Coating alginate beads with cross-linked biopolymers: a novel method based on a transacylation reaction

Stable membranes were formed around alginate beads using a transacylation reaction between polysaccharidic esters, namely propylene glycol alginate (PGA) or pectin, and various proteins (human serum albumin (HSA), ovalbumin, bovine hemoglobin, lactoserum proteins). In a standard procedure, two reagents (PGA or pectin+protein) were added to a Na-alginate solution: beads were formed by dropwise addition into a calcium solution. Then the transacylation reaction was started by alkalinization of the bead suspension. A membrane was formed around the beads, made of a protein directly bound to a polysaccharide through amide linkages. The thickness of the membranes and the lysis time in trypsin were increased by raising the amount of NaOH used for the transacylation step. In a modified procedure, coated beads were obtained, incorporating PGA in the initial Na-alginate solution, and HSA in the transacylation bath. Activated charcoal was encapsulated in HSA-PGA beads, giving particles with adsorption properties towards creatinine. Assays were performed using PGA associated with alkaline phosphatase as the membrane-forming protein. Stable beads were obtained having a relative activity of 39.3%, as compared with free enzyme.