Active biopolymer films from oil-in-water pickering emulsions for food preservation: a mini review

1 Introduction

Global production of synthetic polymers has grown continuously, increasing from 370.7 Mt in 2018 to 430.9 Mt in 2024 (Plastics Europe, 2025). According to Indian researchers, global plastic production was 2 Mt in 1950 and expanded to 368 Mt in 2019 (Pilapitiya and Ratnayake, 2024). Plastic materials are widely used industrially due to their low density, easy processability, and low cost. Highlighting this, a 2023 study by Brazil’s MaxiQuim reported a 2.5% year-over-year increase in domestic plastic packaging consumption (ABREAssociação Brasileira da Embalagem, 2024). However, when considering the food packaging industry–the main client of synthetic polymers–the disadvantages of synthetic polymers need to be carefully evaluated, mainly because they are generally disposable (single-use) packaging. When improperly discarded into the environment and exposed to physical processes of friction, UV radiation, and oxidation, they form so-called microplastics, which cause a harmful effect on the environment (Nunes et al., 2025).

Packaging is an essential element in food preservation. The development of materials for food preservation is of industrial interest and aligns with United Nations Sustainable Development Goals (United Nations, 2015). In this particular case, biodegradable polymer films have been recommended as an alternative to synthetic polymers. Biopolymers from renewable sources, such as polysaccharides (starch, chitosan, pectins, carrageenans, etc.) and proteins (whey proteins, zein, soy proteins, etc.), form biodegradable films. Conversely, the disadvantages of biopolymers are well known. Biopolymers form hydrophilic films with inadequate mechanical properties and limited long-term stability (Parthipan et al., 2026). To overcome these limitations, polymer blends (Bangar et al., 2021; Surendren et al., 2022) and composites (Cataño et al., 2023; Foret et al., 2023; Zhang et al., 2024) have been successfully developed. Particularly in the case of composites, the development of nanocomposites has garnered the attention of numerous researchers. Compared to single-phase polymer films, polymer nanocomposites exhibit significant improvements in mechanical and thermal properties, gas barrier properties, and UV protection. Inorganic nanoparticles (Bangar et al., 2025; Sutharsan et al., 2025) or organic nanoparticles (Cataño et al., 2023; Ramesh and Preetha, 2024; Zha et al., 2025) have been incorporated into biopolymers with applications in the food industry (Sutharsan et al., 2025) and other industrial sectors (Farhat et al., 2026; Mahajan et al., 2026).

More importantly, the functionality of biopolymer films can be further enhanced by incorporating bioactive substances such as essential oils and plant extracts. In films obtained by solvent casting, the “film-forming solution” becomes an active emulsion. After drying, the resulting films retain antioxidant and antibacterial properties, which are very useful in the case of materials produced for food preservation. In this context, so-called Pickering emulsions have been considered suitable systems for the compatibilization between the added hydrophobic phase (oil) and the hydrophilic matrix (biopolymer). These systems are an alternative for conventional synthetic surfactants, which have been proven to be harmful to human health (Amrani et al., 2023).

In this work, the stabilization of oil-in-water emulsions by the Pickering mechanism and the formation of structured and active films resulting from these emulsions are shortly reviewed.

2 Pickering emulsions

Emulsions are thermodynamically unstable systems composed of two immiscible liquids, typically oil and water. Due to the high interfacial tension between the immiscible phases, certain phenomena can be observed over time, such as phase separation, coalescence, creaming, sedimentation, flocculation, and, for nanoemulsions, Ostwald ripening (Muiz et al., 2023; Singh et al., 2017). Consequently, emulsion stabilization has gathered the interest of researchers and industry for many years (Ru et al., 2026; Wu et al., 2026a) because emulsified systems find widespread applications in numerous technological fields, such as pharmaceuticals, food, cosmetics, oil recovery, and drug delivery (Ortiz et al., 2020). Moreover, these systems need to keep their stability over long periods of time.

