Synergistic Noncovalent Mulberry Polysaccharide–Ovalbumin Complexes for Enhanced Functional Properties and Pickering Emulsion Stability

This study systematically investigated the non-covalent interaction mechanisms, structural characteristics, and functional properties of ovalbumin (OVA)-mulberry polysaccharide (MP) complexes under different pH and mixing ratios and further constructed pickering emulsions based on the optimized complex. The phase behavior of the OVA-MP system exhibited significant pH and ratio-dependent variations. As the pH decreased from 6.5 to 2.0, the turbidity of the system followed a "dissolution-aggregation-re-dissolution" pattern, with the maximum aggregation point (pH_opt) corresponding closely to the isoelectric point of OVA (pI ≈ 4.5). Spectroscopic analyses revealed that MP induced OVA conformational relaxation and hydrophobic exposure by reinforcing hydrogen bonding and electrostatic interactions. This process modulated the secondary structural order and hydrogen-bond network stability. Functionally, the OVA-MP complex exhibited significantly enhanced emulsifying activity, thermal stability, and foaming properties. Under the conditions of pH 6.0, volume ratio 2:1, and denaturation temperature (T_d) 95.4°C, the comprehensive performance (ESI = 39.36 ± 0.33 min) was the best. Molecular dynamics (MD) simulations confirmed that OVA-MP binding was a thermodynamically spontaneous process (ΔG = -38.98 ± 0.89 kcal/mol), mainly driven by van der Waals and hydrogen-bonding interactions. The resulting O/W pickering emulsion displayed reduced droplet size, pronounced shear-thinning behavior, higher viscoelasticity (G' > G″), and improved salt and storage stability. Overall, MP modulates OVA conformation and interfacial behavior through synergistic hydrogen bonding and electrostatic attraction, forming a structurally reinforced interface. These findings provide theoretical and technical insights into designing food-grade biopolymer emulsifiers and functional delivery systems with enhanced stability.