EXTRACELLULAR INULINASE FROM 4 YEASTS

Four strains of yeasts, Candida kefyr, Candida pseudotropicalis var. lactosa, Kluyveromyces cicerisporus and Kluyveromyces fragilis, were studied for the production of inulinase. High enzyme activity (22.4-32.0 U/mL; 9.7-16.0 U/mg protein) was detected in the culture supernatant when the yeasts were grown in a medium containing aqueous extract of fresh Jerusalem artichoke (topinambur) tubers as carbon source. Maximum inulinase activity was obtained at 28 °C for C. kefyr and C. pseudotropicalis, and 32 °C for K. cicerisporus and K. fragilis, in 6-day-old cultures. The inulinase activity for all four strains exhibited a pH optimum of 4.7, a temperature optimum of 60 °C; the activation energy ranged from 3.2 to 4.8 Kcal/mole, and the half-life at 45 °C from 25 to 40 h. Ultrafiltration and following dialysis of the supernatants gave a degree of purification of the crude enzyme varying from 5.9 to 12.0. In preliminary experiments with topinambur extract, 89 and 92% of saccharification of 5% fructan expressed as total carbohydrate to fructose at 6 h was obtained with C. pseudotropicalis and K. cicerisporus extracellular enzyme (1 U/mL), respectively.