Dispersed droplets as active fillers in fat-crystal network-stabilized water-in-oil emulsions

Dual functionality of diacylglycerols in water-in-oil emulsion gel systems

Distearin (DS) can be used as an emulsifier, due to its surface activity derived from the amphiphilic nature of the molecule, moreover, it can also crystallize and form a 3D crystal network that can induce oil gelation. The current research aimed to examine the ability to combine both emulsifying and oil gelation properties to structure and stabilize water-in-oil emulsion gel system. Different water contents and DS concentrations produce emulsion gels with different textural attributes while incorporating up to 30% of water in a 15% wt. DS-based oleogel resulted in stable white gels. Microscopy imaging confirmed the formation of a water-in-oleogel type emulsion gel characterized by DS crystallization in the continuous phase and at the interface through Pickering mechanism. A positive relation was observed between the G' and hardness values and water content, suggesting gel strengthening resulted from interactions between the DS crystals at the interface and the continuous phase, as suggested by the active filler theory. Thermal analysis revealed two broad melting events at the temperature range of 42.2-44.9 °C and 55.9-58.6 °C for emulsion gels with 10-30% water content, suggesting initial melting of β' polymorph and transition to β during melting, which was confirmed by XRD. The results showed that homogenization significantly improved the oil retention of the gels due to increased crystal surface area, while water addition slightly reduced it. Compared with traditional emulsions or oleogels, this water-in-oil gel system demonstrated prolonged stability and enhanced mechanical properties due to the dual functionality of DS at the water/oil interface and bulk.

Water Droplets Tailored as Wax Crystal Carriers to Mitigate Wax Deposition of Emulsion

This study explores how the micro-distribution change of wax crystals from the continuous oil phase to the oil-water interface mitigates the macro wax deposition of an emulsion. Two types of interfacial actions between wax crystals and water droplets, interfacial adsorption and interfacial crystallization, which were induced by two different emulsifiers, sorbitan monooleate (Span 80) and sorbitan monostearate (Span 60), respectively, were detected by differential scanning calorimetry and microscopy observation. The wax interfacial crystallization promoted by Span 60 resulted in the wax being nucleated directly at the oil-water interface prior to the continuous oil phase, conferring the nascent wax crystals and water droplets to be combined as coupled particles. The utilization of the wax interfacial crystallization behavior to hinder wax deposition of an emulsion was further explored. When the coupled wax crystal-water droplet particles were formed during the wax deposition process, water droplets acted as wax crystal carriers, entraining these nascent wax crystals to disperse in the emulsion, which significantly reduced the amount of wax crystals available to form the network of the deposit. In addition, this change also led to the basic structural units in the wax deposit evolving from wax crystal clusters/networks to water droplet flocs. The study elucidates that through adjusting the dispersion of wax crystals from the oil phase to the oil-water interface, water droplets could act as a functional component to tailor the properties of the emulsion or resolve related flow and deposition problems in pipeline transportation.

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.

Crystallization of lipids and lipid emulsions treated by power ultrasound: A review

The actual food system with fat is always complex and fat crystal and fat crystal networks have important effects on the physical properties of food. Recently, power ultrasound (PU) had been widely recognized as an auxiliary technology of fat crystallization to modify food properties. This review expounded on the mechanism of ultrasonic crystallization, and summarized effects of various factors in the process of ultrasonic treatment on fat crystallization. Based on the above, combined with the application of ultrasound in emulsions, the ultrasonic fat crystallization effect in the emulsion system was judged and described. Research results indicated that PU could shorten the induction time of crystallization, accelerate the formation of crystal nuclei, and change the polymorphism of fat crystals. The product treated by PU formed smaller and more uniform crystals to produce a more viscoelastic fat crystal network. In emulsion systems, ultrasonic treatments showed the same effect, but the effect of ultrasonic crystallization on the emulsion stability was different due to fat crystals in different emulsion systems. Meanwhile, the importance of ultrasonic crystallization in lipid emulsions was emphasized, thus ultrasonic crystallization had great potential in emulsion systems.

Systematic comparison of structural and lipid oxidation in oil-in-water and water-in-oil biphasic emulgels: effect of emulsion type, oil-phase composition, and oil fraction

BACKGROUND

Because many common foods are emulsions (mayonnaise, margarine, salad dressing, etc.), a better understanding of lipid oxidation is crucial for the formulation, production, and storage of the relevant consumer products. We prepared oil-in-water (O/W) and water-in-oil (W/O) emulgels, and their architecture was characterized before monitoring lipid oxidation under thermally accelerated conditions to systematically compare the effect of emulsion type, oil composition, and oil fraction on the structure and lipid oxidation in thee biphasic emulgel systems.

