Antioxidant Pickering emulsions stabilised by zein/tannic acid colloidal particles with low concentration

Pickering emulsion stabilized by quercetin-β-cyclodextrin-diglyceride particles: Effect of diglyceride content on interfacial behavior and emulsifying property of complex particles

This research develops diacylglycerol (DAG) based Pickering emulsions with enhanced oxidative stability stabilized by self-assembled quercetin/DAG/β-cyclodextrin (β-CD) complexes (QDCCs) using a one-step agitation method. Influence of DAG content (5%, 15%, 40%, and 80%, w/w) on the self-assembly behavior, interfacial properties, and emulsifying ability of complex particles was investigated. SEM, XRD and ATR-FTIR studies confirmed the formation of ternary composite particles. QDCCs in 80% DAG oil had the highest quercetin encapsulation efficiency (6.09 ± 0.01%), highest DPPH radical scavenging rate and ferric reducing antioxidant property (FRAP). β-CD and quercetin adsorption rates in emulsion with 80% DAG oil were 88.4 ± 2.53% and 98.34 ± 0.15%, respectively. Pickering emulsions with 80% DAG had the smallest droplet size (8.90 ± 1.87 μm) and excellent oxidation stability. This research develops a novel approach to regulate the physicochemical stability of DAG-based emulsions by anchoring natural antioxidants at the oil-water interface through a one-pot self-assembly method.

Pickering emulsion gel of polyunsaturated fatty acid-rich oils stabilized by zein-tannic acid green nanoparticles for storage and oxidation stability enhancement

HYPOTHESIS

Poor storage stability and oxidative deterioration are the common drawbacks of edible oils rich in polyunsaturated fatty acids (PUFAs). We hypothesized that the natural zein/tannic acid self-assembly nanoparticles (ZT NPs) could be employed as stabilizers to anchor at the oil-water interface, thus constructing Pickering emulsion gel (PKEG) system for three types of PUFA-rich oils, soybean oil (SO), fish oil (FO) and cod liver oil (CLO), to improve the storage and oxidation stability.

EXPERIMENTS

ZT NPs were prepared by the anti-solvent coprecipitation method, and the three-phase contact angle, FT-IR, and XRD were mainly characterized. To observe the shell-core structure and oil-water interface details of SO/FO/CLO PKEGs by confocal laser scanning microscope and cryo-scanning electron microscope. Accelerated oxidation of FO was performed to assess the protective effect of PKEG on lipids.

FINDINGS

The SO, FO, and CLO PKEGs stabilized by 2 % ZT NPs, with oil fraction (φ = 0.5-0.6), were obtained. PKEGs show high viscoelasticity, clear shell-core structure spatial network structure, and ideal storage stability. Under accelerated oxidation, the degree of oxidative rancidity of FO PKEG was obviously lower than that of free FO. Overall, this work opens up new possibilities for using natural PKEG to prevent oxidative deterioration and prolong the shelf-life of PUFA-rich oils.

Lipid oxidation in emulsions: New insights from the past two decades

Lipid oxidation constitutes the main source of degradation of lipid-rich foods, including food emulsions. The complexity of the reactions at play combined with the increased demand from consumers for less processed and more natural foods result in additional challenges in controlling this phenomenon. This review provides an overview of the insights acquired over the past two decades on the understanding of lipid oxidation in oil-in-water (O/W) emulsions. After introducing the general structure of O/W emulsions and the classical mechanisms of lipid oxidation, the contribution of less studied oxidation products and the spatiotemporal resolution of these reactions will be discussed. We then highlight the impact of emulsion formulation on the mechanisms, taking into consideration the new trends in terms of emulsifiers as well as their own sensitivity to oxidation. Finally, novel antioxidant strategies that have emerged to meet the recent consumer's demand will be detailed. In an era defined by the pursuit of healthier, more natural, and sustainable food choices, a comprehensive understanding of lipid oxidation in emulsions is not only an academic quest, but also a crucial step towards meeting the evolving expectations of consumers and ensuring the quality and stability of lipid-rich food products.

