Enhancing the Retention and Oxidative Stability of Volatile Flavors: A Novel Approach Utilizing O/W Pickering Emulsions Based on Agri-Food Byproducts and Spray-Drying.

Spray-drying is a commonly used method for producing powdered flavors, but the high temperatures involved often result in the loss of volatile molecules. To address this issue, our study focused on a novel approach: developing O/W Pickering emulsions with agri-food byproducts to encapsulate and protect D-limonene during spray-drying and storage. Emulsions formulated with lupin hull, lupin-byproduct (a water-insoluble protein-fiber byproduct derived from the production of lupin protein isolate), and camelina press-cake were subjected to spray-drying at 160 °C. The results revealed that these emulsions exhibited good stability against creaming. The characteristics of the dry emulsions (powders) were influenced by the concentration of byproducts. Quantitative analysis revealed that Pickering emulsions enhanced the retention of D-limonene during spray-drying, with the highest retention achieved using 3% lupin hull and 1% camelina press-cake. Notably, lupin-stabilized emulsions yielded powders with enhanced oxidative stability compared to those stabilized with camelina press-cake. Our findings highlight the potential of food-grade Pickering emulsions to improve the stability of volatile flavors during both processing and storage.

Palmitic acid at high concentration modifies the nanoscale structure of anhydrous milk fat.

We performed a nanoscale study based on X-ray scattering to understand the impact of a promotor of crystallization, palmitic acid (PA), at high concentration, on the networks of triacylglycerols (TAGs) in anhydrous milk fat (AMF). Melted blends containing 10 wt% PA were quenched at 25 °C. X-ray scattering data were compared with those obtained for pure AMF, pure PA, and AMF containing 1 wt% PA. While PA at low concentration did not modify the nanostructure of TAG crystals (direct crystallization in the ß'-2L form), a high concentration of this promotor favored the formation of polymorphic forms suggesting that PA first crystallizes and then directs crystallization of AMF TAGs towards α and ß forms.

Method to prepare aqueous propolis dispersions based on phase separation.

Propolis has many benefits for human health. To facilitate its oral consumption, we designed propolis-in-water dispersions to be used as nutraceuticals. Propolis was first dissolved either in ethanol or in a hydroalcoholic solution. Water being a non-solvent for propolis, its addition produced propolis precipitation. We explored the ternary phase diagram of water, propolis and ethanol to identify the line separating the one phase region where propolis is fully dissolved, and the two-phase region where a concentrated propolis solution coexists with a dilute one. Droplets rich in propolis were produced during the phase separation process under mechanical stirring induced by a rotor-stator device or a microfluidizer, and they were stabilized using gum Arabic as an emulsifier. Ethanol was finally removed by distillation under reduced pressure. Propolis dispersions in the micron and submicron size range could be obtained. They contained between 1.75 and 10.5 wt% polyphenols relative to the total mass.

Isothermal crystallization of anhydrous milk fat in presence of free fatty acids and their esters: From nanostructure to textural properties.

We performed a multiscale study to understand the impact of pure exogenous compounds at low concentration on the crystallization of triacylglycerols (TAGs) in anhydrous milk fat (AMF). We selected butyric acid, an inhibitor of crystallization, and palmitic acid, a promotor, to investigate the influence of the chain length. Tripalmitin was also used as a promotor to assess the impact of fatty acid esterification. Melted blends containing the additives (1 wt%) were quenched at 25 °C. X-ray scattering data showed that AMF TAGs crystallized directly in the ß'-2L form. The presence of additives did not modify the nanostructure of TAG crystals. However, they significantly altered the microstructure of AMF, as revealed by polarized light microscopy and rheology. This study emphasizes the interest of a multiscale approach to gain knowledge about the behavior of complex fat blends and of the use of modulators at low concentration to monitor their textural properties.

Crystallization of emulsified anhydrous milk fat: The role of confinement and of minor compounds. A DSC study.

