Formation and stability of W/O-high internal phase emulsions (HIPEs) and derived O/W emulsions stabilized by PGPR and lecithin

Effect of stigmasterol and polyglycerol polyricinoleate concentrations on the preparation and properties of rapeseed oil-based gel emulsions

Emulsion gels mimic the rheological properties of solid and semi-solid fats, offering a viable solution to replace conventional fats in low-fat food formulations. In this study, gel emulsions stabilized with stigmasterol (ST) and polyglycerol polyricinoleate (PGPR) complexes were prepared. Initially, we examined the effect of the ST/PGPR complex on the mechanism of gel emulsion stabilization. Our findings revealed that the gel emulsion formulated with 3% PGPR and ST exhibited a robust structure, effectively stabilizing the entire system and ensuring uniform distribution, and increasing ST concentration led to greater stability of the gel emulsion system. Stability assessments demonstrated that gel emulsions containing 3% PGPR and varying ST concentrations exhibited remarkable thermal stability and effectively delayed oil oxidation. These results underscore the high stability of gel emulsions stabilized with the ST/PGPR complex, highlighting their potential as a margarine substitute.

Polyglycerol polyricinoleate and lecithin stabilized water in oil nanoemulsions for sugaring Beijing roast duck: Preparation, stability mechanisms and color improvement

Traditional Beijing roast duck often suffers from uneven color and high sugar content after roasting. Water-in-oil (W/O) nanoemulsion is a promising alternative to replace high concentration of sugar solution used in sugaring process according to similarity-intermiscibility theory. Herein, 3% of xylose was embedded in the aqueous phase of W/O emulsion to replace 15% maltose solution. W/O emulsions with different ratios of lecithin (LEC) and polyglycerol polyricinoleate (PGPR) were constructed by high-speed homogenization and high-pressure homogenization. Distribution and penetration extent of solutions and emulsions through the duck skin, as well as the color uniformity of Beijing roast duck were analyzed. Emulsions with LEC:PGPR ratios of 1:3 and 2:2 had better stability. Stable interfacial film and spatial structure were important factors influencing emulsion stabilization. The stable W/O emulsions could more uniformly distribute onto the surface of duck skin and longitudinally penetrate through the skin than solutions.

Regulation of fat crystals in water-in-oil emulsions by high-intensity ultrasound: Crystal size and tracing of droplet distribution

In this paper, two emulsion systems with high and low solid fat contents were prepared from 20 % water phase and 80 % oil phase by adjusting the palm oil/palm stearin/soybean oil ratio. Different ultrasonic power and time were used for the pretreatment of emulsion with different solid fat content, and the application characteristics of ultrasonic in W/O emulsions were explored and evaluated. Directly using high-intensity ultrasound to prepare fatty emulsions would weaken the hardness and storage modulus G' of the samples. Although ultrasound reduced the size of fat crystals in emulsions, the interaction between water droplets and fat crystals needs to be considered. After ultrasonic treatment, water droplets were difficult to immobilize on the crystal surface and thus acted as an active filler to stabilize the emulsion together with the fat crystal network. In high solid fat emulsion systems, an increase in ultrasound power (from 100 W to 200 W) could more affect the crystallization behavior of fats than an increase in ultrasound duration (from 30 s to 60 s), and the distribution of crystals and droplets was more uniform. In the low solid fat emulsion system, the texture of the sample after ultrasonic treatment was softer, and the surface was more delicate and smoother. However, the higher ultrasonic intensity (200 W) was not conducive to the preparation of the spread. Although the ultrasound with excessive intensity promoted the formation of small crystals, it would also lead to the aggregation of small crystals. These small crystals cannot form a uniform crystal network, which increases the fluidity of emulsions.

Plant-Based Emulsions as Dairy Cream Alternatives: Comparison of Viscoelastic Properties and Colloidal Stability of Various Model Products

In the context of growing interest in plant-based food products for their potential health benefits and sustainability, this study investigates the effect of mono- and diglycerides of fatty acids application on physico-chemical properties of various plant-based cream products, compared to lecithin application in rice cream. Rheological and textural parameters, colour profile, and colloidal stability were analysed. The application of mono- and diglycerides modified the creams' viscoelastic behaviour, showing a decrease in viscoelasticity across the samples; although in oat-coconut cream resulted in a higher viscoelasticity, indicating the formation of a gel-like structure. Rice cream with lecithin emulsifier showed lower viscoelastic properties characterised by higher phase angle (tan δ). All samples behaved as pseudoplastic materials (with a flow behaviour index n < 1). For coconut and almond creams, the consistency coefficient increased and flow behaviour index decreased after emulsifier application. Interestingly, the emulsifier addition did not significantly affect the cream's colour profile, characterised by yellow hue angle (h*) as a dominant spectral component. The colloidal stability, indicated by a stability index (SI), was determined as well.

