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

Influences of ultrasonic treatment on the physicochemical properties and microstructure of diacylglycerol-loaded emulsion stabilized with soybean protein isolate and sodium alginate

This study examined the impacts of ultrasonic power (0, 150, 300, 450, 600, and 750 W) and ultrasonic durations (3, 6, 9, 12, and 15 min) on the physicochemical properties and microstructure of diacylglycerol (DAG)-loaded emulsions stabilized with soybean protein isolate (SPI) and sodium alginate (SA). The findings indicated that the smallest particle size, zeta potential, and contact angle for SPI-SA-DAG emulsions were respectively 5.58 μm, -49.85 mV, and 48.65°, achieved at an ultrasonic power of 450 W. The emulsification properties, loss modulus, storage modulus, and apparent viscosity of the emulsions were optimal at this power setting and at a duration of 9 min. Analytical techniques, including confocal laser scanning-, scanning electron-, and atomic force microscopy, revealed that ultrasonication significantly altered emulsion aggregation state, with the surface roughness (Rq) being minimized at 450 W. These results demonstrated that the stability of SPI-SA-DAG emulsions can be effectively enhanced by an appropriate ultrasonic treatment at 450 W for 9 min. This research provides theoretical support for the broad application of sonication techniques in the food industry.

Different interfaces for stabilizing liquid-liquid, liquid-gel and gel-gel emulsions: Design, comparison, and challenges

Interfaces play essential roles in the stability and functions of emulsion systems. The quick development of novel emulsion systems (e.g., water-water emulsions, water-oleogel emulsions, hydrogel-oleogel emulsions) has brought great progress in interfacial engineering. These new interfaces, which are different from the traditional water-oil interfaces, and are also different from each other, have widened the applications of food emulsions, and also brought in challenges to stabilize the emulsions. We presented a comprehensive summary of various structured interfaces (stabilized by mixed-layers, multilayers, particles, nanodroplets, microgels etc.), and their characteristics, and designing strategies. We also discussed the applicability of these interfaces in stabilizing liquid-liquid (water-oil, water-water, oil-oil, alcohol-oil, etc.), liquid-gel, and gel-gel emulsion systems. Challenges and future research aspects were also proposed regarding interfacial engineering for different emulsions. Emulsions are interface-dominated materials, and the interfaces have dynamic natures, as the compositions and structures are not constant. Biopolymers, particles, nanodroplets, and microgels differed in their capacity to get absorbed onto the interface, to adjust their structures at the interface, to lower interfacial tension, and to stabilize different emulsions. The interactions between the interface and the bulk phases not only affected the properties of the interface, but also the two phases, leading to different functions of the emulsions. These structured interfaces have been used individually or cooperatively to achieve effective stabilization or better applications of different emulsion systems. However, dynamic changes of the interface during digestion are only poorly understood, and it is still challenging to fully characterize the interfaces.

Fabrication and Stability Improvement of Monoglyceride Oleogel/Polyglycerol Polyricinoleate-Stabilized W/O High Internal Phase Pickering Emulsions

To decrease the lipid content in water-in-oil (W/O) emulsions, high internal phase Pickering W/O emulsions (HIPPE) were fabricated using magnetic stirring using a combination of monoglyceride (MAG) oleogel and polyglycerol polyacrylate oleate (PGPR) as stabilizers. Effects of MAGs (glyceryl monostearate-GMS, glycerol monolaurate-GML and glycerol monocaprylate-GMC) and internal phase components on the formation and properties of HIPPEs were investigated. The results showed that milky-white stabilized W/O HIPPE with up to 85 wt% aqueous phase content was successfully prepared, and the droplet interfaces presented a network of MAG crystals, independent of the MAG type. All HIPPEs exhibited great stability under freeze-thaw cycles but were less plastic. Meanwhile, GML-oleogel-based HIPPEs had larger particle size and were less thermal stable than GMS and GMC-based HIPPEs. Compared to guar gum, the internal phase components of sodium chloride and sucrose were more effective in reducing the particle size of HIPPEs, improving their stability and plasticity, and stabilizing them during 100-day storage. HIPPEs presented great spreadability, ductility and plasticity after whipping treatment. This knowledge provides a new perspective on the use of oleogels as co-stabilizers for the formation of W/O HIPPEs, which can be used as a potential substitute for creams.