We examined the crystallization and melting of anhydrous milk fat (AMF)-in-water emulsions stabilized by sodium caseinate. Various additives at low concentrations (<5 wt%), differing in their hydrocarbon chain length (propionic vs. palmitic acid), unsaturation (palmitic vs. oleic acid), and esterification state (palmitic acid vs. tripalmitin) were used to modulate AMF crystallization kinetics. Three emulsions with different average droplet diameters were cooled down from 60 °C to 4 °C. Fat crystallization was followed by DSC under dynamic (cooling) and static (isothermal) conditions. Propionic acid did not have any noticeable effect. Oleic acid favored supercooling and the formation of unstable polymorphs at short times but its impact faded after 48 h of isothermal storage. The impact of palmitic acid was related to its amphiphilic properties and vanished after 48 h. Tripalmitin influenced crystallization via volume effects that were persistent. It formed mixed crystals which extended the melting range of AMF.

Food-grade Pickering emulsion as a novel astaxanthin encapsulation system for making powder-based products: Evaluation of astaxanthin stability during processing, storage, and its bioaccessibility.

The use of astaxanthin as a food ingredient is limited due to its poor water solubility in aqueous matrices and highly susceptibility to oxidation; hence microencapsulation of this carotenoid is an appropriate technique to increase its stability and functionally. In this study, astaxanthin oleoresin was encapsulated using a food-grade Pickering emulsion to enhance its stability during spray-drying and storage and its bioaccessibility. The oil-in-water (O/W) emulsions were stabilized by protein-based aggregates obtained from a lupin protein-rich cultivar (AluProt-CGNA). The emulsions containing the astaxanthin microencapsulated in its oil phase (core material) were submitted to a spray-drying process at 160 °C and 140 °C. For this, blends of these protein-based aggregates (LP-APs) and maltodextrin (at different ratios) were used as wall material. The emulsion stability, microstructure, powder characteristics, oxidative stability and concentration of astaxanthin, encapsulation efficiency and bioaccessibility after spray-drying were investigated. The results showed that LP-APs exhibit a great potential to perform as stabilizers for Pickering emulsions. The formed O/W emulsions were highly stable against creaming at high concentrations of LP-APs. The results also indicated that spray-drying can be applied to prepare stable astaxanthin emulsions into powders with good oxidative stability. The astaxanthin content in dry emulsions under storage conditions (25 and 45 °C for 4 weeks) was higher in powders containing a higher LP-APs concentration. The encapsulation efficiency was higher than 90% with the emulsion stabilized with 6% of LP-APs. The bioaccessebility of reconstituted astaxanthin powder (with 6% LP-APs) was around 80%.

Hydroxytyrosol encapsulated in biocompatible water-in-oil microemulsions: How the structure affects in vitro absorption.

Over the last years, the incorporation of natural antioxidants in food and pharmaceutical formulations has gained attention, delaying or preventing oxidation phenomena in the final products. In order to take full advantage of their properties, protection in special microenvironments is of great importance. The unique features of the natural phenolic compound hydroxytyrosol (HT) - including antioxidant, anti-inflammatory, antiproliferative and cardioprotective properties - have been studied to clarify its mechanism of action. In the present study novel biocompatible water-in-oil (W/O) microemulsions were developed as hosts for HT and subsequently examined for their absorption profile following their oral uptake. The absorption of HT in solution was compared with the encapsulated one in vitro, using a coculture model (Caco-2/TC7 and HT29-MTX cell lines). The systems were structurally characterized by means of Dynamic Light Scattering (DLS) and Electron Paramagnetic Resonance (EPR) techniques. The diameter of the micelles remained unaltered after the incorporation of 678 ppm of HT but the interfacial properties were slightly affected, indicating the involvement of the HT molecules in the surfactant monolayer. EPR was used towards a lipophilic stable free radial, namely galvinoxyl, indicating a high scavenging activity of the systems and encapsulated HT. Finally, after the biocompatibility study of the microemulsions the intestinal absorption of the encapsulated HT was compared with its aqueous solution in vitro. The higher the surfactants' concentration in the system the lower the HT concentration that penetrated the constructed epithelium, indicating the involvement of the amphiphiles in the antioxidant's absorption and its entrapment in the mucus layer.