Electron beam irradiation induced aggregation, structural and functional changes of soybean 11S globulin

This study investigated the effects of different irradiation doses of an electron beam (e-beam) (0, 2, 4, 6, 8, and 10 kGy) on the structure, emulsification, foaming, and rheological and gel properties of soybean 11S globulin. The irradiation treatment at 4 and 6 kGy significantly increased the solubility, surface hydrophobicity, disulfide bonding, and ζ-potential of 11S globulin, decreased the particle size of the protein solution, and effectively improved the emulsifying activity and foaming stability of the protein solution. Moreover, irradiation induced moderate cross-linking and aggregation of the proteins, thereby increasing the apparent viscosity and shear stress of the protein solution. In addition, the low-field NMR and microstructure analysis results revealed that protein gels formed a dense and homogeneous three-dimensional mesh structure after irradiation (6 kGy), along with increased content of bound water (T2b) and water not readily flowable (T21) and a decrease content of free water (T22). Overall, our results confirmed that e-beam irradiation could significantly improve the physicochemical properties of soybean 11S globulin. Our study thus provides a new technical means for the application of electron beam irradiation technology toward protein modification and broadens the high-value utilization of soybean 11S globulin in the food processing industry.

Lecithin's Roles in Oleogelation

This manuscript analyzes the research considering the exploitation of lecithin in oleogelation. The main objective of the work was to gather, analyze, and extract from the existing research data the information that enables us to identify lecithin-dependent roles. Oleogelation is still under research, while using various oleogelators and structurants provides changes on different physico-chemical levels. Multivariable formulations do not facilitate the elucidation of the specific role of any of them. Lecithin, due to its complex structure, big molecule, and amphiphilic nature, can provide different functionalities in complex matrices like oleogels. Therefore, this review identifies and categorizes the functionality of lecithin in oleogelation into four main roles: 1. oleogelation facilitator; 2. structure-forming impact; 3. texturing agent; and 4. functionality provider. Also, the origin and structure-forming characteristics of lecithin, as well as a short summary of the oleogelation process itself, are presented. Our critical analysis allowed us to identify the roles of lecithin in the oleogelation process and categorized them as follows: oleogelator, emulsifier, structural organization facilitator, structural modifier, crystal characteristics modifier, self-assembly promoter, thermal behavior changer, hydrogen-bonded networks promoter, hydrogel structure modifier, texture and structural modifier, gel-like state promoter, oil capacity enhancer, functionality provider, shelf life extender, and bioavailability and bioaccessibility enhancer. Lecithin came out as an important and multifunctional compound whose applications in oleogelation need to be thoroughly pre-considered. It is crucial to grasp all the possible roles of used compounds to be able to predict the final functionality and characteristics of formed oleogel matrices.

Plant-Based Oil-in-Water Food Emulsions: Exploring the Influence of Different Formulations on Their Physicochemical Properties

The global focus on incorporating natural ingredients into the diet for health improvement encompasses ω-3 polyunsaturated fatty acids (PUFAs) derived from plant sources, such as flaxseed oil. ω-3 PUFAs are susceptible to oxidation, but oil-in-water (O/W) emulsions can serve to protect PUFAs from this phenomenon. This study aimed to create O/W emulsions using flaxseed oil and either soy lecithin or Quillaja saponins, thickened with modified starch, while assessing their physical properties (oil droplet size, ζ-potential, and rheology) and physical stability. Emulsions with different oil concentrations (25% and 30% w/w) and oil-to-surfactant ratio (5:1 and 10:1) were fabricated using high-pressure homogenization (800 bar, five cycles). Moreover, emulsions were thickened with modified starch and their rheological properties were measured. The physical stability of all emulsions was assessed over a 7-day storage period using the TSI (Turbiscan Stability Index). Saponin-stabilized emulsions exhibited smaller droplet diameters (0.11-0.19 µm) compared to lecithin (0.40-1.30 µm), and an increase in surfactant concentration led to a reduction in droplet diameter. Both surfactants generated droplets with a high negative charge (-63 to -72 mV), but lecithin-stabilized emulsions showed greater negative charge, resulting in more intense electrostatic repulsion. Saponin-stabilized emulsions showed higher apparent viscosity (3.9-11.6 mPa·s) when compared to lecithin-stabilized ones (1.19-4.36 mPa·s). The addition of starch significantly increased the apparent viscosity of saponin-stabilized emulsions, rising from 11.6 mPa s to 2117 mPa s. Emulsions stabilized by saponin exhibited higher stability than those stabilized by lecithin. This study confirms that plant-based ingredients, particularly saponins and lecithin, effectively produce stable O/W emulsions with flaxseed oil, offering opportunities for creating natural ingredient-based food emulsions.