Effect of tannic acid modification on the interface and emulsification properties of zein colloidal particles

BACKGROUND

Interface modification driven by supramolecular self-assembly has been accepted as a valuable strategy for emulsion stabilization enhancement. However, there has been a dearth of comparative research on the effect of simple complexation and assembly from the perspective of the responsible mechanism.

RESULTS

The present study selected zein and tannic acid (TA) as representative protein and polyphenol modules for self-assembly (coined as TA-modified zein particle and TA-zein complex particle) to explore the surface properties and interfacial behavior, as well as the stability of constructed Pickering emulsions to obtain the regulation law of different modification methods on the interfacial behavior of colloidal particles. The results demonstrated that TA-modified zein colloidal particles potentially improved the emulsifying properties. When the TA concentration was 3 mmol L-1 , the optimized TA-modified zein particle was nano-sized (109.83 nm) and had advantageous interfacial properties, including sharply reduced surface hydrophobicity, as well as a low diffusion rate at the oil/water interface. As a result, the shelf life of Pickering emulsion containing 50% oil phase was extended to 90 days.

CONCLUSION

Through multi-angled research on the properties of the interfacial membrane, improvement of emulsion stability was a result of the formation of viscoelastic interfacial film that resulted from the decrease of absorption rate between particles and interface. Using refined regulation to investigate the role of different sample preparation methods from a mechanistic perspective. Overall, the present study has provided a reference for TA to regulate the surface properties and interface behavior of zein colloidal particles, enriched the understanding of colloidal interface assembly, and provided a theoretical basis for the quality control of interface-oriented food systems. © 2023 Society of Chemical Industry.

Fabrication and characterization of oleogels stabilized by metal-phenolic network coatings-decorated zein nanoparticles

Self-assembly coatings are used to functionalize the surface structures of protein. Herein, emulsion-templated approach was adopted to obtain oleogels using metal-phenolic network coatings-decorated zein nanoparticles. Two self-assembly strategies were used to decorate zein nanoparticles: 1) adding (-)-epigallocatechin-3-gallate (EGCG) first and then calcium ions (Ca2+) (zein/EGCG/Ca2+ nanoparticles). 2) adding Ca2+ first and then EGCG (zein/Ca2+/EGCG nanoparticles). The formation of nanoparticles, the stability of emulsions and the rheological behaviors of oleogels were modulated by using different adding sequences of EGCG and Ca2+. Nanoparticles prepared by two self-assembly strategies exhibited increasing diameter (340-360 nm). More Ca2+ participated in the formation of zein/EGCG/Ca2+ nanoparticles, as described by X-ray photoelectron spectroscopy analysis. Metal-phenolic network coatings facilitated the formation of well-structured emulsions and oleogels, which were candidates for fat substitutes and stable carriers. Findings confirmed metal-phenolic network coatings-decorated zein nanoparticles were effective stabilizers for emulsions and oleogels, further expanding the selectivity of oleogelators.

Characterization of quinoa starch nanoparticles as a stabilizer for oil in water Pickering emulsion

Quinoa starch nanoparticles (QSNPs) prepared by nanoprecipitation had a uniform particle size of 191.20 nm. QSNPs with amorphous crystalline structure had greater contact angle than QS with orthorhombic crystalline structure, which can therefore be utilized to stabilize Pickering emulsions. QSNPs-based Pickering emulsions prepared by suitable formulations (QSNPs concentration of 2.0-2.5 %, oil volume fraction of 0.33-0.67) exhibited good stability against pH of 3-9 and ionic strength of 0-200 mM. The oxidative stability of the emulsions increased with increasing starch concentration and ionic strength. Microstructural and rheological results indicated that the structure of the starch interfacial film and the thickening effect of the water phase affected the emulsion stability. The emulsion had excellent freeze-thaw stability and can be produced as a re-dispersible dry emulsion using the freeze-drying technique. These results implied that the QSNPs had great potential for application in the preparation of Pickering emulsions.

