Larger Droplet Size Research Articles

Measuring large lipid droplet sizes by probing restricted lipid diffusion effects with diffusion-weighted MRS at 3T.

PurposeThe in vivo probing of restricted diffusion effects in large lipid droplets on a clinical MR scanner remains a major challenge due to the need for high b‐values and long diffusion times. This work proposes a methodology to probe mean lipid droplet sizes using diffusion‐weighted MRS (DW‐MRS) at 3T.MethodsAn analytical expression for restricted diffusion was used. Simulations were performed to evaluate the noise performance and the influence of particle size distribution. To validate the method, oil‐in‐water emulsions were prepared and examined using DW‐MRS, laser deflection and light microscopy. The tibia bone marrow was scanned in volunteers to test the method repeatability and characterize microstructural differences at different locations.ResultsThe simulations showed accurate and precise droplet size estimation when a sufficient SNR is reached with minor dependence on the size distribution. In phantoms, a good correlation between the measured droplet sizes by DW‐MRS and by laser deflection (R2 = 0.98; P = 0.01) and microscopy (R2 = 0.99; P < 0.01) measurements was obtained. A mean coefficient of variation of 11.5 % was found for the lipid droplet diameter in vivo. The average diameter was smaller at a proximal (50.1 ± 7.3 µm) compared with a distal tibia location (61.1 ± 6.8 µm) (P < 0.01).ConclusionThe presented methods were able to probe restricted diffusion effects in lipid droplets using DW‐MRS and to estimate lipid droplet size. The methodology was validated using phantoms and the in vivo feasibility in bone marrow was shown based on a good repeatability and findings in agreement with literature.

Dynamic Behavior of Droplets and Flashover Characteristics for CFD and Experimental Analysis on SiR Composites

The dynamic mechanism of water droplet formation has recently drawn considerable attention in research and application toward silicon rubber composite insulators. This paper is aimed at numerical simulations and experiments on the dynamic mechanism of water droplet formation with different applied voltages and droplet distribution and induced surface discharges on the insulator surface under the impact of AC electric field. The computational fluid dynamics model and experimental setup of multiple droplets were established to analyze the dynamic behavior of droplets and flashover characteristics. The obtained results reveal that the fusion first occurs between larger size droplets and the fusion is hard to happen along with the rise of the fractal dimension (FD) of droplet distribution. The elongation of droplets merges with more droplets and finally affects the electric field distribution on the insulator surface. With the increase of FD, the maximum electric field intensity shows an increasing tendency. Meanwhile, the experimental results show that with the increase of electric field intensity, the droplet fusion phenomenon becomes more obvious, which is consistent with the simulation results. The flashover voltage on the surface of silicon rubber decreases with the decrease of the FD of droplets, indicating that the complexity of droplet distribution has a significant effect on the flashover voltage.

Preparation of Stable Microemulsions with Different Droplet Size

Microemulsion is a widely used technique for preparing nanoparticles. The droplet size in stable microemulsions is a key parameter for limiting the size and shape of the formed nanoparticles. In this paper, the stable microemulsions were synthesized by two titration methods, the water titration method and the co-surfactant titration. Six reagents with different HLB were used as surfactants, including Span-80, E-1302, EL-10, MOA-9, Triton X-114 and OP-10. Quasi ternary phase diagrams of O/W and W/O microemusions with different surfactants were established according to the composition of surfactant, co-surfactant, oil and water. The size of the microemulsions droplets was characterized by using Zetasizer Nano S90. Within the stable micromulsions region, the droplet size was systemically controlled from 1 nm to 120 nm by changing different surfactants and controlling the quality ratio of components. A complex dependence of the droplet size on the water to surfactant ratio and the co-surfactant to surfactant ratio was established. In the stable microemulsions region, the droplets size increases dramatically with increased the water to surfactant ratio and the larger droplet size is obtained with increasing the co-surfactant amount.