Emulsification of non-aqueous foams stabilized by fat crystals: Towards novel air-in-oil-in-water food colloids.

We designed Air-in-Oil-in-Water (A/O/W) emulsions. First, Air-in-Oil foams were fabricated by whipping anhydrous milk fat. The maximum overrun was obtained at 20 °C. The foams contained 30-35 vol% air and were stabilized solely by fat crystals. To refine the bubble size, foams were further sheared in a Couette's cell. The average bubble size reached a value as small as 6.5 µm at a shear rate of 5250 s-1. The nonaqueous foams were then dispersed in a viscous aqueous phase containing sodium caseinate to obtain A/O/W emulsions. The shear rate was varied from 1000 to 7500 s-1, allowing to obtain Air-in-Oil globules whose average diameter ranged from 15 to 60 µm. To avoid globule creaming, the aqueous phase was gelled by incorporating hydroxyethyl cellulose. Homogeneous emulsions were obtained with fat globules containing around 22 vol% of residual air. The systems were kinetically stable for at least 3 weeks at 4 °C.

O/W Pickering emulsions stabilized by cocoa powder: Role of the emulsification process and of composition parameters.

We fabricated oil-in-water emulsions stabilized by delipidated commercial cocoa powder. The emulsions were characterized in terms of droplets and particles size distribution and interfacial coverage by cocoa powder by developing methods to separate droplets from adsorbed and unadsorbed cocoa particles. Three different processes were compared for their ability to produce fine and stable emulsions: rotor/stator turbulent mixing, sonication and microfluidization. Among those techniques, microfluidization was the most performing one. In this case, micron-sized emulsions with narrow size distributions could be obtained with >90 wt% of the powder insoluble material anchored to the interfaces, and they were still stable after 90 days. It was demonstrated that the mixing process did not generate finer cocoa particles but provoked disentanglement of the large primary particles, providing them an open, expanded structure that facilitated emulsification. It was also shown that the finer insoluble fraction of the powder and the soluble fraction had no significant impact on emulsification and on kinetic stability. In the poor particles regime, the oil-water interfacial area varied linearly with the amount of adsorbed powder, suggesting that the final droplet size was controlled by the so-called limited coalescence process, as already observed in conventional Pickering emulsions stabilized by spherical solid particles.

Monodisperse Oil-in-Water Emulsions Stabilized by Proteins: How To Master the Average Droplet Size and Stability, While Minimizing the Amount of Proteins.

Hexadecane-in-water emulsions were fabricated by means of a microfluidizer using two types of protein stabilizers, sodium caseinate (NaCAS) and ß-lactoglobulin (BLG). A study of the dependence of the mean droplet diameter and protein coverage on protein concentration was performed. At low protein concentrations, the emulsions were monodispersed and their mean droplet size was governed by the so-called limited-coalescence process. In this regime, the interfacial coverage was constant and was deduced from the linear evolution of the total interfacial area as a function of the amount of adsorbed proteins. In emulsions based on NaCAS, almost all of the initial protein contents were adsorbed at the interfaces. Emulsions formulated at very low protein content underwent unlimited coalescence after prolonged storage or when submitted to centrifugation. Additional NaCAS was incorporated in the continuous phase, right after the emulsification process, as a means of ensuring kinetic stability. The interfacial coverage increased after protein addition. Other strategies including acidification and salt addition were also probed to gain stability. Instead, in emulsions based on BLG, only partial adsorption of the initial protein content was observed. The corresponding emulsions remained kinetically stable against coalescence, and no further addition of protein was required after emulsification. Our approach allows to obtain monodisperse, kinetically stable emulsions and to master their average droplet size, while minimizing the amount of proteins.

