Stability of curcumin in oil-in-water emulsions: Impact of emulsifier type and concentration on chemical degradation

Nanoemulgel mediated enhanced skin curcumin penetration/retention for local treatment of cutaneous leishmaniasis: in vitro and in vivo assessment

BACKGROUND

Skin delivery of a therapeutically effective drug is imperative for local cutaneous leishmaniasis (CL) treatment.

OBJECTIVE

This study aimed to formulate, optimize, and characterize curcumin-loaded nanoemulgel for enhanced skin drug retention to treat CL locally.

METHODS

Nanoemulsions were prepared by high-speed homogenization, characterized, and optimized for size, PDI, zeta potential, stability, morphology, drug contents, encapsulation efficiency, in vitro drug release, antileishmanial activity, and cell viability. The optimized nanoemulsion (C3) was then incorporated into a carbopol-based gel and evaluated for pH, viscosity, spreadability, and in vitro drug release. Both formulations were then assessed for ex-vivo and in vivo skin permeation/retention, and pharmacokinetic analysis.

RESULTS

All nanoemulsion formulations had size in nano range with negative surface charge, homogeneously distributed, with spherical droplet geometries, where C3 being highly stable, had good encapsulation efficiency and drug contents (85 ± 5.4 and 68 ± 3.2%), released 90% of drug within 4 h, while C3 gel released the drug significantly sustained up to 46% in 24 h. The C3 formulation demonstrated significant in vitro antileishmanial activity across all tested concentrations, while the IC50 value against NIH3T3 fibroblasts was 0.6202 mM (Log IC50: 2.7, R2: 0.98). The C3 gel showed significantly low skin permeation (341.7 ± 43.6 and 52.6 ± 8.9 µg) with significantly higher skin drug retention (129.5 ± 16.7 and 190.2 ± 33.4 µg) ex-vivo and in vivo, with significantly lower Cmax, AUC0-t, and AUC0-∞.

CONCLUSION

These results suggested that curcumin nanoemulgel could be an effective alternative strategy for treating CL locally.

Nanostructured Strategies for Melanoma Treatment-Part II: Targeted Topical Delivery of Curcumin via Poloxamer-Based Thermosensitive Hydrogels

Background/Objectives: Curcumin (CUR) is a natural compound with notable antitumor properties but faces limitations in topical applications due to poor aqueous solubility, instability, and insufficient skin penetration. To overcome these challenges, a nanomicellar formulation (TPGS30ELP15) was developed to enhance CUR solubility, stability, and skin penetration. This study aimed at evaluating the skin permeation and retention of CUR when delivered through nanomicelles alone or combined with a thermosensitive hydrogel for potential melanoma therapy. Methods: A CUR-loaded nanomicellar formulation containing CUR 5 mM was developed, characterized by particle sizes of 12-25 nm. Skin permeation studies utilized pig ear skin to assess CUR localization using both HPLC quantitative analysis and confocal microscopy. To improve patient comfort and application efficiency, the nanomicellar dispersion was incorporated into a thermosensitive hydrogel based on 16% Kolliphor® P407 and was able to undergo a sol-gel transition at skin temperature (32-36 °C). Formulations were evaluated for physicochemical properties, stability, and CUR distribution within skin layers using in vitro permeation assays. Results: CUR-loaded nanomicelles demonstrated selective localization in the viable epidermis (100-150 µm depth), bypassing the stratum corneum. The addition of the thermosensitive hydrogel enhanced CUR retention and distribution, prolonging contact at the application site and providing a gradual release profile. The hydrogel's sol-gel transition properties can facilitate ease of use and patient compliance. The combined system effectively delivered CUR to the basal epidermis, a target site for melanoma treatment, achieving therapeutically relevant drug concentrations. Conclusions: The incorporation of CUR-loaded nanomicelles into a thermosensitive hydrogel enhanced the solubility, stability, and targeted delivery of CUR to skin layers. This dual system represents a promising strategy for improving topical drug delivery for melanoma therapy, addressing limitations associated with CUR's physicochemical properties while ensuring patient-friendly application and gradual drug release.

Construction and digestive characterization of emulsions stabilized with octenyl succinic anhydride-modified curdlan

To expand the scope of application of the insoluble polysaccharide curdlan (CUR), this study modified CUR with octenyl succinic anhydride (OSA) and evaluated the performance of the emulsion formed from the modified CUR derivative. Fourier transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction analysis showed that properties such as the molecular structure, crystallinity, and hydrophobicity of the OSA-modified CUR (COSA) changed significantly compared with those of the original CUR, indicating that the hydroxyl group of CUR was successfully replaced by OSA. Subsequently, a stable oil-in-water emulsion system of COSA loaded with curcumin was established. The stability of the emulsions was evaluated by analyzing their microstructure, rheological properties, and curcumin retention. The digestion characteristics of the emulsions were evaluated by in vitro simulated digestion experiments, and the COSA emulsion had higher stability and was better able to improve the chemical stability of curcumin compared to CUR. The OSA grafting resulted in emulsions with higher curcumin release rates and antioxidant capacities. These results indicate that COSA has the potential to be used as an encapsulating material for lipophilic nutrient emulsions and provides theoretical support for expanding the applications of chemically modified CUR derivatives.

Effect of gum Arabic on antifungal photodynamic activity of curcumin against Botrytis cinerea spores

This study investigated the effect of gum Arabic on curcumin's phototoxicity against Botrytis cinerea, a significant cause of postharvest losses in horticultural produce. Curcumin-loaded nanoparticle suspensions and emulsions stabilized with gum Arabic were prepared and their absorbance, fluorescence emission, physicochemical properties, antimicrobial photodynamic activity (using response surface methodology (RSM)), and reactive oxygen species (ROS) generation (via electron paramagnetic resonance (EPR) spectroscopy) were evaluated. Fluorescence emission exhibited a blue shift (510-550 nm) in both formulations, with emulsions showing higher intensities due to a more hydrophobic environment. Gum Arabic concentration significantly influenced the physicochemical properties of both suspensions, with nanoparticle size decreasing from 572.80 nm to 202.80 nm as gum Arabic concentration increased from 0.5 % to 2.5 % (at 65 μM curcumin). Nanoparticle suspensions demonstrated higher antimicrobial efficacy, reducing B. cinerea spores by 0.39-3.40 log10(CFU.ml-1), compared to 0.00-0.46 log10(CFU.ml-1) in emulsions. The phototoxic effect was dependent on curcumin concentration and light irradiance, as demonstrated by RSM. EPR confirmed the generation of superoxide anion and hydroxyl radicals in both formulations, which indicated a Type I photodynamic mechanism, with nanoparticle suspensions having a sustained ROS generation. Overall, gum Arabic did not impair curcumin's antifungal photodynamic activity, making it as a promising stabiliser for curcumin-based treatments.

