Advances in emulsion stability: A review on mechanisms, role of emulsifiers, and applications in food

Abstract

Emulsions, as thermodynamically unstable systems with multiscale and multiphase structures, naturally destabilize over time. Their stability plays a vital role in industries like food, cosmetics, and chemical materials. For emulsion-based foods, stability is essential to preserve their nutritional value, texture, appearance, and flavor. Enhancing emulsion stability during transportation, storage, and use not only extends shelf life but also boosts market reliability and consumer trust. This review explores emulsion destabilization mechanisms, evaluates the influencing factors, and discusses strategies to assess and enhance stability. The text outlines key emulsion stabilization methods, focusing on recent progress in emulsifier development, including Pickering particles. This review highlights the application of proteins, polysaccharides, polyphenols, and their complexes as emulsifiers in stabilizing food emulsions. It also explores their potential to enhance product performance while addressing consumer demand and sustainability goals.

Highlights

• •Explored the mechanism of emulsion destabilization.
• •Evaluated the factors affecting destabilization.
• •Discusses the main methods of stabilizing emulsions.
• •Outlining the application of proteins, polysaccharides, polyphenols and their complex-type emulsifiers.
• •Potential for stabilizing emulsions to improve the performance of good products.

Introduction

An emulsion is a multiphase dispersion system that typically consists of two immiscible liquids, with one dispersed in the other as small droplets (Singh & Pulikkal, 2024). Emulsion systems are generally classified as oil-in-water (O/W) or water-in-oil (W/O) emulsions, depending on whether the dispersed phase is oil or water (Liu, Wu, Zhang, Yan, & Mao, 2024). Double emulsions, such as water-in-oil-in-water (W/O/W) or oil-in-water-in-oil (O/W/O), are more complex systems where droplets themselves contain smaller droplets, offering potential for advanced applications in encapsulation and controlled release systems. Emulsions are widely found in food systems such as milk, cream, mayonnaise, and salad dressings (Bai, Huan, Rojas, & McClements, 2021). Emulsions are prone to destabilization during production, processing, and storage due to their inherent thermodynamic instability, since their stability is kinetically achieved by controlling interfacial tension and viscosity, as well as through the use of emulsifiers. The resulting coalescence, Ostwald ripening, flocculation, and phase separation pose challenges to the long-term stability of emulsion systems (Suzuki, Kobayashi, Yamazaki, Tsuji, & Arai, 2024). The formation and stability of emulsions are significantly influenced by the nature of the interfacial layer between the dispersed and continuous phases. These influences mainly include the thickness and structural characteristics of the interfacial layer, the interaction between the emulsifier and the two phases, and the rheological properties of the interface (Cai et al., 2023). Physicochemical indicators such as micromorphology, particle size, and zeta potential are commonly used to evaluate the stability of emulsions. A more uniform distribution of smaller droplets often indicates improved emulsion stability. Additionally, the magnitude of the repulsive forces between droplets, as measured by zeta potential, serves as a key indicator of stability, with higher repulsion reducing the likelihood of coalescence or aggregation (Cao et al., 2023). A single emulsifier is often sufficient to create and stabilize an emulsion, with common options including small-molecule surfactants, phospholipids, proteins, polysaccharides, and other surface-active polymers. In recent years, there has been a global focus on nutrition and healthy diets, with a significant increase in demand for safe, sustainable, and green consumption and the “ingredient list reduction movement,” with the addition of cleaner ingredients. These trends have driven interest in innovative food stabilization technologies. Such as Pickering emulsions, which are stabilized by solid particles (Pickering particles) and can be produced using natural and healthy components. Food-grade particles mainly include protein/polysaccharide particles, lipid crystals, flavonoids, composite particles, food-grade waxes (Boostani et al., 2024). The main advantage of Pickering emulsions is that they utilize the multifunctionality of solid particles, as well as their strong interfacial adsorption capacity, to achieve an organic combination of efficient stability and innovative performance. Their environmental friendliness, ingredient safety, and intelligent response make them an ideal alternative to traditional emulsions, especially for clean label products, high-end pharmaceutical formulations, and green industrial solutions. By chemically or physically modifying the Pickering particles used to stabilize these emulsions to enhance their adsorption at the oil-water interface, highly stable Pickering emulsions can be created. Such emulsions can be used to extend the shelf life of a wide spectrum of products. Advanced methods, such as layer-by-layer assembly, can be applied to form multilayer interfaces on droplet surfaces, increasing the repulsive forces between droplets and further improving emulsion stability (Li et al., 2022). As the demand for “clean label” food and beverage products continues to grow, many researchers are replacing chemically synthesized food emulsifiers with high-quality and efficient food emulsifiers of natural origin to stabilize emulsions. Most natural emulsifiers are of plant origin, including proteins, polysaccharides, phospholipids and saponins, etc. For instance, some hydrocolloids (polysaccharides) can prevent emulsion destabilization by increasing the viscosity of the system, modulating the interfacial properties, and forming a three-dimensional network structure.

The stability of emulsion-based food products is critical for ensuring their safety, quality, and sensory attributes, making it a key focus area in the food industry. Improved emulsion stability enables the development of healthier and more appealing food products for consumers. This review examines the mechanisms, influencing factors, and evaluation methods of emulsion stability, as well as its applications in food products and its role in maintaining product functionality and consumer acceptability.

Stability and instability in emulsions

Instability in emulsions

Emulsions are thermodynamically unstable systems prone to instabilities such as coalescence, Ostwald ripening, flocculation, and phase separation (McClements & Gumus, 2016; Zhang et al., 2023) Fig. 1. Over time, the effectiveness of emulsification decreases, and the oil phase rapidly leaks from the interfacial layer, leading to varying degrees of phase separation (Cheng et al., 2023). Flocculation, a form of instability, occurs when a large portion of dispersed droplets in an oil-in-water emulsion coalescence into flocs. It happens when the mutual attraction between droplets outweighs their mutual repulsion (Ravera, Dziza, Santini, Cristofolini, & Liggieri, 2021). In flocculation, the droplet radius remains unchanged, but the droplets come together to form clusters, which accelerates gravitational separation and compromises emulsion stability (Niu et al., 2023). Coalescence, a manifestation of instability, is the process where oil droplets in an emulsion gradually combine to form larger droplets or clusters. It is primarily influenced by an imbalance of attractive and repulsive forces between droplets. The thickness and viscoelasticity of the interfacial film also play a role in droplet coalescence (Ravera et al., 2021). Ostwald ripening is a phenomenon in which changes in Laplace pressure between different sized droplets in an emulsion lead to diffusion of smaller droplets into larger ones. This process increases the particle size distribution of the emulsion, leading directly to delamination or settling (Koroleva & Yurtov, 2021). An oil phase with high water solubility, such as short-chain triglycerides, can significantly accelerate the rate of Ostwald maturation by enhancing molecular diffusion between droplets. During storage, emulsions may also undergo chemical changes, including lipid oxidation, hydrolysis of triglycerides, and polymerization of unsaturated fatty acids, which impact their stability. For instance, lipid oxidation may occur faster in bulk or continuous phase than in dispersed phase. Oil is encapsulated in O/W, thus being more protected against oxidation (Chang et al., 2023).

Fig. 1.

Oil-in-water emulsions may become physically unstable through numerous physicochemical processes, including gravitation separation, flocculation, coalescence, and phase separation (McClements & Gumus, 2016).

Factors affecting emulsion stability

The stability of an emulsion is influenced by the characteristics of its dispersed phase (e.g., droplet size and distribution), continuous phase (e.g., viscosity and solubility), and interfacial properties (e.g., the effectiveness of emulsifiers in reducing interfacial tension), which will be further discussed in this section.

Dispersed phase

The dispersed phase in emulsions exists as fine droplets. The size of these droplets is influenced by the type of emulsifier used and the conditions under which the emulsion is prepared and stored, including pH, ionic strength, presence of electrolytes, and intensity of homogenization. These factors collectively determine droplet size, which greatly impacts the stability, optical properties, rheological behaviour, and sensory characteristics of the emulsion (Chang et al., 2023). hese factors also affect the solubility of the emulsifier and the interactions between droplets, which, in turn, influence droplet size and overall emulsion stability. Interactions between droplets, such as van der Waals forces, electrostatic forces, and hydrophobic interactions, impact the stability and dispersibility of the dispersed phase in the emulsion. This, in turn, affects the viscosity and textural properties of the system (Ravera et al., 2021). Generally, the smaller the dispersed droplets, the higher the surface area; thus, more emulsifiers are needed to cover the interfacial layers. Moreover, dispersed phase with high packing density, big droplets, and flocculated could impart high stability too due to its viscous characteristics.