Recent advances in studying crystallisation of mono- and di-glycerides at oil-water interfaces

This review focuses on the current understanding regarding lipid crystallisation at oil-water interfaces. The main aspects of crystallisation in bulk lipids will be introduced, allowing for a more comprehensive overview of the crystallisation processes within emulsions. Additionally, the properties of an emulsion and the impact of lipid crystallisation on emulsion stability will be discussed. The effect of different emulsifiers on lipid crystallisation at oil-water interfaces will also be reviewed, however, this will be limited to their impact on the interfacial crystallisation of monoglycerides and diglycerides. The final part of the review highlights the recent methodologies used to study crystallisation at oil-water interfaces.

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.

Influence of varying oil phase volume fractions on the characteristics of flaxseed-derived diglyceride-based Pickering emulsions stabilized by modified soy protein isolate

This research aimed to create Pickering emulsions using modified soy protein isolate (SPI) as a stabilizer and flaxseed-derived diglyceride (DAG) as an oil phase. The SPI was modified through a process involving both heating and ultrasound treatment. The result indicated that the droplet size of emulsions increased with the increase in oil content (p < 0.05). For instance, the largest droplet size (23 µm) was observed at an oil-to-SPI dispersion ratio of 4:1 ratio (φ = 80), whereas the smallest droplet size (6.39 µm) was noticed at the 1:4 ratio. During the 7-day storage period, the emulsions with a 4:1 ratio (φ = 80) showed the lowest droplet size increase (from 23 µm to 25.58 µm). In contrast, the emulsions with a 1:1 ratio displayed the highest increase (from 19.39 µm to 74.29 µm). Creaming index results revealed that emulsions with a 4:1 ratio (φ = 80) showed no signs of creaming and phase separation than all other treatments (p < 0.05). Backscattering fluctuations (ΔBS) and turbiscan stability index (TSI) showed that emulsions with 4:1, 2:1, and 1:1 oil-to-SPI dispersion ratios had consistent ΔBS curves with higher and TSI curves with lower values. Optical microscopy, confocal laser scanning, and cryo-scanning electron microscopy revealed that emulsions with oil-to-SPI dispersion ratios of 4:1 and 2:1 had well-organized structures with no visible coalescence. Macromorphological and microrheological investigations demonstrated that emulsions with 80% oil content had the highest viscosity, both moduli, elasticity index, macroscopic viscosity index, and the lowest fluidity index and solid-liquid balance values. Moreover, these emulsions were more resistant to centrifugation and storage environments. In conclusion, the study determined that flaxseed-derived DAG-based high internal phase Pickering emulsions (φ = 80) had superior stability, improved viscoelasticity, and better rheological properties.

Effect of Diacylglycerol Crystallization on W/O/W Emulsion Stability, Controlled Release Properties and In Vitro Digestibility

Water-in-oil-in-water (W/O/W) emulsions with high-melting diacylglycerol (DAG) crystals incorporated in the oil droplets were fabricated and the compositions were optimized to achieve the best physical stability. The stability against osmotic pressure, encapsulation efficiency and in vitro release profiles of both water- and oil-soluble bioactives were investigated. The presence of interfacial crystallized DAG shells increased the emulsion stability by reducing the swelling and shrinkage of emulsions against osmotic pressure and heating treatment. DAG crystals located at the inner water/oil (W1/O) interface and the gelation of the inner phase by gelatin helped reduce the oil droplet size and slow down the salt release rate. The DAG and gelatin-contained double emulsion showed improved encapsulation efficiency of bioactives, especially for the epigallocatechin gallate (EGCG) during storage. The double emulsions with DAG had a lower digestion rate but higher bioaccessibility of EGCG and curcumin after in vitro digestion. DAG-stabilized double emulsions with a gelled inner phase thus can be applied as controlled delivery systems for bioactives by forming robust interfacial crystalline shells.