Influence of Implants Composition on Melatonin Release from Ethylcellulose Matrix.

BACKGROUND: Melatonin release from Ethylcellulose matrix has never been studied on the whole range of compositions. OBJECTIVE: To perform a comprehensive study about the influence of the melatonin loading on its release from solid ethylcellulose implants, from both a kinetic and structural point of view. METHOD: Cylindrical implants differing in their Melatonin:Ethylcellulose ratio were fabricated to cover a large range of compositions. Drug release was assayed by in vitro dissolution tests in CTAB micellar solutions. The 2D imaging of implant chemical composition during Melatonin release was performed by confocal Raman spectroscopy. FT-IR spectroscopy and Karl-Fisher technique were employed to study implants hydration. RESULTS: A drug radial leakage, whatever the implant composition, is imaged. The apparent diffusion coefficient, D of melatonin was evaluated considering Fickian radial diffusion: its value ranges from 2 to 6 10-12 cm2/s depending on the EC content. The variation of the characteristic drug delivery time with composition was non-monotonous and two different regimes were identified. CONCLUSION: A micellar transport of Melatonin was found. The two regimes in drug release were interpreted considering the polymer barrier effect, the initial porosity and M domains connectivity.

The effect of surfactant crystallization on partial coalescence in O/W emulsions.

Partial coalescence is a ubiquitous instability in emulsions whose dispersed phase is partially crystallized. When emulsions are stabilized with proteins, interfacial stiffness and long-range repulsive surface forces hinder this type of instability. The addition of low molecular weight surfactants modifies the interfacial properties and surface forces, generally promoting partial coalescence. In the present work, various surfactants (Tween® 80, palmitic acid and monoglycerides) differing in their crystallization temperature were probed for their ability to induce partial coalescence in model O/W emulsions stabilized by sodium caseinate. The initially fluid emulsions were submitted to a tempering cycle leading to the gelation of the system. The extent of partial coalescence was evaluated by measuring the bulk storage modulus. DSC was used to determine the melting range of the oil phase and surfactants, while polarized microscopy, Raman imaging, and surface rheology measurements were performed to characterize the oil/water interface. The experimental conditions in terms of droplet size, surfactant-to-protein molar ratio and tempering history favoring partial coalescence were first explored in presence of Tween® 80. We show that partial coalescence is rather marginal when crystallizable surfactants are added, and pronounced with liquid surfactants. The phenomena underlying this result, especially interfacial crystallization of surfactants, are evidenced and discussed.

Direct technique for monitoring lipid oxidation in water-in-oil emulsions based on micro-calorimetry.

An experimental device based on the measurement of the heat flux dissipated during chemical reactions, previously validated for monitoring lipid oxidation in plant oils, was extended to follow lipid oxidation in water-in-oil emulsions. Firstly, validation of the approach was performed by correlating conjugated diene concentrations measured by spectrophotometry and the heat flux dissipated by oxidation reactions and measured directly in water-in-oil emulsions, in isothermal conditions at 60°C. Secondly, several emulsions based on plant oils differing in their n-3 fatty acid content were compared. The oxidability parameter derived from the enthalpy curves reflected the α-linolenic acid proportion in the oils. On the whole, the micro-calorimetry technique provides a sensitive method to assess lipid oxidation in water-in-oil emulsions without requiring any phase extraction.

Free fatty acids and their esters modulate isothermal crystallization of anhydrous milk fat.

