In recent years, due to their semi-solid structure, excellent self-supporting properties, and shear-thinning rheological behavior, high internal phase Pickering emulsions (HIPPEs) have become a research hotspot pursued by researchers (Wang, Li, Hou, Zhang, & Li, 2024). Currently, the development and preparation of Pickering stabilizers for HIPPEs based on proteins in the food industry have been warmly pursued by researchers, owing to their excellent amphiphilicity and superior biocompatibility. Additionally, with consumers paying increasing attention to clean labels and health, exploring and developing plant-based alternative proteins as effective Pickering stabilizers has become the latest trend and ideal choice.

To date, extensive explorations have been conducted on developing plant-based alternative proteins as Pickering stabilizers. For example, soy protein isolate heat aggregation nanoparticles (SPN) can form multi-layer protein films at the oil-water interface, and the SPN-stabilized HIPPEs exhibited good viscoelasticity and recovery rate (Wen, Zhao, Jiang, & Sui, 2024). HIPPEs prepared using potassium metabisulfite-induced pea protein isolate nanoparticles (PPINs) had a gel-like structure and can resist the effects of temperature and ionic strength to a certain extent (Li, Liu, Xu, & Zhang, 2022). Coconut protein (CP), an emerging plant protein source, was commonly obtained from the by-product (coconut meal) after virgin coconut oil extraction. It has a unique flavor, rich nutrition, and a balanced amino acid profile, with high contents of non-essential amino acids such as glutamic acid, arginine, and aspartic acid (Chen et al., 2024). Meanwhile, CP has been demonstrated to possess multiple health benefits, including antioxidant, hypolipidemic, and antidiabetic effects (Remya, Chikku, Renjith, Arunima, & Rajamohan, 2013; Salil, Nithya, Nevin, & Rajamohan, 2014). However, it is worth noting that the solubility, environmental resistance, and emulsifying properties of CP were significantly lower than those of other plant proteins (Zou et al., 2025). HIPPEs solely formed using CP can hardly meet the required stability and gel-like texture. However, due to the complexity of the technology, time-consuming processes, and high costs, traditional methods for improving the emulsifying properties of plant proteins are difficult to adapt to the themes of low carbon, economy, and sustainable development in today's food industry. Therefore, the development of facile, green, and efficient modifying approaches to improve the emulsifying performance of CP was extremely urgent.

The ingenious design and combination of proteins, polysaccharides, and polyphenols to self-assemble via non-covalent interactions into multi-component complex particles offered a promising solution strategy for improving the emulsifying properties of plant proteins. The main role of polysaccharides was to increase the viscosity of the aqueous phase. The binding of polyphenols to proteins can improve the structure and emulsifying properties of proteins. However, such non-covalent interactions have a limited effect on enhancing emulsifying performance (Dai et al., 2024). Interestingly, it has recently been found that polyphenols with catechol or galloyl groups can chelate with metal ions through coordination bonds to form supramolecular metal-polyphenol networks (MPNs). These MPNs coatings exhibited multifunctional properties such as high adhesion, strong mechanical strength, and easy cross-linking, which have been widely applied in fields such as food, medicine, and cosmetics (Xi, Wang, Li, Zhang, & Du, 2020). MPNs can be used as microcapsules for encapsulating and delivering food nutrients and can also serve as preservative coatings for fruits to extend the shelf life of food (Chen et al., 2021; Park et al., 2017). Tannic acid (TA), also known as gallic acid, was a polyphenol easily obtained from plants. It was rich in numerous galloyl and catechol groups, which can provide multidentate ligands for chelating metal ions, thus readily forming stable metal-polyphenol networks with metal ions (Cheng et al., 2022; Zhang et al., 2023). It was reported that TA can chelate with 18 kinds of metal ions through coordination bonds to form metal-polyphenol networks (MPNs), and the performance of the combination of TA and Fe3+ was particularly typical and excellent (Ejima et al., 2013). In addition, studies have shown that as the valence of the metal ions used increased, the coordination binding between metal ions and polyphenols in MPNs tended to increase as well (Zhao, Jia, Cheng, Liu, & Gao, 2018). Feng, Wang, Feng, Li, and Wei (2024) confirmed that TA-Fe3+ modified the nano-microspheres, which possessed excellent antioxidant, photothermal stability, and antibacterial properties. Qin et al. (2019) successfully fabricated novel multifunctional modified starch nanoparticles by introducing TA-Fe3+, which exhibited desirable pH responsiveness, antioxidant activity, antibacterial properties, and biocompatibility. Although there have been relevant reports on MPNs-modified particles, research on protein-polysaccharide complex particles and their HIPPEs remains limited. Furthermore, the interfacial behavior and stabilization mechanism of protein-polysaccharide complex particles modified by TA-Fe3+ remained unclear. Therefore, it is necessary to conduct further comprehensive investigations to determine the potential of MPNs as an emerging technology in the food industry.

In this work, we prepared a novel CP-PE-TA-Fe3+ by modifying coconut protein-pectin complex particles (CP-PE) with TA-Fe3+, which aimed to improve the stability and functional properties of CP-stabilized HIPPEs. The formation of CP-PE-TA-Fe3+ was confirmed using UV–Vis spectroscopy, FTIR, and XPS. More importantly, the interfacial behavior of CP-PE-TA-Fe3+ was systematically characterized by interfacial dilatational rheology. Finally, the rheological properties, stability, and 3D printing characteristics of CP-PE-TA-Fe3+-stabilized HIPPEs were evaluated. This study provided new insights into CP as an effective Pickering stabilizer and broadened the application scenarios of MPNs in emulsion systems.