Optimisation of Inulinase Production by Kluyveromyces bulgaricus
Darija Vranešić1, Želimir Kurtanjek1*, Andrelina M. P. Santos2 and Francisco Maugeri2
1Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia
2Department of Food Engineering, Universidade Estadual de Campinas, SP, CP 6121, Cep 13081-970, Brazil
Article history:
Received: November 19, 2001
Accepted: January 28, 2002
Key words:
Kluyveromyces marxianus var. bulgaricus, inulin, inulinase, optimisation, response surface analysis
Summary:
The present work is based on observation of the effects of pH and temperature of fermentation on the production of microbial enzyme inulinase by Kluyveromyces marxianus var. bulgaricus. Inulinase hydrolyzes inulin, a polysaccharide which can be isolated from plants such as Jerusalem artichoke, chicory or dahlia, and transformed into pure fructose or fructooligosaccharides. Fructooligosaccharides have great potential in food industry because they can be used as calorie-reduced compounds and noncariogenic sweeteners as well as soluble fibre and prebiotic compounds. Fructose formation from inulin is a single step enzymatic reaction and yields are up to 95 % the fructose. On the contrary, conventional fructose production from starch needs at least three enzymatic steps, yielding only 45 % of fructose. The process of inulinase production was optimised by using experimental design method. pH value of the cultivation medium showed to be the most significant variable and it should be maintained at optimum value of 3.6. The effect of temperature was slightly lower and optimal values were between 30 and 33 °C. At a low pH value of the cultivation medium, the microorganism was not able to produce enough enzyme and enzyme activities were low. Similar effect was caused by high temperature. The highest values of enzyme activities were achieved at optimal fermentation conditions and the values were: 100.16–124.36 IU/mL (with sucrose as substrate for determination of enzyme activity) or 8.6–11.6 IU/mL (with inulin as substrate), respectively. The method of factorial design and response surface analysis makes it possible to study several factors simultaneously, to quantify the individual effect of each factor and to investigate their possible interactions. As a comparison to this method, optimisation of a physiological enzyme activity model depending on pH and temperature was also studied.
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