Continuous phase

The continuous phase supports and surrounds the dispersed phase droplets in an emulsion, playing a critical role in maintaining stability. A higher viscosity in the continuous phase can slow down the settling or creaming rate of dispersed phase droplets, thereby enhancing emulsion stability (Zhang et al., 2025). This effect arises because a higher viscosity in the continuous phase increases the droplet resistance to movement. For example, hydroxyethyl cellulose (HEC), which has modified hydrophilic and lipophilic properties, provides both colloid-protecting and thickening effects that stabilize emulsions. This stabilization is particularly pronounced in the three-dimensional network structures formed by the modified HEC, which exhibit strong elastic properties (Akiyama et al., 2005). Biopolymer substances (e.g. polysaccharides, proteins) and hydrocolloids are used as thickeners or gelling agents to enhance the stability in emulsion systems by changing the rheological properties, e.g., Li et al. added xanthan gum (XG) to soybean isolate protein (SPI), and the addition of XG altered the conformation of SPI, and due to the high viscosity and gelling properties of XG, it can form a viscous elastic interfacial layer with a gel network structure when combined with SPI. Due to its high viscosity and gelling properties, when combined with SPI, it can form a viscoelastic interfacial layer with a gel network structure, which prevents oil droplets from aggregating by forming a spatial barrier on the droplet surface. These properties result in SPI-XG-stabilized emulsions with improved storage, thermal, and ionic strength stability (Li, Wang, Ji, & Xia, 2024). In addition, they can act synergistically or competitively with emulsifiers to form complex stabilization mechanisms. For example, Mao et al. found that sucrose esters and xanthan gum acted synergistically to stabilize emulsions better than a single emulsifier. Xanthan gum and proteins can form protein-polysaccharide complexes, and there are also a hydrophobic interactions between sucrose esters and xanthan gum. The properties of xanthan gum can improve the stability of walnut protein emulsions by affecting the mechanical properties of the emulsions, and the combination of sucrose esters and xanthan gum can better stabilize large proteins (Liu, Wu, Zhang, & Mao, 2024).

Gel-like or gel-forming substances present in the continuous phase strengthen it and slow down droplet movement, thereby enhancing emulsion stability. For example, natural corn starch increases the viscosity of the emulsion, reducing droplet mobility and collision frequency (Yang et al., 2022). The concentration of solutes in the continuous phase also significantly affects stability. For instance, Ries et al. demonstrated that replacing unadsorbed proteins with water substantially reduced the oxidative stability of emulsions, likely due to the loss of protective protein effects at the interface. Conversely, increasing protein concentration in the continuous phase improved oxidative stability by enhancing interfacial protection and reducing oxidative reactions (Ries, Ye, Haisman, & Singh, 2010). The environmental conditions to which the continuous phase is exposed significantly influence emulsion stability. Heat treatment, in particular, alters the flow properties of the emulsion by modifying the continuous phase. For example, the heating of whey protein has been shown to produce stabilized nanoparticles and aggregates, which enhance emulsion stability by providing a protective interface and reducing droplet coalescence (Dybowska, 2011).

Interface layer

The interfacial layer that contacts and separates the oil and water phases plays a crucial role in stabilizing the two phases. The properties of the interfacial layer surrounding the dispersed phase droplets in an emulsion often determine its stability (Guan, Jiang, Lin, & Ngai, 2024). The physicochemical properties of the interfacial layer, such as its thickness, structure, the interactions between adsorbed emulsifiers, and interfacial rheological properties, largely govern the formation and stabilization of emulsions. The strength of spatial interaction forces between emulsion droplets depends on the thickness of the interfacial layer. For instance, polysaccharides belong to hydrophilic colloids and are generally used as stabilizers (thickeners or gelling agents). The physicochemical properties of the interfacial layer such as thickness, structure, interaction between adsorbed emulsifiers, and interfacial rheological properties, largely determine the formation and stabilization of emulsions. The strength of spatial interaction forces between emulsion droplets depends on the thickness of the interfacial layer. For example, polysaccharides are hydrophilic colloids that are generally used as stabilizers (thickeners or gelling agents). Li et al. compared substances five processing methods to extract pectin stabilized emulsion from hawthorn. The results showed that pectin extracted by hot air drying had good emulsification ability while the emulsion stability, and blackening treatment had the worst effect. The emulsification performance of high molecular weight pectin is better (Li et al., 2022).

The thick interfacial layer formed by the polysaccharide emulsifier stabilizes the emulsion through spatial repulsive forces. In contrast, thinner interfacial layers, such as those formed by globular proteins, stabilize emulsion droplets through a combination of electrostatic interactions and spatial repulsive forces (Xu, Wang, Xin, Zhang, & Liu, 2025). Dickinson compared the interfacial film thickness of emulsions stabilized by surfactants, proteins, hydrocolloids, and solid particles. The results showed that solid particles (10 nm to a few millimeters) and hydrocolloids (5–10 nm) had a significant advantage in forming thicker interfacial films compared to surfactants (0.5–1 nm) and proteins (1–5 nm) (Dickinson, 2009). Thus multilayers are thicker than monolayers and therefore emulsions stabilized by multilayers tend to have greater long-term stability than monolayers. The polarity of the interfacial layer affects emulsion stability. The polarity of the interfacial layer can be measured to a certain extent by the hydrophilic-lipophilic value (HLB), which is a key parameter for characterizing the relative strengths of hydrophilic and lipophilic groups in the molecules of surfactants (especially emulsifiers). The lower the HLB value, the more lipophilic the substance; the higher the HLB value, the more hydrophilic the substance. Upon the introduction of the emulsifier into the oil-water system, the lipophilic portion of the emulsifier extends into the oil phase, while the hydrophilic portion extends into the water phase. These groups align at the oil-water interface, forming an interfacial film. This alignment alters the interfacial properties and significantly reduces the interfacial tension between the oil and water phases. As a result, the repulsion between oil droplets and water is minimized, allowing the oil droplets to be stably dispersed in the aqueous phase, thereby forming stable emulsions. For oil-in-water emulsions, a more hydrophilic interfacial layer improves resistance to coalescence, as emulsifiers with higher water solubility better stabilize droplets in the aqueous continuous phase (Zembyla, Murray, & Sarkar, 2020).

Other influencing factor

The stability of emulsions is susceptible to external environmental conditions such as salt ions, pH, temperature, etc. External factors directly or indirectly disrupt the dynamic equilibrium of an emulsion by altering the interfacial film strength, inter-droplet forces, or the nature of the continuous phase. For example, the addition of ions of different compositions to emulsion foodstuffs can cause flocculation and instability at high ionic strengths, limiting their use in some commercial products. Some researchers have reported that emulsion foods can be stabilized by biopolymers. For example, emulsions exhibit excellent salt tolerance when stabilized by arabinoxylan hydrolysate-SPI conjugates. This property stems from the ability of the conjugate to inhibit the electrostatic shielding effect of salt ions, thus avoiding the weakening of electrostatic repulsion between emulsion droplets (Li, Sun, et al., 2022). In addition, the conjugate is able to form a multilayer structure at the interface, which effectively prevents the migration of the oil phase from droplet, to droplet and thus inhibiting droplet coalescence. In addition, the effect of pH on emulsion stability is multifaceted and involves a number of factors, such as surface charge, emulsifier solubility, protein denaturation, interfacial tension, chemical reactions, and microbial growth. Similar toof protein-stabilized emulsions, proteins have a low surface charge at pH values close to their pI and may not provide sufficient electrostatic repulsion to prevent droplet aggregation and agglomeration. Researchers have found that the emulsion stability of microalgal proteins (MP) is limited to strongly alkaline conditions; but by complexing with carboxymethyl chitosan (CMCS), complex-stabilized emulsions exhibit good stability at pH 2, 4, and 7 (Wang et al., 2024). Typically, some emulsion food products undergo a series of temperature changes during production, transportation, storage, and use, especially protein-stabilized emulsions (beverages) whichare highly sensitive to heat treatment. When proteins are heated above their denaturation temperature, they are denatured and further aggregated, a process that causes a significant increase in the viscosity of protein-stabilized oil-in-water (O/W) emulsions, and thus a decrease in emulsion stability. In addition, protein-stabilized emulsion foodstuffs are also treated by freezing, where low-temperature treatment may lead to denaturation of the proteins and a series of physicochemical changes occur during the freezing process, mainly involving phase transitions, changes in interfacial properties, and disruption of microstructures as a result of temperature changes.