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.

Improving the Stability of Water-in-Oil Emulsions with Medium Internal Phase by the Introduction of Gelatin

The water-in-oil (W/O) emulsion with a medium aqueous phase may be limited in food and cosmetics due to its poor stability and high cost. Herein, this work proposed a facile strategy to improve the W/O emulsion stability by introducing gelatin. The influence of different gelatin concentrations (0, 0.5%, 1.0%, 2.0%, and 4.0%) on the stability and properties of W/O emulsions was mainly investigated. Results showed that the obtained emulsions still belonged to W/O emulsions after adding gelatin to the aqueous phase. As the gelatin concentration increased (0~4.0%), the interfacial tension decreased, which is conducive to promoting the interface adsorption of polyglycerol polyricinoleate (PGPR). Furthermore, introducing gelatin also improved the water-holding capacity (WHC) (33.50~6.32%) and viscosity of W/O emulsions and reduced the droplet size (37.47~8.75 μm) of emulsions. The enhanced interfacial adsorption and aqueous gelation induced by gelatin addition promoted the formation of a tight overall emulsion network structure by the interaction between the interfacial adsorbed PGPR, as well as PGPR and gelatin in the aqueous phase. The enhancement of the overall network effectively improved the storage stability (35 d), thermal stability (20 min, 80 °C), and freeze-thaw stability (10 cycles) of emulsions, especially at 4.0% gelatin concentration. Hence, this study can provide guidance for the improvement and regulation of the stabilities of W/O emulsions.

Rheological and physicochemical properties of Spirulina platensis residues-based inks for extrusion 3D food printing

Novel food matrices (such as microalgae, plants, fungi, and microbial proteins) with high protein content and biological value, good amino acid profile, and functionality have been explored. Phycocyanin and active polysaccharides extracted from Spirulina platensis are used as food additives, treatment of colitis, as well as obesity prevention. However, most of the remaining Spirulina platensis residues are mainly used as fish feed at present. 3D food printing is one of the promising development techniques used in the food industry. The aim of this study was to develop a novel 3D printing material of Spirulina platensis residues with shear thinning characteristics, high viscosity and rapid recovery. The effects of moisture content and pretreatment method on the rheological properties of Spirulina platensis residues were clarified. Scanning electron microscopy was used to observe the microstructure and texture profile analysis was used to determine the texture characteristics of Spirulina platensis residues, rheology was used to determine the key 3D printing factors such as viscosity and modulus of Spirulina platensis residues. More importantly, the printing process could be realized under ambient conditions. The development of microalgae residue ink promoted the high-value and comprehensive utilization of microalgae, and also broadened the application of microalgae in the food field.

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.

Network Structure and Nanoplatelet Characterization of the Edible Fat Crystallization in Low-Fat W/O Emulsions

Fat crystals provided the strength of the colloidal network in W/O emulsions and stabilized water droplets. To understand the stabilizing effect of fat-regulated emulsions, W/O emulsions with different edible fats were fabricated. The result indicated that more stable W/O emulsions were produced by palm oil (PO) and palm stearin (PS), whose proportions of fatty acids were similar. Meanwhile, water droplets inhibited the crystallization of emulsified fats but participated in the formation of the colloidal network with fat crystals in emulsions, and the Avrami equation showed a slower crystallization rate of emulsified fats than the corresponding fat blends. However, water droplets participated in the formation of a colloidal network of fat crystals in emulsions, and the adjacent fat crystals were connected through a bridge constructed by water droplets. Fats in the emulsion containing palm stearin crystallized faster and more easily formed the β-polymorph. The small-angle X-ray scattering (SAXS) data were interpreted by the unified fit model to determine the average size of crystalline nanoplatelets (CNPs). The larger CNPs (>100 nm) with a rough surface of emulsified fats and a uniform distribution of their aggregates was confirmed.