Targeting Interfacial Location of Phenolic Antioxidants in Emulsions: Strategies and Benefits

It is important to have larger proportions of health-beneficial polyunsaturated lipids in foods, but these nutrients are particularly sensitive to oxidation, and dedicated strategies must be developed to prevent this deleterious reaction. In food oil-in-water emulsions, the oil-water interface is a crucial area when it comes to the initiation of lipid oxidation. Unfortunately, most available natural antioxidants, such as phenolic antioxidants, do not spontaneously position at this specific locus. Achieving such a strategic positioning has therefore been an active research area, and various routes have been proposed: lipophilizing phenolic acids to confer them with an amphiphilic character; functionalizing biopolymer emulsifiers through covalent or noncovalent interactions with phenolics; or loading Pickering particles with natural phenolic compounds to yield interfacial antioxidant reservoirs. We herein review the principles and efficiency of these approaches to counteract lipid oxidation in emulsions as well as their advantages and limitations.

Fabrication of Antioxidant Pickering Emulsion Based on Resveratrol-Grafted Zein Conjugates: Enhancing the Physical and Oxidative Stability

Lipid oxidation is still a major problem complicating the development of food emulsions. In this study, an antioxidant Pickering emulsion stabilized by resveratrol-grafted zein (Z-R) conjugates and pectin (P) complex particles was prepared. The hydrophilic pectin successfully adjusted the wettability of Z-R; when the mass ratio of Z-R to P was 2:1 (Z-R/P_2:1), the three-phase contact angle was 90.68°, and the wettability of the particles was close to neutral. Rheological analysis showed that the emulsion formed an elastic gel structure. FTIR spectra indicated that there was a hydrogen bond and electrostatic interaction between Z-R and P. The disappearance of characteristic infrared peaks of corn oil was due to a dense protective film formed on the surface of oil drops by Z-R/P_2:1 particles, which was confirmed by confocal laser scanning microscopy. The emulsion stabilized by Z-R/P_2:1 had excellent physical stability at a wide range of pH values (4-9), salt ion concentrations (0.04-0.15 mol·L^-1) and storage times (0-30 days). The anti-lipid oxidation ability of the emulsion was outstanding; after storage for 14 days at room temperature, the MDA content in the emulsion was only 123.85 μmol/kg oil. In conclusion, the Z-R/P_2:1 particles prepared in this study can effectively stabilize a Pickering emulsion and expand the usability of the method for constructing antioxidant Pickering emulsions.

A review of protein-phenolic acid interaction: reaction mechanisms and applications

Phenolic acids (PA) are types of phytochemicals with health benefits. The interaction between proteins and PAs can cause minor or extensive changes in the structure of proteins and subsequently affect various protein properties. This study investigates the protein/PA (PPA) interaction and its effects on the structural, physicochemical, and functional properties of the system. This work particularly focused on the ability of PAs as a subgroup of phenolic compounds (PC) on the modification of proteins. Different aspects including the influence of structure affinity relationship and molecular weight of PA on the protein interaction have been discussed in this review. The physicochemical properties of PPA change mainly due to the change of hydrophilic/hydrophobic parts and/or the formation of some covalent and non-covalent interactions. Furthermore, PPA interactions affecting functional properties were discussed in separate sections. Due to insufficient studies on the interaction of PPAs, understanding the mechanism and also the type of binding between protein and PA can help to develop a new generation of PPA. These systems seem to have good capabilities in the formulation of low-fat foods like high internal Phase Emulsions, drug delivery systems, hydrogel structures, multifunctional fibers or packaging films, and 3 D printing in the meat processing industry.

