Crystallizable W/O/W double emulsions made with milk fat: Formulation, stability and release properties

Impact of oil phase volume fraction on the characteristics of w/o/w emulsions stabilized with alkali-heat-treated rice residue glutelin

Rice residue glutelin was used as a raw material and modified using alkali-heat treatment to prepare water-in-oil-in-water (w/o/w) double emulsions with 2.5 % and 3.0 % protein content by one-step emulsification method. The structure, centrifugal stability and freeze-thaw stability of the emulsion were varied by adjusting the oil phase volume. As the oil phase volume fraction increased, the emulsion droplets formed a stronger network structure, leading to an increase in apparent viscosity and an overall enhancement of viscoelasticity. When the oil phase volume reached 75 %, the macroscopic structure transitioned from a low-viscosity fluid to a gel-like form, resulting in a significant boost in the emulsion's viscoelasticity, enhanced thixotropy, and improved centrifugal stability. When the oil phase exceeded 75 %, the emulsion exhibited a polydisperse distribution, and its stability was primarily maintained by the stacking of droplets. Insufficient protein content and mutual compression between interfaces induced a bridging effect, leading to the appearance of larger droplets within the emulsion. Rheological and microstructural analysis further revealed that the high internal phase emulsion with 3.0 % protein content exhibited greater overall stability compared to the emulsion with 2.5 % protein concentration. This study may provide insights into the potential application of rice residue glutelin and the construction of stable double emulsion.

Electrostatic spraying encapsulation of probiotic-loaded W/O/W emulsion in sodium alginate microspheres to enhance probiotic survival stability

Water-oil-water (W/O/W) double emulsions have been widely studied and applied in probiotic encapsulation. However, challenges remain in enhancing emulsion stability, protecting encapsulated probiotics from adverse environmental conditions, and improving their viability. This study aimed to optimize the functional components of each phase of the W/O/W emulsion to address these issues. First, the prebiotic fructooligosaccharide, which promotes bacterial growth, was incorporated into the inner water phase. The oil phase (O) was composed of sunflower oil, polyglyceryl polyricinoleate, and different proportions of cocoa butter to investigate the critical role of cocoa butter in maintaining emulsion stability. The effect of varying ratios of whey protein isolate and gum arabic complexes in the outermost water phase on emulsion stability was also systematically investigated. Finally, combined with electrostatic spraying technology, sodium alginate was used as the encapsulating wall material for the probiotic-encapsulated emulsion, and the stability of the system during in vitro gastrointestinal digestion was evaluated. This study utilized electrostatic spray technology to create a protective "armor" around the emulsion encapsulating probiotics. The combination of emulsion encapsulation and electrostatic spray encapsulation significantly improved the survival stability of probiotics, providing a method for maintaining high viability in complex food media.

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.

Preparation and stability mechanisms of double emulsions stabilized by gelatinized native starch

Double emulsions are promising carrier systems for foods, pharmaceuticals, and cosmetics. However, their limited stability hinders their practical applications. We used gelatinized starch to develop stable double emulsions as carrier materials. The oil/water/water (O/W/W) double emulsions were formed by 5 wt% native corn starch, while oil/water/oil (O/W/O) double emulsions were formed by 7 wt% native corn starch and high-amylose starch with 60 % and 75 % amylose contents investigated by optical microscopy. Furthermore, the storage stability of double emulsions was revealed by droplet size distribution, microstructure, backscattering, rheological profiles, and low-field nuclear magnetic resonance (LF-NMR) imaging. Results confirmed that the O/W/O double emulsions stabilized by 7 wt% native corn starch had a smaller mean droplet size (11.400 ± 0.424 μm) and excellent storage stability (14 days) than O/W/W and O/W/O double emulsions prepared with high-amylose starch. Such unique double emulsions prepared with gelatinized native corn starch are good candidates of carrier materials.

Impact of fat crystallization on the resistance of W/O/W emulsions to osmotic stress: Potential for temperature-triggered release

Water-in-oil-in-water (W/O/W) emulsions can be designed to encapsulate, protect, and release both hydrophilic and hydrophobic functional compounds. In this study, we examined the impact of crystallizing the fat phase on the resistance of W/O/W emulsions to osmotic stress, with the aim of developing osmotic-responsive systems. Polyglycerol polyricinoleate (PGPR) was used as a hydrophobic surfactant to stabilize the inner water droplets, while Quillaja saponin and whey protein isolate (WPI) were used as hydrophilic surfactants to coat the oil droplets. The impact of fat crystallization was examined by using either a liquid (soybean oil, SO) or semi-solid (hydrogenated soybean oil, HSO) fat as the oil phase. An osmotic stress was generated by establishing a sucrose concentration gradient between the internal and external water phases. Alterations in the droplet size, morphology, and stability of the W/O/W emulsions was measured when the sucrose concentration gradient was changed. The W/O droplets in the SO-emulsions swelled/shrank when the external sucrose concentration was below/above the internal sucrose concentration, which is indicative of water diffusing into/out of the droplets. Conversely, there was no change in the size of the W/O droplets in the HSO-emulsions under the same conditions, which was attributed to the mechanical strength of the fat crystal network resisting swelling or shrinking. HSO-emulsions did exhibit swelling when they were heated above a critical temperature, due to melting of the fat crystals and disruption of the crystal network. Our results demonstrate that crystallization of the oil phase of W/O/W emulsions can prevent water transport due to osmotic stress, which may be useful for developing temperature-triggered delivery systems for application in foods, cosmetics, pharmaceuticals, or personal care products.