Assessing emulsion stability

Evaluating emulsion stability is essential for understanding the physicochemical properties that influence the performance and shelf life of emulsion-based products. Key parameters assessed include emulsification activity, emulsion stability, surface hydrophobicity, droplet size, zeta potential, contact angle, and rheological properties, among others.

Emulsifying activity and emulsion stability

The emulsification activity index (EAI) and emulsion stability index (ESI) are key indicators of emulsifier performance in emulsion systems. The EAI measures the rapid adsorption capacity of surfactants at the water-oil interface, reflecting their ability to reduce interfacial tension effectively (Cao et al., 2024; Tian et al., 2023).

The ESI evaluates the ability of surfactants, including proteins, to adsorb at the water-oil interface, stabilize the emulsion, and prevent droplet coalescence (Han et al., 2024). These indices are particularly important for assessing the suitability of natural emulsifiers, such as proteins, in food products like milk, yogurt, and ice cream. Generally, higher EAI and ESI values indicate better emulsification activity and emulsion stability, respectively, making them valuable metrics for comparing the performance of emulsifiers to create stable emulsions (Wang, Li, Chen, Fu, & Liu, 2022).

Surface hydrophobicity

Hydrophobicity refers to the tendency of non-polar substances to aggregate in an aqueous environment. This property arises because nonpolar solutes in water are energetically driven to minimize contact with polar water molecules, leading to aggregation. Surface hydrophobicity, a critical parameter in emulsion science, can be measured using fluorescence spectroscopy with probes such as 1-naphthylamine naphthalene-8-sulfonic acid (ANS) and cis-naphthalenesulfonic acid (CPA) (Zhang et al., 2021). Investigations have demonstrated that the hydrophobic character of particles used as emulsifiers is crucial for the stability of oil-water emulsions. Where Hydrophilic-Lipophilic Balance (HLB value) reflects the degree of balance between hydrophilic and hydrophobic groups in the molecule. Particles exhibiting moderate hydrophobicity in certain areas are particularly effective as emulsifiers, thereby improving the stability of the emulsion (Maaref, Kantzas, & Bryant, 2019). urface hydrophobicity plays an important role in determining the physicochemical properties and stability of emulsions. For instance, when peanut proteins are hydrolyzed to prepare stabilized emulsions, the surface hydrophobicity of the resulting peptides decreases significantly. This sharp reduction in surface hydrophobicity destabilizes protein-stabilized emulsions (Zhang & Lu, 2015). Surface hydrophobicity is closely related to the interfacial tension at the droplet surface. Higher surface hydrophobicity usually leads to higher interfacial tension, which enhances the emulsification process and improves emulsion stability. In addition, for hydrophobic-hydrophobic interactions, the surface of the oil droplet usually exhibits hydrophobicity in emulsion systems. When oil droplets are dispersed in a continuous phase (e.g., aqueous phase), hydrophobic-hydrophobic interactions encourage the oil droplets to move closer to each other to reduce the contact area with the aqueous phase, thus lowering the free energy of the system. This interaction is important for emulsion stability because it can effectively inhibit the aggregation and merging of oil droplets, thus enhancing the stability of emulsions. For example, Xie et al. prepared Pickering emulsions stabilized by complex particles with pea isolate protein-zearaldehyde soluble protein (PPI-Zein) through hydrophobic interactions with good storage stability (Xie et al., 2024).

Droplet size

Droplet size is a critical parameter for assessing emulsion stability. One of the most common methods for evaluating emulsion stability involves monitoring changes in droplet size over time. This approach reflects the significant influence of droplet size on gravity-driven separation processes in emulsions. Larger droplets tend to flocculate or settle more rapidly, negatively impacting emulsion stability (Shao et al., 2020). Conversely, for high bulk density emulsions or high internal phase emulsions, larger droplets can be stabilized. Methods for determining emulsion droplet size include particle size analyzing techniques such as diffraction-based particle sizing, Coulter counters, optical microscopy, and electron microscopy (Zhang et al., 2023). Laser diffraction-based particle sizing and optical microscopy are among the most commonly used techniques to measure droplet size.

Zeta potential

The zeta potential represents the electrostatic potential at the interface between a moving droplet or particle and the surrounding continuous phase. It is measured using methods such as electrophoresis, electroosmosis, and electroacoustics (Bommakanti et al., 2022). Zeta potential serves as an indicator of the surface charge density of proteins, polysaccharides, and other charged molecules solution. Zeta potential data can be complemented by information from other methods, such as X-ray analysis, adsorption isotherms, and Fourier-transform infrared spectroscopy, to better characterize the surface properties of materials (Mohammadi-Jam, Waters, & Greenwood, 2022). The zeta potential of droplets and particles is determined by the type and concentration of surface charges and ions in the surrounding medium, which significantly influences emulsion stability (Collini & Jackson, 2023). The evaluation of emulsion stability has shown that the zeta potential is influenced by a variety of contributors, including surfactants, hydroxide ions, and functional groups such as carboxylates, amides, and sulfates. These factors enhance the stability of oil-in-water emulsions by increasing the surface charge of the droplets. Higher surface charges prevent droplet coalescence, resulting in greater stability, whereas lower surface charges allow droplets to attract, aggregate, and grow in size, leading to less-stable emulsions. It has been reported that rice bran protein-catechin complex-stabilized emulsions exhibit significantly higher zeta potential magnitude, leading to greater electrostatic repulsion compared to those stabilized by rice bran protein alone, thereby enhancing emulsion stability. When the catechin concentration in the complex was increased to 0.15 % (w/v), the zeta potential nearly doubled, resulting in the highest observed stability (Li et al., 2020).

Contact angle

The contact angle is an important parameter for assessing particle wettability, reflecting the balance between hydrophilicity and hydrophobicity. It serves as an effective indicator of emulsification efficiency, emulsion stability, and the type of emulsion formed (W/O or O/W), particularly for Pickering emulsions (Erbil, 2021). When the contact angle (θ) of solid particles is 0° or 180°, they exhibit extreme hydrophilic or hydrophobic properties, respectively, preventing the formation of stable emulsions. At θ < 90°, the particles are hydrophilic and tend to sink into the aqueous phase, favoring the formation of O/W emulsions. Conversely, at θ > 90°, particles are hydrophobic, favoring the formation of W/O emulsions (Sun et al., 2022). W/W emulsions formed by mixing polyethylene oxide (PEO) and dextran (DEX) are stable only when the contact angle with the continuous phase is less than 90°, confirming the hypothesis that the contact angle can indeed be a determining factor in the stability of W/W emulsions (Meng & Nicolai, 2023). Natural proteoglycan complexes (PPCs) extracted from mushroom roots have also proven to be highly effective stabilizers for high-internal-phase emulsions (HIPEs). PPCs possess excellent amphiphilic properties, with a triple-phase contact angle close to 90°, enabling superior long-term storage stability, heat resistance, and suitability for 3D printing applications (Zong et al., 2022).

Rheological properties

Rheological methods are commonly used to quantify the interactions between components in emulsions. Food manufacturers routinely assess parameters such as apparent shear viscosity, modulus of elasticity, and yield stress, which are derived from stress-shear or stress-strain curves (Yang et al., 2022). Viscosity data provide insight into how emulsions behave under static (storage) and dynamic (processing, such as shear) conditions. Emulsion viscosity is known to be shear dependent. Niu et al. observed that emulsions containing xanthan gum exhibited significantly higher viscosity at low shear rates with increasing xanthan gum concentration. At high shear rates, however, shear-thinning effects dominated, reducing xanthan gum's impact on viscosity (Niu et al., 2023). The viscoelastic properties of emulsions are typically expressed as elastic (G′) and viscous (G″) moduli. For most emulsions, G″ exceeds G′ across all frequencies, indicating predominantly fluid-like behaviour. Xanthan gum and similar hydrocolloids are widely used in O/W emulsions to modulate viscosity (Meng, Nicolai, Benyahia and Nicol, 2022). Yan et al. investigated the rheological properties of Pickering emulsions stabilized by soybean protein isolate nanoparticles, focusing on the effects of tea saponin concentration and the order of its addition. They observed that as the tea saponin concentration increased, the G′ value of Pickering emulsions decreased slightly, and the gap between G′ and G″ gradually increased. This indicated that the emulsions retained a predominantly fluid-like consistency. When the tea saponin concentration reached 1.0 %, the G′ value stabilized, suggesting the formation of a uniform and stable emulsion structure (Yan et al., 2022).