Effects of the Combination of Protein in the Internal Aqueous Phase and Polyglycerol Polyricinoleate on the Stability of Water-In-Oil-In-Water Emulsions Co-Encapsulating Crocin and Quercetin

This study aimed to diminish the reliance on water-in-oil-in-water (W/O/W) emulsions on the synthetic emulsifier polyglycerol polyricinoleate (PGPR). Considering the potential synergistic effects of proteins and PGPR, various protein types (whey, pea and chickpea protein isolates) were incorporated into the internal aqueous phase to formulate W/O/W emulsions. The effects of the combination of PGPR and protein at different ratios (5:0, 4:1, 3:2, 1:1 and 2:3) on the stability and encapsulation properties of W/O/W emulsions co-encapsulating crocin and quercetin were investigated. The findings indicated that the combination of PGPR and protein resulted in a slight reduction in the encapsulation efficiency of the emulsions, compared to that of PGPR (the control). Nonetheless, this combination significantly enhanced the physical stability of the emulsions. This result was primarily attributed to the smaller droplet sizes and elevated viscosity. These factors contributed to increased retentions of crocin (exceeding 70.04%) and quercetin (exceeding 80.29%) within the emulsions after 28 days of storage, as well as their improved bioavailability (increases of approximately 11.62~20.53% and 3.58~7.98%, respectively) during gastrointestinal digestion. Overall, combining PGPR and protein represented a viable and promising strategy for reducing the amount of PGPR and enhancing the stability of W/O/W emulsions. Notably, two plant proteins exhibited remarkable favorability in this regard. This work enriched the formulations of W/O/W emulsions and their application in the encapsulation of bioactive substances.

High internal phase emulsion stabilized by sodium caseinate:quercetin complex as antioxidant emulsifier

High internal phase emulsion (HIPE) was produced and stabilized using a novel antioxidant emulsifier formed by the complexation between sodium caseinate (SC) and quercetin (Q). Colloidal complexes, produced via an alkaline process, showed great ability to reduce the interfacial tension between oil-water phases, promoting stabilization of the HIPEs even at low concentrations (1.5% w/v in the aqueous fraction). HIPEs at 0.80 volume fraction of dispersed phase presented remarkable viscosity due to the high-packing network of oil droplets surrounded by a thin liquid layer. Moreover, the emulsions showed a gel-like behavior and kinetic stability for 45-days at 25 °C. The approach of SC:Q complexes on HIPEs development is promising to reduce lipid oxidation, translated by the formation of hydroperoxides and malondialdehyde during storage, especially for the complex formed with the highest amount of the phenolic compound. In this study, the development of HIPEs with outstanding kinetic and oxidative stability is reported as a potential alternative for the development of healthier products with reduced saturated and trans-fat content.

Analytics and applications of polyglycerol polyricinoleate (PGPR)-Current research progress

Polyglycerol polyricinoleate (PGPR) is a synthetic food additive containing a complex mixture of various esters. In recent years, there has been a growing trend to use PGPR-stabilized water-in-oil (W/O) emulsions to replace fat in order to produce low-calorie food products. In this respect, it is essential to comprehensively characterize the PGPR molecular species composition, which might enable to reduce its required amount in emulsions and foods based on a better understanding of the structure-activity relationship. This review presents the recent research progress on the characterization and quantitative analysis of PGPR. The influencing factors of the emulsifying ability of PGPR in W/O emulsions are further illustrated to provide new insights on the total or partial replacement of PGPR. Moreover, the latest progress on applications of PGPR in food products is described. Current studies have revealed the complex structure of PGPR. Besides, recent research has focused on the quantitative determination of the composition of PGPR and the quantification of the PGPR concentration in foods. However, research on the quantitative determination of the (poly)glycerol composition of PGPR and of the individual molecular species present in PGPR is still limited. Some natural water- or oil-soluble surfactants (e.g., proteins or lecithin) have been proven to enable the partial replacement of PGPR in W/O emulsions. Additionally, water-dispersible phytosterol particles and lecithin have been successfully used as a substitute of PGPR to create stable W/O emulsions.