In conventional emulsions, the function of low molecular weight surfactants consists in reducing interfacial tension (γ_ow). The adsorption of molecules is dynamic; molecules can migrate from the interface to the oil and water phases. Energy barriers are low; there is a tendency for droplet coalescence and a greater propensity for instability (e.g., under heating or shear) (Sarkar and Dickinson, 2020). By contrast, Pickering emulsion stabilization is characterized by the potentially irreversible adsorption of solid micro- or nanoparticles at the oil-water interface (Ajayi et al., 2025; Dickinson, 2017; Funami et al., 2025). This behavior is attributed to the high energy of desorption (△G_d) associated with the displacement of the particle from the interface. For a spherical colloidal particle of radius r, adhered to the oil-water interface with interfacial tension (γ_ow) and contact angle θ, the energy △G_d required to remove this particle from the interface is expressed by Equation 1 (Dickinson, 2012; Sarkar and Dickinson, 2020).where r is the radius of the spherical particle, γ_αβ is the interfacial tension (γ_ow, γ_wo, depending on whether the emulsion is oil-water or water-oil), and θ is the equilibrium contact angle, associated with the wettability of the particle in the two phases, measured through the water phase.

△ G d , sphere = γ α β π r 2 1 − cos θ 2 (1)

The contact angle θ depends on whether the particle is preferentially hydrophilic or hydrophobic (Dickinson, 2012). As expected, solid particles should have suitable wettability toward both aqueous and oil phases, which means that Pickering emulsions are stabilized by amphiphilic particles. By contrast, the r value for solid particles is typically on the order of tens to hundreds of nanometers, substantially larger than the r value for the average molecular size of conventional surfactants. Consequently, ΔG_d reaches very high values in these cases, compared to the same value in conventional emulsions, which explains the high stability of Pickering emulsions (Dickinson, 2012).

It is noteworthy to emphasize that Pickering systems, besides enabling emulsion physical stability and controlled release of bioactive substances, also represent a protection barrier against environmental stimuli, such as temperature, oxygen, and light, to which bioactive molecules are highly susceptible (Cheng et al., 2024).

2.1 Pickering emulsions stabilizing agents

Encapsulation of bioactive substances in the oil phase of Pickering emulsions has attracted widespread attention. Inorganic- and organic-based particles have been used as stabilizing agents for Pickering emulsions. Inorganic particles (SiO₂, TiO₂, Ag, etc.) were the first to be used as emulsion stabilizing agents. Because of their non-amphiphilic character, they are used after surface chemical modification or in mixtures with appropriate substances. Silica nanoparticles are considered a classic emulsifier because of their chemical stability and the ease with which their surface can be chemically modified. Some authors mixed hydrophilic silica nanoparticles with oligomeric amines. The adsorption of the oligomeric amines to the silica surface was promoted by hydrogen bonds (Wang et al., 2025). Recently, Wu et al. (2026b) showed that the appropriate choice of size and surface charge of silica nanoparticles leads to the effective stabilization of Pickering emulsions. Nanoparticles with antibacterial properties (based on Ag, ZnO, and TiO₂) were developed. However, high levels of heavy metals, resulting from migration into food, lead to serious problems for human health (Meng and Nag, 2026).

Organic stabilizing agents, polysaccharide nanoparticles, and proteins offer inherent biodegradability, biocompatibility, bioaccessibility, sustainability, and food safety, with lower environmental impact and applicability in the food industry (Shabir et al., 2023). Cellulose nanocrystals (CNCs) and nanofibers (CNFs) are the most used Pickering stabilizers. CNCs, obtained from the hydrolysis of cellulose in the presence of sulfuric acid, are an example (Li et al., 2026; Rahmi et al., 2025). The introduced sulfate group prevents the coalescence of the formed capsules. However, when the volume fraction of the oil phase exceeds a certain limit, due to the hydrophilic nature of CNCs, the system collapses and the oil phase leaks out. Because of this limiting factor, chemical or physical modifications have been suggested. Among these, were reported chemical modifications (Chen et al., 2018; Xu et al., 2026), complex formation with the cationic surfactant ethyl lauroyl arginate (Bai et al., 2018), or the formation of composite particles (Lin et al., 2023). CNFs can be prepared by physical modification, such as high-pressure homogenization or ultrasonication, and offer improved barrier resistance, mechanical strength, and controlled release of bioactive substances (Cao et al., 2026). Nanochitins have also been reported as stabilizing agents. Highly stable oil-in-water Pickering emulsions were prepared with carboxylated chitin nanocrystals (C-ChNWs), obtained by ammonium persulfate oxidation of chitin (Shuang et al., 2024). The emulsions in which the volume fraction of the oil phase was higher than 0.74, also called high internal phase Pickering emulsions (HIPPEs), were also shown to be suitable for the development of 3D-printed foods (Shuang et al., 2024). Proteins are amphiphilic biopolymers; they naturally adsorb on the oil−water interface and decrease the interfacial tension between the phases. Animal proteins (whey proteins and egg proteins) have been used in food products and packaging. Nowadays, plant proteins are preferred as stabilizing agents in food systems. Studies carried out by Sridharan et al. (2020) revealed that pea protein molecules stabilize oil-in-water emulsions at pH 3 primarily via protein adsorption and interfacial network formation, rather than the protein particle-based Pickering mechanism. To accomplish the objective of stabilizing tea polyphenols and lutein emulsions, some authors extracted the protein from the edible mushroom Flammulina velutipes (He et al., 2026). The authors demonstrated that F. velutipes protein alone was capable of effectively stabilizing oil-in-water HIPPEs (He et al., 2026).

