Exploring the techno-functional properties of urea in a model infant formula protein system

Model infant formula protein systems (MIFPSs) composed of dairy ingredients selected to have low innate urea contributions were formulated to simulate a stage 1 (0-6 months) infant formula. The impact of urea concentration on the techno-functional properties of the MIFPSs was investigated through the addition of urea at low (0.9 mM), medium (1.7 mM) and high (3.7 mM) concentrations, designed to span the concentrations of urea reportedly found in human milk and infant formula (2-6 mM). For further insights, the effects of urea at a higher concentration (∼12 mM) were also investigated. All data were compared with a control system, containing no added urea. Techno-functional analyses included dynamic foam analysis, heat stability, viscosity during thermal processing, buffering capacity, zeta potential and solubility of each of the systems across a pH range of 6.4-7.4, with protein profiling of the thermally processed samples also conducted. Increased concentrations of urea increased the foamability, heat stability and buffering capacity. In contrast, solubility indices remained low across all systems (sediment volumes typically ≤ 0.20 mL across pH 6.4–7.4), indicating minimal impact of urea on protein solubility. Similarly, zeta potential values showed only minor variation between treatments, remaining within a narrow range of approximately -14 to -18 mV across all pH conditions. SDS-PAGE analysis confirmed no evidence of irreversible protein aggregation following thermal processing. The findings of this study have advanced the understanding of the role that urea plays in these techno-functions, so if removed or altered, the implications for physical stability and functionality of such products can be predicted.