Simultaneous phytase production and rock phosphate solubilization by Aspergillus niger grown on dry olive wastes

Dry olive waste (DOW), an agro-industrial material derived from the two-phase-manufacture of olive oil, was used as a substrate for phytase production by Aspergillus niger. A series of experiments were performed in conditions of solid-state fermentation in the presence of rock phosphate. Both enzyme production and phosphate solubilization depended on water medium content, type of nitrogen source, inoculum size and the presence and initial concentration of phosphate in the medium. It was found that at optimized process conditions (moisture 70%; corn steep liquor as a nitrogen source; inoculum size of 3–4 ml; presence of slow release phosphate), the filamentous fungal culture was able to produce 58 U phytase/g dry substrate and 31 mg soluble phosphate per flask.