Optimization of Pea Protein Isolate-Stabilized Oil-in-Water Ultra-Nanoemulsions by Response Surface Methodology and the Effect of Electrolytes on Optimized Nanoemulsions

Nanoemulsions are optically transparent and offer good stability, bioavailability, and control over the targeted delivery and release of lipophilic active components. In this study, pea protein isolate (PPI)-stabilized O/W nanoemulsions were evaluated using response surface methodology to obtain optimized ultra-nanoemulsions of Sauter mean diameter (D3,2) < 100 nm using a high-pressure homogenizer (HPH). Furthermore, the effect of food matrix electrolytes, i.e., the pH and ionic strength, on the emulsion (prepared at optimized conditions) was investigated. The results revealed that the droplet size distribution of emulsions was mainly influenced by the PPI concentration and the interaction of oil concentration and HPH pressure. Moreover, a non-significant increase in droplet size was observed when the nanoemulsions (having an initial D3,2 < 100 nm) were stored at 4 °C for 7 days. Based on the current experimental design, nanoemulsions with a droplet size < 100 nm can effectively be prepared with a high PPI concentration (6.35%), with less oil (1.95%), and at high HPH pressure (46.82 MPa). Such emulsions were capable of maintaining a droplet size below 100 nm even at ionic conditions of up to 400 mM NaCl and at acidic pH.

Oxidative stability of Pickering emulsions

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Oxidative stability of O/W Pickering emulsions depends on their interfacial layer.

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Solid particles can reduce Pickering emulsion oxidation by creating a thick interface.

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Manipulating the charge of the interface can control Pickering emulsion oxidation.

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Adding antioxidants to solid particles can reduce oxidation in Pickering emulsions.

In recent years, Pickering emulsions have been the focus of growing interest because of their possible role as alternatives to conventional emulsions. Some reviews have investigated the physical stability of Pickering emulsions, but the oxidative stability of these emulsions remains largely unexplored. In this review, the oxidation mechanism and factors affecting lipid oxidation rates in Pickering emulsions are discussed. Then, different food-grade solid particles are evaluated for their ability to stabilize Pickering emulsions. Finally, several strategies are reviewed for improving the oxidative stability of Pickering emulsions. These strategies are based on efforts to manipulate the physical and chemical properties of the interfacial layer, increase the concentration of antioxidants at the interfacial layer through incorporating them into solid particles, cause oil droplets to crowd at high packing fractions, trap oil droplets in a gel network and increase the viscosity of the continuous phase.

The Potential Application of Pickering Multiple Emulsions in Food

Emulsions stabilized by adsorbed particles—Pickering particles (PPs) instead of surfactants and emulsifiers are called Pickering emulsions. Here, we review the possible uses of Pickering multiple emulsions (PMEs) in the food industry. Food-grade PMEs are very complex systems with high potential for application in food technology. They can be prepared by traditional two-step emulsification processes but also using complex techniques, e.g., microfluidic devices. Compared to those stabilized with an emulsifier, PMEs provide more benefits such as lower susceptibility to coalescence, possible encapsulation of functional compounds in PMEs or even PPs with controlled release, etc. Additionally, the PPs can be made from food-grade by-products. Naturally, w/o/w emulsions in the Pickering form can also provide benefits such as fat reduction by partial replacement of fat phase with internal water phase and encapsulation of sensitive compounds in the internal water phase. A possible advanced type of PMEs may be stabilized by Janus particles, which can change their physicochemical properties and control properties of the whole emulsion systems. These emulsions have big potential as biosensors. In this paper, recent advances in the application of PPs in food emulsions are highlighted with emphasis on the potential application in food-grade PMEs.

Towards the systematic design of multilayer O/W emulsions with tannic acid as an interfacial antioxidant

