a carbon source for the growth of fungi. We have used this waste as substrate in the solid state fermentation to the production of industrial fungal enzymes. The advantage of the solid fermentation is that allows obtaining a concentrated suspension of biomass, with a high content of enzyme. The goal of this work was to produce two enzymes: catalase (CAT) and endoglucanase (ENG) because to their biotechnological importance. Aspergillum Niger was selected as producer fungus of both enzymes. It was assayed the effect of: the mass ratio buffer/waste, inductor presence like hydrogen peroxide (only in the case of CAT) and incubation time. The incubation was performed at 30C. A multivariable analysis was used. It was found that the soy skin waste was the best substrate for the production of CAT in the presence of H2O2 (0.3%) with a mass ratio buffer/waste of 50g/4g, the major enzymatic activity was found after 5 days of incubation. Low o no CAT activity was found in the medium with crop corn in the absence and presence of H2O2. Aspergillus niger was grown in a specific medium for the CAT production. By comparing the results the activity recovery in the medium using soybean skin was 70% of the specific medium. These results show the utility of using soybean skin as a carbon source for fungal growth and production of the enzyme catalase. The best experimental conditions found for the production of Endogluconase were: soybean skin 15 g / 40g buffer, pH 4.6 containing: (NH4)2SO4, KH2PO4 and peptone. The culture showed a higher production of enzyme at 5 days. CAT is an intracellular enzyme, (with an isoelectric pH around 6.2) then the aqueous suspension was sonicated to release the enzyme. Endoglucanase (isoelectric pH 4.5) is released to the medium by the fungi, so only a filtration process was necessary to obtain a protein solution biomass free. Both enzymes were recovered from the solution free of biomass by precipitation with a negative or positive polyelectrolyte. Proteins form a non-soluble complex with the polyelectrolytes through coulombic interactions. CAT was precipitated forming by complex formation with polyacrylate at pH 4.0 (a negative charged polyelectrolyte) while ENG was precipitated complex formation with chitosan at pH 6.0 (a positive charged polyelectrolyte). The recoveries obtained in each case were 60 % for CAT and 65% for ENG, while the purification factor was in the order of 3.