Invertase activity of Saccharomyces cerevisiae cells immobilized in gelatin hydrogels:: Kinetics, thermostability, and reusability

In this work, a novel biocatalyst possessing medium feeding capability was prepared by immobilizing Saccharomyces cerevisiae cells into gelatin by crosslinking with chromium salts. Optimum chromium salt concentrations were found as 0.016 mol/dm(3) chromium III acetate and 0.008 mol/dm 3 chromium III sulfate. The developed biocatalyst was characterized with respect to its pH, temperature tolerances, kinetic properties and reusability. It was observed that immobilization shifted the pH for maximum activity from 4.6 to 7.2. Thermal stabilities below 60 degrees C were positively affected by immobilization. V-max values obtained for immobilized samples were 1.85 and 1.87 mu mol sucrose/mg.min, whereas the value was 0.0262 mu mol sucrose/mg.min for free cells. Thus, a 70-fold increase of V-max was obtained by immobilization and reuse experiments showed no activity decline for 10 reuses in 28 days which were attributed to continuous cell growth of immobilized whole cells using glucose (from sucrose hydrolysis) and gelatin as nutrients.