Metal-polyphenol network-hardened coconut protein-carboxymethyl cellulose complex coacervates: Fabrication, characterization, environmental stability, and release kinetics

Metal-polyphenol networks (MPNs), as a novel surface structure modifier, whether it can have a hardening effect on complex coacervate microcapsules is still unknown. In this work, piperine (PIP)-loaded coconut protein (CCP)-carboxymethyl cellulose (CMC) complex coacervates (CP) microcapsules were hardened using tannic acid-Fe³⁺ networks (TA-Fe³⁺) to improve the stability of microcapsules. The results showed that the optimal coacervation conditions for CCP-CMC were at pH = 3.2 and a CCP: CMC ratio of 2:1 (w/w). TA-Fe³⁺ formed a network-decorated coating with a supramolecular structure on the CP surface. TA:Fe³⁺ ratios significantly affected the structural cohesion of TA-Fe³⁺-hardened piperine-loaded CCP-CMC complex coacervates (TF) and thus the hardening effect. At low Fe³⁺ levels, TF formed a dense and uniform structure, and at high Fe³⁺ levels, the TF structure became looser. Besides, 2TA-1Fe³⁺-CP exhibited excellent encapsulation efficiency, desirable stability, and favorable antioxidant ability. After long-term storage, light irradiation, and pH treatment, the retention of PIP in 2TA-1Fe³⁺-CP was increased by 119 %, 133 %, and 111 % compared to CP, respectively. Moreover, the release kinetics results proved that TA-Fe³⁺ delayed the release of CP in the food simulants. This study provided some valuable information for exploring a novel hardening microcapsule approach based on the complex coacervation.