Fabrication of fat-reduced water-in-oil emulsion and the application in 3D printing

Water-in-oil (W/O) emulsion is promising to design fat-reduced foods for 3D printing. In this study, oleogel-based W/O emulsion containing 65% water fraction was prepared by sunflower wax (SW, 1.0 wt%) and soybean phosphatidylethanolamine (SP, 0.5 wt%) with stability exceeding 30 days. Besides reducing interfacial tension, from X-ray diffraction and rheological results, SP was considered co-oleogelator to change the crystal habit of SW to enhance the external SW-based oleogel structure. The strong external oleogel structure was not only good for reducing droplets movements to improve physical stability, but facilitating the molding and supporting abilities of the emulsion gel in 3D printing. Based on rheological measurements, the emulsion gels were shown improved printing performance with SP increasing: extrusion (shear-thinning behavior), recovery (excellent thixotropy), and self-supporting (sufficient storage modulus and deformation resistance). In 3D printing, the emulsion gels with growing SP were displayed better shape retention and allowed printing the designs with more delicate and vivid features. This study provided new insight for W/O emulsion formation using natural ingredients for 3D printing to create fat-reduced foods.

Mechanisms of lipid oxidation in water-in-oil emulsions and oxidomics-guided discovery of targeted protective approaches

Lipid oxidation is an inevitable event during the processing, storage, and even consumption of lipid-containing food, which may cause adverse effects on both food quality and human health. Water-in-oil (W/O) food emulsions contain a high content of lipids and small water droplets, which renders them vulnerable to lipid oxidation. The present review provides comprehensive insights into the lipid oxidation of W/O food emulsions. The key influential factors of lipid oxidation in W/O food emulsions are presented systematically. To better interpret the specific mechanisms of lipid oxidation in W/O food emulsions, a comprehensive detection method, oxidative lipidomics (oxidomics), is proposed to identify novel markers, which not only tracks the chemical molecules but also considers the changes in supramolecular properties, sensory properties, and nutritional value. The microstructure of emulsions, components from both phases, emulsifiers, pH, temperature, and light should be taken into account to identify specific oxidation markers. A correlation of these novel oxidation markers with the shelf life, the organoleptic properties, and the nutritional value of W/O food emulsions should be applied to develop targeted protective approaches for limiting lipid oxidation. Accordingly, the processing parameters, the application of antioxidants and emulsifiers, as well as packing and storage conditions can be optimized to develop W/O emulsions with improved oxidative stability. This review may help in emphasizing the future research priorities of investigating the mechanisms of lipid oxidation in W/O emulsion by oxidomics, leading to practical solutions for the food industry to prevent oxidative rancidity in W/O food emulsions.

Fabrication porous adsorbents templated from aqueous foams using astragalus membranaceus and attapulgite as stabilizer for efficient removal of cationic dyes

The water-based foam stabilized by the natural surfactant applied in the fabrication of porous materials has attracted extensive attention, as the advantages of cleanness, convenience and low cost. Particularly, the development of a green preparation method has became the main research focus and frontier. In this work, a green liquid foam with high stability was prepared by synergistic stabilization of natural plant astragalus membranaceus (AMS) and attapulgite (APT), and then a novel porous material with sufficient hierarchical pore structure was templated from the foam via a simple free radical polymerization of acrylamide (AM). The characterization results revealed that the amphiphilic molecules from AMS adsorbed onto the water-air interface and formed a protective shell to prevent the bubble breakup, and APT gathered in the plateau border and formed a three-dimensional network structure, which greatly slowed down the drainage rate. The porous material polyacrylamide/astragalus membranaceus/attapulgite (PAM/AMS/APT) showed the excellent adsorption performance for cationic dyes of Methyl Violet (MV) and Methylene Blue (MB) in water, and the maximum adsorption capacity could reach to 709.13 and 703.30 mg/g, respectively. Furthermore, the polymer material enabled to regenerate and cycle via a convenient calcination process, and the adsorption capacity was still higher than 200 mg/g after five cycles. In short, this research provided a new idea for the green preparation of porous materials and the treatment of water pollution.