Improvement of NaCas/DGMO complex emulsion on resveratrol stability, in vitro bioaccessibility, in vivo bioavailability and gut microbiota

Evaluation for biological impact of food emulsions is fundamental for their application. In present study, we utilized a NaCas-DGMO (sodium caseinate-decylglycerol monooleate) stabilized emulsion to improve resveratrol's (Res) stability, and bioavailability. The in vivo interaction between complex emulsion and gut microbiota was further explored. Results indicated NaCas-DGMO emulsion achieved a loading rate of 92 % for Res and significantly enhanced storage and photo stability of Res. In vitro gastrointestinal digestion highlighted a significant improvement in Res's bioaccessibility. In vivo pharmacokinetic tests showed a notable 3.1-fold increase in oral bioavailability, with a prolonged Tmax of 6 h post-administration. Gut microbiota analysis revealed that the emulsion promoted beneficial bacteria, like Blautia, which produce short-chain fatty acids. Consequently, the findings proved potential of NaCas-DGMO stabled emulsion as carriers for bioactive substances in the food industry. The innovative methodology employed in assessing biological effects provides valuable insights for future research in related field.

Perilla oil emulsions stabilized by casein-dextran sulfate nanocomplexes with and without curcumin

Protein-polysaccharide nanocomplexes are potential particulate emulsifiers to improve physical and chemical stability of emulsions containing polyunsaturated fatty acids. This study prepared nanocomplex dispersions with 2.0 % w/v sodium caseinate and 0-0.4 % w/v dextran sulfate (DS) with and without 0.1 % w/v curcumin. The dispersions exhibited a Z-average diameter of 124.61-182.46 nm, a polydispersity index of 0.37-0.52, and a zeta potential between -30.1 and -34.9 mV, with a curcumin encapsulation efficiency of higher than 75 %. These nanocomplexes were used to emulsify 60 % v/v perilla oil (PO) through shear homogenization and sonication. Emulsions showed discrete droplets in light and confocal laser scanning microscopy. The creaming index decreased as DS concentration increased, remaining below 6 % after 30 days of storage Emulsions had >70 % DS, >80 % caseinate, and 100 % curcumin adsorbed on the oil droplet surface. For oxidative stability at 55 °C for 15 days, emulsions prepared with 2.0 % w/v caseinate and 0.4 % w/v DS, with and without curcumin, showed a maximum of 40 % reduction in the peroxide value and 71 % reduction in the thiobarbituric reactive substances value from those of bulk PO. The present study showed the significance of casein-DS nanocomplexes for the physical and chemical stability of PO emulsions.

Nanocurcumin-Based Sugar-Free Formulation: Development and Impact on Diabetes and Oxidative Stress Reduction

The objective of this study is the development of innovative nanocurcumin-based formulations designed for the treatment and prevention of oxidative stress and diabetes. Nanocurcumin was obtained through a micronization process and subsequently encapsulated within biopolymers derived from corn starch and fenugreek mucilage, achieving encapsulation rates of 75% and 85%, respectively. Subsequently, the encapsulated nanocurcumin was utilized in the formulation of sugar-free syrups based on Stevia rebaudiana Bertoni. The stability of the resulting formulations was assessed by monitoring particle size distribution and zeta potential over a 25-day period. Dynamic light scattering (DLS) revealed a particle size of 119.9 nm for the fenugreek mucilage-based syrup (CURF) and 117 nm for the corn starch-based syrup (CURA), with polydispersity indices PDIs of 0.509 and 0.495, respectively. The dissolution rates of the encapsulated nanocurcumin were significantly enhanced, showing a 67% improvement in CURA and a 70% enhancement in CURF compared with crude curcumin (12.82%). Both formulations demonstrated excellent antioxidant activity, as evidenced by polyphenol quantification using the 2.2-diphenyl 1-pycrilhydrazyl (DPPH) assay. In the evaluation of antidiabetic activity conducted on Wistar rats, a substantial reduction in fasting blood sugar levels from 392 to 187 mg/mL was observed. The antioxidant properties of CURF in reducing oxidative stress were clearly demonstrated by a macroscopic observation of the rats' livers, including their color and appearance.

Stability and gastrointestinal behavior of curcumin-loaded emulsion stabilized by multi-conformation soy proteins: Influence of oil volume fraction

The aim of this work was to assess the potential of nanoemulsions stabilized by mixed soy protein with multi-conformation as curcumin carrier, and the influence of oil volume fraction on stability and gastrointestinal behavior of curcumin-loaded emulsion was investigated. Loading efficiency showed a slight increase with higher oil content, though the difference was not statistically significant. With the increase of oil, the viscosity (Pa‧s), thixotropy (area of hysteresis loop) and particle size of the emulsion increased, which facilitated the physical and chemical stability of curcumin-loaded emulsion. However, the free fatty acid release rate and bioaccessibility of curcumin was negatively correlated with the oil volume fraction and the particle size of emulsion after gastric digestion. Notably, the digestion in stomach did not affect the structure of interfacial protein, demonstrating that protein-based nanoemulsions exhibited resistance to gastric digestion. This study provides theoretical guidance for the application of protein-based emulsion in curcumin delivery.