Pickering Emulsion Stabilized by β-Cyclodextrin and Cinnamaldehyde/β-Cyclodextrin Composite

A Pickering emulsion was prepared using β-cyclodextrin (β-CD) and a cinnamaldehyde (CA)/β-CD composite as emulsifiers and corn oil, camellia oil, lard oil, and fish oil as oil phases. It was confirmed that Pickering emulsions prepared with β-CD and CA/β-CD had good storage stability. The rheological experiments showed that all emulsions had G' values higher than G″, thus confirming their gel properties. The results of temperature scanning rheology experiments revealed that the Pickering emulsion prepared with β-CD and CA/β-CD composites had high stability, in the range of 20-65 °C. The chewing properties of Pickering emulsions prepared by β-CD and corn oil, camellia oil, lard, and herring oil were 8.02 ± 0.24 N, 7.94 ± 0.16 N, 36.41 ± 1.25 N, and 5.17 ± 0.13 N, respectively. The chewing properties of Pickering emulsions made with the CA/β-CD composite and corn oil, camellia oil, lard, and herring oil were 2.51 ± 0.05 N, 2.56 ± 0.05 N, 22.67 ± 1.70 N, 3.83 ± 0.29 N, respectively. The texture properties confirmed that the CA/β-CD-composite-stabilized-emulsion had superior palatability. After 28 days at 50 °C, malondialdehyde (MDA) was detected in the emulsion. Compared with the β-CD and CA + β-CD emulsion, the CA/β-CD composite emulsion had the lowest content of MDA (182.23 ± 8.93 nmol/kg). The in vitro digestion results showed that the free fatty acid (FFA) release rates of the CA/β-CD composite emulsion (87.49 ± 3.40%) were higher than those of the β-CD emulsion (74.32 ± 2.11%). This strategy provides ideas for expanding the application range of emulsifier particles and developing food-grade Pickering emulsions with antioxidant capacity.

Tracing distribution and interface behavior of water droplets in W/O emulsions with fat crystals

Sucrose palmitate (P170) and sucrose laurate (L195) were used as emulsifiers to control the crystallization behavior of AMF and to stabilize W/O emulsions. In this study, the P170 promoted crystallization and led to strong fat crystal networks with smaller AMF crystals (60-80 μm) in emulsions, retaining flocculation. Water droplets were squeezed into irregular shapes between the strong network but the P170 formed an interface layer with better strength to resist the aggregation. Contrarily, the L195 inhibited crystallization and formed larger AMF spherulites (more than 100 μm) resulting in a low strength of fat crystal networks and unstable emulsions. Meanwhile, the water droplets were easily fixed on the surface of AMF crystals because of the existence of sucrose esters. Protruding crystals on the surface of larger spherulites could pierce the water-oil interface, leading to a greater coalescence and forming larger water droplets. Therefore, a weak crystal network could not prevent the sedimentation and phase separation caused by gravity.

Future of Structured Lipids: Enzymatic Synthesis and Their New Applications in Food Systems

Structured lipids (SLs) refer to a new type of functional lipid obtained by modifying natural triacylglycerol (TAG) through the restructuring of fatty acids, thereby altering the composition, structure, and distribution of fatty acids attached to the glycerol backbones. Due to the unique functional characteristics of SLs (easy to absorb, low in calories, reduced serum TAG, etc.), there is increasing interest in the research and application of SLs. SLs were initially prepared using chemical methods. With the wide application of enzymes in industries and the advantages of enzymatic synthesis (mild reaction conditions, high catalytic efficiency, environmental friendliness, etc.), synthesis of SLs using lipase has aroused great interest. This review summarizes the reaction system of SL production and introduces the enzymatic synthesis and application of some of the latest SLs discussed/developed in recent years, including medium- to long-chain triacylglycerol (MLCT), diacylglycerol (DAG), EPA- and DHA-enriched TAG, human milk fat substitutes, and esterified propoxylated glycerol (EPG). Lastly, several new ways of applying SLs (powdered oil, DAG plastic fat, inert gas spray oil, and emulsion) in the future food industry are also highlighted.

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.