Solubilization mechanism of self‐assembled walnut protein nanoparticles and curcumin encapsulation

Abstract

BACKGROUND: Native walnut protein is an alkali-soluble protein that seriously limits the application of walnut protein. The pHshifting method could improve the solubility of walnut proteins and enable the encapsulation of active ingredients. The present study aimed to prepare water-soluble nanoparticles of curcumin using walnut protein and evaluate the process of walnut protein self-assembly, interaction between walnut protein and curcumin, encapsulation properties, and stability of nanoparticles. RESULTS:The solubility of native walnut protein was poor, but the solubility of walnut protein nanoparticles (WPNP) formed by walnut protein after pH-shifting significantly improved to 91.5 ± 1.2%. This is because, during the process of pH changing from 7 to 12 and back to 7, walnut protein first unfolded under alkaline conditions and then refolded under pH drive, finally forming an internal hydrophobic and external hydrophilic shell-core structures. The quenching type of walnut protein and curcumin was static quenching, and the quenching constant was 2.0 × 10 14 mol −1 L −1 s −1 , indicating that the interaction between walnut protein and curcumin was non-covalent. Adding curcumin resulted in the formation of nanoparticles with small particle size compared with the no-load. The loading capacity of curcumin-loaded walnut protein nanoparticles (WPNP-C) was 222 mg g −1 walnut protein isolate. Under the same mass, the curcumin equivalent concentration in aqueous solution of WPNP-C was 17 000 times higher than that of the native curcumin.CONCLUSION: The solubility of the self-assembled WPNP significantly increased after pH-shifting treatment. The walnut protein carrier could improve the stability of the encapsulated curcumin. Therefore, walnut proteins could be used as water-soluble carriers for hydrophobic drugs.

Self‐assembled pea vicilin nanoparticles as nanocarriers for improving the antioxidant activity, environmental stability and sustained‐release property of curcumin

“…The fluorescence quenching of Cur against walnut protein showed a similar result. 31 According to Fig. 2(D), the n value of 7S-Cur complexes was about 1, which suggested that there was a binding site for 7S to bind with Cur.…”

“…When curcumin was present, the hydrophobic core of walnut protein took Cur as a core and began to self-assemble around it, eventually forming smaller nanocomplexes. 31 Interestingly, the values of ζ-potential had no significant differences between 7S-pH 12-pH 7 and 7S-Cur, suggesting that 7S nanoparticles could be used as stable delivery carriers for Cur. In addition, the PDI value of 7S-Cur was 0.15, lower than 0.30, indicating that the 7S-Cur composite particles had a good uniformity.…”

“…With reference to Zhang et al, 34 the particle size of powdered PPI-Cur complexes was smaller than that of PPI alone, suggesting that the presence of Cur enhanced the hydrophobic interaction within the complexes to form a more compact structure. Lv et al 31 prepared self-assembled walnut protein nanoparticles to encapsulate Cur inside the protein, and the hydrophobic groups of walnut protein started to self-assemble around Cur, resulting in the formation of nanoparticles with smaller sizes.…”