Functional properties and Pickering emulsion stability of whey protein isolate–inulin complexes enhanced by covalent modification of proanthocyanidins

Abstract BACKGROUND Ultrasound‐assisted covalent modification offers a promising approach for fabricating protein–polysaccharide–polyphenol ternary complexes as advanced Pickering emulsion stabilizers, yet facile preparation strategies remain underexplored. This study aimed to develop an ultrasound‐assisted covalent modification strategy for preparing whey protein isolate–inulin–proanthocyanidin (WPI‐I‐PC) ternary complexes and evaluate their functional performance, particularly as Pickering emulsion stabilizers. RESULTS The WPI‐I‐PC complexes were prepared by pH adjustment and wet‐heating method with or without ultrasonic assistance. The incorporation of PC markedly decreased the particle size and surface hydrophobicity while altering the secondary structure of WPI. Compared with WPI‐PC binary complexes (covalent or non‐covalent) and WPI‐I‐PC ternary non‐covalent complexes, the WPI‐I‐PC covalent complexes prepared with ultrasound‐assisted wet‐heating method at pH 10 exhibited superior thermal stability, emulsifying activity, and antioxidant capacity. Notably, ultrasound‐assisted preparation for 72 min (WPI‐I‐PC (c)) achieved comparable functionality to the 4 h wet‐heating method (WPI‐I‐PC (4 h)), with a smaller particle size (384.50 versus 476.03 nm). In Pickering emulsions, the WPI‐I‐PC covalent complexes markedly improved emulsion performance, as reflected by a reduction in flocculation index (from 32.00% for WPI to 7.92% for WPI‐I‐PC (4 h) and 8.24% for WPI‐I‐PC (c)) and an increase in interfacial protein adsorption content (from 76.80% to 84.92% and 84.37%, respectively). Furthermore, WPI‐I‐PC (c) demonstrated outstanding stability and enhanced antioxidant activities. CONCLUSION Ultrasound‐assisted covalent modification enabled rapid fabrication of WPI‐I‐PC ternary complexes with enhanced structural and functional properties. The resulting Pickering emulsions demonstrated outstanding stability and antioxidant activity, offering an efficient strategy for developing novel food‐grade emulsion stabilizers with potential applications in functional food delivery systems. © 2026 Society of Chemical Industry.