Characterization of invertase entrapped into calcium alginate beads

A solution of 10 g/L of sodium alginate (Satialgine(R) types used [Sanofi trademark]: SG800(R) and S1100(R) with manuronic/guluronic ratio of 0.5 and 1.2, respectively) containing invertase (0.08 g of protein/L) was dropped into 0.1 M CaCl2 solution buffered at pH 4.0, 7.0, or 8.0. The beads were left to harden in CaCl2 solution for 24 h. The high immobilization yield of 60% occurred with SG800 at pH 8.0. The activity of soluble and insoluble invertase was measured against PH (2.8-8.0), sucrose concentration (4.5-45 mM), and temperature (30-60 degrees C). Both forms presented an optimum pH of 4.6. However, the soluble invertase was stable at the overall pH interval studied, whereas insoluble invertase lost 30% of its original activity at pH > 5.0. At temperatures above 40 degrees C, the insoluble form was more stable than the soluble one. The kinetic constants and activation energies (E-a) for free invertase were K-M = 41.2 mM, V-max = 0.10 mg of TRS/(min.mL), and E-a 28 kJ/mol for entrapped invertase they were (K-M)(ap) = 7.2 mM, (V-max)(ap) = 0.060 mg of TRS/(min.mL), and (E-a)(ap) = 24 kJ/mol.