Drift of Droplets from Air-Induction Nozzles

Abstract. For more than 20 years, air-induction or air-inclusion (AI) nozzles have had increased use for pesticide application due to their drift reduction capabilities. The pressure drop created by the pre-orifice and the venturi chamber results in a slower-moving liquid sheet exiting the main orifice, which in turn results in larger droplet sizes, which are less prone to drift. However, two additional factors somewhat mitigate the advantage of larger droplets from AI nozzles: the lower initial spray jet momentum from AI nozzles (compared to standard nozzles of the same flow rating at the same pressure) means that droplets from AI nozzles are more affected by lateral crosswind, and the lower effective liquid density of droplets from AI nozzles due to the presence of air inclusions means that AI droplets are more affected by aerodynamic drag than pure liquid droplets of comparable sizes from standard nozzles. In this work, theoretical and numerical models are developed to quantify these effects and develop tools for accurate drift prediction from sprayers using AI nozzles. The reduction in spray density due to the presence of air inclusions is in the range of 12% to 36%. This reduction in density affects the aerodynamic drift of the spray droplets, with the result that a droplet with 30% air inclusions would have the drift characteristics of a normal droplet with 20% smaller diameter. HighlightsSprays from air induction (AI) nozzles typically contain 12% to 36% air inclusions by volume.A droplet with 30% air inclusions would have the same drift characteristics as a water droplet of 20% smaller diameter.An analytical model is developed to predict the drift distances of small droplets. Keywords: Air induction, Droplet size, Nozzles, Pesticides, Sprayers.

Supersaturation with water explains the unusual adhesion of aggregate glue in the webs of the moth-specialist spider, Cyrtarachne akirai

Orb webs produced by araneoid spiders depend upon aggregate glue-coated capture threads to retain their prey. Moths are challenging prey for most spiders because their scales detach and contaminate the glue droplets, significantly decreasing adhesion. Cyrtarachne are moth-specialist orb-weaving spiders whose capture threads adhere well to moths. We compare the adhesive properties and chemistry of Cyrtarachne aggregate glue to other orb-weaving spiders to test hypotheses about their structure, chemistry and performance that could explain the strength of Cyrtarachne glue. We show that the unusually large glue droplets on Cyrtarachne capture threads make them approximately 8 times more adhesive on glass substrate than capture threads from typical orb-weaving species, but Cyrtarachne adhesion is similar to that of other species after normalization by glue volume. Glue viscosity reversibly changes over 1000-fold in response to atmospheric humidity, and the adhesive strength of many species of orb spiders is maximized at a viscosity of approximately 105–106 cst where the contributions of spreading and bulk cohesion are optimized. By contrast, viscosity of Cyrtarachne aggregate glue droplets is approximately 1000 times lower at maximum adhesive humidity, likely facilitating rapid spreading across moth scales. Water uptake by glue droplets is controlled, in part, by hygroscopic low molecular weight compounds. NMR showed evidence that Cyrtarachne glue contains a variety of unknown low molecular weight compounds. These compounds may help explain how Cyrtarachne produces such exceptionally large and low viscosity glue droplets, and also why these glue droplets rapidly lose water volume after brief ageing or exposure to even slightly dry (e.g. < 80% RH) conditions, permanently reducing their adhesion. We hypothesize that the combination of large glue droplet size and low viscosity helps Cyrtarachne glue to penetrate the gaps between moth scales.

The volumetric properties of water/AOT/isooctane microemulsions with larger-size droplets

The densities of water/AOT/isooctane microemulsions with prepared molar ratios ω of water to AOT being (7, 8, 10, 15, 20, 30 and 40) in a wide concentration range were measured at T = 303.15 K with an improved experimental method. The apparent volumes of the quasi-pure solute (water/AOT), the volumetric interaction parameters α and the apparent specific volumes of water and AOT in droplets were deduced. The volumetric properties were found to be sensitive for detecting the structure transformation of the microemulsion droplets. A thermodynamic model was proposed to analyze the stability boundaries of the microemulsion droplets and the mechanisms of their instability.

