Ultrasound-assisted pH-shifting for structuring rutin-loaded zein-soy protein isolate-inulin nanoparticles: Structural reorganization, interfacial stabilization, and gastrointestinal delivery.

Ultrasound-assisted pH-shifting integrates alkaline pH-induced protein unfolding, ultrasound-assisted dispersion, and neutralization-driven reassembly to regulate the formation of multicomponent biopolymer nanoparticles. This study investigated the effects of ultrasound-assisted pH-shifting on the structural characteristics, colloidal stability, and gastrointestinal delivery performance of rutin-loaded zein-soy protein isolate-inulin nanoparticles (ZSI-R). Compared with pH-shifting alone, ultrasound-assisted pH-shifting produced ZSI-R nanoparticles with a higher encapsulation efficiency (92.20 ± 1.48%), smaller particle size, a more negative zeta potential, and greater resistance to centrifugal, ionic, and storage stresses. Spectroscopic and diffraction results suggested that the combined treatment induced protein conformational reorganization, altered noncovalent interactions among zein, soy protein isolate, inulin, and rutin, and promoted the incorporation of rutin in an amorphous state within the nanoparticle matrix. The apparent dispersibility of rutin increased from 137.47 ± 1.80 μg/mL for free rutin to 1791.99 ± 10.27 μg/mL for ZSI-R nanoparticles prepared by ultrasound-assisted pH-shifting. During gastrointestinal evaluation, these nanoparticles showed slower gastric-phase dialysis-based diffusion and an intestinal bioaccessibility of 80.70%. Changes in particle size, zeta potential, infrared spectra, and fluorescence profiles were consistent with digestion-associated changes in the composition and microenvironment of the particle-digesta interface. Overall, under the experimental conditions used in this study, ultrasound-assisted pH-shifting improved the encapsulation, colloidal stability, apparent dispersibility, and gastrointestinal delivery performance of rutin in zein-soy protein isolate-inulin nanoparticles.