A time-saving pH-ultrasonic-shifting method for insoluble pea protein isolate to encapsulate polyphenol: Binding mechanism, structure, and functional characteristics

The application of the commercial pea protein isolate (CPPI) and polyphenols are often limited by their poor solubility. To address it, a time-saving pH-ultrasonic-shifting method was skillfully developed by combining the pH-shifting and ultrasonic methods to efficiently encapsulate polyphenols, and this final obtained nanoparticles was named CPPI-NAR-4. CPPI-NAR-4 has shown higher encapsulation efficiency (EE, 93.81 ± 0.56%) and loading capacity (LC, 8.58 ± 0.05%) for NAR, smaller particle size (126.40 ± 3.84 nm) and lower zeta potential (−18.50 ± 0.98 mV) as compared to nanoparticles prepared by other three known methods. This high EE and LC of CPPI-NAR-4 were attributed by both CPPI-NAR-4 and CPPI-4 having the higher surface hydrophobicity, the higher fluorescence intensity, and more protein expansion in their comparison. Multi-spectra evaluations indicated that the pH-ultrasonic-shifting process might produce more hydrogen bonding in the combination of CPPI and NAR. As to the interaction mechanisms between CPPI and NAR in CPPI-NAR nanoparticles, molecular docking results showed that hydrogen bonds, van der Waals forces, and hydrophobic interactions were dominant in the binding of NAR and CPPI; further molecular dynamics simulations revealed that NAR and CPPI had more interactions at pH 12 than at pH 7. Based on these experimental and simulative results, it could be suggested that the effects of ultrasonic on the binding between CPPI and NAR might be better at pH 12 than at pH 7. In conclusion, this pH-ultrasonic-shifting method was expected to be further developed for industrial fabricating protein-polyphenol nanoparticles such as CPPI-NAR.