The effect of free fatty acids with different chain lengths or unsaturation degree on anhydrous milk fat (AMF) crystallization was evaluated. The impact of esterification was also studied using three triglycerides. Melted blends containing the additives at concentrations lower than 12wt.% were quenched at 25°C and isothermal crystallization was monitored by pulsed low-resolution nuclear magnetic resonance. In parallel, polarized light microscopy was used to observe the microstructure. Compounds based on long chain saturated fatty acids, i.e. palmitic, stearic, eicosanoic acids, tripalmitin and tristearin accelerated crystallization. Conversely, propanoic, hexanoic and oleic acids slowed down the process, while triacetin had no impact. Interestingly, above a critical concentration, the addition of palmitic, stearic or eicosanoic acids caused a transition from a one-step to two-step process. Gompertz model was used to fit the experimental data and to assess the influence of the molecular properties of the additives on the kinetic parameters.

Water-in-oil microemulsions versus emulsions as carriers of hydroxytyrosol: an in vitro gastrointestinal lipolysis study using the pHstat technique.

Water-in-oil (W/O) microemulsions and emulsions based on medium chain triglycerides (MCT) were successfully formulated with the addition of emulsifiers and used as encapsulation matrices for hydroxytyrosol (HT), an antioxidant naturally found in extra virgin olive oil. The digestibility of these edible W/O dispersions by recombinant dog gastric lipase (rDGL) and porcine pancreatic lipase (PPL) was then tested at different pH values using a pHstat device. rDGL and PPL displayed a much lower activity on the W/O microemulsion than that on the W/O emulsion and MCT alone. This was explained by the presence of higher amounts of emulsifiers (4.9% w/w lecithin and monoglycerides) in the composition of W/O microemulsions compared to W/O emulsions (1.3% w/w emulsifiers). These surfactants also induced a shift of maximum lipase activity towards lower pH values, which usually reflects the competition between surfactants and lipases for binding at the lipid-water interface. rDGL and PPL were then used consecutively in a two-step digestion model mimicking the conditions found in the human gastrointestinal tract. Direct titration and back-titration of free fatty acids allowed the continuous estimation of lipolysis rates under both gastric and duodenal conditions. Gastric lipolysis of W/O microemulsions was reduced 6 to 9-fold compared to W/O emulsions. This inhibition had a major impact on the overall lipolysis, although duodenal lipolysis was less affected by the dispersion type. The presence of HT had also some minor effects on lipolysis rates.

Influence of formulation on the oxidative stability of water-in-oil emulsions.

The oxidation of water-in-oil (W/O) emulsions was investigated, emphasizing the impact of compositional parameters. The emulsions had approximately the same average droplet size and did not show any physical destabilization throughout the study. In the absence of pro-oxidant ions in the aqueous phase, lipid oxidation of the W/O emulsions was moderate at 60°C and was in the same range as that measured for the neat oils. Oxidation was significantly promoted by iron encapsulation in the aqueous phase, even at 25°C. However, iron chelation reduced the oxidation rate. Emulsions based on triglycerides rich in polyunsaturated fatty acids were more prone to oxidation, whether the aqueous phase encapsulated iron or not. The emulsions were stabilized by high- and low-molecular weight surfactants. Increased relative fractions of high molecular weight components reduced the oxidation rate when iron was present.

Characterization of lipid oxidation in plant oils by micro-calorimetry.

A new experimental device was developed, based on the measurement of the heat flux dissipated during chemical reactions. The technique was exploited for real time monitoring of lipid oxidation in plant oils. The thermopiles were used in adiabatic configuration in order to measure the entire heat flux and improve sensitivity. Measurements were operated with a resolution of few µW as required to follow low exothermic reactions like oxidation. The validation of the device was performed by correlating conjugated diene concentrations measured by spectrophotometry and the heat flux dissipated by oxidation reactions. Our experimental approach involved several plant oils analyzed in isothermal conditions. This novel technique provides a versatile, sensitive, solvent-free and yet low-cost method to assess lipid oxidation stability, particularly suitable for the fast screening of plant oils.

Microemulsion versus emulsion as effective carrier of hydroxytyrosol.

