Production and immobilization of extracellular Saccharomyces cerevisiae invertase using soybean residue as a substrate

The production of extracellular invertase by solid- state fermentation (SSF) of Saccharomyces cerevisiae NRRL Y-12632 using okara (soybean residue) as a substrate was in-vestigated. Optimal cultural conditions for enzyme production were achieved using medium III which contained okara supplemented with 7 nutrient components (initial moisture 90%), at the 5th day of growth resulting in a yield of 235 U/g dry okara. The produced enzyme was immobilized on different carriers using different techniques including physical adsorption, ionic binding, covalent binding, and entrapment. The immobilized enzyme prepared by co-valent binding on chitin through 2.5% glutaraldehyde had the highest immobilization yield (73%). The optimum pH of the immobilized enzyme was shifted to more acidic range (pH 5.0) with a stability at pH range 4.0-7.0. The optimum reaction temperature of the immobilized enzyme was shifted from 35 to 40 C, and the thermal stability was significantly improved up to 70 C. The immobilized enzyme exhibited higher Km and Vmax values compared to those of the free one. The immobilized invertase retained 75% of its initial activity after 15 repeated uses.