RESULTS

Higher susceptibility of lipids to oxidation (>2.5 times) was observed in the biphasic O/W and W/O emulgels than in soybean oil owing to an interfacial region. In the heterogeneous emulsion systems, W/O emulgels had oxidation resistance than O/W emulgels did. Compared with the oil-phase composition of high oleic sunflower, soybean, and flaxseed oils, oxidation sensitivity of emulsified lipids was significantly raised as the degree of unsaturation increased from 100.72 to 203.07. Moreover, increasing oil fraction from 75% to 85% led to an obvious increase in total oxidation in O/W emulgels but a decrease in W/O emulgels. In addition to emulsion size and oil unsaturation, viscoelasticity had a remarkable effect on the low-unsaturated oil oxidation (e.g. high oleic sunflower oil).

CONCLUSION

Physical and structural phenomena played important roles in lipid oxidation based on a mass transport principle. These findings provide novel information for designing the structures of emulsion gels for controlling lipid oxidation through the cooperation of both formulation and architecture principles. © 2022 Society of Chemical Industry.

Fabrication and characterization of oleogels and temperature-responsive water-in-oil emulsions based on candelilla (Euphorbia cerifera) wax

Developing novel fats with zero trans and low saturated fatty acids represents a research hotspot in the colloid field today. Herein, natural candelilla (Euphorbia cerifera) wax was used as an oleogelator to construct oleogel systems, and can make strong oleogels at low concentrations (3 wt%). These oleogels were further employed as continuous phases to fabricate surfactant-free W/O emulsions with excellent stability (at least 30 days). Microstructural observation confirmed that the stability of emulsions was attributed to the interface and bulk phase crystallization of wax. All oleogels and emulsions were pseudoplastic fluids whose gel properties could be tuned via regulating oleogelator concentration. Water content also influenced the emulsion rigidity, denoting the droplets acted as "active fillers". Additionally, the emulsions displayed a temperature-responsive property, beneficial in mimicking the "fat-like" melt-in-the-mouth effect. These findings greatly enrich the formulation of surfactant-free W/O emulsions, providing technical support for the development of novel fats.

Development and characterization of structured water-in-oil emulsions with ethyl cellulose oleogels

The food industry confronts an enormous challenge to develop stable margarine-type water-in-vegetable oil (W/O) emulsion-based table spreads with reduced concentration of saturated fat and without trans fats. In the present work, we developed a gelled W/O emulsion (Gelled-W/O-E) containing 20% of water using a mixture of a conventional W/O emulsion (W/O-E) stabilized with glycerol monostearate (GMS), and an ethyl cellulose (EC) oleogel. The mechanical, microstructure and stability of the resulting gelled emulsion (Gelled-W/O-E) was compared with control systems consisting of conventional W/O emulsions (W/O-E) and EC-GMS oleogels (EC-GMS-O; no water added) formulated using the same GMS (0.5% and 1.0%) and EC (7%) concentration as in the Gelled-W/O-E. The Gelled-W/O-E showed higher elasticity and emulsion stability in comparison with the control systems. This in spite the EC and GMS concentrations used were below the minimal concentration required to develop a gel, and the tentatively lower solid content in the Gelled-W/O-E than in the EC-GMS-O because the presence of water. We observed that by increasing the GMS concentration in the Gelled-W/O-E, the water droplet size decreased as gel elasticity and W/O emulsion stability significantly increased. We associated this behavior to a synergistic GMS-EC interaction that kept the GMS at the water-oil droplet interface. These results showed the role of water droplets as active fillers in determining the rheological properties of the Gelled-W/O-E, and that the GMS efficiency as emulsifier increased in the presence of EC in the oil phase. After comparing the microstructural properties of commercial margarine spreads with those of the Gelled-W/O-E, we concluded that the structured W/O emulsion is a novel way to achieve similar functionality to margarine spreads, without the use of saturated and trans-fats.

Tailored rigidity of W/O Pickering emulsions using diacylglycerol-based surface-active solid lipid nanoparticles

Pickering water-in-oil (W/O) emulsions were fabricated by using medium-long chain diacylglycerol (MLCD)-based solid lipid nanoparticles (SLNs) and the connection between the characteristics of the SLNs and the colloidal stability of the emulsions was established. Via melt-emulsification and ultrasonication, MLCD-based SLNs with particle sizes of 120-300 nm were obtained with or without other surfactants. The particle size of the SLNs was influenced by the chemical properties of the surfactants, and surfactants decreased the contact angle of SLNs at the oil-water interface. Gelation was observed in SLNs modified by sodium stearoyl lactylate and lecithin, whereas the addition of Tween 20 resulted in a homogeneous SLN solution. The adsorption of surfactants onto SLN surfaces caused the production of higher amounts of α crystals accompanied by delayed crystallization onset which contributed to the reduction of particle size, interfacial tension and oil wetting ability. The W/O emulsions with higher rigidity and physical stability can be obtained by varying surfactant types and by increasing SLN mass ratios to 60%, whereby more SLNs are adsorbed at the droplet surface as a Pickering stabilizer. This study provides useful insights for the development of diacylglycerol-based SLNs and Pickering W/O emulsions which have great potential for food, cosmetic and pharmaceutical applications.