Effects of microbial transglutaminase treatment on physiochemical properties and emulsifying functionality of faba bean protein isolate

The potential use of microbial transglutaminase (MTG)-treated faba bean protein isolate (FBPI) as emulsifiers to maintain physical and oxidative stability of oil-in-water (O/W) emulsion was investigated. MTG-treated FBPIs (MTG-FBPIs) were prepared by incubating with MTG for 60, 120 or 240 min. O/W emulsions were stabilized by 3% (w/v) of MTG-FBPIs or control-FBPI (treated with inactive MTG) and stored at 37 °C for 7 days. MTG treatments induced cross-linking in FBPI, raised the protein net surface charges by 5%–8%, and increased the emulsion particle size by 19%–135%. MTG treatment for 120 and 240 min but not 60 min induced excessive surface hydrophobicity, resulting in decreased emulsifying activity and physical stability of emulsion. By day 7, all MTG-treated FBPIs showed similar inhibiting effects against lipid oxidation in emulsion, indicated by less conjugated dienes and hexanal production. MTG-FBPIs moderately promoted protein oxidation (120 min > 240 min ≈60 min). Thus, prolonged MTG treatment should be avoided to prevent accelerated protein oxidation and droplets coalescence. MTG treatment for 60 min makes FBPI a potential emulsifier to maintain physical stability while improving lipid oxidative stability in emulsion, potentially attributed to thicker interfacial layer, larger droplet size, and protective effect of protein.

Spatio‐temporal variability of warm rain events over southern West Africa from geostationary satellite observations for climate monitoring and model evaluation

This article presents the spatio‐temporal variability of warm rain events over southern West Africa (SWA) during the summer monsoon season for the first time, using Spinning Enhanced Visible Infrared Radiometer (SEVIRI) observations on the Meteosat geostationary satellites. The delineation of warm rain events is based on the principle that precipitating low‐level clouds are associated with either sufficient water content or large cloud droplet size. Capitalising on the ability of space‐borne radar to resolve vertical cloud structures and detect the presence of precipitation, the delineation is trained by collocated SEVIRI and CloudSat observations.The resulting 12 years of observations from SEVIRI are used to examine the spatial, diurnal, seasonal and interannual variability of warm rain events over SWA. Warm rain events predominate during the monsoon in August, with little interannual variability, and persist over orography in the morning and the coasts after midday, likely enhanced by orographic lifting and land–sea breeze effects. Warm clouds have a much higher probability of precipitation along the coastlines of Liberia and Nigeria compared to the central SWA coastline and further inland. Finally, when evaluating an 8‐day yet high‐spatial resolution model simulation, we find that warm rain frequencies from the simulation agree well with SEVIRI near the coast but simulated warm cloud cover and thus warm rain frequencies are too low over the Gulf of Guinea. The probability of precipitation of warm clouds is also too low inland. The newly developed observations of warm rain create opportunities to further investigate the diurnal cycle of warm rain, study aerosol–cloud–precipitation interactions, and assess the role of warm rain in the water cycle across Africa and beyond.

Investigation of the thermal-hydraulic non-equilibrium in a 7 × 7 rod bundle during reflood