Pickering Emulsions Based in Inorganic Solid Particles: From Product Development to Food Applications

Pickering emulsions (PEs) have attracted attention in different fields, such as food, pharmaceuticals and cosmetics, mainly due to their good physical stability. PEs are a promising strategy to develop functional products since the particles’ oil and water phases can act as carriers of active compounds, providing multiple combinations potentiating synergistic effects. Moreover, they can answer the sustainable and green chemistry issues arising from using conventional emulsifier-based systems. In this context, this review focuses on the applicability of safe inorganic solid particles as emulsion stabilisers, discussing the main stabilisation mechanisms of oil–water interfaces. In particular, it provides evidence for hydroxyapatite (HAp) particles as Pickering stabilisers, discussing the latest advances. The main technologies used to produce PEs are also presented. From an industrial perspective, an effort was made to list new productive technologies at the laboratory scale and discuss their feasibility for scale-up. Finally, the advantages and potential applications of PEs in the food industry are also described. Overall, this review gathers recent developments in the formulation, production and properties of food-grade PEs based on safe inorganic solid particles.

New food, new technology: innovative spreadable cream with strawberry syrup

A strawberry spreadable cream was developed, valorizing regional raw materials, contributing to food waste reduction and agri-food ecosystem sustainability. Spreadable creams are water-in-oil emulsions whose lipid phase normally contains a blend of vegetable oils, natural colourants, stabilizers, emulsifiers, flavourings, antioxidants, lecithin, and fat-soluble vitamins. The aqueous phase normally contains skim milk proteins and small quantities of other ingredients, such as salt, preservatives, thickeners, and water-soluble vitamins. The methodology involved the experimental technological development articulated with microbiological, proximal, physicochemical, and sensorial analysis. This new product revealed nutritional advantages over similar products already on the market. The final prototype was subjected to food pairing and food design with incremental acceptance according to gastronomic use, in addition to its direct use as a spreadable cream. This work was part of the project Agrio et Emulsio—new products development (POCI-01-0145-FEDER-023583), whose main objective was the formulation and design of innovative food emulsions based on processed raw materials, with potential application in certain markets such as gourmet, diet, and vegan.

Effects of high-pressure homogenization on physicochemical and functional properties of enzymatic hydrolyzed soybean protein concentrate

This paper investigates the effect on the physicochemical and functional properties of soybean protein concentrate (SPC) by using Alcalase protease and high-pressure homogenization (HPH) (0, 20, 40, 60, 80, and 100 MPa) for the combined modification. The results showed that the degree of hydrolysis of SPC was 4.1% and the antigen protein was degraded after Alcalase hydrolysis, when the homogenization pressure (HP) was 6 0Mpa, the particle size of the SPC was the smallest, the zate potential absolute value up to 33.45 mV, the secondary structure has the lowest β-sheet content, the highest random coil content, and the highest surface hydrophobicity (H0), the size of protein fragments on the microstructure surface is the smallest, the lowest denaturation temperature (T d ) and enthalpy (△H) are 72.59°C and 1.35 J/g, the highest solubility is 80.54%, and the highest water and oil holding capacities are 7.73 g/g and 6.51 g/g, respectively. The best emulsifying activity and emulsifying stability were 43.46 m2/g and 190.35 min, the most even distribution of emulsion droplets. This indicates that the HPH treatment destroys the structure of enzymatic hydrolyzed SPC, changes its physicochemical properties, and improves its functional properties. In this study, SPC was modified by HPH and enzyme combined treatment, in order to improve the functionality and application range of SPC, and provide a theoretical basis for its high-value utilization in the food field.

Fabrication and Characterization of W/O/W Emulgels by Sipunculus nudus Salt-Soluble Proteins: Co-Encapsulation of Vitamin C and β-Carotene

W/O/W emulsions can be used to encapsulate both hydrophobic and hydrophilic bioactive as nutritional products. However, studies on protein stabilized gel-like W/O/W emulsions have rarely been reported, compared to the liquid state multiple emulsions. The purpose of this study was to investigate the effect of different oil–water ratios on the stability of W/O/W emulgels fabricated with salt-soluble proteins (SSPs) of Sipunculus nudus. The physical stability, structural characteristics, rheological properties, and encapsulation stability of vitamin C and β-carotene of double emulgels were investigated. The addition of W/O primary emulsion was determined to be 10% after the characterization of the morphology of double emulsion. The results of microstructure and rheological properties showed that the stability of W/O/W emulgels increased with the increasing concentration of SSPs. Additionally, the encapsulation efficiency of vitamin C and β-carotene were more than 87%, and 99%, respectively, and still could maintain around 50% retention of the antioxidant capacity after storage for 28 days at 4 °C. The aforementioned findings demonstrate that stable W/O/W emulgels are a viable option for active ingredients with an improvement in shelf stability and protection of functional activity.

