Ultrasound-modulated whey protein isolate fibrils for curcumin delivery: Structural changes, functional properties, and bioaccessibility.

Whey protein isolate fibrils (WPIF) are promising biomacromolecular carriers, but their entanglement-prone structure and limited interfacial activity restrict hydrophobic bioactive substance delivery. This study evaluated the effects of ultrasound power (0-600 W) and treatment time (0-15 min) on WPIF structural characteristics, functional properties, and curcumin (Cur) delivery efficiency. Circular dichroism, FTIR, intrinsic fluorescence, and surface hydrophobicity analyses revealed that moderate ultrasound disrupted intermolecular interactions, reduced β-sheet content, and exposed hydrophobic and sulfhydryl groups. Optimal conditions (500 W, 6 min) transformed long entangled fibrils into short rod-like nanofibrils, reducing particle size from 358 to 118 nm and increasing zeta potential from +35 to +44 mV, while enhancing dispersibility, emulsifying, foaming, and radical scavenging activity. The optimized UWPIF achieved 91.7% Cur encapsulation efficiency, and in vitro gastrointestinal digestion simulation demonstrated significantly improved Cur bioaccessibility. This work provides a theoretical foundation for ultrasound-mediated protein fibril modulation and bioactive substance delivery.