The current research aims at investigating the thermal–hydraulic non-equilibrium encountered in the dispersed flow film boiling (DFFB) regime under reflood conditions. A series of constant reflood tests have been performed at the 7 × 7 Rod Bundle Heat Transfer (RBHT) test facility and the experimental results have been analyzed in detail. The data not only is useful for the development of theoretical models for two-phase interfacial mass and heat transfer, void fraction, pressure drop, and rod bundle cooling prediction, but also can be used as a benchmark data base for evaluating the performance of various thermal–hydraulic analysis codes. In this paper, a complete data reduction methodology is employed to reveal and interpret important two-phase flow phenomena during reflood transients. The results show that for the region far away from the quench front location, significant thermal non-equilibrium may exist during reflood and thus poor heat removal capability of the flow mixture is expected. On the other hand, for the region immediately downstream of the quench front, the two-phase flow is found to be close to the thermal equilibrium state, indicating that both the interfacial heat transfer and the heat transfer between the rod surface and fluid mixture are very efficient. In addition, based on the liquid droplet measurement and force balance calculations, it is found that the slip ratio between the two separate phases is a strong function of the droplet size and reflood time. With a larger droplet size and a shorter distance from the quench location, the slip ratio is larger. The liquid carryover fraction at the exit of the test section is also determined as a function of the reflood time. Results indicate that only a small portion of the injected coolant mass is stored within the bundle. A significant amount of liquid mass into the test section is either evaporated or entrained in the vapor flow and eventually left the bundle.

Annular two-phase flow in vertical smooth and corrugated pipes

Two-phase flow in ribbed or corrugated pipes is of interest in many industrial applications. Experiments are performed to assess the flow regime characteristics in upward annular flow through vertical smooth and corrugated pipes. From high speed recordings, the flow regime and temporal film characteristics are obtained. A novel implementation of a planar laser-induced fluorescence (PLIF) method is used to measure the film thickness, preventing strong reflections from deteriorating the measurements. Liquid accumulation between the ribs of the corrugated pipe is also measured using a PLIF technique. Furthermore, droplet sizing is performed combining shadowgraphic and interferometric techniques to capture a large droplet size range. The measurements show that the presence of pronounced corrugations at the pipe wall causes a strong increase in entrainment of liquid into the gas flow. The entrainment is correlated to the filling of the corrugations with liquid; it is significantly reduced (from 90% entrainment to 50%) when the corrugations are entirely filled with liquid. The amount of liquid filling of the corrugations is related to the superficial liquid film flow velocity. The liquid filling fraction (α) scales with the Weber and liquid Reynolds number, and the obtained scaling also holds when the experiments are repeated with a different liquid (mono-ethylene glycol) and with a larger corrugation geometry. Droplets occurring in corrugated pipe flow are 30–50% larger compared to the smooth pipe, as a consequence of the locally (at the locations of the cavities) increased film thickness.

Modelling of ex situ dissolution for CO2 sequestration

In this paper, a model for diffusion-controlled dissolution of carbon dioxide (CO2) droplets is presented. This model is applied to a system of co-current turbulent horizontal pipe flow of carbon dioxide–brine mixture in order to determine the feasibility of dissolving carbon dioxide within the pipe before injecting underground. Depending on the droplet size, there are two regimes of dissolution within the pipe: turbulent for large droplet size and laminar (pure diffusion) for smaller sizes. Since the droplet (while dissolving and therefore shrinking in size) may undergo both regimes, the droplet size at which it transitions from turbulent to diffusion-controlled dissolution is estimated and used to find the total time spent in diffusion-controlled dissolution regime. It was observed that diffusive dissolution is of similar order of magnitude to turbulent dissolution, and so both mechanisms must be taken into account in the evaluation of the total dissolution time. This diffusive dissolution time should be combined with the time spent in the turbulent regime to determine time pipe lengths required for complete dissolution of carbon dioxide droplets.

Sweeping of the entrapped fluid out of the groove in a three-dimensional channel using lattice Boltzmann method

