Formation of Double (W1/O/W2) Emulsions as Carriers of Hydrophilic and Lipophilic Active Compounds

Dual-Mechanism Gastroretentive Tablets with Encapsulated Gentian Root Extract

Background/Objectives: This study aimed to develop gastroretentive tablets based on mucoadhesive-floating systems with encapsulated gentian (Gentiana lutea, Gentianaceae) root extract to overcome the low bioavailability and short elimination half-life of gentiopicroside, a dominant bioactive compound with systemic effect. The formulation also aimed to promote the local action of the extract in the stomach. Methods: Tablets were obtained by direct compression of sodium bicarbonate (7.5%) and solid lipid microparticles (92.5%), which were obtained with lyophilizing double emulsions. A quality by design (QbD) was employed to evaluate the impact of formulation factors and processing parameters on emulsion viscosity, powder characteristics (moisture content, encapsulation efficiency, flowability), and tablet characteristics (floating lag time, gentiopicroside release, and assessment of dispersibility during in vitro dissolution). Results: The trehalose content and high-shear-homogenization (HSH) time of primary emulsion were critical factors. Trehalose content positively influenced emulsion viscosity, moisture content, floating lag time, encapsulation efficiency, and the release rate of gentiopicroside. HSH time positively affected powder stability and negatively gentiopicroside release. The selected powder had a high gentiopicroside encapsulation efficiency (95.13%), optimal stability, and good flowability. The developed tablets exhibited adequate floating lag time (275 s), mucoadhesive properties, and gentiopicroside biphasic release (29.04% in 45 min; 67.95% in 6 h). Furthermore, the optimal tablet formulation remained stable for 18 months and was primarily digested by duodenal enzymes. Conclusions: Dual-mechanism gastroretentive tablets with encapsulated gentian root extract were successfully developed. The in vitro digestion study demonstrated that the optimal formulation effectively resisted gastric enzymes, ensuring the release of its contents in the small intestine, even in the case of premature gastric evacuation.

An Updated Comprehensive Overview of Different Food Applications of W1/O/W2 and O1/W/O2 Double Emulsions

Double emulsions (DEs) present promising applications as alternatives to conventional emulsions in the pharmaceutical, cosmetic, and food industries. However, most review articles have focused on the formulation, preparation approaches, physical stability, and release profile of encapsulants based on DEs, particularly water-in-oil-in-water (W1/O/W2), with less attention paid to specific food applications. Therefore, this review offers updated detailed research advances in potential food applications of both W1/O/W2 and oil-in-water-in-oil (O1/W/O2) DEs over the past decade. To this end, various food-relevant applications of DEs in the fortification; preservation (antioxidant and antimicrobial targets); encapsulation of enzymes; delivery and protection of probiotics; color stability; the masking of unpleasant tastes and odors; the development of healthy foods with low levels of fat, sugar, and salt; and design of novel edible packaging are discussed and their functional properties and release characteristics during storage and digestion are highlighted.

Impact of the lipid phase composition and state on the in vitro digestibility and chlorophyllin bioaccessibility of W1/O/W2 emulsions into whole milk

Water-in-oil-in-water (W1/O/W2) emulsions offer the potential to deliver hydrophilic bioactive compounds into foods, yet their application remains limited due to their instability. Thus, the impact of lipid phase composition and state on the colloidal stability, in vitro lipid digestibility and chlorophyllin (CHL) bioaccessibility of W1/O/W2 emulsions before and after incorporation into whole milk was studied. Medium-chain triglyceride oil (MCT) was used as a liquid lipid phase and MCT with glyceryl stearate (GS) or pure hydrogenated palm oil (HPO) as gelled lipid phases. The lipid phase composition was crucial to forming W1/O/W2 emulsions. MCT or MCT+GS allowed the successful formation of W1/O/W2 emulsions, being more stable upon gastric conditions those formulated with MCT+GS than pure MCT. In contrast, the use of HPO led to phase separation, which was maintained after the gastric conditions. Regarding their lipid digestibility, W1/O/W2 emulsions formulated with MCT or MCT+GS were fully digested, whereas only 40% of the lipid was digested using HPO. In accordance, the CHL bioaccessibility was higher using MCT or MCT+GS than HPO. When co-digested with whole milk, the colloidal stability and lipid digestibility of the W1/O/W2 emulsions with MCT or MCT+GS were not altered, whereas the W1/O/W2 emulsion-HPO showed enhanced colloidal stability and lipid digestibility (57.71 ± 3.06%), due to the surface-active properties of milk protein. The present study provides useful information to develop stable functional foods enriched with hydrophilic bioactive compounds by using W1/O/W2 emulsions.

