Investigating the effect of novel capsule materials on the stability of EZhenJiaoWan capsules based on material migration research

The stability of soft capsules is considerably influenced by material migration, with distinct shell materials exhibiting notable differences in this regard. Therefore, selecting an appropriate shell material is crucial for preventing stability issues in the preparation of soft capsules. In this study, gelatin soft gel capsules (GSC) and plant gum soft capsules (PSC) were prepared using EzhenJiaoWan as the content and either gelatin or plant gums as shell materials, respectively. LC-MS, ICP-MS, thermogravimetric analysis, x-ray diffraction, and scanning electron microscopy were utilized to compare migration of the two shell materials in terms of content composition, iron, and moisture. The analysis revealed that the migration of organic acids and iron from the contents of GSC to the shell material resulted in cross-linking reactions, compromising the structural integrity of the shell and ultimately leading to considerable stability issues. The iron content in the GSCs decreased by 28.54%, compared to 2.44% increase in PSCs. The iron content in the GSC shell increased by 11.38%, whereas the PSC shell showed a 2.71% increase. In contrast to GSC, no notable migration of these substances was observed in the PSC shell. Although moisture migration is known to influence the moisture content of the capsule shell, the moisture absorption rate and critical relative humidity of the PSC shell remained stable, demonstrating better stability. Furthermore, no notable difference in thermal stability was observed between PSC and GSC within the temperature range of 20–40 °C. When water was balanced, the surface morphology of PSC appeared flatter. Utilizing plant gums as an alternative to gelatin for the capsule shell material can effectively prevent stability issues arising from material migration.