Exploiting Natural Niches with Neuroprotective Properties: A Comprehensive Review

Natural products from mushrooms, plants, microalgae, and cyanobacteria have been intensively explored and studied for their preventive or therapeutic potential. Among age-related pathologies, neurodegenerative diseases (such as Alzheimer's and Parkinson's diseases) represent a worldwide health and social problem. Since several pathological mechanisms are associated with neurodegeneration, promising strategies against neurodegenerative diseases are aimed to target multiple processes. These approaches usually avoid premature cell death and the loss of function of damaged neurons. This review focuses attention on the preventive and therapeutic potential of several compounds derived from natural sources, which could be exploited for their neuroprotective effect. Curcumin, resveratrol, ergothioneine, and phycocyanin are presented as examples of successful approaches, with a special focus on possible strategies to improve their delivery to the brain.

pH-responsive niosome-based nanocarriers of antineoplastic agents

Differences in pH between the tumour interstitium and healthy tissues can be used to induce conformational changes in the nanocarrier structure, thereby triggering drug release at the desired site. In the present study, novel pH-responsive nanocarriers were developed by modifying conventional niosomes with hexadecyl-poly(acrylic acid)n copolymers (HD-PAAn). Niosomal vesicles were prepared by the thin film hydration method using Span 60, Span 60/Tween 60 and cholesterol as main constituents, and HD-PAA modifiers of different concentrations (0.5, 1, 2.5, 5 mol%). Next, two model substances, a water-soluble fluorescent dye (calcein) and a hydrophobic agent with pronounced antineoplastic activity (curcumin), were loaded in the aqueous core and hydrophobic membrane of the elaborated niosomes, respectively. Physicochemical properties of blank and loaded nanocarriers such as hydrodynamic diameter (Dh), size distribution, zeta potential, morphology and pH-responsiveness were investigated in detail. The cytotoxicity of niosomal curcumin was evaluated against human malignant cell lines of different origins (MJ, T-24, HUT-78), and the mechanistic aspects of proapoptotic effects were elucidated. The formulation composed of Span 60/Tween 60/cholesterol/2.5% HD-PAA17 exhibited optimal physicochemical characteristics (Dh 302 nm; ζ potential -22.1 mV; high curcumin entrapment 83%), pH-dependent drug release and improved cytotoxic and apoptogenic activity compared to free curcumin.

Enhanced curcumin transportation across epithelial barrier by mucus-permeable soy protein nanoparticles-mediated dual transcytosis pathways

Nanocarrier-delivered bioactive compounds are highly desirable for their improved stability and applicability, but their bioavailability is still limited due to the strong mucus and epithelial cell barriers. Herein, a series of self-assembled soy protein nanoparticles (SPNPs) with different mucus permeabilities were prepared and their delivery efficiency upon Curcumin (Cur) encapsulation was evaluated. Results demonstrated that the formed SPNPs-Cur exhibited high compatibility and cellular antioxidant accessibility. Besides, SPNPs enhanced the cellular uptake and transmembrane permeation of Cur, especially promoted the transportation of proto-Cur in addition to Cur metabolites. The SPNPs with the rapid mucus diffusion capacity presented more efficient transcytosis across the Caco-2 cell monolayer, which was mediated by a combination of paracellular and transcellular pathways. This work verified that mucus-permeable soy protein nanoparticles could be a promising delivery system for improving the bioavailability of bioactive compounds.

Arabinoxylan hydrolysates improved physical and oxidative stability of oil-in-water emulsions

This study was to improve the physical and oxidative stability of sodium caseinate (NaCas)-stabilized oil-in-water (O/W) emulsions with arabinoxylan hydrolysates (AXHs). AXHs with different molecular sizes were prepared using xylanase treatment for 0 (AXH0), 30 (AXH30), 60 (AXH60), and 120 (AXH120) min, respectively. Compared with the emulsion without AXHs, all AXHs emulsions showed increased coalescence stability, evidenced by no change occurred in the droplet size with the pH variation from 7.0 to 5.0. Moreover, at pH 7.0 and 5.0, AXH60 and AXH120 emulsions showed no flocculation, coalescence, or creaming before and after 21 d storage. All the AXH samples showed excellent antioxidant capacities, demonstrated by the slow accumulation of lipid hydroperoxides and thiobarbituric acid reactive substances during storage. In sum, rice bran arabinoxylans hydrolyzed ≥60 min possess a potential as effective antioxidants to form physically and oxidatively stable O/W emulsions at pH above the emulsifier pI, and substances with high antioxidant activity below the emulsifier pI still need to be explored.

Recent developments in nanoemulsions against spoilage in cold-stored fish: A review

Nanoemulsion-based technology is developing rapidly in the food industry, especially in the design of delivery systems for bioactive compounds. This review presents an in-depth understanding of the composition, function, antibacterial mechanism and successful application of nanoemulsions as preservative agents against fish spoilage. The results showed that the inclusion of bioactive substances in the food-grade nanoemulsions encapsulation system could improve its stability, control its release, inhibit the microbial growth and reproduction through a variety of targets. These nanoemulsions can inhibit fish spoilage via reducing microbial load and retarding the oxidation of proteins and lipids, thereby maintaining quality attributes of fish. In addition, nanoemulsions could be coupled with vacuum package for enhancing microbial destruction, retaining nutritional value and extending the shelf-life of fish. Accordingly, nanoemulsions are suggested as a promising strategy to inhibit fish spoilage.

The bioavailability, metabolism and microbial modulation of curcumin-loaded nanodelivery systems

Curcumin (Cur), the major bioactive component of turmeric (Curcuma longa) possesses many health benefits. However, low solubility, stability and bioavailability restricts its applications in food. Recently, nanocarriers such as complex coacervates, nanocapsules, liposomes, nanoparticles, nanomicelles, have been used as novel strategies to solve these problems. In this review, we have focused on the delivery systems responsive to the environmental stimuli such as pH-responsive, enzyme-responsive, targeted-to-specific cells or tissues, mucus-penetrating and mucoadhesive carriers. Besides, the metabolites and their biodistribution of Cur and Cur delivery systems are discussed. Most importantly, the interaction between Cur and their carriers with gut microbiota and their effects of modulating the gut health synergistically were discussed comprehensively. In the end, the biocompatibility of Cur delivery systems and the feasibility of their application in food industry is discussed. This review provided a comprehensive review of Cur nanodelivery systems, the health impacts of Cur nanocarriers and an insight into the application of Cur nanocarriers in food industry.

