Construction of galangin-loaded soy extract nanoparticles using pH-driven method: Process optimization, stability evaluation, and structure characterization

Flavonoids have a variety of bioactivities, but their poor solubility, low bioavailability, and weak stability limit their application as functional factors in food systems. Soy extracts (SE) mainly composed of soy proteins and soluble polysaccharides at mass ratios of 4.1–5.8: 1 and possessing good bioactivity and nutritional property might be candidate functional encapsulation carriers to improve defects of flavonoids and enhance overall nutritional quality. In this study, galangin (Gal), a poorly water-soluble flavonoid, was used as an example to evaluate the application potential of SE in flavonoid delivery system. Gal-loaded SE nanoparticles (Gal-loaded SE NPs) with high Gal solubility, encapsulation efficiency and bioaccessibility were successfully constructed by pH-driven method. The solubilizing effect of SE on Gal largely depended on the concentrations of SE and Gal. Combining the encapsulation efficiency and retention rate, the optimal conditions were identified as SE concentration of 40 mg/mL, binding time of 5 min, and Gal to SE mass ratio of 1%. Gal-loaded SE NPs showed good storage, thermal, redissolution, and sodium ions stabilities. Based on Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscope analysis, the proteins in SE might undergo a typical de-folding and re-folding process during pH-shifting and mainly combine with Gal by hydrophobic interaction to form Gal-loaded SE NPs with spherical shape (particle diameter <100 nm). This study broadened the application of SE in flavonoid delivery system and provided new ideas for the design and development of new plant-based health food ingredients with multiple functional factors and high nutritional quality.