Methods for improving emulsion stability

Emulsion stability is critical to ensuring that products maintain their performance, quality, and safety throughout production, storage, and use. Instability, such as phase separation or ingredient degradation, can compromise product safety and limit the emulsion's suitability for various applications. As a result, developing strategies to enhance stability is essential.

Emulsion stabilization using emulsifiers

In O/W emulsions, an “emulsifier” is an amphiphile that adsorbs onto the surface of oil droplets to reduce interfacial tension and prevent droplet coalescence. Emulsifiers commonly used in the food industry include proteins, polysaccharides, phospholipids, and small-molecule surfactants (McClements & Gumus, 2016). Ideally, natural emulsifiers should have the ability to quickly adsorb to the surface of oil droplets generated during homogenization, significantly reduce oil-water interfacial tension (thereby promoting droplet fragmentation), and form a protective coating (to inhibit droplet coalescence within the homogenizer). For example, phospholipids are amphiphilic molecules derived from plantand microbial cell membranes. Its high surface activity is attributed to its combination of hydrophilic and hydrophobic properties, which enables it to adsorb at the oil-water interface and stabilize oil droplets. The phospholipid-based functional ingredient used as an emulsifier in commercial products is often referred to as lecithin, which can be isolated from a variety of biological sources, the most common of which include soy, egg, milk, and rapeseed (Thy, Duy, & Dat, 2025). It stabilizes emulsions through mechanisms such as the reduction of interfacial tension, formation of interfacial films, and electrostatic repulsion. For example, researchers have used flaxseed oil and soy lecithin or saponin to prepare oil-in-water emulsions thickened with modified starch and have shown that lecithin-stabilized emulsions display a greater negative charge (Quezada, Urra, Mella, Zúñiga, & Troncoso, 2024). In addition, the compatibility of the hydrophobic tail of the emulsifier with the fatty acids in the oil phase is one of the most important factors affecting the stability of the emulsion. The hydrophobic tails of the emulsifier can interact with the fatty acids in the oil phase to construct a stable interfacial film through van der Waals forces and hydrophobic interactions. This compatibility not only affects the adsorption behaviour of the emulsifier at the oil-water interface but also determines the particle size distribution of the emulsion and its long-term stability. Therefore, when selecting emulsifiers, the structural characteristics of their hydrophobic tails should be fully considered to ensure their compatibility with specific oil phases to achieve efficient emulsification and guarantee the long-term stability of emulsions.

Stabilized emulsions using biopolymers

There is an increasing interest in incorporating biopolymers into emulsions to enhance their stability. Biopolymers can modulate emulsion stability through several key mechanisms. First, unadsorbed macromolecules create steric hindrance within the emulsion, acting as physical barriers that reduce direct contact and collisions between droplets. Second, the electrostatic repulsion between droplets with the same electric charge prevents aggregation and maintains dispersion. Finally, hydrophilic macromolecules adsorbed at the droplet interface form a stabilizing layer, creating a stable spatial structure that further improves the emulsion stability. They can also regulate the viscosity of the external phase, thus inhibiting the movement and coalescence of oil droplets. On the other hand, biopolymers can also be used as thickeners or gelling agents to further improve the rheological properties of the emulsion system and to prevent the incorporation of oil droplets (Zembyla et al., 2020). Common biopolymers used for stabilization include proteins, polysaccharides, and other related compounds (Tamang et al., 2022).

Stabilizing emulsions using protein

Proteins are widely used to stabilize emulsions due to their amphiphilicity and unique surface-active nature. as shown in Fig. 2. By forming a thick adsorption layer at the droplet interface, proteins prevent oil droplets from aggregating or coalescing, thereby stabilizing the emulsion (Liu, Wu, Zhang, Yan, & Mao, 2024). The composition and physicochemical properties of proteins determine their ability to stabilize emulsions. In protein-stabilized emulsion systems, stability is achieved when sufficient protein molecules adsorb to droplet surfaces, forming a protective interfacial layer (Li, Geng, Tan, Teng, & Li, 2024). The structure and characteristics of this adsorbed layer at the interfaces are key factors in determining the effectiveness of proteins in stabilizing emulsions (Cai et al., 2023). Various proteins, including caseins, whey proteins, egg proteins and plant proteins are used in food industry as emulsifiers. Due to their different structures and properties, they stabilize emulsions through different modes of action. For example, casein tends to form a thick and low-viscoelastic interfacial layer that effectively stabilizes oil droplets, mainly due to its low hydrophobicity and high electrostatic charge (Kim, Wang, & Selomulya, 2020). The emulsification properties of casein are closely related to its structural arrangement and interfacial conformation at the oil-water interface, which is influenced by its micellar or sub-micellar coalescence behaviour in the aqueous phase (Yan et al., 2024). it is shown that all four types of casein could adsorb at the oil-water interface, forming interfacial layers with varying thicknesses. For instance, αs1-casein formed an interfacial layer with a thickness of 5.4 nm, while β-casein formed a significantly thicker interfacial layer of 11.1 nm. In emulsions stabilized by casein, the interfacial layer was found to consist of two distinct regions: a densely packed, protein-rich inner layer and a thinner, less dense outer layer. Notably, emulsions exhibiting high interfacial elasticity correlated with improved stability. Li, et al.et al. observed that casein type also significantly affects stability. At 1.5 % and 2.5 % concentrations, Recombined Dairy Creams (RDCs) containing micellar casein concentrates (MCCs) generally exhibited larger particle sizes compared to recovered milk creams (RDCs) containing CaC (calcium caseinate) NaC (sodium caseinate), but they exhibited higher stability (Li, Li, et al., 2020).

Fig. 2.

a: Whey isolated proteinaceous (WPI) fiber stabilized emulsion; b: Spatial repulsion conformation between protein layers adsorbed at the oil-water interface of emulsion droplets: “chain,” “loop,” and “tail” conformations (Liu, Wu, Zhang, Yan, & Mao, 2024).

Animal proteins, while effective as emulsifiers, often have higher production costs and environmental impacts. To address these challenges, plant-based proteins (e.g. soy, pea, and corn zein) have been developed as sustainable and cost-effective alternatives. Their ability to form stable films at the oil-water interface makes them suitable for use as emulsifiers and stabilizers (Kim et al., 2020). The emulsifiability of soy, potato, pea, and whey proteins has been investigated, with soy protein-stabilized emulsions forming the smallest droplet sizes under the tested conditions Fig. 3. These emulsions also exhibited the highest emulsion consistency and continuous phase viscosity, suggesting that soy protein can play a dual role as an emulsifier and a thickener. Such properties highlight its potential for applications requiring viscous emulsions, although the choice of protein may ultimately depend on specific formulation needs (Krstonošić, Kalić, Dapčević-Hadnađev, Lončarević, & Hadnađev, 2020). The properties of plant protein-based emulsions are highly influenced by factors such as pH, ionic strength, temperature, and preparation methods, as these parameters affect the structure of proteins at the oil-water interface (Lima, Stephani, Perrone, & de Carvalho, 2023). For example, Othmeni et al. found that treatment of pea protein at pH 5 during preparation was the least effective in stabilizing the emulsion compared to untreated pea protein (Othmeni, Blecker, & Karoui, 2025).

Fig. 3.

upper left: The particle size distribution of oil-in-water emulsions containing 4 % of different proteins on protein native pH value and pH 9.0 and 15 % of oilDown on the left: Creaming index values of potato, whey and pea protein stabilized emulsions A) at different protein concentration and B) at different oil phase concentration Right A, B: Images of pea protein stabilized emulsions (4 % protein concentration) at: A) native pH and B) pH 9.0 at different oil concentrations: a) 5 %, b) 15 %, c) 30 %, after storage for 7 days (Reproduced from Krstonošić et al., 2020).

