Functional and Interfacial Responses of Honeybee Pupa Water-Soluble Proteins to pH, Ionic Strength, and Sucrose

The interfacial and functional properties of water-soluble protein (WP) from honeybee pupa are highly sensitive to environmental conditions, which govern its applicability in food systems. This study investigated the effects of pH (3-11), ionic strength (0-1 M NaCl), and sucrose concentration (0-1 M) on the colloidal behavior, surface hydrophobicity, sulfydryl exposure, functional properties, and interfacial characteristics of WP. These findings provide valuable reference data for future processing of bee pupa protein. Acidic conditions (pH 3) resulted in a high surface hydrophobicity (H₀). Conversely, alkaline conditions enhanced protein interfacial activity. Specifically, the foaming capacity (FC) increased significantly with pH, reaching 90.88% at pH 11, which was approximately 2.5 times higher than that at pH 5 (35.10%). Moderate ionic strength (≤0.05 M NaCl) exerted minimal effects on particle size, while high salt levels (≥0.5 M) promoted aggregation via salting-out, increasing H₀ from 219.91 (0 M) to 459 (1 M). Sucrose had little impact on particle size but significantly altered system viscosity. Interfacial measurements confirmed that moderate ionic strength (0.05 M NaCl) combined with sucrose addition (0.05 M) improved protein spreadability, yielding low contact angles of 9.60° and 9.93°, respectively. From the perspective of oil-water interfacial tension, increased pH and moderate sucrose concentrations reduce interfacial tension, promoting protein adsorption, whereas high salt and high sugar concentrations inhibit surfactant activity. Functional property evaluations indicated that alkaline conditions enhance foaming and emulsifying activity. Under conditions near pH 5, both foam and emulsion stability were optimal (foam stability ~99.95%), while the emulsifying capacity (~64.83%) was achieved at pH 11. As ion concentration increases, EC decreases. Sucrose concentration has no significant effect on emulsifying properties. These findings provide a quantitative reference for the tailored processing of honeybee pupa protein as a functional ingredient in food systems.