Immobilization of Sporothrix schenckii 1099-18 exo-polygalacturonase in magnetic mesoporous silica yolk-shell spheres: Highly reusable biocatalysts for apple juice clarification

Abstract In this study, a heterologously expressed exo-polygalacturonase from Sporothrix schenckii 1099-18 was purified and then its two magnetic immobilized counterparts were prepared in yolk–shell-structured mesoporous silica. The exo-polygalacturonase was initially precipitated on porous calcium carbonate in the presence of Fe3O4 magnetic nanoparticles. Then, a silica layer was created on the surface of the precipitated particles. The obtained immobilized exo-polygalacturonase (silica@Fe3O4/SsExo-PG) was further treated with glutaraldehyde (silica@Glu- Fe3O4/SsExo-PG). Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy techniques were used to confirm the immobilization of polygalacturonase. The optimum pH and temperature of all the exo-polygalacturonase preparations were determined to be 4.0 and 60 °C, respectively which are also optimum conditions for apple juice clarification. The silica@ Fe3O4/SsExo-PG and silica@Glu- Fe3O4/SsExo-PG showed 3- and 3.7-fold much stability, respectively than the free exo-polygalacturonase at 60 °C. The free and immobilized SsExo-PG preparations were used for the clarification of apple juice and the result showed that the turbidity of apple juice was reduced by 82% after 1 h treatment time. After ten consecutive uses, silica@Fe3O4/SsExo-PG and silica@Glu-Fe3O4/SsExo-PG retained 80% and 90% of their initial activities, respectively. Altogether, biochemical, thermal-stability, and apple juice clarification characteristics of the immobilized SsExo-PG suggest a high potential for biodegradation of pectin.