Lycopene (LYC) is a natural fat-soluble pigment which is rich in tomatoes, carrots and watermelons. It can only be ingested from food and cannot be synthesized in human and animal bodies. It has many physical benefits such as antioxidation, anti-inflammation, hypolipidemic effects, anti-cancer and cardiovascular protection [1]. Despite its nutritional benefits, the application of LYC is restricted by its low water solubility, poor bioavailability, and instability under high temperature and oxygen. Specifically, the degradation rate of LYC increased 2.4 times above 80 °C, and the loss of LYC is approximately 3 times under aerobic conditions [2]. In order to break these limitations, various kinds of deliveries like emulsions, hydrogels, nanostructured lipid carriers, micelles and microcapsules are designed and constructed to improve the stability and enhance the bioaccessibility of LYC [3]. Among these deliveries, the emulsion that is composed of an oil phase and an aqueous phase shows greater potential to be used as carriers of fat-soluble active substance. Fat-soluble bioactive components are solubilized in the oil phase and encapsulated by the aqueous phase, leading to a sustained release in vivo.

The emulsion stabilized by solid particles rather than surfactants is considered as Pickering emulsions (PEs). When the oil phase volume fraction (φ) exceeds 0.74, the Pickering emulsion formed is defined as high internal phase Pickering emulsion (HIPPEs) [4]. The higher oil content enables the encapsulation of more lipophilic bioactive components. Moreover, the thicker interfacial layer can not only prevent the degradation of the bioactive components, but also significantly reduce the interaction between the bioactive components with the oxygen, which further improves the stability of the lipophilic bioactive components [5]. Nowadays, proteins are widely used as amphiphilic materials to stabilize HIPPEs. In general, heating food-grade proteins above their denaturation temperature for several hours under acidic condition (pH values below their isoelectric point) with low ionic strength can produce amyloid-like protein fibrils [6]. The amyloid-like protein fibrils which possess high aspect ratio, high rigidity, ordered structure and surface multifunctional groups exhibit better emulsifying properties and show great potential for stabilizing HIPPEs compared with the native proteins [7]. Zhao et al. [8] showed that the HIPPEs stabilized by rice bran protein fibrils were able to stabilize the β-carotene and enhance its bioaccessibility. It has been also reported that the encapsulation of curcumin in the PEs stabilized by rice glutelin fibrils displayed a slow and sustained release and higher bioavailability [9]. Bovine serum albumin (BSA) is a food-grade protein with a molecular weight of 66.4 kDa and it can form positively charged BSA amyloid-like fibrils (BSAF) after acid-heat treatment [10].

In recent years, food-grade nanoparticles produced by electrostatic interactions between protein amyloid-like fibrils and polysaccharides are considered as a promising carrier to stabilize PEs [11]. In previous studies, LYC was encapsulated in pomelo peel derived nanocellulose [12] or enzymatically cross-linked α-lactalbumin nanoparticles [13], and such single-component stabilizers for PEs may suffer from insufficient interfacial stability, poor environmental adaptation, and monofunctionality. To address these challenges, this study introduced a dual-component system comprising positively charged BSAF and negatively charged gum arabic (GA) to stabilize HIPPEs. GA serves as a polysaccharide emulsifier which is commonly used to prepare the emulsions [14]. This innovative approach has the following advantages. On the one hand, the interfacial rigidity of BSAF and the electrostatic repulsion from GA enhances the stability of LYC under gastrointestinal conditions. On the other hand, the inherent mucoadhesive properties of GA can effectively prolong the gastrointestinal retention time of LYC.

Therefore, in this study, BSAF was prepared and mixed with GA to form the complex of BSAF/GA through electrostatic interactions. Subsequently, the BSAF/GA complex was employed to stabilize the Pickering emulsions with oil phase volume fractions ranging from 0.5 to 0.84 (from PEs to HIPPEs). After encapsulation, the thermal stability, antioxidant capacity and bioaccessibility of LYC in the PEs and HIPPEs were investigated. Moreover, the safety of Pickering emulsions was evaluated in vivo. This study may offer a theoretical guidance for the construction of stable and effective carriers for LYC and promote the application of LYC in functional foods.