Stabilizing emulsions using polysaccharides

Some polysaccharides are widely used in the food industry for their ability to stabilize emulsions. as shown in Table 1. Their amphiphilic nature allows them to adsorb at the oil-water interface, with hydrophilic polysaccharide chains anchored in the aqueous phase and hydrophobic groups (e.g. methoxyl and acetyl groups) oriented toward the oil phase (Hu, Jiang, Du, & Meng, 2023). This self-arranging behaviour at the interface contributes to their effectiveness in preventing phase separation and maintaining emulsion stability (Lv et al., 2024) Fig. 4a. This arrangement reduces the van der Waals forces between oil droplets, thereby effectively preventing their coalescence. Certain natural polysaccharides, such as gum Arabic, pectin, and galactomannans, contain proteins or non-polar groups within their hydrophilic carbohydrate chains, which impart emulsifying properties (Zhang et al., 2020). Studies have shown that water-soluble soybean polysaccharide (SSPS) is a naturally occurring emulsifier and can be used as a stabilizer for O/W emulsions. SSPS stabilizes emulsions by adsorbing onto the surface of oil droplets, where its protein components contribute to forming a stabilizing film. The polysaccharide component of SSPS plays a key role in extending its hydrophilic portion into the aqueous phase, forming a hydrated layer around the oil droplets. This layer creates a spatial barrier on the particle surface, effectively preventing flocculation and agglomeration (Udomrati et al., 2020).

Table 1.

Cases of polysaccharide stabilized emulsions.

Biopolymers	primary role	Main findings	bibliography
Chitosan (CS)	Emulsification/ thickening	Modified chitosan improves the spatial site resistance, increases the viscosity of the continuous phase, improves the electrostatic stability, and the prepared O/W emulsion maintains the encapsulation efficiency of hesperidin >80 %	(Dammak & José do Amaral Sobral, 2018)
Sodium alginate (SA), carboxymethyl cellulose (CMC), pectin (PC), gum arabic (GA)	emulsification	The 0.5 % SA stabilized emulsion remained stable for 4 h after 6 h by microchannel emulsification.	(Tan, Nakajima, & Tan, 2018)
Tea polysaccharides (TPS)	emulsification	0.1 wt% TPS resulted in a lipid digestibility of 88.6 ± 5.8 % and inhibited droplet flocculation. In addition, 0.1 wt% TPS significantly improved the bioaccessibility of lycopene.	(Wang et al., 2023)
Chitosan (CH)-Corn Fiber Gum (CFG)	emulsification	The synergistic effect of CH and CFG in stabilizing emulsions at pH 4 leads to the formation of a three-dimensional droplet network in the emulsion, which can improve the stability of emulsions	(Wang et al., 2022a)
Locust bean gum (LBG) - κ-carrageenan gum (KCM)	emulsification	KCMs+LBG (0.2–0.5 wt%) stabilized emulsions remained stable after 3 consecutive freeze-thaw cycles.	(Jiang et al., 2024)
Corn Starch (HCS)	emulsification	Corn starch stabilized emulsion > emulsion of high straight chain corn starch > emulsion of glutinous corn starch. And the corn starch emulsion remained stable after 90 d of storage	(Guo et al., 2020)
Sodium alginate (ALG)	emulsification	The optimal concentration of ALG was 0.35 wt%, and wrapping the oil body with ALG significantly improved the stability of the emulsion against freeze-thaw cycles.	(Su et al., 2018)
Agarose (A-MG)	emulsification	A-MG with an agarose concentration of 2 % builds an interfacial film on the surface of oil droplets, which avoids the aggregation of oil droplets and improves the stability of the emulsion.	(Jiang et al., 2023)
Pomegranate peel pectin	emulsification	When the concentration of pectin is increased to 2.0 %, stable emulsions containing 50 % oil phase can be obtained. In addition, pectin has good emulsion stability at pH 2.0–6.0 and good resistance to Ca2+ and Na+.	(Yang et al., 2018)

Fig. 4.

a: Mechanism of emulsion stabilization by okra polysaccharides b: Oil droplets encapsulated by natural proteins and protein-polysaccharide couplers (Lv et al., 2024; Nooshkam & Varidi, 2020).

These researchers demonstrated that polysaccharides, such as sodium carboxymethyl cellulose, sodium alginate, high-methoxyl pectin, and low-methoxyl pectin, have structural properties that can emulsify and stabilize high-internal-phase emulsions (HIPEs) by forming a 3D mesh-like membrane structure. This stability can be attributed to the tight wrapping of oil droplets by the mesh membrane and their interconnection through the branched chain structure of the polysaccharides. The branched chains contribute to steric hindrance, preventing oil droplets from approaching too closely. This effect reinforces the stability of the interfacial membrane networks. Additionally, these branched chains act as structural linkers within the continuous phase, increasing its viscosity. Polysaccharide molecules further enhance stability by creating spatial resistance through the formation of a protective layer on the surface of oil droplets, which prevents coalescence during collisions. For instance,

Chitosan is a positively charged polysaccharide. Stabilizes O/W emulsions through spatial stabilization mechanisms (Udomrati et al., 2020). Liu et al. compared the interfacial properties and molecular structure of pectin in emulsions formed by various pectin derivatives, including unmodified or native pectin, apple pectin, and citrus pectin. Their findings revealed that native pectin significantly outperformed apple pectin and citrus pectin in emulsification properties, primarily due to its lower interfacial tension (15.57 mN/m). Emulsions prepared with native pectin exhibited higher viscosity, more uniform droplet size distribution, stronger electrostatic repulsion, and thicker interfacial layers. At the molecular level, the emulsifying ability of native pectin was attributed to its acetyl and methyl groups, while its stability was linked to monosaccharide side chains and ionized carboxyl groups (Liu et al., 2022). Interactions between polysaccharides can be used to stabilize emulsions by forming interpenetrating network structures that enhance the strength and stability of the interfacial layer. Liu et al. studied a mixture of psyllium polysaccharide and citrus pectin as an emulsifier and found it to be the most effective at a 1:1 mass ratio. Citrus pectin improved the dispersion of oil droplets, while psyllium polysaccharide modulated the emulsion's fluidity, restricted droplet movement, reduced droplet coalescence, and provided electrostatic repulsion. Collectively, this mixture substantially enhanced emulsion stability (Liu, He, Huang, Yin, & Nie, 2024).

Emulsion stabilization using protein-polysaccharide complexes

Proteins and polysaccharides often coexist in food, and in emulsion-based formulations, they interact with each other in the continuous phase as well as on the surface of emulsified droplets (Liu et al., 2022). As shown in Table 2, These interactions can be classified as non-covalent or covalent, with binding mechanisms that include physical interaction, chemical cross-linking, enzymatic cross-linking, and the Maillard reaction (Wu et al., 2024). Studies have shown that covalent bonding between proteins and polysaccharides results in stable complexes with improved rheological properties, emulsification, foaming, and thermal stability compared to proteins or polysaccharides alone (Nooshkam & Varidi, 2020) Fig. 4b. Covalent binding interactions are primarily achieved through protein glycosylation during the initial phase of the Maillard reaction (Ke, Zhang, Yang, & Li, 2024). In most cases, non-covalent binding arises from electrostatic interactions, a phenomenon known as complex coacervation, as proteins and polysaccharides typically exist as charged molecules in solution. The resulting complex coacervates are widely applied to stabilize hydrophilic-hydrophobic interfaces, such as oil-water and air-water interfaces (Babu, Shams, Dash, Shaikh, & Kovács, 2024). Li et al. prepared glycosylated (conjugated) products from soybean isolate protein/peptide (SPI/SP) and ginseng polysaccharides (SP) and used them as emulsifiers in emulsions. These conjugates had a loose/flexible structure, which enabled their rapid and stable adsorption at the oil-water interface, outperforming non-glycosylated complexes. SP-GP conjugates showed excellent emulsification performance across various pH conditions. Emulsions stabilized by these conjugates had smaller, more uniform droplet sizes, higher magnitude of zeta potential, and resisted gravity separation during storage. The emulsions stabilized by SP-GP conjugates showed lower POV and TBARS values, indicating improved oxidative stability. The type of polysaccharide used in conjugates influences their interfacial properties, thereby affecting their emulsification performance (Li, Wang, et al., 2024). Shi et al. evaluated the efficacy of sodium alginate (SA), xanthan gum (XG), and acacia gum (AG) for stabilizing soybean protein nanofiber (SPIF)-based emulsions. SA reduced interfacial tension and enhanced emulsification properties. Under acidic conditions, SPIF-SA emulsions outperformed SPIF-AG and SPIF-XG, showing smaller particle sizes, higher zeta potential, and uniform droplet distribution Fig. 5. These polysaccharides improved the electrostatic interactions at the interface, thereby enhancing the stability of the emulsions (Shi, Cao, Li, & Yang, 2024).