This work discusses the possibility of designing multilayer oil-in-water emulsions to introduce the maximum possible amount of an antioxidant at the droplet interfaces for the optimal protection of a linseed oil core against oxidation, using a systematic three-step colloidal procedure. An antioxidant (here Tannic Acid - TA) is chosen and its interactions with a primary emulsifier (here Bovine Serum Albumin - BSA) and several polysaccharides are first examined in solution using turbidity measurements. As a second step, LbL deposition on solid surfaces is used to determine which of the polysaccharides to combine with BSA and tannic acid in a multilayer system to ensure maximum presence of tannic acid in the films. From UV-vis and polarization modulation infrared reflection-absorption (PM-IRRAS) spectroscopic measurements it is suggested that the best components to use in a multilayer emulsion droplet, together with BSA and TA, are chitosan and pectin. BSA, chitosan and pectin are subsequently used for the formation of three-layer linseed oil emulsions, and tannic acid is introduced into any of the three layers as an antioxidant. The effect of the exact placement of tannic acid on the oxidative stabilization of linseed oil is assessed by monitoring the fluorescence of Nile red, dissolved in the oil droplets, under the attack of radicals generated in the aqueous phase of the emulsion. From the results it appears that the three-stage procedure presented here can serve to identify successful combinations of interfacial components of multilayer emulsions. It is also concluded that the exact interfacial placement of the antioxidant plays an important role in the oxidative stabilization of the valuable oil core.

Synergistic stabilization of oil in water emulsion with chitin particles and tannic acid

The aim of the present study was to explore the effect of CP and TA on stability of oil in water emulsion stabilized by the two components, so as to fabricate the most efficient chitin based emulsifying agents. It was found that there was synergistic effect for CP and TA in stabilizing emulsion, specifically, the complex of chitin particles (CP) (3 g/L) with tannic acid (TA) (2 g/L) produced the most physically and oxidatively stable oil-in-water emulsion compared with other groups in this study. This is because CP-TA (3/5) complex had the lowest zeta potential, the lowest the oil water interfacial tension, the highest viscosity and the highest content of TA with excellent antioxidant activity. Furthermore, this is because there was intense interaction between CP and TA in CP-TA complex from results of FTIR, XRD and ITC, which then result in the formation of large CP-TA particles.

Prolamin-based complexes: Structure design and food-related applications

Prolamins are a group of safe food additives that are biocompatible, biodegradable, and sustainable. Zein, gliadin, kafirin, and hordein are common prolamins that have been extensively studied, particularly as these form colloidal particles because of their amphiphilic properties. Prolamin-based binary/ternary complexes, which have stable physicochemical properties and superior functionality, are formed by combining prolamins with polysaccharides, polyphenols, water-soluble proteins, and surfactants. Although the combination of prolamins with other components has received attention, the relationship between the structural design of prolamin-based complexes and their functionalities remains uncertain. This review discusses the production methods of prolamin-based complexes, the factors influencing their structural characteristics, and their applications in the food industry. Further studies are needed to elucidate the structure-function relationships between prolamins and other biopolymers, as well as the toxicological effects of these complexes in food.

Metal-Phenolic Network Covering on Zein Nanoparticles as a Regulator on the Oil/Water Interface

Interfacial self-assembly has become a powerful force for regulating the amphipathy of Pickering emulsions on the oil/water interface. Herein, metal-phenolic supramolecular coatings, acting as a regulator on the oil/water interface, were fabricated on the surface of zein nanoparticles (NPs), as a consequence of which the prepared Pickering emulsions stabilized by the decorated zein NPs exhibited diverse properties, decided by different concentrations of zein, tannic acid (TA), and metal ions (Fe³⁺). Metal-phenolic network-decorated zein NPs named ZTFex NPs (ZTFe NPs represented zein/TA/Fe³⁺ NPs, and x represented different concentrations of compounds) exhibited increasing diameters of 100-110 nm. Three-phase contact angles also showed that the strong hydrophobicity of zein NPs could be decreased as a result of the formation of metal-phenolic networks. As for corresponding Pickering emulsions, the covering of TA-Fe³⁺ networks on zein NPs could enhance the stability of zein NP-based emulsion obviously, which might be due to the fact that ZTFex NPs revealed the ability to form strong films on the oil/water interfaces. ZTFe4 was selected as an optimal concentration because of its minimum size and excellent storage stability. Besides, it was also found that the diameter of ZTFe4-based emulsion enhanced with the increase in the oil phase. The rheological measurement results showed that both G' and G″ increased with the increase of x and the oil phase. In general, our paper not only highlighted a straightforward method for the interfacial nanofabrication of solid particles but also provided a novel and potential strategy in Pickering emulsion applications.