Two edible Water-in-Oil (W/O) dispersions, an emulsion that remains kinetically stable and a microemulsion which is spontaneously formed, transparent and thermodynamically stable, were developed for potential use as functional foods, due to their ability to be considered as matrices to encapsulate biologically active hydrophilic molecules. Both systems contained Medium Chain Triglycerides (MCT) as the continuous phase and were used as carriers of Hydroxytyrosol (HT), a hydrophilic antioxidant of olive oil. A low energy input fabrication process of the emulsion was implemented. The obtained emulsion contained 1.3% (w/w) of surfactants and 5% (w/w) aqueous phase. The spontaneously formed microemulsion contained 4.9% (w/w) of surfactants and 2% (w/w) aqueous phase. A comparative study in terms of structural characterization of the systems in the absence and presence of HT was carried out. Particle size distribution obtained by Dynamic Light Scattering (DLS) technique and interfacial properties of the surfactants' layer, examined by Electron Paramagnetic Resonance (EPR) spectroscopy indicated the involvement of HT in the surfactant membrane. Finally, the proposed systems were studied for the scavenging activity of the encapsulated antioxidant toward galvinoxyl stable free radical showing a high scavenging activity of HT in both systems.

Delivery of functional polyelectrolytes from complexes induced by salt addition: impact of the initial binding strength.

This paper focuses on polyelectrolyte complexes (PECs) soft nanoparticles and how dissociation occurs upon salt addition. The system is composed of a strong polyanion (polystyrene sulfonate, PSS) and a weak polycation (poly(allylamine) hydrochloride, PAH) in large excess. Soft nanoparticles were obtained by pouring a PSS solution into a PAH one under constant stirring. As the charge density of PAH chain depends on the pH of the polyelectrolyte solution, PEC particles exhibit distinct behaviors under salt addition depending on the pH of the continuous phase. At pH=5.5, PAH chains are fully charged and the addition of salt produces particle aggregation followed by sedimentation. Conversely, at pH=10 where PAH is only partially charged, the addition of salt drives a progressive disentanglement of the two polyelectrolytes, as revealed by both viscosimetric and spectroscopic measurements. At sufficiently high ionic strength, the two electrolytes are fully dissociated. Our results emphasize differences in behavior (binding reversibility) between strongly and weakly bound polyelectrolytes of opposite charge upon addition of salt. We discuss the potential use of these systems as stimulus responsive materials for the delivery of scale nucleation inhibitors in application around petroleum recovery.

Pickering emulsions: what are the main parameters determining the emulsion type and interfacial properties?

We synthesized surface-active lipophilic core-hydrophilic shell latex particles, and we probed their efficiency as emulsion stabilizers. The relative weight percentage of the shell, RS/P, was varied to trigger the balance between lipophilicity and hydrophilicity of the particles. Particle wettability could concomitantly be tuned by the pH of the aqueous phase determining the surface charge. Emulsions covering a wide range of RS/P and pH values were fabricated, and their type, oil-in-water (O/W) or water-in-oil (W/O), and kinetic stability were systematically assessed. By adapting the particle gel trapping technique to pH-variable systems and by exploiting the limited coalescence process, we were able to determine the proportion of oil/water interfacial area, C, covered by the particles as well as their contact angle, θ. All of these data were gathered into a single generic diagram showing good correlation between the emulsion type and the particle contact angle (O/W for θ < 90° and W/O for θ > 90°) in agreement with the empirical Finkle rule. Interestingly, no stable emulsion could be obtained when the wettability was nearly balanced and a "bipolar"-like behavior was observed, with the particles adopting two different contact angles whose average value was close to 90°. For particles such that θ < 90°, O/W emulsions were obtained, and, depending on the pH of the continuous phase, the same type of particles and the same emulsification process led to emulsions characterized either by large drops densely covered by the particles or by small droplets that were weakly covered. The two metastable states were also accessible to emulsions stabilized by particles of variable origins and morphologies, thus proving the generality of our findings.