# Ultrasound-assisted construction of pea protein isolate-folic acid covalent complex as self-assembled nanocarrier: Enhancing the stability, precise release property, and bioaccessibility of curcumin

## TL;DR

Researchers used ultrasound to create a pea protein and folic acid complex that improves curcumin's stability, controlled release, and absorption in the body.

## Contribution

A green ultrasound-assisted method to create a covalent pea protein-folic acid complex for curcumin delivery.

## Key findings

- Ultrasound-assisted grafting improved folic acid loading and solubility of pea protein.
- The complex enhanced curcumin's stability, controlled release, and bioaccessibility.
- PPI-FA15-Cur showed significantly higher curcumin loading and bioaccessibility than other forms.

## Abstract

•Applying an efficient and green ultrasound-assisted grafting method to prepare pea protein isolate folic acid conjugates.•The covalent complexation of folic acid improved the binding affinity of pea protein isolate for curcumin.•Encapsulation within pea protein isolate-folic acid realized the gastrointestinal controlled release for curcumin.•Pea protein isolate-folic acid-curcumin complex showed excellent stability, cellular uptake efficiency, and bioaccessibility.

Applying an efficient and green ultrasound-assisted grafting method to prepare pea protein isolate folic acid conjugates.

The covalent complexation of folic acid improved the binding affinity of pea protein isolate for curcumin.

Encapsulation within pea protein isolate-folic acid realized the gastrointestinal controlled release for curcumin.

Pea protein isolate-folic acid-curcumin complex showed excellent stability, cellular uptake efficiency, and bioaccessibility.

Curcumin (Cur) is a hydrophobic phenolic compound with superior biological activity, but the limited water solubility, chemical instability, and poor bioaccessibility of curcumin restrict its application. This study developed pea protein isolate (PPI)-folic acid (FA) covalent complexes as nanocarriers for the encapsulation, protection, and precise delivery of curcumin. The results of SDS-PAGE, XPS, and FTIR demonstrated that covalent complexation between PPI and FA was formed through an ultrasound-assisted free radical grafting method. Notably, ultrasonication for 15 min (PPI-FA-US15) achieved a higher FA loading capacity (44.78 ± 0.37 µg/mg) than the traditional free radical grafting for 24 h (36.45 ± 0.43 µg/mg). The ultrasonic treatment and covalent complexation of FA greatly improved the solubility of PPI (from 61.34 ± 0.67% to 97.02 ± 0.88%). Curcumin was efficiently encapsulated within the core of PPI-FA-US15 conjugates to form PPI-FA15-Cur nanocomplexes by hydrogen bonding and hydrophobic interaction. The complexation of FA improved the binding affinity of PPI for curcumin. PPI-FA15-Cur demonstrated a 1.97-fold superior loading capacity for curcumin compared to PPI-Cur. Meanwhile, PPI-FA15-Cur displayed a spherical morphology, and maintained a stable particle size distribution during 77-d storage. The heating stability, photochemical stability and antioxidant property of curcumin were significantly improved. Furthermore, in vitro digestion studies demonstrated that PPI-FA15-Cur showed a sustained release of curcumin. The bioaccessibility of curcumin within PPI-FA15-Cur was about 4.75-fold and 1.11-fold higher than that of free curcumin and PPI-Cur, respectively. This study provides a promising approach for developing plant protein-based carriers that enable precise delivery of curcumin in functional foods.