Development and In Vitro Analysis of Layer-by-Layer Assembled Membranes for Potential Wound Dressing: Electrospun Curcumin/Gelatin as Middle Layer and Gentamicin/Polyvinyl Alcohol as Outer Layers

Nanofibrous membranes made of hydrogels have high specific surface areas and are suitable as drug carriers. Multilayer membranes fabricated by continuous electrospinning could delay drug release by increasing diffusion pathways, which is beneficial for long-term wound care. In this experiment, polyvinyl alcohol (PVA) and gelatin were used as membrane substrates, and a sandwich PVA/gelatin/PVA structure of layer-by-layer membranes was prepared by electrospinning under different drug loading concentrations and spinning times. The outer layers on both sides were citric-acid-crosslinked PVA membranes loaded with gentamicin as an electrospinning solution, and the middle layer was a curcumin-loaded gelatin membrane for the study of release behavior, antibacterial activity, and biocompatibility. According to the in vitro release results, the multilayer membrane could release curcumin slowly; the release amount was about 55% less than that of the single layer within 4 days. Most of the prepared membranes showed no significant degradation during immersion, and the phosphonate-buffered saline absorption rate of the multilayer membrane was about five to six times its weight. The results of the antibacterial test showed that the multilayer membrane loaded with gentamicin had a good inhibitory effect on Staphylococcus aureus and Escherichia coli. In addition, the layer-by-layer assembled membrane was non-cytotoxic but detrimental to cell attachment at all gentamicin-carrying concentrations. This feature could be used as a wound dressing to reduce secondary damage to the wound when changing the dressing. This multilayer wound dressing could be applied to wounds in the future to reduce the risk of bacterial infection and help wounds heal.

Physicochemical and In Vitro Digestion Properties of Curcumin-Loaded Solid Lipid Nanoparticles with Different Solid Lipids and Emulsifiers

Curcumin-loaded solid lipid nanoparticles (Cur-SLN) were prepared using medium- and long chain diacylglycerol (MLCD) or glycerol tripalmitate (TP) as lipid matrix and three kinds of surfactants including Tween 20 (T20), quillaja saponin (SQ) and rhamnolipid (Rha). The MLCD-based SLNs had a smaller size and lower surface charge than TP-SLNs with a Cur encapsulation efficiency of 87.54-95.32% and the Rha-based SLNs exhibited a small size but low stability to pH decreases and ionic strength. Thermal analysis and X-ray diffraction results confirmed that the SLNs with different lipid cores showed varying structures, melting and crystallization profiles. The emulsifiers slightly impacted the crystal polymorphism of MLCD-SLNs but largely influenced that of TP-SLNs. Meanwhile, the polymorphism transition was less significant for MLCD-SLNs, which accounted for the better stabilization of particle size and higher encapsulation efficiency of MLCD-SLNs during storage. In vitro studies showed that emulsifier formulation greatly impacted on the Cur bioavailability, whereby T20-SLNs showed much higher digestibility and bioavailability than that of SQ- and Rha-SLNs possibly due to the difference in the interfacial composition. Mathematical modeling analysis of the membrane release further confirmed that Cur was mainly released from the intestinal phase and T20-SLNs showed a faster release rate compared with other formulations. This work contributes to a better understanding of the performance of MLCD in lipophilic compound-loaded SLNs and has important implications for the rational design of lipid nanocarriers and in instructing their application in functional food products.

Physico-Chemical Study of Curcumin and Its Application in O/W/O Multiple Emulsion

Curcuma is a world-renowned herb known for its immense health benefits. In this study, physicochemical analyses were performed on the curcumin standard sample and curcumin multiple emulsions. The emulsions were analysed for thermal and structural stability for 21 days. Confocal laser microscopy (CLSM) was performed in order to observe the emulsion encapsulation. Modulated differential scanning calorimetry (MDSC) and HPLC methods revealed a variety of curcuminoids (curcumin, demethoxycurcumin, bisdemethoxycurcumin, and cyclocurcumin) in the investigated curcumin standard. In addition, the MDSC method was found to be suitable and comparable to HPLC for determining the curcuminoid substances. The analysis of the curcumin release revealed a value of 0.18 w.% after 14 days as the equilibrium value. Furthermore, an increase in the sizes of the emulsions was observed at the end of the 21-day study. The emulsion stability index (ESI) was used to measure the stability of multiple emulsions. The ESI reached 55.8% between 7 and 21 days later. Nano droplets of the oil phase loaded with dispersed curcumin particles captured inside the water-based carboxymethylcellulose micelles were clearly observed by CLSM.

Development and characterization of a fucoidan-based nanoemulsion using Nigella sativa oil for improvement of anti-obesity activity of fucoxanthin in an obese rat model

The anti-obesity activity of encapsulated fucoxanthin in fucoidan-based nanoemulsion was investigated. Then, high-fat diet (HFD) induced-obese rats were fed along with different treatments including administration of encapsulated fucoxanthin (10 mg/kg and 50 mg/kg/day), fucoidan (70 mg/kg), Nigella sativa oil (250 mg/kg), metformin (200 mg/kg), and free form of fucoxanthin (50 mg/kg) by oral gavage daily for 7 weeks. The study discovered that fucoidan-based nanoemulsions with a low and high dose of fucoxanthin had droplet size in the range of 181.70-184.87 nm and encapsulation efficacy of 89.94-91.68 %, respectively. Also exhibited 75.86 % and 83.76 % fucoxanthin in vitro release. The TEM images and FTIR spectera confirmed the particle size and encapsulation of fucoxanthin, respectively. Moreover, in vivo results revealed that encapsulated fucoxanthin reduced body and liver weight compared with a HFD group (p < 0.05). Biochemical parameters (FBS, TG, TC, HDL, LDL) and liver enzymes (ALP, AST, and ALT) were decreased after fucoxanthin and fucoidan administration. According to the histopathological analysis, fucoxanthin and fucoidan attenuated lipid accumulation in the liver.