Table 2.

Summarizing the emulsion stability of protein-polysaccharide complexes prepared by different binding modes.

Protein source	Sources of polysaccharides	cohesion pattern	conclude	Enhanced Stability Type	bibliography
Pea isolate protein (PPI) (solution)	Beet pectin, gum arabic (GA), guar gum, gellan gum(solution)	noncovalent binding	Pectin-PPI and GA-PPI complexes were mixed in a 1:1 ratio, and emulsions stabilized with pectin showed stability at both pH 8.0 and pH 4.5, whereas emulsions stabilized with GA only showed significant aqueous phase separation after 28 days of storage	Physical and chemical stability (pH, storage stability)	(Guldiken, Saffon, Nickerson, & Ghosh, 2023)
Soybean isolate protein (SPI), pea isolate protein (PPI), mung bean isolate protein (MPI) (solution)	Xanthan Gum (XG) and Gellan Gum (GG) (solution)	noncovalent binding	The particle size of SPI and MPI emulsions is smaller than that of PPI emulsions. SPI group has the best emulsification activity index and emulsion stability index, especially GG-SPI, GG can stabilize the large interfacial area.	physical stability	(Zhang, Liang, & Li, 2022)
Rice protein (RP) (solution)	Gum Arabic (GA) (solution)	noncovalent binding	The ability to stabilize oil-in-water emulsions was demonstrated by 0.4 or 1.0 wt% GA (RP:GA mass ratio of 1:0.4 or 1:1.0) in the mixtures at pH 3.0 or 5.0.RP:GA emulsions were stored without degreasing or coalescing for at least 21 days.	Physical and chemical stability (pH, storage stability)	(Igartúa, Dichano, Morales Huanca, Palazolo, & Cabezas, 2024)
Whey Protein Isolate (WPI) (solution)	Polysaccharide (TLH-3) (solution)	noncovalent binding	Oil-in-water emulsion stabilized by whey protein-polysaccharide complexes and successfully loaded with lycopene. Lycopene was more stable in the emulsion-based nanofibers with better photostability and thermal stability.	Storage stability (light stability, heat stability)	(Chen et al., 2026)
Whey Protein Isolate (WPI) (solution)	Prickly pear fruit polysaccharide (RTFP) (solution)	covalent binding	WPI-RTFP was prepared at a mass ratio of 1:1 (final protein concentration of 5 mg/mL). the WPI-RTFP coupling showed good EAI and ESI. and the encapsulated emulsion had enhanced antioxidant properties.	antioxidant properties	(Yu-Tong, Chun, Yue-Ming, Bao and Xiong, 2022)
Whey Protein Isolate (WPI) (solution)	Citrus peel pectin (CP) Apple pomace pectin (AP) Sugar beet pectin (SBP) (solution)	covalent binding	The EAI and ESI of the couplings were significantly higher compared to the mixtures.The best EAI and ESI were obtained for WPI-HG, with an increase in EAI from 901.61 m2/g to 1729.63 m2/g and ESI from 11.1 min to 215.5 min.	Storage stability	(Hou, Fu, Chen, & Niu, 2024)
Soybean isolate protein (SPI) (solution)	Hydroxypropyl Methyl Cellulose (HPMC) Xanthan Gum (XG) (solution)	noncovalent binding	SPI-XG stabilized emulsions have high storage, thermal and ionic stability	Storage stability, thermal stability, ionic stability	(Li, Geng, et al., 2024)
Hemp isolate protein (HPI) (solution)	Gum Arabic (GA), Sodium Alginate (SA), Pectin (NP) (solution)	noncovalent binding	Hemp oil and HPI-GA composite prepared emulsions with smaller particle size, less creamy layer and higher stability during storage. The ectopic formation of the composite condensate provided better thermal and salt stability.	Storage stability, temperature stability, ionic stability	(Liu, Xue, & Adhikari, 2023)
Soybean isolate protein (SPI), sodium caseinate protein (SC) (solution)	Isoflavone tree seed gum (AHSG), carrageenan (kC) (fine powder)	covalent binding	HIPEs prepared with SC-type conjugates had lower emulsification indices and oil removal rates than HIPEs prepared with SPI-type conjugates over a 21-day storage period;	Storage stability	(Tirgarian, Farmani, Farahmandfar, Milani, & Van Bockstaele, 2022)

Fig. 5.

Left:Mean diameter (a), ζ-potential (b), EAI (c) and ESI (d) of SPIF and SPIF- polysaccharide complexes emulsions at different oil fraction volumes.Right:Microscopy pictures of SPIF and SPIF- polysaccharide emulsions at different oil fraction volumes (scale bar: 50 μm) and emulsion appearance (upper right, left, 0 day; right, 2 day) (Shi et al., 2024)

Emulsion stabilization using solid particle

Pickering emulsions are multiphase systems stabilized by solid particles that adsorb at the liquid-liquid interface, offering controllability and high stability (Hei et al., 2025). In contrast, conventional emulsions rely on small-molecule surfactants as emulsifiers, which stabilize emulsions by lowering interfacial tension and inducing electrostatic repulsion. However, synthetic surfactants are increasingly less preferred by consumers (Liu, He, Huang, Yin, & Nie, 2024).

Pickering emulsions are stabilized through three primary mechanisms: particle adsorption at the oil-water interface, network formation, and steric hindrance (Tian et al., 2024) Fig. 6. Various colloidal particles obtained from natural substances, including protein, polysaccharide, polyphenol, and their complexes, have shown that they can effectively stabilize Pickering emulsions (Najari, Dokouhaki, Juliano, & Adhikari, 2024). While single protein particles have limited stabilizing ability, they can interact with polysaccharides and polyphenols to form complex Pickering particles with better emulsifying properties. The application of nanosized Pickering particles has been shown to significantly improve the stability of Pickering emulsions(Yan, Regenstein, Qi, & Li, 2023).

Fig. 6.

left: Schematic representation of adsorption and deformation of plant protein Pickering particles at the oil-water interface. Right: Schematic representation of the 3D network structure formed by excess plant protein Pickering particles in Pickering emulsion. Mechanism of depletion stabilization of protein fibers (Tian et al., 2024).

Protein-polysaccharide complexes for stabilizing pickering emulsions

For particles to function as effective Pickering stabilizers, they must maintain structural integrity at the interface and achieve a balance between hydrophobicity and hydrophilicity (Wang, Li, et al., 2022). In this regard, protein-polysaccharide complexes fare better, as the complexation of proteins with polysaccharides modulates hydrophilicity and enhances interfacial properties, making them suitable for Pickering stabilization(Wu et al., 2022). Because particle adsorption at the interface is irreversible, Pickering emulsions exhibit greater stability than conventional emulsions (Xia, Xue, & Wei, 2021). Li et al. investigated the stability aspect of Pickering emulsions using chitosan (CS)-barley wheat (HBG) alkyd protein complexes and found that the electrostatic interactions within the complexes enhanced their solubility and surface wettability. Emulsions stabilized by these complexes showed excellent rheological properties, as well as thermal and storage stability when tested at pH 4.0, a chitosan-to-protein concentration ratio of 1:40, and an oil fraction of 50 %. After 30 days of storage, the emulsion remained phase-separated. This is attributed to the strong interaction between Cs and HBG (Li et al., 2024). Pickering particles can be more stably adsorbed at the oil-water interface, forming a dense protein structural layer, which effectively isolates the oil from oxidation caused by the external environment, such as oxygen and light Fig. 7. Moreover, Pickering emulsion gels are also emerging as effective delivery systems for bioactive compounds. Yan et al. investigated the stability of Pickering emulsions using pea protein isolate (PPI), PPI microgel particles (PPIMP), a mixture of PPIMP and sodium alginate (PPIMP-SA), and PPIMP-SA complexation. The results showed that the PPIMP-SA complexation formed a thick, robust interfacial layer around the oil droplets, enhancing the emulsion's resistance to coalescence and environmental stresses, including heat, light, and freeze-thaw cycles (Yan, Peng, et al., 2024). Additionally, emulsions stabilized by PPIMP-SA complexes significantly enhanced the photothermal stability of hydrophobic bioactive compounds. Pickering emulsions stabilized by protein microgels and protein-polysaccharide complexes have shown promising potential as animal fat substitutes. For instance, rapeseed protein-xanthan gum-based Pickering emulsions have been shown their potential to replace fat in meat products (Rezaee & Aider, 2023).

