Inulinase production, using various naturally occurring inulin-containing agricultural plants as carbon sources and pure inulin (chicory, Sigma, Chem., Co., USA), was studied with an indigenously isolated actinomycete strain. All substrates depicted some activity but profile varied among them. Maximum inulinase activity was observed with garlic (Allium sativum) (524 IU/L). The enzyme activity was about 1.6-fold higher than activity obtained by using pure inulin as a carbon source. This is quite interesting attractive feedstock for large-scale fermentation, whereas pure inulin (chicory, Sigma, Chem., Co., USA) is only available in limited quantities and at very high cost. The present study suggests a significant impact of their use in industrial processes, considering the high cost of commercially pure inulin. The optimum temperature and pH for enzyme activity were 60 degrees C and 6.0, respectively. All metal salts except NaHCO3, AgNO3 and CoCl2 were not well tolerated and did adversely affect inulinase activity. The effect of thermal stabilizers on inulinase activity was studied. Consequently, glycerol and mannitol have been shown to have a protective effect on enzyme activity. All these conditions make Streptomyces sp., a potential candidate for industrial enzymatic production of high fructose syrup and in other large-scale biotechnological processes. (c) 2005 Elsevier Ltd. All rights reserved.