Effect of the degree of polymerization of inulin on the rate of hydrolysis using immobilized inulinase

The present paper addresses two crucial features in the industrial development of fructose production by enzymatic hydrolysis of inulin: the use of immobilized biocatalyst in the hydrolysis of crude extracts of chicory roots and the evaluation of the effect of degree of biocatalyst consisted of inulinase covalently bound to Sepabeads®supports It was demonstrated that its catalytic activity towards crude inulin extract (real substrate) was much higher than that exhibited towards pure inulin (synthetic solution). Experiments revealed that in applications of practical interest with real substrate, the activity of immobilized enzyme was as high as 63 % of that of free enzyme in homogeneous solution. This certainly was a driving force to potential industrial application of this immobilized enzyme preparation. Therefore, the effect of pure and crude substrates on the kinetics of the reaction catalysed by the nimmobilized enzyme was investigated. The kinetic analysis revealed a Michaelis-Menten dependence of the reaction rate on substrate concentration for both pure (high molecular mass) and crude (low molecular mass) inulin. Interesting results were derived from the comparison of Km and Vmax values in the two cases. In particular, it was found that increasing degree of polymerization of the substrate caused Vmax decrease and Km increase. After evaluation of mass transport effects, this was mainly associated with a different substrate/enzyme affinity when exploiting inulin characterized by different (low or high) degree of polymerization.