Mechanical properties of the capsules of chitosan–soy globulin polyelectrolyte complex

The mechanical properties of chitosan–soy globulin capsules depend strongly on the pH values of chitosan and soy globulin solutions in the polyelectrolyte complex formation. When a solution of chitosan was dropped into a solution of soy globulin, a thin chitosan-globulin membrane was formed on the surface of the capsules. These capsules were mechanically weaker than the capsules made by complex formation between sodium alginate and chitosan. In this study 5.0 wt% globulin solution and 2.0 wt% chitosan solution were used. The diameter of the capsules obtained was approximately 3 mm. By immersing the capsules into alkaline solution the composite capsule, having a gel core of chitosan, was obtained. Mechanical properties of the capsule were estimated from compressive force–deformation curves derived from large deformation experiments. The mechanical strength of the capsule was found to depend on the pH values of the chitosan and globulin solutions. The capsules prepared from the chitosan solution with pH 5 and the globulin solution with pH 8 showed high mechanical strength. Moreover, reaction time for capsule formation had an effect on the strength of the capsule.