As consumer health awareness continues to grow, the development of functional foods enriched with bioactive ingredients has become a key research focus in food science (Tufail et al., 2024). β-carotene, a naturally occurring fat-soluble nutrient, holds significant value in functional food development due to its potent pro-vitamin A activity, remarkable antioxidant capacity, and potential anticancer properties. However, the structural instability of β-carotene, combined with its sensitivity to light, heat, and metal ions, as well as its vulnerability to oxidative degradation, leads to low bioavailability, significantly hindering its effective application in the food sector (Xu et al., 2023). The emulsion delivery system is a colloidal dispersion in which lipophilic bioactives are uniformly dispersed and stably encapsulated as micro- to nano-sized droplets within an aqueous phase, achieved through the combined action of emulsifiers and mechanical processing (e.g., high-pressure homogenization or high-speed stirring) (Banasaz et al., 2020). The emulsion delivery system markedly enhances the stability of lipophilic actives by effectively suppressing oxidation and phase separation, thereby ensuring long-term colloidal uniformity. Moreover, this system provides effective protection specifically for lipophilic active ingredients that are susceptible to light and oxygen, thereby significantly enhancing their storage stability.

Soy protein isolate (SPI), as a widely available, environmentally friendly, highly nutritious natural plant protein with favorable processing adaptability (e.g., water holding, emulsification, and thickening) (Dehnad, Emadzadeh, Ghorani, & Rajabzadeh, 2023; Paidari et al., 2024), rapidly adsorbs and diffuses at the oil-water interface due to its excellent amphiphilicity, markedly reducing interfacial tension and thereby effectively stabilizing the emulsion system (An et al., 2025; Eranda et al., 2024). However, emulsions stabilized solely by SPI exhibit limited antioxidant capacity, making it difficult to inhibit the oxidation reaction of interfacial lipids. This leads to reduced stability of the emulsion system, resulting in issues such as phase separation, flocculation, or flavor deterioration. This limitation restricts the application of SPI in foods requiring long-term oxidative stability (Gong et al., 2024). Polyphenols, a class of natural antioxidants (Castro-Muñoz et al., 2024), can protect nutrients such as proteins, lipids, and vitamins from oxidation. Tannic Acid (TA) is a polyphenolic compound formed by multiple gallic acid units connected to a glucose backbone through ester bonds. Its molecular structure, rich in phenolic hydroxyl groups (-OH), allows for efficient binding with proteins via hydrogen bonds, hydrophobic interactions, and covalent cross-linking (Hu et al., 2023). Li, Wang, et al. (2023) found that emulsions stabilized by the SPI-TA complex exhibited both physical and oxidative stability, effectively retarding lipid oxidation. The interactions between proteins and polyphenols are mainly divided into covalent and non-covalent interactions. In comparison to non-covalent complexes, covalent conjugates (e.g., SPI-polyphenol conjugates) exhibit a more stable molecular structure (Ramli et al., 2025). Consequently, emulsions stabilized by covalent conjugates demonstrate superior thermal stability and antioxidant activity.

Currently, three primary methods are employed for the synthesis of protein-polyphenol conjugates: alkaline treatment, free-radical grafting, and enzymatic catalysis. Among these, alkaline treatment is the most widely adopted owing to its operational simplicity and cost-effectiveness (Hernández-Pinto et al., 2024). The reaction proceeds via alkaline-induced oxidation of polyphenols to quinones, which then undergo nucleophilic addition with protein nucleophiles (e.g., amino or thiol groups) to yield covalent protein–polyphenol conjugates (Pan et al., 2022). However, the traditional alkaline method for preparing protein-polyphenol conjugates has low efficiency and a long reaction time, mainly due to the inherent rigid structure of proteins, which sterically hinders access to the polyphenol binding sites, thereby limiting molecular interactions.

Modern food processing technologies can enhance the interaction between proteins and polyphenols by modulating protein structure. For example, ultrasound-assisted treatment can induce the unfolding of protein structure, alter protein conformation, and increase the exposure of active sites, thereby improving the functional properties of protein-polyphenol conjugates to better meet the processing requirements of specific food systems. Zhang et al. (2022) found that, compared with the traditional alkaline method, ultrasound-assisted alkaline treatment not only reduced the conjugation reaction time between lactoferrin and epigallocatechin-3-gallate from 24 h to 40 min but also significantly enhanced the functional properties of the protein. Compared to ultrasound, hydrodynamic cavitation (HC) is a novel treatment technology that is easier to operate, more energy-efficient, and more suitable for large-scale production. The technology is based on the cavitation effect generated by pressure changes during liquid flow. Its core principle involves inducing the formation of cavitation bubbles through a local pressure drop as the liquid passes through a flow constriction (e.g., an orifice plate). These bubbles then collapse in the pressure recovery zone, releasing intense shock waves and localized high-temperature, high-pressure energy (Zheng, Zheng, & Zhu, 2022), which can be harnessed to promote various physical and chemical processes. Asaithambi et al. (2022) compared the effects of HC and ultrasound (US) on the functional properties of egg white protein (EWP). The results showed that, compared to US treatment, EWP treated with HC exhibited significantly enhanced foaming, emulsifying, and gelling properties, as well as improved solubility and in vitro digestibility. Gregersen et al. (2019) found that HC treatment reduced both the viscosity and particle size of protein solutions, and this reduction in viscosity remained stable during storage. In a study on the physicochemical and functional properties of casein treated with HC, Patil et al. (2023) found that HC markedly improved its in vitro digestibility, protein content, emulsifying capacity, and solubility. Our recent study demonstrated that HC treatment effectively promoted the conjugation between SPI and polyphenols, significantly enhancing the emulsifying activity and antioxidant properties of the resulting complexes (Wei et al., 2025). Building on this, we will further develop antioxidant emulsions stabilized by HC-mediated SPI-polyphenol conjugates and construct an efficient delivery system for bioactive ingredients.

In this study, SPI-TA conjugates with enhanced polyphenol binding capacity and superior interfacial properties were synthesized via a novel hydrodynamic cavitation-assisted alkaline treatment, and were subsequently utilized to fabricate a stable emulsion delivery system. The microstructure and rheological properties of the emulsion were characterized. We focused on investigating the physical and oxidative stability of the emulsion during storage. Additionally, the impact of this delivery system on the physicochemical stability of β-carotene was evaluated. The findings from this work may offer insights and potential strategies for developing novel functional food delivery systems.