Multifunctional hydrogels based on chitosan, hyaluronic acid and other biological macromolecules for the treatment of inflammatory bowel disease: A review

Hydrogel is a three-dimensional network polymer material rich in water. It is widely used in the biomedical field because of its unique physical and chemical properties and good biocompatibility. In recent years, the incidence of inflammatory bowel disease (IBD) has gradually increased, and the disadvantages caused by traditional drug treatment of IBD have emerged. Therefore, there is an urgent need for new treatments to alleviate IBD. Hydrogel has become a potential therapeutic platform. However, there is a lack of comprehensive review of functional hydrogels for IBD treatment. This paper first summarizes the pathological changes in IBD sites. Then, the action mechanisms of hydrogels prepared from chitosan, sodium alginate, hyaluronic acid, functionalized polyethylene glycol, cellulose, pectin, and γ-polyglutamic acid on IBD were described from aspects of drug delivery, peptide and protein delivery, biologic therapies, loading probiotics, etc. In addition, the advanced functions of IBD treatment hydrogels were summarized, with emphasis on adhesion, synergistic therapy, pH sensitivity, particle size, and temperature sensitivity. Finally, the future development direction of IBD treatment hydrogels has been prospected.

Curcumin-encapsulated hydrophilic gelatin nanoparticle to stabilize fish oil-loaded Pickering emulsion

Herein, pH-cycle method was explored to prepare curcumin-encapsulated hydrophilic bovine bone gelatin (BBG/Cur) nanoparticle and then the obtained nanoparticle was applied to stabilize fish oil-loaded Pickering emulsion. The nanoparticle had a high encapsulation efficiency (93.9 ± 0.5 %) and loading capacity (9.4 ± 0.1 %) for curcumin. The nanoparticle-stabilized emulsion had higher emulsifying activity index (25.1 ± 0.9 m²/g) and lower emulsifying stability index (161.5 ± 18.8 min) than BBG-stabilized emulsion. The pH affected the initial droplet sizes and creaming index values of the Pickering emulsions: pH 11.0 < pH 5.0 ≈ pH 7.0 ≈ pH 9.0 < pH 3.0. Curcumin provided obvious antioxidant effect for the emulsions, which was also dependent on pH. The work suggested pH-cycle method could be used to prepare hydrophobic antioxidant-encapsulated hydrophilic protein nanoparticle. It also provided basic information on the development of protein nanoparticles for Pickering emulsion stabilization.

Improving shikonin solubility and stability by encapsulation in natural surfactant-coated shikonin nanoparticles

It is significant to develop a colloidal delivery system to improve the water solubility, stability, and bioavailability of shikonin, which is a hydrophobic plant polyphenol with a variety of physiological activities. In this study, three kinds of natural surfactants (saponin, sophorolipid, and rhamnolipid) were used to prepare shikonin nanoparticles by the pH-driven method. The physicochemical and structural properties of the shikonin nanoparticles were characterized, including particle size, zeta potential, and morphology. The encapsulation efficiencies of shikonin nanoparticles coated with saponin and sophorolipid were 97.6% and 97.3%, respectively, which were much higher than that of rhamnolipid-coated shikonin nanoparticles (19.0%). Shikonin nanoparticles coated with saponin and sophorolipid showed good resistance to heat and light and maintained long-term stability during storage. Moreover, shikonin nanoparticles coated with saponin and sophorolipid improved their in vitro-bioavailability. PRACTICAL APPLICATION: These article results are of great importance for improving the stability and bioavailability of shikonin in functional foods, dietary supplements, or pharmaceutical preparations. Moreover, this study provided theoretical and practical guides for further research of shikonin nanoparticles and may promote the development of natural colloidal delivery systems.

In Vitro-In Vivo Study of the Impact of Excipient Emulsions on the Bioavailability and Antioxidant Activity of Flavonoids: Influence of the Carrier Oil Type

The influence of the carrier oil type on the bioavailability and bioactivity of flavonoids (quercetin, kaempferol, and apigenin) was examined using in vitro digestion, in situ intestinal perfusion, and pharmacokinetic studies. Here, medium-chain triglycerides (MCTs), long-chain triglycerides (LCTs), or MCT/LCT mixtures (1:1, w/w) served as the oil phase of excipient emulsions. Overall, the bioavailability and antioxidant activity of flavonoids increased when they were coingested with excipient emulsions. The in vitro bioaccessibility of flavonoids was affected by the carrier oil: LCT (17.9-22.8%) > MCT/LCT (12.1-13.7%) > MCT (9.2-12.6%). These differences were mainly attributed to the fact that the mixed micelles formed after the digestion of LCTs had larger hydrophobic domains to solubilize more flavonoids. However, in vivo pharmacokinetic experiments showed that the flavonoid concentrations in rat serum were comparable for all carrier oils (p > 0.05). Our results assist in formulating excipient emulsions to enhance the efficacy of flavonoids.

Preparation and Optimization of O/W Emulsions Stabilized by Triglycerol Monolaurate for Curcumin Encapsulation

Curcumin is one of the most studied chemo-preventive agents, which may cause suppression, retardation, or inversion of carcinogenesis. But its application is currently limited because of its poor water-solubility and bioaccessibility. A curcumin O/W emulsion was prepared by high-pressure homogenization, using triglyceride monolaurate as an emulsifier and medium chain triglycerides (MCT) as the oil phase. The effects of emulsifiers, emulsifier concentration, oil type, oil-to-water ratio, and homogenization pressure and processing cycles on the physical stability and droplet size distribution of curcumin-encapsulated O/W emulsions were evaluated in this study. The results showed that the mean droplet size of the O/W emulsions remained remarkably stable during 60 days of storage under both light and dark conditions. Curcumin retentions in O/W emulsions after 60 days of storage under light and dark conditions were 97.9% and 81.6%, respectively. In addition, during the simulated gastrointestinal digestion process, the mean droplet size of the O/W emulsions increased from 260 nm to 2743 nm after incubation with simulated gastric fluid (SGF) for 24 h, while the mean droplet size remained unchanged after incubation with simulated intestinal fluid (SIF). The results displayed negligible changes in curcumin content during incubation with simulated gastrointestinal fluids, indicating that effective protection of curcumin was achieved by encapsulation in the O/W emulsion. It is expected that curcumin will acquire high bioaccessibility and bioavailability when the O/W emulsion is to be used in clinical applications.