Although single polysaccharide- and protein-based emulsifying agents meet the requirements for emulsion stabilization, improvements were achieved by complex formation or simply combining two or more of those agents, particularly in some HIPPPEs (Liu et al., 2025). Recently, polysaccharide-polysaccharide nanoparticles (Barros et al., 2026) and polysaccharide-protein systems were developed (Gao et al., 2026; Hong et al., 2025; Ji et al., 2025; Lee et al., 2026; Zhao et al., 2026).

3 Emulsion films

With the objective of preserving food and extending its shelf life while maintaining quality, so-called active packaging has emerged. Active packaging interacts with the product and its surrounding environment through the controlled release of bioactive substances previously incorporated into it. Active packaging avoids the need to add active agents directly to the food. Active packaging is mainly used for packaging perishable food, such as fish, meat, bread, cheese, and fruits and vegetables (Figure 1). Pickering emulsions of essential oils and extracts with antimicrobial and antioxidant properties against foodborne pathogens are generally incorporated into polysaccharide or protein matrices to achieve that goal.

Essential oils are natural antibacterials, fragrant concentrated liquids extracted from plant materials (stems, bark, leaves, fruits, and flowers). Essential oils are mainly constituted of a complex mixture of secondary metabolites, such as terpenes, terpenoids, aliphatic compounds, alkaloids, isoflavones, flavonoids, phenolic acids, aldehydes, and carotenoids (Farias et al., 2025; Pezantes-Orellana et al., 2024). Extracts used in food packaging are produced by green solvents. Their antioxidant properties are attributed to polyphenols, flavonoids, vitamins, and other constituents, depending on their source.

Seafood products are known as highly susceptible to spoilage by microbial contamination and lipid oxidation. A double-layer film of chitosan and alginate, incorporated with the essential oil (tea tree essential oil) from Melaleuca alternifolia at 3% concentration, was shown to effectively prolong the freshness of shrimp with no spoilage detected at 4 °C for 3 days (Tang et al., 2025). The antibacterial capacity was attributed to the interaction of the essential oil with the phospholipids on the bacterial cell walls (Tang et al., 2025). Turmeric essential oil Pickering emulsions added to a chitosan-modified lysozyme amyloid fibrils matrix acted as antimicrobial agents to preserve salmon filets by inhibiting the growth of E. coli, S. aureus, and L. monocytogenes. According to the authors, the antibacterial activity of the lysozyme amyloid fibril-chitosan complex comes from the interaction of the positively charged amino groups of chitosan with negatively charged bacterial cell membranes. This electrostatic interaction would promote the disruption of the bacterial cell membrane. This mechanism would act synergistically with the intrinsic enzymatic activity of fibrous lysozyme, which also provides structural stability to the complex. The films also delayed lipid oxidation, showed reduced water vapor and oxygen permeability, and had satisfactory mechanical properties. The antioxidant properties of the system were attributed to the encapsulated turmeric essential oil, which is rich in terpenoids and other free radical-scavenging components (Guo et al., 2026).

