Statistical optimization of an acid protease production by a local Aspergillus niger MH109542 using a medium based on decommissioned dates

Abstract

The production of an acid protease by liquid fermentation is performed on a medium based on decommissioned dates by a local mold isolated from an extreme environment. The used mold is isolated from the thermal soil in Hammam Safsaf of Teleghma (Algeria). Phenotypic and molecular identification has shown that it is Aspergillus niger. This fungi strain exhibited exo-protease activity on milk agar. The fermentation medium based on decommissioned dates is enriched by other factors according to a statistical method; the plan of Plackett and Burman. This method (N = 8 experiments and N-1 factors) allowed the optimization of the enzyme production and the growth of the mold. The statistical analysis of the obtained results shows an increased enzyme activity (650.20U), in the presence of yeast extract and salts with probabilities p = 0.239 for the first and p = 0.190 for the second. Furthermore, the corn-steep-liquor (p = 0.229) and yeast extract (p = 0.053) present a significant effect on mold growth. In conclusion, the culture of A. niger on optimized medium gives good yields of biomass and proteolytic activity compared to the basal medium. These results are encouraging. In fact, the use of a cheap and available substrate such as decommissioned dates saves the cost price of fermentation on an industrial scale.