Water-in-oil Pickering emulsions stabilized solely by a naturally occurring steroidal sapogenin: Diosgenin

In this study, stable water-in-oil emulsions stabilized solely by a naturally occurring steroidal sapogenin was reported for the first time. The results show that a concentrated emulsion with an internal water ratio of up to 60% can be obtained with only 3% of diosgenin concentration. The concentration of diosgenin had a significant effect on the microstructure and rheological properties of the emulsions. More importantly, the emulsion has excellent freeze/thaw stability and thermal stability. The results of polarized light microscopy, CLSM, and XRD indicate that the great structural properties and high stability of the emulsion can be attributed to the combined action of the diosgenin crystal shells on the droplet surface and needle-crystals in the continuous phase. That is, Pickering stabilization and network stabilization acting synergistically on stabilization of the emulsions. This novel food grade water-in-oil emulsions demonstrated great potential for application in food and biomedical-related fields.

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.

A novel strategy to fabricate stable oil foams with sucrose ester surfactant

HYPOTHESIS

Can a mixture of sucrose ester surfactant in vegetable oil be aerated to yield stable oleofoams? Is foaming achievable from one-phase molecular solutions and/or two-phase crystal dispersions? Does cooling a foam after formation induce surfactant crystallisation and enhance foam stability?

EXPERIMENTS

Concentrating on extra virgin olive oil, we first study the effect of aeration temperature and surfactant concentration on foamability and foam stability of mixtures cooled from a one-phase oil solution. Based on this, we introduce a strategy to increase foam stability by rapidly cooling foam prepared at high temperature which induces surfactant crystallisation in situ. Differential scanning calorimetry, X-ray diffraction, infra-red spectroscopy, surface tension and rheology are used to elucidate the mechanisms.

FINDINGS

Unlike previous reports, both foamability and foam stability decrease upon decreasing the aeration temperature into the two-phase region containing surfactant crystals. At high temperature in the one-phase region, substantial foaming is achieved (over-run 170%) within minutes of whipping but foams ultimately collapse within a week. We show that surfactant molecules are surface-active at high temperature and that hydrogen bonds form between surfactant and oil molecules. Cooling these foams substantially increases foam stability due to both interfacial and bulk surfactant crystallisation. The generic nature of our findings is demonstrated for a range of vegetable oil foams with a maximum over-run of 330% and the absence of drainage, coalescence and disproportionation being achievable.

Effect of Water Content and Pectin on the Viscoelastic Improvement of Water-in-Canola Oil Emulsions

This study aimed to investigate gelation in glycerol monooleate (GMO)-stabilized water-in-canola oil (W/CO) emulsions by increasing water content (20–50 wt.%) and the addition of low methoxyl pectin (LMP) in the aqueous phase. A constant ratio of GMO to water was used to keep a similar droplet size in all emulsions. Hydrogenated soybean oil (7 wt.%) was used to provide network stabilization in the continuous phase. All fresh emulsions with LMP in the aqueous phase formed a stable and self-supported matrix with higher viscosity and gel strength than emulsions without LMP. Emulsion viscosity and gel strength increased with an increase in water content. All emulsions showed gel-like properties (storage moduli (G’) > loss moduli (G’’)) related to the presence of LMP in the aqueous phase and increased water content. Freeze/thaw analysis using a differential scanning calorimeter showed improved stability of the water droplets in the presence of LMP in the aqueous phase. This study demonstrated the presence of LMP in the aqueous phase, its interaction with GMO at the interface, and fat crystals in the continuous phase that could support the water droplets’ aggregation to obtain stable elastic W/CO emulsions that could be used as low-fat table spreads.

