Optimization of Culture Condition for Production of Extracellular Inulinase and Invertase from Aspergillus Niger ATCC 20611

In industry, filamentous fungus like Aspergillus niger is generally used as an enzyme source. Amongst the enzymes that are industrially produced by this fungus are inulinase and invertase. Inulinase and invertase constitute a significant class of enzymes for production of fructooligosaccharide and fructose, which are commonly used in food industry and pharmaceutical. Inulinase and invertase production are affected by medium composition in fermentation and optimum medium formulate is usually strain dependent. Therefore, optimization studies were conducted to determine the best parameters for inulinase and invertase production. Different sources and concentrations of carbon, and nitrogen sources, metal ions and surfactants were examined in this study. It was found that, A. niger ATCC 20611 produced high amount of inulinase after 96h of incubation with 6% (v/v) inoculum, pH 6.5, temperature 35°C and 100 rpm shaking rate in the presence of 25% (w/v) sucrose as a carbon source, 0.5% (w/v) meat extract as an organic nitrogen source, 1.5% (w/v) NaNO3 as the best inorganic nitrogen sources and 2 mM (v/v) Zn2+ as metal ion. Under this optimum condition, inulinase enzyme was produced at 3199 U/ml. However, it was also observed that surfactant (Triton X-100) played inhibitory effect on enzyme production by this fungus. The activity of the inulinase exposed at 50oC were maintained at 92.0%, 89.0% and 53.0% for 30 min, 60 min and 120 min, respectively. Meanwhile, the production of invertase was improved using different nutrient and physical factors. Medium containing 10% (w/v) sucrose, 1% (w/v) yeast extract, 1.5% (w/v) NaNO3, 1mM (v/v) Ca2+ and 1% (v/v) Triton X-100 was found to be optimal for invertase production. The optimal physical factors were at temperature 30°C, pH 6.0, inoculum size of 6% (v/v) and agitation rate of 200 rpm. Under this optimum condition, invertase was produced at 3072 U/ml. The activity of the invertase exposed at 50oC were maintained at 90%, 49% and 15% for 60 min, 120 min and 180 min,respectively. The potential of these two media for the production of inulinase and invertase could be explored in a large scale fermentation to produce enzymes of industrially feasible and economical.

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