Shellac Micelles Loaded with Curcumin Using a pH Cycle to Improve Dispersibility, Bioaccessibility, and Potential for Colon Delivery

Delivery systems smaller than 50 nm are advantageous for cancer prevention. In this study, curcumin was dissolved in shellac micelles following co-dissolving at pH 13.0 and neutralization using glucono-delta-lactone. With 5% w/v shellac and 0.5-5 mg/mL curcumin, the loading capacity and encapsulation efficiency were up to 8.0 and 92.6%, respectively, and the nanocapsules had an average diameter of 20 nm. Differential scanning calorimetry, FTIR spectroscopy, and fluorescence spectroscopy results confirmed the encapsulation of curcumin in an amorphous state in shellac micelles. The neutral nanocapsule dispersions maintained the particle dimension and had less than 10% curcumin degradation during 4 week storage at 4 °C. Nanoencapsulating curcumin enhanced in vitro bioavailability and antiproliferation activity against colon cancer cells. After simulated digestions, ∼60% of the nanoencapsulated curcumin was not available for intestinal absorption, nanocapsules retained their structure, and nanoencapsulated curcumin remained active against colon cancer cells, indicating the potential delivery for colorectal cancer prevention.

Polysaccharide-based nano-delivery systems for encapsulation, delivery, and pH-responsive release of bioactive ingredients

Polysaccharides are natural polymers isolated from plants, microorganisms, algae, and some animals they are composed of aldoses or ketoses linked by glycosidic bonds. Due to the affordability, abundance, safety, and functionality, polysaccharides are widely used in the foods and medicines to construct oral delivery systems for sensitive bioactive ingredients. In this article, the characteristics and applications of nanoscale polysaccharide-based delivery carriers are reviewed, including their ability to encapsulate, protect, and deliver bioactive ingredients. This review discusses the sources, characteristics, and functional properties of common food polysaccharides, including starch, pectin, chitosan, xanthan gum, and alginate. It also highlights the potential advantages of using polysaccharides for the construction of nano-delivery systems, such as nanoparticles, nanogels, nanoemulsions, nanocapsules, and nanofibers. Moreover, the application of delivery systems assembled from polysaccharides is summarized, with a focus on pH-responsive delivery of bioactives. There are some key findings and conclusions: Nanoscale polysaccharide delivery systems provide several advantages, including improved water-dispersibility, flavor masking, stability enhancement, reduced volatility, and controlled release; Polysaccharide nanocarriers can be used to construct pH-responsive delivery vehicles to achieve intestinal-targeted delivery and controlled release of bioactive ingredients; Polysaccharides can be used in combination with other biopolymers to form composite delivery systems with enhanced functional attributes.

Evaluation of the synergistic effect of plant-based components on the stability of curcuminoid emulsion

In this study, the effect of matrix compounds from natural curcuminoid resources on the stability of curcuminoids and emulsions thereof was evaluated. Curcuminoid emulsions were prepared curcuminoid rich sources (curcuminoid extract, an aqueous turmeric concentrate and turmeric powder) with medium-chain triglyceride oil as lipid phase, lecithin, and pectin as emulsifiers. The curcuminoid emulsions were exposed to light in the visible wavelength range (300 nm–800 nm) at the specific energy input of 0.47 kW/m2 for 7 days and to the temperature of 4 °C, 25 °C, 40 °C for 49 days. The total curcuminoid retention (TC), droplet size (DS) change, instability index (InI), and yellowness reduction (YR) was observed during the storage time. The half-life of curcuminoids in emulsions was increased to 21 h, while the half-life of free curcuminoids was 1.3 h in the light exposure test. The co-compounds from the curcuminoid sources contributed to the emulsion stability by increasing the viscosity. In the thermal exposure test, the matrix compound system retained more than 93% curcuminoids after 49 days of storage at 40 °C, whereas the phase separation increased significantly. However, the TC reduction was independent of the InI change and droplet agglomeration. The YR depended on the TC and the amount of co-components in the emulsion.

Mixed Biopolymer Systems Based on Bovine and Caprine Caseins, Yeast β-Glucan, and Maltodextrin for Microencapsulating Lutein Dispersed in Emulsified Lipid Carriers

Lutein is an important antioxidant that quenches free radicals. The stability of lutein and hence compatibility for food fortification is a big challenge to the food industry. Encapsulation can be designed to protect lutein from the adverse environment (air, heat, light, pH). In this study, we determined the impact of mixed biopolymer systems based on bovine and caprine caseins, yeast β-glucan, and maltodextrin as wall systems for microencapsulating lutein dispersed in emulsified lipid carriers by spray drying. The performance of these wall systems at oil/water interfaces is a key factor affecting the encapsulation of lutein. The highest encapsulation efficiency (97.7%) was achieved from the lutein microcapsules prepared with the mixed biopolymer system of caprine αs1-II casein, yeast β-glucan, and maltodextrin. Casein type and storage time affected the stability of lutein. The stability of lutein was the highest (64.57%) in lutein microcapsules prepared with the mixed biopolymer system of caprine αs1-II casein, yeast β-glucan, and maltodextrin, whereas lutein microcapsules prepared with the biopolymer system of bovine casein, yeast β-glucan, and maltodextrin had the lowest (56.01%). The stability of lutein in the lutein microcapsules dramatically decreased during storage time. The antioxidant activity of lutein in the lutein microcapsules was closely associated with the lutein concentration.