Some authors developed composite film-forming solutions of a konjac glucomannan/carrageenan blend (KGC) and Litsea cubeba essential oil Pickering emulsion (LCPE), stabilized by a cellulose nanocrystal/tannic acid complex (Ni et al., 2025). Dipping pork in this active solution created a protective film that preserved the meat. They observed that the oil droplets were homogeneously dispersed in the polysaccharide matrix and that the components interacted by intermolecular hydrogen bond formation. Compared to the KGC film, the composite films presented improved mechanical and barrier properties. Some of them presented contact angles higher than 90°, which indicates a hydrophobic surface. The film with a large composition in LCPE inhibited Escherichia coli and Staphylococcus aureus reproduction. Litsea cubeba essential oil (LCEO) presents antimicrobial and antioxidant activities. The antibacterial properties of this essential oil and its emulsion films were attributed to LCEO large composition of bioactive aldehydes (citral, citronellal, citral isomers, and citronellal isomers). LCEO disrupts the structural integrity of bacterial cell membranes, altering their permeability and leading to the leakage of cytoplasmic contents. Moreover, pork oxidation was reduced during storage. Besides the antioxidant properties of LCEO, the reduction in pork lipid oxidation was attributed to the light barrier properties (particularly UV light) of the composite film (Ni et al., 2025). In another study, cellulose nanocrystals and lignin nanoparticles were prepared from coffee-leaf agricultural waste. Coffee essential oil Pickering emulsions, stabilized by the lignin nanoparticles, were incorporated into a gelatin matrix reinforced with the cellulose nanocrystals. In relation to the control gelatin film, the composite films showed improved barrier, mechanical, and thermal properties. Tests also proved their excellent antioxidant and antibacterial properties (against Staphylococcus aureus and Escherichia coli). The films were effective in preserving fresh pork stored at 4 °C for 8 days. The authors attributed the properties of the emulsion films mainly to the antioxidant and antibacterial properties of coffee essential oil, particularly to its polyphenols, tocopherols, and phytosterols components. The presence of lignin nanoparticles as the emulsion stabilizer contributed to the antioxidant properties of the system (Sun et al., 2026).

Bread has a high water activity, making it susceptible to mold growth. To prevent bread spoilage, Tan et al. (2025) developed active chitosan films incorporated with cinnamaldehyde and citral Pickering emulsions. As a stabilizer, they used shellac nanoparticles. The films were submitted to mechanical, optical, moisture content, water vapor, and oxygen permeability tests, which revealed better properties than the control chitosan film. Antifungal tests against Aspergillus niger and Penicillium citrinum showed satisfactory results, attributed to the synergistic effect of cinnamaldehyde and citral. Above all, the active films extended the shelf life of bread slices kept at 25 °C by 5 days (Tan et al., 2025).

Cheese is considered a staple food for several societies. It is rich in nutrients such as protein and fat and particularly susceptible to microbiological contamination. During distribution and storage, cheese should be protected from mechanical damage, moisture loss, and microbiological spoilage. Cheese packaging should be adjusted according to moisture content, degree of ripening, microflora, etc. (Płoska et al., 2024). An example of a high-moisture cheese, the Egyptian Karish cheese, was coated with oregano essential oil encapsulated in chitosan nanoparticles. The coated cheeses maintained their sensory quality, reduced mass loss, and other initial characteristics when kept at 4 °C for 28 days. In this case, the cheese surface would be protected by a physical and biological barrier provided by the controlled release of nanoencapsulated oregano oil (Hamouda et al., 2025).

Fruits and vegetables are important sources of vitamins, minerals, fiber, and antioxidants. However, they are especially susceptible to spoilage during harvest, transportation, and storage. Numerous studies have reported on the use of different active emulsion films for the preservation of perishable fruit products. An oregano essential oil emulsion, stabilized by carboxylated cellulose nanocrystals, was added to a pectin solution at different compositions. The resulting emulsion films were characterized by tensile tests, contact angle measurements, and UV-vis absorption spectroscopy. The results showed enhanced mechanical strength, increased hydrophobicity, and improved UV-shielding capabilities. The films were also submitted to antioxidant and antibacterial tests, which revealed improved properties in relation to controls. Phenolic and terpene compounds present in oregano oil acted as free radical scavengers and reducing agents, enhancing the antioxidant activity of the composite films. By contrast, carvacrol and thymol, also present in oregano essential oil, are known to damage bacterial external membranes and cause cell death. Coated cherries with the film-forming emulsions were preserved at 25 °C for 7 days (Yang et al., 2024). Zou et al. (2025) developed chitosan films incorporated with an alga-derived oil Pickering emulsion, stabilized by soy protein isolate for strawberry preservation. The presence of the oil, rich in polyunsaturated fatty acids and carotenoids, contributed to reducing the hydrophilicity of the chitosan film and, consequently, reducing the water vapor permeability of the composite films. The antioxidant properties determined for the films were improved as the composition in the dispersed phase increased. The high radical scavenging ability of the emulsion films was attributed mainly to the high content of n-3 polyunsaturated fatty acids (docosahexaenoic acid and eicosapentaenoic acid) and astaxanthin (a red ketocarotenoid) in the alga-derived oil. Limited changes in antibacterial properties were observed as the oil composition increased in the emulsion films. These results led the authors to appoint the chitosan matrix as the main responsible component for the antibacterial properties presented by the films. When the films were applied to strawberry preservation, weight loss was reduced, fruits kept their firmness, and they showed a better retention of titratable acidity than the controls (Zou et al., 2025).

