Enhancement in β-galactosidase activity of Streptococcus lactis cells by entrapping in microcapsules comprising of correlated silica nanoparticles.

With the advent of nanotechnology there has been an impetus towards sol gel encapsulation of biocatalyst in mesoporous silica. In this study cells of Streptococcus lactis expressing β-galactosidase activity were entrapped in silica microcapsules using evaporation induced assembly through spray drying technique. These microcapsules were characterized using complementary techniques of electron microscopy and neutron/X-ray scattering. Under optimized conditions of spray drying process, the cells immobilized in silica microcapsules had higher biocatalytic activity than the free cells. Immobilized cells showed threefold increase in enzyme activity than free cells. Free cells and immobilized Streptococcus lactis cells exhibited pH optimum at 5.0 and 7.0, respectively, whereas, the temperature optimum for both the systems was observed at 45 °C. Michaelis constant for free cells and immobilized cells was 8.33 mM and 4.16 mM, respectively, while V for free cells and immobilized cells was 71.43 μmoles min and 125 μmoles min, respectively. The decrease in apparent K is correlated with the fold increase in apparent V and can be interpreted as favorable for enzyme substrate complex formation when cells were entrapped in microcapsules. Herein, the concept of immobilization using spray dryer at optimal inlet temperature has emerged as an efficient mode for enhancing the catalytic activity of the microencapsulated microbial cells and a plausible mechanism is suggested.