The inulinase production by yeast K marxianus var. bulgaricus growing in yacon extract was investigated. The microorganism showed good development in yacon, higher enzymatic activities were achieved at 30% and 40% (v/v) of extract. The cultivation temperature (20, 25, 30, 35, 40 degreesC) neither influenced the growth or the enzymatic activity. The optimum cultivation pH was 3.5. The highest activity was observed at 60 degreesC and pH 4.0. At temperature of 55 C and 60 C occurred sharp decrease in the enzyme activity. (C) 2004 Elsevier Ltd. All rights reserved.