Production of high fructose syrup from Asparagus inulin using immobilized exoinulinase from Kluyveromyces marxianus YS-1

Abstract

Extracellular exoinulinase from Kluyveromyces marxianus YS-1, which hydrolyzes inulin into fructose, was immobilized on Duolite A568 after partial purification by ethanol precipitation and gel exclusion chromatography on Sephadex G-100. Optimum temperature of immobilized enzyme was 55 degrees C, which was 5 degrees C higher than the free enzyme and optimal pH was 5.5. Immobilized biocatalyst retained more than 90% of its original activity after incubation at 60 degrees C for 3 h, whereas in free form its activity was reduced to 10% under same conditions, showing a significant improvement in the thermal stability of the biocatalyst after immobilization. Apparent K (m) values for inulin, raffinose and sucrose were found to be 3.75, 28.5 and 30.7 mM, respectively. Activation energy (E (a)) of the immobilized biocatalyst was found to be 46.8 kJ/mol. Metal ions like Co(2+) and Mn(2+) enhanced the activity, whereas Hg(2+) and Ag(2+) were found to be potent inhibitors even at lower concentrations of 1 mM. Immobilized biocatalyst was effectively used in batch preparation of high fructose syrup from Asparagus racemosus raw inulin and pure inulin, which yielded 39.2 and 40.2 g/L of fructose in 4 h; it was 85.5 and 92.6% of total reducing sugars produced, respectively.