Fig. 7.

Left:Effect of thermal sterilization treatments (65 °C for 30 min and 90 °C for 3 min) on the particle size (D4,3) of Pickering emulsion prepared by Cs-HBG complex under different pH (A, D), concentration ratios (B, E) and oil fractions (C, F), respectively. The HBG concentration was 0.5 % (w/v), without NaCl. Right:The appearance of Pickering emulsion prepared by Cs-HBG complex under different pH, concentration ratios and oil fractions after storage at 4 °C for 1 day, 3 days, 7 days, 14 days and 30 days, respectively. The HBG concentration was 0.5 % (w/v), without NaCl (Li et al., 2024).

Protein-polyphenol complexes for stabilizing pickering emulsions

Phenolic compounds are abundantly present in fruits and vegetables and exhibit significant antioxidant properties. Chemically, phenolics are defined by the presence of at least one phenolic hydroxyl group, often linked to aromatic rings or conjugated sugars, which influence their bioactivity and functional properties (Liu et al., 2021). Proteins and polyphenols can interact through covalent and non-covalent mechanisms, and the resulting complex particles contribute to the stability of Pickering emulsions. Covalent conjugates of protein-and phenolic compounds are stable and offer better protection against oxidation (e.g. of unsaturated fatty acids) compared to non-covalent complexes (Li et al., 2021). Binding of proteins with phenolic compounds also imparts their antioxidant capacity, thermal stability, and emulsification properties. Chen et al. prepared bovine serum albumin-polyphenol complexes and used them to stabilize high- internal-phase Pickering emulsions. They found that polyphenols with a higher number of hydroxyl groups in their structure enhanced protein-polyphenol interactions through stronger hydrogen bonding and hydrophobic forces. This complexation extended the protein conformation (making it more flexible), which enabled better adsorption at the oil-water interface and the formation of a dense interfacial layer. The resulting emulsions exhibited improved stability and rheological properties (Chen et al., 2023). Emulsions stabilized by protein-polyphenol complexes can function as delivery systems, effectively encapsulating and delivering bioactive compounds. For instance, they have been used to encapsulate carotenoids, curcumin, and lutein, achieving higher bioavailability and stability for these substances (Alu'datt et al., 2022). Geng et al. prepared microgel particles by covalently conjugating soybean protein isolate and epigallocatechin-3-gallate. These microgel particles stabilized high internal phase Pickering emulsions containing β-carotene, maintaining its stability and bioaccessibility for 42 days Fig. 8. The presence of polyphenols significantly enhanced emulsion stability and carotenoid delivery capacity. This study highlights the potential of protein-polyphenol complexes as valuable ingredients for use as emulsifiers and encapsulating shell materials (Geng et al., 2022).

Fig. 8.

A: Flowchart of the process of SPI-EGCG composite microgel particles. B: a) Creaming index, b) chemical stability of the β-carotene-loaded-HIPPEs during the 42 d of storage at 25 °C C: a) DPPH radical scavenging activity, b) ABTS· + radical scavenging activity of the SPI microgel particles conjugated with different EGCG concentrations. Different small letters indicate significant differences (p < 0.05) (Geng et al., 2022)

Protein-polysaccharide-polyphenol for stabilizing pickering emulsions

Proteins, polysaccharides, and polyphenols can form stable ternary complexes, in which polyphenols play an important role in enhancing the properties of these complexes. By interacting with proteins, polyphenols enhance the hydrophobicity of the complexes, thereby improving surface properties, rheological behaviour, and overall stability (Huang, Luo, Ning, Ye, & Liu, 2024). Similarly, complexing with proteins, polysaccharides enhances protein dispersion, which increases the stability of Pickering emulsions. The presence of polyphenols has also been shown to improve surface wettability and hydrophobicity of proteins (Wang et al., 2022b). These are the reasons why protein-polysaccharide-polyphenol complex particles are preferable in Pickering emulsions. Liu et al. prepared HIPE using pea protein, pectin, and epigallocatechin gallate. The particles of the resulting ternary complex showed suitable surface wettability, the ability to form a stable interfacial layer, and uniformly encapsulated oil droplets, resulting in high Pickering emulsion stability (Liu et al., 2021). Similarly, Feng et al. reported that ternary complexes prepared from pea protein isolate, high-methoxyl pectin, and epigallocatechin gallate effectively stabilized HIPE by forming smaller particle sizes, which contributed to improved emulsion stability (Feng et al., 2022).

Other methods

Nanotechnology-stabilized emulsions

In recent years, there has been renewed interest in creating nanoparticle-stabilized nanoemulsions. This is primarily due to the fact that the physical properties of nanoemulsions distinguish them from larger microscale emulsions. One of the points is that the particle size of the nanoemulsion has a significanteffect on the transparency of the solution. When the particle size of nanoemulsions is 50–200 nm, the emulsions are transparent; when the particle size exceeds 500 nm, they appear milky and turbid. Droplet size and distribution are crucial for emulsion stability (Wang, Anton, Vandamme, & Anton, 2023). The smaller droplet size and narrower size distribution may be the main reasons for the higher stability of the nanoemulsions. Therefore, tiny particles can be obtained by using high pressure equipment. Currently, both high-energy and low-energy emulsification methods can be utilized to create nanoemulsions. High-energy methods include high-pressure homogenization, micro-jetting and ultrasonication (Liu, Wang, Cao, Wu, & Yao, 2025). For example, Yang et al. successfully prepared gel-like emulsions with an ordered interfacial structure using, the pH cycling method, with γ-oligosoluble protein particles as the main components. By adjusting the homogenization pressure (ranging from 0.1 to 120 MPa), the stability, droplet size, microstructure, and rheological properties of the emulsion can be effectively regulated. When using microfluidic homogenization (pressures between 40 and 120 MPa), the emulsions exhibit higher stability and smaller droplet sizes (Yang et al., 2022). These methods involve the use of mechanical devices to reduce droplet size. However, they are not suitable for some heat-sensitive drugs and large molecules. In addition, in some commercial applications, low-energy technologies are favored for their ease of operation and lack of dependence on expensive or complex production equipment, in contrast to high-energy homogenization technologies. Low-energy emulsification techniques are physicochemical in nature and cover a wide range of technologies, including phase inversion temperature (PIT), phase inversion composition (PIC), spontaneous emulsification, and the lesser-known D-phase emulsification (DPE) method. For example, Yao et al. developed a low-energy emulsification method for the preparation of gelatin-stabilized emulsions with low oil-phase volume fractions by stirring only, and revealed that a change in pH improves the emulsification capacity of stirred gelatin (Yao et al., 2024).

Stabilization of emulsions by enzymatic technology

In recent years, the development of enzymes biotechnology has been rapid, in and protein modification has become a key factor in promoting the progress of enzyme technology (Cheng et al., 2025). Enzyme modification is mainly divided into two categories: enzyme hydrolysis modification and non-hydrolysis modification.Various enzymes are widely used for protein modification. After enzyme catalysis, the protein molecular structure is reconfigured, exposing more hydrophobic groups, which enhances the interaction between the protein and oil phase. This alteration optimizes the interfacial properties of the emulsion and significantly improves its stability. This technology mainly utilizes biocatalysts, such as proteases and transglutaminases, to covalently cross-link or controllably hydrolyze proteins. Enzymatic cross-linking induces the formation of a three-dimensional network structure between protein molecules, enhancing the mechanical strength of the interfacial membrane and effectively preventing the coalescence of droplets in the emulsion. For example, Xu et al. crosslinked three types of gelatins with TG enzyme and found that all TG-modified gelatins produced emulsions with smaller droplet sizes than the corresponding unmodified gelatins, and the emulsions stabilized with the TG-modified gelatins were more stable than those stabilized with the corresponding unmodified gelatins. Moderate hydrolysis can expose the hydrophobic groups of proteins, thereby enhancing their adsorption capacity at the interface and reducing the tension at the oil-water interface. Modified proteins can be rapidly anchored to the droplet surface by their amphiphilic peptides (Xu et al., 2022). Gao et al. investigated O/W emulsions co-constructed from soy protein hydrolysate (SPH) prepared by pineapple protease, pepsin, and protease, together with gum Arabic (GA). The results showed that SPH/GA emulsions had smaller particle size, higher negative charge, higher interfacially adsorbed protein content, and more stable emulsion systems than unhydrolyzed SPI/GA emulsions (Gao, Chen, Chi, Li, & Teng, 2024). Compared with traditional chemical modification methods, the enzymatic method has the advantages of mild reaction conditions, fewer by-products, and high specificity, providing an efficient solution for developing highly stable emulsion products with clean labels.