Double emulsions as delivery systems for iron: Stability kinetics and improved bioaccessibility in infants and adults

Iron deficiency is one of the main causes of anemia in the world, especially in children and women, so food fortification through microencapsulation is a viable alternative to combat this deficiency. The present work aimed to encapsulate iron in a water-in-oil-in-water double emulsion (W₁/O/W₂), which was formed with whey protein isolate and polyglycerol polyricinoleate as the emulsifying agents, tara gum as a thickening agent, and sucrose as an osmotic active substance. The double emulsion formed with 12% whey protein isolate, 0.8% tara gum, and 2% sucrose presented high encapsulation efficiency (96.95 ± 1.00%) and good stability (up to 7 days). Additionally, after the in vitro gastrointestinal simulations, the bioaccessibility was high for adults (49.54 ± 5.50%) and infants (39.71 ± 2.33%). Finally, the study show that double emulsions can form stable systems with high iron bioaccessibility even in infant gastric systems, which indicates the possibility of using double emulsions to fortify food with iron.

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Stable double emulsions were obtained using WPI and PGPR as emulsifiers.

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Tara gum ensured an increase in the general stability of the emulsion.

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High bioaccessibility of iron were obtained for adults and infants.

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Emulsions are presented as a potential alternative to be used in iron-fortified food.

Encapsulation of bitter peptides in water-in-oil high internal phase emulsions reduces their bitterness and improves gastrointestinal stability

Many peptides exhibit beneficial physiological functions, but their application in foods is limited because of their undesirable taste and their tendency to degrade when exposed to gastrointestinal conditions. In this study, water-in-oil high internal phase emulsions (W/O HIPEs) were used to encapsulate bitter peptides. A combination of confocal fluorescence and electron microscopy was used to confirm the formation of W/O HIPEs. The presence of high concentrations of bitter peptides increased the apparent shear viscosity, shear modulus and sedimentation stability. They also improved the oxidative stability of the HIPEs. Electronic-tongue and sensory analysis showed that encapsulated peptides within the HIPEs substantially reduced their bitterness. Moreover, a simulated gastrointestinal study showed that W/O HIPEs protected peptides from being released in the stomach. Our results show that W/O HIPEs can be used to mask the bitterness and improve the gastrointestinal stability of peptides, which may increase their utilization as bioactive ingredients in foods.

W/O high internal phase emulsion featuring by interfacial crystallization of diacylglycerol and different internal compositions

High internal phase emulsions (HIPEs) show promising application in food and cosmetic industries. In this work, diacylglycerol (DAG) was applied to fabricate water-in-oil (W/O) HIPEs. DAG-based emulsion can hold 60% water and the emulsion rigidity increased with water content, indicating the water droplets acted as "active fillers". Stable HIPE with 80% water fraction was formed through the combination of 6 wt% DAG with 1 wt% polyglycerol polyricinoleate (PGPR). The addition of 1 w% kappa (κ)-carrageenan and 0.5 M NaCl greatly reduced the droplet size and enhanced emulsion rigidity, and the interfacial tension of the internal phase was reduced. Benefiting from the Pickering crystals-stabilized interface by DAG as revealed by the microscopy and enhanced elastic modulus of emulsions with the gelation agents, the HIPEs demonstrated good retaining ability for anthocyanin and β-carotene. This study provides insights for the development of W/O HIPEs to fabricate low-calories margarines, spread or cosmetic creams.

Impact of polysaccharide mixtures on the formation, stability and EGCG loading of water-in-oil high internal phase emulsions

Water-in-oil (W/O) high internal phase emulsions (HIPEs) were prepared using polyglycerol polyricinoleate (PGPR) and polysaccharide blends consisting of konjac glucomannan (KGM) and octenyl succinic anhydride starch (OSA-starch). The formation, stability, and functionality of these emulsions were varied by adjusting the ratio of KGM and OSA-starch. Interfacial tension measurements indicated that the OSA-starch co-adsorbed to the water-oil interface with PGPR, which would have led to the formation of a polysaccharide-layer that helped prevent separation of the HIPEs. The centrifugal stability, rheological and microstructural results indicated that the W/O HIPEs exhibited well pH, ionic and thermal stability. The encapsulation efficiency, stability, and bioaccessibility of the EGCG in the W/O HIPEs were evaluated by using EGCG as a model hydrophilic nutraceutical. This study provides useful insights into the utilization of emulsion technology to reduce the fat content and improve the nutritional profile of foods with oily continuous phases, such as spreads.