Emulgels Containing Perilla frutescens Seed Oil, Moringa oleifera Seed Oil, and Mixed Seed Oil: Microemulsion and Safety Assessment

P. frutescens seed oil and M. oleifera seed oil consist of fatty acids and sterols that are beneficial for skin. Mixing of these oils at 1:1 ratio has shown to increase antioxidant activity of oils. This study aims to formulate emulgels containing microemulsions of P. frutescens seed oil, M. oleifera seed oil, and mixed P. frutescens and M. oleifera seed oils. The chemical constituents of P. frutescens seed oil, M. oleifera seed oil, and mixed seed oil are analyzed by gas chromatography/mass spectrometry (GC/MS). The microemulsions are formulated by a phase titration method and characterized for the droplet size, polydispersity index, and zeta potential value using a dynamic light scattering technique. The physical and chemical stability of the microemulsions are investigated using a rheometer and UV-Visible spectrophotometer, respectively. The safety of microemulsion is evaluated on PBMC and human subjects. Emulgels containing three different types of microemulsion are formulated. The results show that P. frutescens seed oil is mainly composed of alpha-linolenic acid, linoleic acid, and oleic acid, whereas M. oleifera seed oil contains a high proportion of oleic acid. Mixed seed oil contains a comparable amount of alpha-linolenic acid and oleic acid. All types of oils are composed of β-sitosterol as the major plant sterol. Microemulsions of all types of oils are successfully prepared by using Tween 80 as a surfactant due to the largest transparent region of pseudoternary phase diagram. The size, polydispersity index, and zeta potential values of all types of microemulsion are in the acceptable range upon storage at 30 °C for 1 month. Microemulsions exhibit pseudoplastic flow behavior. The percent of remaining oils in all types of microemulsion is more than 90% after storage at 30 °C for 1 month. Emulgels containing three types of microemulsions exhibit good characteristics and no change in viscosity after storage at 4, 30, and 45 °C for 1 month. The safety results reveal that three types of microemulsion do not induce cytotoxicity to PBMC nor induce skin irritation and allergic reactions. Emulgels containing microemulsions developed in this study can be used to safely deliver P. frutescens seed oil, M. oleifera seed oil, and mixed seed oil to human skin.

Proposed Methods for Testing and Comparing the Emulsifying Properties of Proteins from Animal, Plant, and Alternative Sources

The food industry is trying to reformulate many of its products to replace functional ingredients that are chemically synthesized or isolated from animal sources (such as meat, fish, eggs, or milk) with ingredients derived from plant or microbial sources. This effort is largely a result of the demand for foods that are better for the environment, human health, and animal welfare. Many new kinds of plant- or microbial-derived proteins are being isolated for potential utilization as functional ingredients by the food industry. A major challenge in this area is the lack of standardized methods to measure and compare the functional performance of proteins under conditions they might be used in food applications. This information is required to select the most appropriate protein for each application. In this article, we discuss the physicochemical principles of emulsifier functionality and then present a series of analytical tests that can be used to quantify the ability of proteins to form and stabilize emulsions. These tests include methods for characterizing the effectiveness of the proteins to promote the formation and stability of the small droplets generated during homogenization, as well as their ability to stabilize the droplets against aggregation under different conditions (e.g., pH, ionic composition, temperature, and shearing). This information should be useful to the food industry when it is trying to identify alternative proteins to replace existing emulsifiers in specific food applications.

Effect of operating parameters on the physical and chemical stability of an oil gelled-in-water emulsified curcumin delivery system

BACKGROUND

Curcumin is a natural antioxidant with important beneficial properties for health, although its low bioavailability and sensitivity to many environmental agents limits its use in the food industry. Furthermore, some studies mention a potential synergistic effect with omega-3 polyunsaturated fatty acids, comprising other bioactive compounds extremely unstable and susceptible to oxidation. A relatively novel strategy to avoid oxidation processes is to transform liquid oils into three-dimensional structures by adding a gelling agent and forming a self-assembled network that can later be vectorized by incorporating it into other systems. The present study aimed to design and optimize an oil gelled-in-water curcumin-loaded emulsion to maximize curcumin stability and minimize lipid oxidation in terms of some critical operating parameters, such as dispersed phase, emulsifier and stabilizer concentrations, and homogenization rate.

RESULTS

The operating conditions that had a significant effect on the formulation were the dispersed phase weight fraction affecting droplet size and total lipid oxidation, homogenization conditions affecting droplet size and primary lipid oxidation, and emulsifier concentration affecting droplet size (significance level = 95%). The optimal formulation for maximizing curcumin load and minimizing lipid oxidation in the oleogelified matrix was 140.4 g kg^-1 dispersed phase, 50.0 g kg^-1 emulsifier, 4.9 g kg^-1 stabilizer and homogenization speed 1016 × g.

CONCLUSION

The results obtained in the present study provide a valuable tool for the rational design and development of oil gelled-in-water emulsions that stabilize and transport bioactive compounds such as curcumin. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fabrication and Characterization of Prochloraz Nanoemulsion against Penicillium citrinum for the Postharvest Storage of Navel Oranges

Nanoemulsions have become extremely popular water-insoluble pesticide delivery systems in recent years. In this study, prochloraz nanoemulsions were obtained by selecting the mixing ratio of surfactants (6:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:6), surfactant concentration, and shearing time. The optimal formula was 10 wt % prochloraz, 6 wt % surfactant (2 wt % CO-100 + 4 wt % CO-360) dissolved in 6 wt % hydrocarbon solvent (S-100A), and deionized water replenished to 100 wt %. This formula meets the quality index standards of the Food and Agriculture Organization. Compared with oil-in-water emulsion (EW), the prochloraz nanoemulsion exhibited higher antifungal activity against Penicillium citrinum in vitro (lower LC₅₀ of 1.17 mg L^-1) and in vivo (fewer lesions). In addition, the L02 cells treated with the nanoemulsion had a higher survival rate and lower apoptosis rate at the same concentration. Results showed that the toxicity of the prochloraz nanoemulsion on L02 cells was lower than that of EW. The findings provide an important method for developing an efficient, safe, and environment-friendly nanoemulsion for postharvest fruit storage.

