The preparation,characterization,and application of silica-coated magnetic nanoparticles for papain immobilization is reported.Papain was covalently attached onto the(3-chloropropyl) trimethoxysilane-modified silica-coated magnetic nanoparticles. The enzyme-immobilized nanoparticles were characterized by Fourier transform infrared spectroscopy,X-ray powder diffraction,scanning electron microscopy,and vibrating sample magnetometry techniques.Response surface methodology combined with statistical analyses using Minitab were employed to evaluate optimum operating conditions to immobilize papain on the magnetic nanoparticles.The optimum conditions were: temperature = 27.3℃,pH of the enzyme solution = 7.1,concentration of papain = 3.3 mg/mL,and immobilization time = 10 h.Compared with the free papain,the immobilized papain displayed enhanced enzyme activity,better tolerance to variations in the medium pH and temperature,improved storage stability,and good reusability.Both the free and immobilized enzymes were effective for the clarification of pomegranate juice.
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