Structural Characteristics of Agar-Based Emulsified Fluid Gels Designed for Enteral Nutrition

This study aimed to develop a novel method for preparing agar-based emulsified fluid gels as a thickened enteral feeding formula using different oil-structuring approaches: no emulsifier, the emulsifier polyglycerol polyricinoleate (PGPR), or monoglycerides/diglycerides of fatty acids (MDFA), which function as both emulsifiers and gelling agents. We examined sample stability, oil-holding capacity, particle sedimentation, size, morphology, rheological and textural properties, and the maximum injection force required to deliver the system through syringes fitted with tubes of different diameters. Adding PGPR, decreased the polydispersity index (span 2.21), apparent viscosity (588.88 mPa·s), and yield stress (0.39 Pa), reducing the force required to inject the fluid gel through the syringe. MDFA addition destabilized the system, resulting in a high polydispersity index (span 14.07) and reduced stability (68.75% under static and 79.64% under dynamic conditions). While the fluid gel with oil without emulsifier/stabilizer exhibited high stability (100%), it also showed high viscosity and yield stress values, affecting the increase in maximum injection force, which is a negative aspect. The results showed that such a different oil structuring approach affects the microstructure of the fluid gel formulations, resulting in differences in stability and rheological properties. This study provides mechanistic insights into the structural relationships between suspended agar particles and oil droplets, providing a feasible strategy for designing agar-based fluid gels with a lipophilic phase. The PGPR-containing fluid gels could serve as enteral nutrition formulations for the targeted delivery of lipophilic and hydrophilic nutrients and drugs. While lipophilic phase inclusion without an emulsifier or stabilizer also looks very promising, the high viscosity and yield stress should be reduced by adjusting the fluid gel preparation conditions.