Nanoencapsulated curcumin emulsion utilizing milk cream as a potential vehicle by microfluidization: Bioaccessibility, cytotoxicity and physico-functional properties

Curcumin loaded milk cream emulsion was microfluidized at different pressures (50-200 MPa) and passes (1-4) using a full-factorial experimental design. Ultrasonicated and microfluidized emulsion was evaluated for particle size, morphological characteristics, antioxidant activity, rheological properties, bioaccessibility and cytotoxicity. Significant reduction was observed in the average particle size (358.2 nm) after microfluidization at 100 MPa/2nd pass. Transmission electron micrographs of the control (homogenized) and microfluidized (100 MPa/2nd pass) samples showed uniform distribution of fat globules in the microfluidized sample with partially dissolved curcumin particles (50-150 nm). Encapsulation efficiency of microfluidized emulsion was found to be significantly higher (97.88%) after processing as compared to control (91.21%). Two-fold (100%) increase in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and 25% increase in ferric-reducing antioxidant power (FRAP) was observed for microfluidized emulsions over control. Infrared spectrums of the emulsion exhibited shift in high intensity peaks indicating bond cleavage after microfluidization. After characterization, emulsions were subjected to in vitro digestion (oral, gastric and intestinal phase) to evaluate its bioaccessibility which was found to be remarkably increased by 30% after microfluidization. For assessing processing induced safety of the formulation, in vitro cytotoxicity of the microfluidized nanocurcumin emulsion was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on HepG2 cells, wherein high % of cell viability (>93%) was seen even at a dose as high as 900 µg/mL revealing no toxic effect of the processing technique (microfluidization). This study highlights the efficacy of microfluidization as a technique and that of milk cream as an inexpensive, yet potential vehicle for generating stable and bio-accessible nano-curcumin emulsion.

Improvement of stability and bioaccessibility of β-carotene by curcumin in pea protein isolate-based complexes-stabilized emulsions: Effect of protein complexation by pectin and small molecular surfactants

The impact of different complexes on the properties of β-carotene-loaded emulsions was investigated by measuring the droplet size, encapsulation efficiency, droplet morphology, and physical stability. The photo and thermal stability of β-carotene and its bioaccessibility during digestion were also analyzed. Comparing to the emulsions stabilized by other complexes, the emulsion stabilized by the high methoxyl pectin-rhamnolipid-pea protein isolate-curcumin (HMP-Rha-PPI-Cur) complex had the smallest droplet size (17.53 ± 0.15 μm) and the maximum encapsulation efficiency for curcumin (90.33 ± 0.03 %) and β-carotene (92.16 ± 0.01 %). The emulsion stabilized by the HMP-Rha-PPI-Cur complex exhibited better physical stability against creaming. The retention rate of β-carotene in the HMP-Rha-PPI-Cur complex-stabilized emulsion was 17.75 ± 0.02 and 33.64 ± 0.02 % after UV irradiation and thermal treatment. The HMP-Rha-PPI-Cur complex-stabilized emulsion also had a higher level of free fatty acid released (43.67 %) and higher bioaccessibility of β-carotene (32.35 ± 0.02 %).

Polysaccharide conjugates from Chin brick tea (Camellia sinensis) improve the physicochemical stability and bioaccessibility of β-carotene in oil-in-water nanoemulsions

A natural antioxidant emulsifier, tea polysaccharide conjugate (TPC), was isolated from Chin brick tea. The impact of TPC on β-carotene stability and bioaccessibility in oil-in-water nanoemulsions was assessed. TPC exhibited strong antioxidant activity and could be used to fabricate stable nanoemulsions (d < 140 nm). The extent of lipid digestion was considerably lower for lipid droplets coated by TPC (68%) than Tween 80 (94%) or whey protein isolate (WPI) (89%), probably because TPC formed interfacial layers that hindered the access of lipases to lipids. The chemical stability of β-carotene in TPC-nanoemulsions was markedly higher than in those formulated with Tween 80 or WPI due to the high antioxidant activity of TPC. The bioaccessibility of β-carotene (20-30%) was independent of emulsifier type. TPC from Chin brick tea can therefore be used as a dual-purpose functional ingredient in emulsified foods.

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.

Curcumin-loaded metal oxide aerogels: supercritical drying and stability

Curcumin, known as a potential antioxidant and anti-inflammatory agent, has major limitations for its therapeutic use because of its lack of water solubility and relatively low bioavailability. We report for the first time the loading of different metal oxide aerogels with curcumin. The aerogels were prepared via the sol–gel process and dried under supercritical conditions. Mixing curcumin with the metal precursors prior to the formation of the solid network ensures maximum entrapment. The curcumin–network interactions stabilize the organic moiety and create hybrid aerogels as potential vehicles for curcumin in various media. The aerogels were characterized by FTIR spectroscopy, thermogravimetric analysis, electron microscopy, and fluorescence spectroscopy to confirm their hybrid nature. The stability study by fluorescence spectroscopy revealed three distinct behaviors depending on the nature of the metal oxide: (i) a minor interaction between curcumin and the solid network slightly affecting the microenvironment; (ii) a quenching phenomenon when iron is present explained by a coordination between the iron ions and curcumin; and (iii) a strong complexation of the metal ions with curcumin after gelation.

Metal oxide aerogels are investigated as encapsulation media for curcumin, a polyphenol having potential uses in medicine, probing, and sensing.

Carboxymethyl chitosan microspheres loaded hyaluronic acid/gelatin hydrogels for controlled drug delivery and the treatment of inflammatory bowel disease

A major drawback of oral treatment of inflammatory bowel disease (IBD) is the non-specific distribution of drugs during long-term treatment. Despite its effectiveness as an anti-inflammatory drug, curcumin (CUR) is limited by its low bioavailability in IBD treatment. Herein, a pH-sensitive composite hyaluronic acid/gelatin (HA/GE) hydrogel drug delivery system containing carboxymethyl chitosan (CC) microspheres loaded with CUR was fabricated for IBD treatment. The composition and structure of the composite system were optimized and the physicochemical properties were characterized using infrared spectroscopy, X-ray diffraction, swelling, and release behavior studies. In vitro, the formulation exhibited good sustained release property and the drug release rate was 65% for 50 h. In vivo pharmacokinetic experiments indicated that high level of CUR was maintained in the colon tissue for more than 24 h; it also played an anti-inflammatory role by evaluating the histopathological changes through hematoxylin and eosin (H&E), myeloperoxidase (MPO), and immunofluorescent staining. Additionally, the formulation substantially inhibited the level of the main pro-inflammatory cytokines of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) secreted by macrophages, compared to the control group. The pharmacodynamic experiment showed that the formulation group of CUR@gels had the best therapeutic effect on colitis in mice. The composite gel delivery system has potential for the effective delivery of CUR in the treatment of colitis. This study also provides a reference for the design and preparation of a new oral drug delivery system with controlled release behavior.