Optimization of Inulinase Production by a Fungal Species Isolated From Rotten Garlic Samples

Introduction: Inulinases are β-fructohydrolase enzymes that catalyze the hydrolysis of inulin. Recently, this enzyme has gained much importance mainly due to its ability to produce high-density fructose syrup using inulin as a raw material. In the current study, screening of inulinase-producing microorganisms was carried out from the rhizosphere soil of the Dahlia plant and rotten garlic samples.  
Materials and Methods: The inulinase activity was detected with the help of 3,5-dinitrosalicylic acid (DNSA) and Seliwanoff’s method, and the organism showing the highest potential was selected for further optimization studies.
Results: The optimum culture conditions for inulinase production, by the test fungal culture, were observed when 5% inoculum was added to the minimal medium (pH 5.5) containing 1% inulin/ costus root powder as a carbon source and 0.15% NaNO₃/ NH₄Cl as a nitrogen source, and incubated at 30°C for 48h under shaker conditions (200 rpm). Maximum enzyme activity was observed at pH level of 5 and temperature level of 45°C, with thermal stability noted between 35°C-55°C. The I/S value of the crude enzyme was calculated to be 0.45 indicating true inulinase activity. It showed no significant inhibition in the presence of metal ions such as Zn⁺², Mg^+2, and Fe⁺³. The Ca⁺² ions showed partial inhibition whereas Cu⁺² ions showed an enhancement in the enzyme activity.
Conclusions: These factors may present the test fungal culture isolated in the present study to be a potential candidate for the production of thermo-tolerant and metal resistant inulinase enzyme in order to be used for various biotechnological processes.