4 Discussion

Many challenges should be overcome to ensure that the growing global population (estimated to reach 9.7 billion in 2050) has access to a healthy diet. Entire populations suffer from food shortages. One of the challenges is reversing the substantial food loss during production, transportation, and storage. As extreme weather events become more frequent, they are causing widespread declines in agricultural productivity, straining supply chains, and inducing inflationary pressure on global food prices. Rapid assistance to communities affected by disasters is critical to saving lives, requiring the immediate availability of preserved food. Packaging makes a difference; it protects food from chemical, physical, and biological attacks, thus preserving the food, extending its shelf life, and maintaining its physical, sensory, and nutritional qualities.

Plastic packaging is widely used. However, food packaging is disposable. Plastic waste accumulates in rivers, lakes, and oceans, resulting in environmental pollution, which significantly affects human health. Biopolymers provide a sustainable alternative for food packaging, promoting both preservation and ecological safety. These polymers disintegrate and undergo biodegradation by enzymatic processes. Because they consume carbon dioxide during biosynthesis, they give rise to the concept of “carbon-neutral materials.”

The incorporation of bioactive substances (present in essential oils and plant extracts) into packaging material led to the concept of active packaging. This concept expands the functionality of the packaging. Active packaging prevents microbial contamination (bacteria and fungi), oxidative degradation of nutrients, loss of the original organoleptic properties of the food, and the generation of potentially toxic substances. Although it provides desirable functionality, the addition of bioactive substances to biopolymer dispersions produces thermodynamically unstable emulsions. Due to the high interfacial tension between the immiscible phases, certain phenomena can be observed over time. Using organic solid particles as stabilizers for emulsions (Pickering emulsions) ensures enhanced stability, biocompatibility, and food safety. Protein molecules and nanoparticles, polysaccharide nanoparticles, and mainly their complexes have been successfully used as Pickering stabilizers. The incorporation of such stabilized emulsions in biopolymer films enables the development of active food packaging with antioxidant and antibacterial properties, capable of preserving common food products. Other improvements observed in biopolymer films consist in enhancing barrier properties against water vapor. It would also potentially meet the rising demand for sustainable materials, minimize food waste, and support the United Nations Sustainable Development Goals. However, depending on the system, the addition of Pickering emulsions may interfere negatively with the mechanical properties, leading to films with lower tensile strength. Because of these potential limitations, biopolymer films incorporated with Pickering emulsions should be characterized extensively as for their structural, morphological, barrier, and mechanical properties. Despite offering several advantages, the industrial application of oil-in-water Pickering emulsions poses some challenges. Among them, solid particles should be prepared on a large scale, reproducibly and in a cost-effective manner. Emulsions are high-viscosity systems and require process adaptability. Long-term stability under varying environmental conditions, such as temperature, pH, and ionic strength, is also a remaining challenge. Multidisciplinary efforts aimed at solving these challenges will still be necessary to advance experimental studies and achieve the manufacture of commercially viable products. In the context of active films loaded with Pickering emulsions, future research should focus on optimizing the controlled release of active substances, safety, economic viability, and on sensory analyses to evaluate consumers’ acceptability.

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The author(s) declared that generative AI was not used in the creation of this manuscript.

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Footnotes

Edited by: Andresa Gomes, University of São Paulo, Brazil

Reviewed by: Fangda Sun, Northeast Agricultural University, China