Biosilica-coated kappa-carrageenan microspheres for yeast alcohol dehydrogenase encapsulation

In this study, a novel polysaccharide/inorganic hybrid biocomposite was prepared through biomineralization-inspired process for efficient immobilization of yeast alcohol dehydrogenase (YADH). YADH-encapsulated kappa-carrageenan microspheres (KCM) were first coated with chitosan, which was used to guide and catalyze the biomimetic formation of silica, and then coated with silica derived from tetraethoxysiliane (TEOS). Scanning electron microscopy (SEM) equipped with a energy dispersive X-ray spectrometer (EDX) was employed to investigate the composition and thickness of silica film. Compared with KCM, the silica-coated kappa-carrageenan microspheres (SKCM) containing YADH exhibited improved anti-swelling and catalytic properties. Enzyme leakage of YADH in KCM was detected to be 63.9% after 1 h, while the enzyme leakage in SKCM was as low as 18.2%. The KCM adsorbed water promptly and after 1 h maximum water uptake can be as high as 1576 wt%, while the water uptake of SKCM was only 143 wt% even after 48 h. The optimum pH and temperature for encapsulated YADH were pH 6.5 and 25 degrees C, which were just the same as those for free YADH, but the encapsulated YADH exhibited broader pH and temperature ranges for high activity. Furthermore, the relative activity of YADH in KCM declined almost to zero after 8 recycles, while the relative activity of YADH in SKCM still maintained more than 50%. The significantly increased recycling stability of YADH in SKCM may be attributed to the effective inhibition of enzyme leakage by the compact biosilica layer.