Enhancing (−)-epigallocatechin gallate thermal stability in emulsified oil droplets: Designing a thermal insulation interface for O/W emulsion

In this study, we constructed a thermal insulation interface layer for O/W emulsion using composite nanoparticles formed through the aggregation of CaCO₃ particles, which was mediated by sodium casein (SC) and chitosan oligosaccharide (CHO). As a representative of hydrophilic thermo-sensitive active ingredients, the (−)-epigallocatechin gallate (EGCG) was dispersed in a blended oil comprising peppermint essential oil (PEO) and sunflower seed oil (SO). The retention rate of EGCG in the emulsion, which had a thermal insulation protective layer, increased by 34.37% after heating, compared to the control emulsion. Furthermore, our research findings indicate that the thermal degradation process of EGCG in emulsified oil droplets involves initial isomerization into (−)-gallocatechin gallate (GCG), followed by subsequent degradation. Notably, the presence of the thermal insulation interface layer effectively suppresses the thermal degradation of GCG. This can be primarily attributed to the numerous mesopores in SC&CHO&CaCO₃ particles and low thermal diffusivity of the thermal insulation interface layer. This study provides a reliable solution for the stable encapsulation of thermo-sensitive active ingredients in emulsified oil droplets of O/W emulsion through the design of a thermal insulation interface layer, thus effectively improving their stability.