Influence of Emulsifiers and Dairy Ingredients on Manufacturing, Microstructure, and Physical Properties of Butter

The influence of emulsifiers and dairy solids on churning and physical attributes of butter was investigated. Commercial dairy cream was blended with each of the ingredients (0.5%, w/w) separately, aged overnight (10 °C), and churned (10 °C) into butter. The employed additives showed a distinctive impact on the macroscopic properties of butter without largely affecting the melting behavior. In fresh butter, polyglycerol polyricinoleate (PGPR) emulsifier having dominated hydrophobic moieties significantly (p < 0.05) enhanced the softness. Among dairy solids, sodium caseinate (SC) was the most effective in reducing the solid fat fraction, hardness, and elastic modulus (G'), while whey protein isolate (WPI) and whole milk powder (WMP) produced significantly harder, stiffer, and more adhesive butter texture. As per tribological analysis, PGPR, Tween 80, and SC lowered the friction-coefficient of butter, indicating an improved lubrication property of the microstructure. The extent of butter-setting during 28 days of storage (5 °C) varied among the samples, and in specific, appeared to be delayed in presence of WPI, WMP, and buttermilk solids. The findings of the study highlighted the potential of using applied emulsifiers and dairy-derived ingredients in modifying the physical functionality of butter and butter-like churned emulsions in addition to a conventional cream-ageing process.

Hybrid oil-in-water emulsions applying wax(lecithin)-based structured oils: Tailoring interface properties

This study addressed the impact of fruit wax(lecithin)-based oleogels as dispersed phase in formation and stability of oil-in-water emulsions. These hybrid emulsions were prepared above the melting point of the oleogels, using Tween 80 (T80) or whey protein isolate (WPI) as emulsifiers. Both mono- and mixed-component oleogels comprised of fruit wax (FW) or FW + lecithin (FWLEC), respectively, were studied as lipid phases. After hot-homogenization, emulsions were submitted to quiescent cooling and stored over 14 days at 5 or 25 °C, in such temperatures supposed to assist or hinder oleogelation, respectively. Time course promoted a slight decrease in zeta potential only for WPI-stabilized emulsions and particle size distribution was shifted to larger size values, but showing a lesser extent to those stored at 5 °C. The presence of oleogels improved kinetic stability of emulsions compared to liquid oil at both temperatures, disclosing the role of the combined effects of the type of emulsifier and oleogelator(s)-emulsifier interactions. These outcomes are associated with the interfacial activity played by both oleogelators, but mainly lecithin that led to lower values of interfacial tension. In addition FWLEC combined with WPI showed the lowest complex modulus from dilational rheology, which can be related with WPI-LEC complex formation. Overall, results suggest that oleogelators migrated to the O/W interface of dispersed droplets, no longer reflecting oleogel bulk properties and showing a more complex behavior. However, the formation of more complex structures at the interface favored greater stability of the emulsions. Thus, the new perspective of oleogel-inspired fat droplets in hybrid systems can expand the conventional approach of oil structuring to create mixed interfaces tailoring oil-in-water emulsions properties.

Effect of diacylglycerol interfacial crystallization on the physical stability of water-in-oil emulsions

The influence of diacylglycerol (DAG) combined with polyglycerol polyricinoleate (PGPR) on the stability of water-in-oil (W/O) emulsions containing hydrogenated palm oil (HPO) was studied. Polarized light microscope revealed that DAG promoted HPO to crystallize at the water-oil interface, providing the combination of Pickering and network stabilization effects. It was proposed that the molecular compatibility of fatty acids in DAG with HPO accounted for the promotional effect. The interfacial crystallization of DAG together with the surface activity of PGPR led to the formation of emulsions with uniform small droplets and high freeze-thaw stability. Further exploration of physical properties indicated that the combination of DAG and PGPR dramatically improved the emulsion's viscoelasticity and obtained a larger deformation yield. Water droplets in DAG-based emulsions acted as active fillers to improve the network rigidity. Therefore, DAG is a promising material to be used as emulsifier to enhance the physical stability of W/O emulsions.

Regression modelling of the impact of confectioner's sugar and temperature on palm oil crystallization and rheology

The relationship between microscopic and macroscopic properties in fat-continuous dispersions is multifaceted compared to bulk oils, which limits the ability to extrapolate results from bulk systems towards complex formulations. The impact of confectioner's sugar on the crystallization and rheology of palm oil (PO) and mid-fraction blend (PMF) was investigated in this study. Adding sugar significantly increased storage modulus (G') and firmness (F) of the oils while exhibiting increased sensitivity towards processing conditions. Multiple regression analysis was used to create predictive models that correct for the effects caused by confectioner's sugar, such as altered fat crystal morphology and increased network rigidity, through the binary variable ζ. With limited studies on the use of PO in confectionery applications, these models may be used by industry as tools for production that do not rely on anecdote and overcome any shortcomings associated with the extrapolation from bulk systems.

Effect of the monostearate/monopalmitate ratio on the oral release of active agents from monoacylglycerol organogels

GMP/GMS organogels are promising systems for oral delivery in functional or medical foods.