DPD Simulation on the Transformation and Stability of O/W and W/O Microemulsions

The dissipative particle dynamics simulation method is adopted to investigate the microemulsion systems prepared with surfactant (H1T1), oil (O) and water (W), which are expressed by coarse-grained models. Two topologies of O/W and W/O microemulsions are simulated with various oil and water ratios. Inverse W/O microemulsion transform to O/W microemulsion by decreasing the ratio of oil-water from 3:1 to 1:3. The stability of O/W and W/O microemulsion is controlled by shear rate, inorganic salt and the temperature, and the corresponding results are analyzed by the translucent three-dimensional structure, the mean interfacial tension and end-to-end distance of H1T1. The results show that W/O microemulsion is more stable than O/W microemulsion to resist higher inorganic salt concentration, shear rate and temperature. This investigation provides a powerful tool to predict the structure and the stability of various microemulsion systems, which is of great importance to developing new multifunctional microemulsions for multiple applications.

Preparation of Water-in-Oil Nanoemulsions Loaded with Phenolic-Rich Olive Cake Extract Using Response Surface Methodology Approach

In this study, we aimed to prepare stable water-in-oil (W/O) nanoemulsions loaded with a phenolic-rich aqueous phase from olive cake extract by applying the response surface methodology and using two methods: rotor-stator mixing and ultrasonic homogenization. The optimal nanoemulsion formulation was 7.4% (w/w) of olive cake extract as the dispersed phase, and 11.2% (w/w) of a surfactant mixture of polyglycerol polyricinoleate (97%) and Tween 80 (3%) in Miglyol oil as the continuous phase. Optimum results were obtained by ultrasonication for 15 min at 20% amplitude, yielding W/O nanoemulsion droplets of 104.9 ± 6.7 nm in diameter and with a polydispersity index (PDI) of 0.156 ± 0.085. Furthermore, an optimal nanoemulsion with a droplet size of 105.8 ± 10.3 nm and a PDI of 0.255 ± 0.045 was prepared using a rotor-stator mixer for 10.1 min at 20,000 rpm. High levels of retention of antioxidant activity (90.2%) and phenolics (83.1–87.2%) were reached after 30 days of storage at room temperature. Both W/O nanoemulsions showed good physical stability during this storage period.

W/O high internal phase emulsions (HIPEs) stabilized by a piperazinyl based emulsifier

In this study, a piperazinyl-based emulsifier (EA/AMPA) was synthesized to prepare water-in-oil (W/O) high internal phase emulsions (HIPEs). Using kerosene as the oil phase, stable HIPEs with internal phase fractions of up to 98% were prepared. This enabled the EA/AMPA to have a high efficiency, as the HIPEs with a 90% internal phase fraction could be easily prepared with 0.1% of EA/AMPA. In addition, the formation of HIPEs was not affected by the addition of Na⁺. Because of the fact that EA/AMPA has a hydrophilic head with two tertiary amines, EA/AMPA could be easily recovered from the oil phase by adjusting the pH to acidic values. Moreover, the unique structure promoted the formation of stable HIPEs, even with crude oil used as the oil phase. The results indicate that EA/AMPA has the potential to significantly contribute to the preparation of W/O HIPEs and that the design of the hydrophilic head with two tertiary amines can provide a reference for the fabrication of new W/O emulsifiers.

Recent advances on food-grade water-in-oil emulsions: Instability mechanism, fabrication, characterization, application, and research trends

Owing to their promising application prospects, water-in-oil (W/O) emulsions have aroused continuous attention in recent years. However, long-term stability of W/O emulsions remains a particularly challenging problem in colloid science. With the increasing demand of consumers for natural, green, and healthy foods, the heavy reliance on chemically synthesized surfactants to achieve long-term stability has become the key technical defect restricting the application of W/O emulsions in food. To design and manufacture W/O emulsions with long-term stability and clean label, a comprehensive understanding of the fundamentals of the W/O emulsion system is required. This review aims to demystify the field of W/O emulsions and update its current research progress. We first provide a summary on the essential basic knowledge regarding the instability mechanisms, including physical and chemical instability in W/O emulsions. Then, the formulation of the W/O emulsion system is introduced, particularly focusing on the use of natural stabilizers. Besides, the characterization and application of W/O emulsions are also discussed. Finally, we propose promising research trends, including (1) developing W/O high internal phase emulsions (HIPEs) as fat mimetic and substitute, (2) promising formulation routine for long-term stable double emulsions, and (3) searching for novel plant-derived stabilizers of W/O emulsions.

