Effect of Storage Temperature on the Physicochemical Properties of Soft Gelatin Capsule Shells

Abstract

The effect of storage temperature on the physicochemical properties of soft gelatin capsule shells was studied to interpret a change in the internal structure of those capsule shells whose disintegration time was remarkably prolonged by storage at 40 °C or more. The capsules were stored at 25, 40 or 60 °C for a maximum of 6 months. The time-courses of the disintegration time of these capsules were determined and compared with those of the following three physicochemical properties of the shells: the equilibrium swelling ratio (Seq), the gel strength of the swollen shells, and the percent of gelatin dissolved after 10 min (D10) from the shells. From these evaluations, it was found that the prolongation of the disintegration time of the capsules stored at 40 °C was based on a decrease in Seq of the shells and/or Dl0of gelatin from the shells, and/or an increase in the gel strength of the swollen shells. In addition, these physicochemical properties of the shells stored at different temperatures were compared with those of shells treated with formaldehyde. The three properties of the shells stored at 40 °C for 6 months were, on the whole, similar to those of the shells treated with a 1% formaldehyde solution. Furthermore, in the relationships between D10or gel strength, and Seq, no fundamental difference was observed between the shells stored at various temperatures and those treated with formaldehyde. Thus, we demonstrated that the prolongation of the disintegration time of the soft gelatin capsules stored at 40 °C or more is brought about by a change in the internal structure of the capsule shells in a manner similar to the case of shells treated with formaldehyde. © 1994, The Pharmaceutical Society of Japan. All rights reserved.