The entrapment of fluid inside a groove is an important topic of research from past few decades. In many engineering applications, it is seen that the droplet is displaced under the action of gravitational force on one of the wetted grooved wall of a rectangular three-dimensional channel. It is reported in literature that the entrapment of droplet fluid inside groove is undesirable in various applications. Thus, the present study deals with the method of sweeping out the entrapped fluid inside the groove by the displacement of a large size three-dimensional immiscible droplet under gravity. To analyze this problem, a three-dimensional lattice Boltzmann method (LBM) is used and Shan–Chen (S-C) model has been implemented to incorporate multiphase-multicomponent flow. The present problem deals with the single grooved wetted wall of a rectangular three-dimensional channel. The wettability of the groove surface is considered as uniform hydrophobic in two different cases, whereas the wettability of the three-dimensional channel wall outside of the groove is considered as uniform hydrophilic. The analysis shows that the sweeping of entrapped fluid out of the groove largely depends on the capillary number and groove dimensions. It is also observed that sweeping of entrapped fluid takes place only for uniform hydrophobic surface of the groove with contact angle equal to 118°. In case of hydrophobic surface with contact angle equal to 90°, the large size droplet completely trapped inside the groove and does not able to sweep out the previously entrapped fluid.

Effects of casein micellar structure on the stability of milk protein-based conjugated linoleic acid microcapsules

The effects of casein micellar structure on the stability of milk protein-based conjugated linoleic acid (CLA) microcapsules were investigated. CLA emulsions were prepared with milk protein concentrates (MPC) or a mixture of whey protein isolates (WPI) and sodium caseinate (SC). Larger droplet sizes and wider size distributions were observed for MPC-CLA emulsions, where the varied sizes and heterogeneous protein particles with different rigidity discontinuously adsorbed on the oil droplets. Aggregated oil droplets with porous walls were found on the inner surface of MPC-CLA spray-dried powders. These microcapsules also had lower encapsulation efficiency and unfavorable oxidative stability. For MPC-CLA, 17% of the CLA remained after 45 days at 35 °C, while ∼80% was retained for the WPI+SC-CLA microcapsules. The adverse effect of the casein micellar structure suggested that modification of casein micelles will be needed to improve the efficiency and chemical stability of such microcapsules.

Characterization of essential oil distribution in the root cross-section of Valeriana officinalis L. s.l. by using histological imaging techniques

BackgroundThe essential oil is an important compound of the root and rhizome of medicinally used valerian (Valeriana officinalis L. s.l.), with a stated minimum content in the European pharmacopoeia. The essential oil is located in droplets, of which the position and distribution in the total root cross-section of different valerian varieties, root thicknesses and root horizons are determined in this study using an adapted fluorescence-microscopy and automatic imaging analysis method. The study was initiated by the following facts:A probable negative correlation between essential oil content and root thickness in selected single plants (elites), observed during the breeding of coarsely rooted valerian with high oil content.Higher essential oil content after careful hand-harvest and processing of the roots.ResultsIn preliminary tests, the existence of oil containing droplets in the outer and inner regions of the valerian roots was confirmed by histological techniques and light-microscopy, as well as Fourier-transform infrared spectroscopy. Based on this, fluorescence-microscopy followed by image analysis of entire root cross-sections, showed that a large number of oil droplets (on average 43% of total oil droplets) are located close to the root surface. The remaining oil droplets are located in the inner regions (parenchyma) and showed varying density gradients from the inner to the outer regions depending on genotype, root thickness and harvesting depth.ConclusionsFluorescence-microscopy is suitable to evaluate prevalence and distribution of essential oil droplets of valerian in entire root cross-sections. The oil droplet density gradient varies among genotypes. Genotypes with a linear rather than an exponential increase of oil droplet density from the inner to the outer parenchyma can be chosen for better stability during post-harvest processing. The negative correlation of essential oil content and root thickness as observed in our breeding material can be counteracted through a selection towards generally high oil droplet density levels, and large oil droplet sizes independent of root thickness.

