The Neutral Protease Immobilization: Physical Characterization of Sodium Alginate-Chitosan Gel Beads

Sodium alginate and chitosan were cross-linked to form composite gel spheres, which were entrapped to immobilize the free neutral protease. The matrix of the immobilized neutral protease was detected and characterized by using Fourier transform infrared spectroscopy and energy-dispersive X-ray. The optimum immobilization conditions were determined by orthogonal test, in which the concentration of sodium alginate was 3.5%, CaCl₂ 2.5%, chitosan 2.5%, and immobilizing time 1.5 h. Meanwhile, the activities of immobilized neutral protease and free enzyme were compared. The results showed that the pH value of immobilized enzyme was 5-8, the relative activity was above 90%, the free enzyme was above 80%, the relative activity of immobilized enzyme was above 80% in 30-80 °C, and the free enzyme was above 64% in 40-80 °C. The immobilized enzyme is better than the free enzyme in the constant of pH and temperature. The relative activity of immobilized enzyme was 50% after six hydrolysis cycles, and 80% after 11 days of storage.