Optimization of inulinase production by a newly isolated strain Aspergillus flavus var. flavus by solid state fermentation of Saccharum arundinaceum

The present study deals with the use of mangrove soil, a new source for the isolation of an inulinase producing strain followed by the enzyme production and optimization using hardy sugarcane, “Saccharum arundinaceum”, a novel substrate. Four fungal isolates were obtained from the primary screening in inulin media. In the secondary screening, only Aspergillus flavus var. flavus strain ATCC 16883, a new strain, showed the zone of hydrolysis surrounding the fungal growth on the inulin medium plate. The action pattern of inulinase was determined by thin layer chromatography which confirmed it to be exoinulinase in nature. Solid state fermentation of A. flavus ATCC 16883 using Saccharum arundinaceum showed a maximum inulinase activity of 3.48U/gds after 96 h. The inulinase nature of the enzyme was confirmed by the resultant I/S ratio of 2.56. Central Composite Design (CCD) was used to optimize the media components and obtain a quadratic model using the five significant nutrients namely, inulin, K₂HPO₄, (NH₄)₂SO₄, KH₂PO₄ and NaCl. Using the optimum conditions of (g/gds) inulin- 0.1, K₂HPO₄- 0.05, (NH₄)₂SO₄- 0.002, KH₂PO₄- 0.005 and NaCl- 0.02, the inulinase activity was determined as 8.57U/gds which was 2.50-fold higher than the initial unoptimized conditions.