Influence of Glyceride Crystallization and Morphological Transformation on the Stability of Pickering Water-in-Oil Emulsions

Glyceride crystals stabilize water-in-oil (W/O) emulsions through two complementary mechanisms: formation of a crystalline layer around water droplets (Pickering stabilization) and development of a crystal network within the continuous oil phase. To better understand how glyceride crystallization influences emulsion stability during storage, this study examined the crystallization behavior of monoglycerides (MGs) and triglycerides (TGs) with defined acyl chain lengths in W/O emulsions formulated with medium-chain triglyceride (MCT) oil. During cooling after emulsification, MGs crystallized both at the droplet interface and in the bulk oil, providing direct evidence of combined Pickering and network stabilization, whereas TGs crystallized mainly as spherulites in the oil phase, leading to rapid phase separation. Among the MGs investigated, glycerol monostearate (GMS) provided substantially greater long-term stability than monopalmitin (MP), whose crystals underwent significant morphological changes during storage. Synchrotron small-angle and wide-angle X-ray scattering revealed that both MP-MCT and GMS-MCT systems initially formed metastable crystalline phases that transformed into the thermodynamically stable β phase upon ageing. However, MP β crystals continued to grow through Ostwald ripening, causing progressive emulsion destabilization, while GMS crystals remained structurally stable and maintained emulsion integrity. These findings establish clear links between glyceride crystallization, polymorphic transformations, and emulsion stability, providing valuable guidance for selecting effective Pickering stabilizers and designing crystallization pathways to enhance the long-term stability of W/O emulsions.