Morphological Characterization, Interaction Mechanisms, and Functional Properties of a Non-Covalent Whey Protein Isolate–Ellagic Acid Complex

Abstract

Sarcopenia, characterized by loss of muscle mass and strength, causes difficulty in standing and walking and increases fracture risk in older adults, making its prevention a priority for healthy aging. Whey protein isolate (WPI) promotes muscle protein synthesis, while ellagic acid (EA), a polyphenol, alleviates symptoms by reducing oxidative stress. However, WPI is prone to oxidative damage during processing, and EA suffers from low stability and bioaccessibility. For these reasons, a non-covalent complex was prepared from WPI and EA, and its preparation conditions were systematically optimized through single-factor experiments followed by orthogonal design. The objectives were to enhance the stability and bioaccessibility of EA through the protective effect of WPI, thereby enabling synergistic anti-sarcopenia effects. Multi-spectroscopic techniques and molecular simulations were employed for morphological characterization and interaction analysis. The optimal preparation conditions were pH 5.0, a 2 h reaction, and a WPI: EA molar ratio of 1:2.5. Under these conditions, the antioxidant activity of the WPI-EA non-covalent complex increased by 27.20% (p < 0.05). At the same time, protein digestibility decreased by 3.04% (p < 0.05). EA bound non-covalently near the tryptophan and tyrosine residues of WPI, altering its secondary and tertiary structures. WPI-EA non-covalent complex exhibited a 38.94% reduction in its surface hydrophobicity (p < 0.05) and a 2.42% increase in α-helix content (p < 0.05). These conformational changes provided a structural basis for the improved bioaccessibility of WPI. The spectroscopic observations were corroborated by molecular docking and MD simulations, which revealed that both hydrophobic interactions and hydrogen bonds contributed to the stable binding of EA to β-Lg, with hydrophobic contacts predominating in the binding mode and hydrogen bonds playing a critical role in maintaining conformational stability throughout the simulation. In summary, the WPI-EA non-covalent complex exhibited good antioxidant activity, indicating its potential as a functional ingredient for sarcopenia management and for improving skeletal muscle health in aging individuals.