Emulsion-Based Delivery Systems to Enhance the Functionality of Bioactive Compounds: Towards the Use of Ingredients from Natural, Sustainable Sources

In recent years, the trend in the population towards consuming more natural and sustainable foods has increased significantly. This claim has led to the search for new sources of bioactive compounds and extraction methods that have less impact on the environment. Moreover, the formulation of systems to protect these compounds is also focusing on the use of ingredients of natural origin. This article reviews novel, natural alternative sources of bioactive compounds with a positive impact on sustainability. In addition, it also contains information on the most recent studies based on the use of natural (especially from plants) emulsifiers in the design of emulsion-based delivery systems to protect bioactive compounds. The properties of these natural-based emulsion-delivery systems, as well as their functionality, including in vitro and in vivo studies, are also discussed. This review provides relevant information on the latest advances in the development of emulsion delivery systems based on ingredients from sustainable natural sources.

Dynamic viscosity, centrifugation test and kinetic investigation in emulsions with pumpkin oil

The emulsion stability of different pumpkin O/W emulsions was investigated. Preparation of emulsions were performed with oil phase between 10 and 40 percent, water and soybean protein isolate. To determine emulsion properties different methods were used. Density, viscosity, centrifugation tests and spectroscopic measurements were performed for their investigations. The emulsions were stored for two weeks to determine their kinetic. Influence of the oil phase was presented and connected with the stability of them.

Development of Lipid-Based Gastroretentive Delivery System for Gentian Extract by Double Emulsion-Melt Dispersion Technique

Gentian (Gentiana lutea L., Gentianaceae) root extract (GRE) is used for the treatment of gastrointestinal disorders. However, its bioactive potential is limited in conventional forms due to the low bioavailability and short elimination half-life of the dominant bioactive compound, gentiopicroside. The aim of study was to encapsulate GRE in the lipid-based gastroretentive delivery system that could provide high yield and encapsulation efficiency, as well as the biphasic release of gentiopicroside from the tablets obtained by direct compression. Solid lipid microparticles (SLM) loaded with GRE were prepared by freeze-drying double (W/O/W) emulsions, which were obtained by a multiple emulsion-melt dispersion technique, with GRE as the inner water phase, Gelucire^® 39/01 or 43/01, as lipid components, with or without the addition of porous silica (Sylysia^® 350) in the outer water phase. Formulated SLM powders were examined by SEM and mercury intrusion porosimetry, as well as by determination of yield, encapsulation efficiency, and flow properties. Furthermore, in vitro dissolution of gentiopicroside, the size of the dispersed systems, mechanical properties, and mucoadhesion of tablets obtained by direct compression were investigated. The results have revealed that SLM with the macroporous structure were formulated, and, consequently, the powders floated immediately in the acidic medium. Formulation with porous silica (Sylysia^® 350) and Gelucire^® 43/01 as a solid lipid was characterized with the high yield end encapsulation efficiency. Furthermore, the mucoadhesive properties of tablets obtained by direct compression of that formulation, as well as the biphasic release of gentiopicroside, presence of nanoassociates in dissolution medium, and optimal mechanical properties indicated that a promising lipid-based gastroretentive system for GRE was developed.

Encapsulation of volatile compounds in liquid media: Fragrances, flavors, and essential oils in commercial formulations

The first marketed example of the application of microcapsules dates back to 1957. Since then, microencapsulation techniques and knowledge have progressed in a plethora of technological fields, and efforts have been directed toward the design of progressively more efficient carriers. The protection of payloads from the exposure to unfavorable environments indeed grants enhanced efficacy, safety, and stability of encapsulated species while allowing for a fine tuning of their release profile and longer lasting beneficial effects. Perfumes or, more generally, active-loaded microcapsules are nowadays present in a very large number of consumer products. Commercial products currently make use of rigid, stable polymer-based microcapsules with excellent release properties. However, this type of microcapsules does not meet certain sustainability requirements such as biocompatibility and biodegradability: the leaking via wastewater contributes to the alarming phenomenon of microplastic pollution with about 4% of total microplastic in the environment. Therefore, there is a need to address new issues which have been emerging in relation to the poor environmental profile of such materials. The progresses in some of the main application fields of microencapsulation, such as household care, toiletries, cosmetics, food, and pesticides are reviewed herein. The main technologies employed in microcapsules production and the mechanisms underlying the release of actives are also discussed. Both the advantages and disadvantages of every technique have been considered to allow a careful choice of the most suitable technique for a specific target application and prepare the ground for novel ideas and approaches for encapsulation strategies that we expect to be proposed within the next years.

Formation and Stabilization of W1/O/W2 Emulsions with Gelled Lipid Phases

Water-in-oil-in-water (W₁/O/W₂) emulsions are emulsion-based systems where the dispersed phase is an emulsion itself, offering great potential for the encapsulation of hydrophilic bioactive compounds. However, their formation and stabilization is still a challenge mainly due to water migration, which could be reduced by lipid phase gelation. This study aimed to assess the impact of lipid phase state being liquid or gelled using glyceryl stearate (GS) at 1% (w/w) as well as the hydrophilic emulsifier (T80: Tween 80 or lecithin) and the oil type (MCT:medium chain triglyceride or corn oil (CO) as long chain triglyceride) on the formation and stabilization of chlorophyllin W₁/O/W₂ emulsions. Their colloidal stability against temperature and light exposure conditions was evaluated. Gelling both lipid phases (MCT and CO) rendered smaller W₁ droplets during the first emulsification step, followed by formation of W₁/O/W₂ emulsions with smaller W₁/O droplet size and more stable against clarification. The stability of W₁/O/W₂ emulsions was sensitive to a temperature increase, which might be related to the lower gelling degree of the lipid phase at higher temperatures. This study provides valuable insight for the formation and stabilization of W₁/O/W₂ emulsions with gelled lipid phases as delivery systems of hydrophilic bioactive compounds under common food storage conditions.