Applications of emulsions in the food sector

Emulsions have a wide range of applications in the food industry, acting mainly as stabilizers, thickeners, and flavor carriers. They optimize the texture of food products, extend their shelf life, and effectively disperse fats and water-soluble ingredients for homogeneous mixing. As shown in Fig. 9, they are widely used in sauces, ice cream, beverages, and spreads.

Fig. 9.

Application of emulsions in in various food products.

Cryogenic foods

Ice cream is a frozen aerated emulsion composed of immiscible water and fat phases, stabilized by emulsifiers (Hei et al., 2024). Its structure consists of fat droplets, an unfrozen viscous emulsion, ice crystals, and small air bubbles. Typically, ice cream contains 10–16 % fat, which plays a crucial role in its physicochemical properties, such as melting resistance, shape retention, and smoothness after freezing. During production, the cream (fat) and water phases are homogenized to achieve uniform dispersion of fine particles within the ice cream matrix. This dispersion stabilizes the emulsion, ensuring a smooth texture and preventing the separation of fat (oil) and water phases during storage (Akbari, Akbari, Eskandari, & Davoudi, 2019). Gao et al. developed an effective fat substitute for ice cream using a low-oil Pickering emulsion gel. Ice cream formulated with this fat substitute exhibited the lowest melt rate during a 45-min melt test and demonstrated desirable thermal stability under practical conditions. It also showed remarkable stability in the presence of various ions from commonly used salts. This stability contributed to the appealing sensory properties of the low-oil Pickering emulsion gel. Additionally, freeze-thaw stability, a critical factor for frozen foods, was notably improved.(Gao et al., 2023). Hei et al. heat-treated soy isolate proteins and crosslinked them with transglutaminase (TGase) to generate Pickering particles for the production of stable freeze-thaw Pickering emulsions. Plant-based ice creams prepared with these emulsions stabilized by Pickering particles exhibited desirable texture and improved freeze-thaw stability. Since the mouthfeel of ice cream is closely associated with emulsion stability, its control during the manufacturing process is essential for ensuring product quality and consumer satisfaction (Hei et al., 2024).

Stabilizing cream products

Cream is a stirred and aerated emulsion system, typically prepared by combining fat, hydrophilic colloids, emulsifiers, and water to form an oil-in-water emulsion. This emulsion undergoes mechanical stirring, producing a product with a complex foam structure, where stability is primarily conferred by the interaction of fat crystals at the air-liquid interface. The stability of the cream was evaluated using key parameters such as whipping time, texture, storage stability, foam stabilization time, and microstructural analysis of its cross-section (Zhang et al., 2024). Fat globules in cream partially aggregate as fat crystals form within the droplets, a process that contributes to cream stability when moderated. To further enhance stability, researchers have increasingly turned to plant proteins in recent years. These proteins can be engineered into nanoparticles with tailored shapes, sizes, and stability, offering significant advantages in stabilizing cream products. Liu et al. demonstrated that alcohol-soluble corn protein nanoparticles combined with monoacylglycerides can stabilize emulsions. In their study, the gel network formed by emulsion droplets and air pockets in churned cream was stabilized by these nanoparticles. Alternatively, stabilization was achieved using free nanoparticles instead of relying on the network formed by the agglomeration of oil droplets in conventional products (Liu, Zhao, Shehzad, Wang, & Sun, 2023). Wu et al. developed a novel dairy-free whipped cream using a Pickering emulsion, which avoided the need for hydrogenated vegetable oils. Their study showed that the viscosity of the emulsion increased with higher oil content and protein particle concentration, both of which enhanced the formation of a stronger creamy structure by improving bubble the filling. The texture of the cream was strongly influenced by the stability of the emulsion, which depended on several parameters, including the choice of emulsifier, oil-to-water ratio, mixing method, and selection of additives. These parameters were optimized holistically, resulting in stable cream emulsions with smooth textures and desirable sensory properties (Wu et al., 2023).

Stabilizing salad dressings, sauces, and mayonnaise

Salad dressings are typically oil-in-water (O/W) emulsions, where small oil droplets are dispersed in the aqueous phase. Sauces (e.g. condiments or toppings for various foods) and salad dressings require physical stability to maintain their structural integrity throughout their shelf lives. To achieve this, polysaccharides such as xanthan gum, guar gum, and Arabic gum are commonly added to improve the sensory quality and rheological properties. This is particularly important for low-oil-content products, such as commercially available salad dressings, in which polysaccharides stabilize oil droplets and prevent phase separation. These polysaccharides also compensate for the reduced thickening properties associated with lower oil content in salad dressings (Bindereif, Karbstein, & van der Schaaf, 2023). Mayonnaise is a traditional and commercially successful O/W-type emulsion product that typically consists of oil (70–80 %), egg yolk, emulsifier, vinegar, sugar, and salt (Taslikh et al., 2022). To provide product diversity, Bi et al. developed a plant-based mayonnaise using a pea protein-xanthan gum complex, reportedly achieving a similar appearance, microstructure, and rheological properties to those of traditional mayonnaise (Bi, Bi, Qie, Liu, Gao, & Zhou, 2024).

Beverages

Oil-in-water (O/W) emulsions are widely used in the beverage industry. They typically consist of flavoured or turbid oils as the dispersed phase, water as the continuous phase, and emulsifiers for stability (Devaki & Ghosh, 2024). The commercial viability of emulsion-based beverages depends largely on their ability to maintain physical and chemical stability throughout production, storage, distribution and sales. However, exposure to fluctuating environmental conditions in real-world settings can lead to instability, caused by the loss of ingredient functionality, accelerated chemical degradation, and physical destabilization. Research and innovation are continuing to address these challenges. For instance, recent studies have shown that citrus O/W emulsions with high oil droplet concentrations (up to 20 mL/L) can be successfully stabilized using cellulose as a stabilizer. This highlights the importance of developing novel methods to improve the stability of emulsion-based beverages, considering the environmental conditions encountered during their lifecycle (Shen, Guo, Wu, Zhang, & Abid, 2016).

Conclusion and outlook

Stabilization of emulsions is essential to ensure the quality and shelf life of emulsified food products, as well as to improve the bioavailability of the functional ingredients they contain. This paper focuses on the use of emulsifiers (proteins, polysaccharides, polyphenols, and their complexes) to stabilize emulsions. The application of certain cutting-edge technologies, like nanotechnology and enzyme technology, has gained attention. While numerous natural and synthetic emulsifiers are capable of stabilizing emulsions and are deemed appropriate for use in commercial food products, several challenges persist. For instance, many emulsifiers fail to maintain stability under particular environmental stressors, such as fluctuations in pH, ionic strength, and temperature. This highlights the critical need for the development of innovative emulsifiers and the implementation of novel approaches, which are especially relevant and beneficial to the food industry. In the future, multi-scale simulation technology can be used to systematically reveal the intrinsic mechanism of emulsion stability by integrating computational models at different spatial and temporal scales, and provide theoretical guidance for optimizing emulsifier design and process parameters, such as through the integrated application of molecular dynamics and fluid dynamics. In addition, it is necessary to identifynatural emulsifiers with stronger functionality for certain applications in the food industry. For example, emulsifiers have beeninvestigated for functions such as stabilizing during freeze-thaw processes, protectionactive ingredients from chemical degradation, and achievement of controlled release. Therefore, it remains important for researchers to continue to search for new sources of emulsifiers in nature.

CRediT authorship contribution statement

Tianlong Xiao: Writing – original draft, Software, Methodology, Data curation, Conceptualization. Xiaojie Ma: Visualization, Validation, Supervision. Hui Hu: Project administration, Investigation. Fei Xiang: Supervision, Formal analysis. Xinyu Zhang: Methodology, Investigation. Yichen Zheng: Software, Investigation. Hao Dong: Visualization, Resources. Benu Adhikari: Writing – review & editing. Qiang Wang: Resources, Project administration, Funding acquisition. Aimin Shi: Resources, Project administration, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data will be made available on request.