Optimization of Conditions for Protease Production from Aspergillus niger under Solid State Fermentation

Abstract

The main objective of this study was to optimize the conditions for protease production by Aspergillus
niger under solid state fermentation using locally available agricultural substrates. Fifty one fungal
isolates were recovered from different sources. The isolates have shown typical A. niger characteristics
and they were screened for the production of protease enzyme. Screening was done qualitatively using
the Agar Plate Assay and the isolates that gave the widest hydrolysis zone diameters were
quantitatively screened in submerged culture using the shake flask method. A.niger isolate that showed
the highest production value in the shake flask assay was tested for protease production potential in
solid state fermentation using five different agro-waste substrates moistened either with water or with a
salt solution. The culture conditions that affect production capacity were then investigated. Results
showed that 30 of the fungal isolates have shown typical A.niger characteristics. Of these, 16 have
shown clear zones of casein hydrolysis on skimmed milk agar. The maximum activity of the produced
protease (15.42U/ml) was recorded for isolate NAF6ii while the minimum (6.45U/ml) was recorded for
isolate NAF7i. Therefore, A.niger isolate NAF6ii has been selected for production of protease by solid
state fermentation using the five agro-materials as substrates. NAF6ii recorded the maximum protease
activity (12.60U/ml) when Mesquite (Prosopis juliflora) fruit powder has been moisturized either with salt
solution or with water (11.46U/ml). Results also showed that the optimum conditions for protease
enzyme production were: 3.0% of spores’ inoculum (16.80U/ml), pH 7.0 (18.19U/ml), 5.0% of NH4NO3 as
a nitrogen source (13.28U/ml), 3.0% of fructose as a carbon source (11.38U/ml) during 96hrs incubation
period. These results indicate the potentiality of this fungus as a source for protease production. In
addition, the proteases produced from the treatment of local agro-waste could be used in a variety of
industrial applications.