The Stability, Microstructure, and Microrheological Properties of Monascus Pigment Double Emulsions Stabilized by Polyglycerol Polyricinoleate and Soybean Protein Isolate

Monascus pigment is a natural food pigment and is commonly used for coloring and as antiseptic of cured meat products, confectionery, cakes, and beverages. However, Monascus pigment is sensitive to environmental conditions. The main aim of this study was to investigate the effect of polyglycerol polyricinoleate (PGPR) and soy protein isolate (SPI) on the particle size, zeta potential, physical stability, microstructure, and microrheological properties of Monascus pigment double emulsions. The effects of ionic strength, heating, and freeze thawing treatment on the stabilities of Monascus pigment double emulsions were also characterized. It was found that the optimum PGPR and SPI concentrations for fabricating Monascus pigment double emulsion were 3.6 and 3.0 wt%, respectively. The fabricated Monascus pigment double emulsion was composed of fine particles with narrow and uniform size distributions. Microrheological property results suggested that the elastic characteristic of the Monascus pigment double emulsion was dominated with increasing PGPR and SPI contents. It was mainly due to the increased collision and interaction between the droplets during the movement resulting in force increasing. Monascus pigment double emulsions with <5 mM CaCl2 prevented calcium to destroy the physical stability of emulsions, while Monascus pigment double emulsions with more than 10 mM CaCl2 formed creaming. After freeze thawing treatment, creaming occurred in Monascus pigment double emulsion. However, it was stable against heating treatment due to heating leading to a dense network structure. It could be contributed to the practical applications of Monascus pigment double emulsions in food products.

Structure and stability of W1/O/W2 emulsions as influenced by WPC and NaCl in inner aqueous phase

Effect of WPC and NaCl in internal aqueous phase (W₁) of W₁/O/W₂ type double emulsions was studied. Pre-emulsion and final emulsion were prepared using microfluidizer and Ultra-Turrax high shear mixer, respectively. The emulsions prepared using salt exhibited uniform droplet size distribution and structural integrity. WPC at 6% and NaCl at 2 or 4% levels demonstrated better sedimentation stability (> 99%) and encapsulation stability (> 95%) during preparation and storage of double emulsions. Samples without added NaCl showed poor emulsion stability and structural integrity. Higher level of WPC i.e. 8% resulted in poor stability and encapsulation efficiency of double emulsions at all salt levels. Combined use of optimum levels of WPC and NaCl along with processing interventions resulted in stable double emulsions even after storage at room temperature for 10 days. This study highlights the fact that structural integrity of internal aqueous phase (W₁) depends upon presence of osmotic agent i.e. salt and stabilising proteins i.e. WPC.

In vitro digestibility and release of a mango peel extract encapsulated within water-in-oil-in-water (W1/O/W2) emulsions containing sodium carboxymethyl cellulose

Mango peel is a rich source of phenolic compounds (PC), which can be used in food fortification. The use of water-in-oil-in-water (W₁/O/W₂) emulsions represents a potential strategy to encapsulate, protect and incorporate PC from mango peel into food products. Moreover, even though non-digestible biopolymers are usually incorporated into emulsions to enhance stability, little is known about the effect on the digestibility and release of PC. In this study, a mango peel extract (MPE) was encapsulated using W₁/O/W₂ emulsions containing sodium carboxymethyl cellulose (CMC; 0, 0.5, 1.0% w/w) in W₂, and their colloidal stability, lipid digestibility kinetics (free fatty acid release), and release (in terms of antioxidant activity) under in vitro digestion conditions were evaluated. The presence of CMC in emulsions caused flocculation of droplets, which remained unchanged during the gastric phase, suggesting that bridging flocculation occurred. Moreover, a slower lipid digestion rate was observed in emulsions containing CMC, with k-values ranging between 0.21 and 0.25 min^-1, compared to emulsions without CMC (around 0.14 min^-1). However, although CMC may slow down the lipolysis reaction during the first 40 min due to physical or steric hindrance, at the end of the intestinal phase, emulsions with or without CMC had a similar final FFA release. Moreover, MPE release was triggered under gastric conditions, probably by osmotic imbalance, showing a constant antioxidant activity value during the intestinal phase only in emulsions containing CMC. This study provides relevant insights to design double emulsions as delivery systems of water-soluble bioactive compounds with antioxidant activity, such as PC.