Various inulin containing vegetal substrates were evaluated for inulinase production by an indigenous isolate, Aspergillus niger NK-126. Highest inulinase activity was observed with dandelion tap root extract (52.3 IU/ml). The enzyme activity was fourfold higher than that observed in media containing pure chicory inulin (12.3 IU/ml). The fungus showed good growth on a medium containing 40% (v/v) of dandelion tap root extract composed of 50 g tap roots blended with 200 ml water and 2% yeast extract medium and produced 55 IU/ml in 96 h at 30 degrees C and 150 rpm. The TLC analysis of end products revealed that inulinase hydrolyzed inulin into fructose, inulobiose (172) and other inulooligosaccharides (IOSs) with higher degrees of polymerization (dp). As compared to other complex substrates, the Inulinase:Sucrase (I/S) ratio was much higher (6.6) in case of dandelion extract medium. Results suggest that the dandelion tap root extract induced endoinulinase synthesis in A. niger NK-126 and can be utilized as a potential substrate for inulinase production. (c) 2007 Elsevier Ltd. All rights reserved.