Pharmaceutical formulation analysis of gelatin-based soft capsule film sheets using near-infrared spectroscopy

In order to investigate the properties of gelatin film sheets for soft gelatin shell capsules, we compared gelatin and succinylated gelatin film sheets using dynamic vapor sorption (DVS), static near infrared (NIR), and dynamic NIR during tensile strength measurements. A steep increase in the amount of water vapor absorbed was observed with relative humidity >70% for both gelatin and succinylated gelatin film sheets. From the static NIR measurement, it was considered that the OH alcohol groups in glycerin were coordinated with gelatin or succinylated gelatin molecules by replacing H2O in the gelatin or succinylated gelatin film sheets as the glycerin concentration increased. It was found that gelatin molecules showed a change in the molecular net structure before and after stress, but this phenomenon was not observed for the succinylated gelatin film sheets. The properties of gelatin simultaneously explained the flexibility and stronger resistance to contortion. In relation to these results, we considered that the gelatin molecules made a stronger net structure among gelatin-water-glycerin complexes because of the free ε-NH2 groups compared with succinylated gelatin.