Development of a GC-FID method for the quantitative determination of polyglycerol polyricinoleate (PGPR) in foods

Polyglycerol polyricinoleate (PGPR) is a powerful lipophilic emulsifier used in low-fat spreads and chocolate. It should be used at the lowest level at which the desired technological effect is achieved, not exceeding the specified maxima according to Annexe II to Regulation (EC) No 1333/2008. A gas chromatography-flame ionisation detection (GC-FID) method was developed for quantification of PGPR. This method is based on estimating the content of ricinoleic acid using 12-hydroxyoctadecanoic acid as an internal standard, from which the PGPR concentration was deduced. The method involved saponification, methylation, a two-step solid phase extraction (SPE) separation of the fatty acid methyl esters (FAMEs), silylation, and GC-FID analysis. The limits of detection and quantification of ricinoleic acid were 2.2 and 6.7 μg/mL, respectively, at 0.1 µL injection volume. Considering the average content of ricinoleic acid in PGPR (i.e. 86.63 ± 2.0 wt%) and the amount of food product that is used in the proposed protocol (i.e. 20 mg), this resulted in a LOD and LOQ of 0.76 and 2.32 μg PGPR per mg of food product, respectively. The developed method was validated by determining PGPR recovery from a high oleic sunflower oil (HOSO) solution, from chocolate spiked with a commercially available PGPR, and from commercially available low fat spreads with a known PGPR content. The actual recovery was more than 95% for all matrices, indicating the accuracy of the developed analytical technique. Moreover, the method proved to be very reproducible, with RSD < 4% for concentrations ranging from 0.2 to 5 wt%. The results showed that our proposed GC-FID method enables the reliable and quantitative determination of the PGPR concentration in commercial food products with various fat contents.

Effect of Surfactant Molecular Structure on Emulsion Stability Investigated by Interfacial Dilatational Rheology

Polyglycerol polyricinolate (PGPR) and polyglycerol-2 dioleate were selected as model surfactants to construct water-in-oil (W/O) emulsions, and the effect of interfacial rheological properties of surfactant film on the stability of emulsions were investigated based on the interfacial dilatational rheological method. The hydrophobicity chain of PGPR is polyricinic acid condensed from ricinic acid, and that of polyglycerol-2 dioleate is oleic acid. Their dynamic interfacial tensions in 15 cycles of interfacial compression-expansion were determined. The interfacial dilatational viscoelasticity was analyzed by amplitude scanning in the range of 1–28% amplitude and frequency sweep in the range of 5–45 mHz under 2% amplitude. It was found that PGPR could quickly reach adsorption equilibrium and form interfacial film with higher interfacial dilatational viscoelastic modulus to resist the deformation of interfacial film caused by emulsion coalescence, due to its branched chain structure and longer hydrophobic chain, and the emulsion thus presented good stability. However, polyglycerol-2 dioleate with a straight chain structure had lower interfacial tension, and it failed to resist the interfacial disturbance caused by coalescence because of its lower interfacial dilatational viscoelastic modulus, and thus the emulsion was unstable. This study reveals profound understanding of the influence of branched structure of PGPR hydrophobic chain on the interfacial film properties and the emulsion stability, providing experimental reference and theoretical guidance for future design or improvement of surfactant.

pH-Sensitive W/O Pickering High Internal Phase Emulsions and W/O/W High Internal Water-Phase Double Emulsions with Tailored Microstructures Costabilized by Lecithin and Silica Inorganic Particles

Synergistic stabilization of Pickering emulsions by a mixture of surfactants and colloidal particles has received increasing interest in recent years but only a few of them can produce high internal phase double emulsions (HIPDEs) with good stability. In this study, we present a feasible and common method of preparing Pickering high internal phase emulsions (HIPEs) with tunable inner morphology costabilized by a biosurfactant lecithin and silica nanoparticles. We investigate the influence of the pH value on the interfacial behavior of lecithin and elucidate the synergistic mechanism between lecithin and silica nanoparticles in different conditions in the stability of as-prepared emulsions. Specifically, water-in-oil (W/O) Pickering HIPEs can be successfully stabilized by lecithin and hydrophobic silica nanoparticles in a wide pH range (pH 1-10), while catastrophic phase inversion occurred at high pH values (pH ≥ 11). Interestingly, stable water-in-oil-in-water (W/O/W) high internal phase double emulsions (HIPDEs) can also be prepared via a two-step method by the cooperation of lecithin and silica nanoparticles. Moreover, functional interconnected porous monoliths and microspheres are facilely fabricated by emulsion templates and their potential applications are explored.