Investigation of injector coking effects on spray characteristic and engine performance in gasoline direct injection engines

Spray and droplet characteristics of a coked injector were compared to those of a clean injector at the atmospheric conditions and investigated using high-speed imaging and a Phase Doppler Particle Analyzer (PDPA). Scanning Electron Microscope (SEM) and X-ray 3D microtomography images were analysed to understand the physical characteristics of injector nozzle deposits. Furthermore, Energy Dispersive X-Ray Spectroscopy (EDS) was utilized to obtain the elemental composition of the deposit. A single cylinder optical gasoline direct injection (GDI) engine was used to compare diffusion flames for each injector. In this study, the location and topography of the deposits demonstrated that they extensively formed in the external holes of the injector, and reduced in size and quantity through the internal holes. Elemental analysis of the deposits exhibited that carbon (C) and oxygen (O) were the predominant elemental components through both the internal and external holes of the injector. The coked injector exhibited higher penetration lengths, smaller plume angles, larger spray cone angles, higher mean droplet velocity and larger droplet size as compared to the clean injector. Images of the optical engine indicated strong diffusion flames around the coked injector tip. In-cylinder pressure measurements indicated that the coked injector produced lower in-cylinder pressures, implying lower combustion stability compared with the clean injector. This work was carried out to obtain a comprehensive study of injector coking effects on spray behaviour and engine performance.

Investigation of oil-in-water emulsion stability with relevant interfacial characteristics simulated by dissipative particle dynamics

Oil-in-water (O/W) emulsions were prepared by using non-ionic surfactants, Tween 80 and Span 20, and the stability of the emulsions was investigated under conditions of varied HLB, emulsifier concentration, stirring time and stirring intensity. It was found that the HLB of emulsifier has a significant effect on the emulsion stability. Moreover, the structures and properties of the interfacial film formed by emulsifier molecules with different HLB were characterized by dissipative particle dynamics (DPD) simulations. The results show that the interfacial film thickness increases with the HLB values changing from 9 to 15, while the most stable emulsion appears when HLB is 13 with the minimum interfacial tension. Neither too small nor too large oil droplet size, determined by molecular volume of emulsifier as well as the volume ratio of hydrophilic head and hydrophobic tail, could improve the emulsion stability when the preparation technology is the same. Therefore, the influence of HLB on the emulsion stability is essentially affected by the comprehensive result of interfacial film thickness, interfacial tension and molecular structure of emulsifier. This study could contribute to the development of controlling and preparation of emulsions with suitable stability from the point of view of emulsifier.

Model for Fuel Droplet Evaporation in Combustion Chamber of Liquid Propellant Rocket Engines

Complete burning of liquid propellants droplets is very important to avoid combustion instability and to get higher specific impulse from liquid rocket engines. Combustion takes place in gaseous phase and reaction is fast. So, the time consumed by a droplet for complete burning is the time taken by a droplet to get evaporated. An analytical mono component fuel droplet evaporation model is developed and proposed for droplet evaporation in liquid rocket engine based on heat and mass transfer. Effect of the fuel droplet curvature on vapor pressure is incorporated in the model. The model is applied on a small-scale combustion chamber of bi-propellant liquid rocket engine where fuel concentration away from droplet is not zero. A code is generated and applied. The results of the model show that fuel droplet diameter, combustion chamber pressure, chamber diameter, mass flow rate and droplet relative velocity with hot gas has significant effects on the life of droplet and characteristic length. Effects of chamber pressure and diameter are more significant for larger droplet size.

Instability Mechanisms of Water-in-Oil Nanoemulsions with Phospholipids: Temporal and Morphological Structures.

Many food preparations, pharmaceuticals, and cosmetics use water-in-oil (W/O) emulsions stabilized by phospholipids. Moreover, recent technological developments try to produce liposomes or lipid coated capsules from W/O emulsions, but are faced with colloidal instabilities. To explore these instability mechanisms, emulsification by sonication was applied in three cycles, and the sample stability was studied for 3 h after each cycle. Clearly identifiable temporal structures of instability provide evidence about the emulsion morphology: an initial regime of about 10 min is shown to be governed by coalescence after which Ostwald ripening dominates. Transport via molecular diffusion in Ostwald ripening is commonly based on the mutual solubility of the two phases and is therefore prohibited in emulsions composed of immiscible phases. However, in the case of water in oil emulsified by phospholipids, these form water-loaded reverse micelles in oil, which enable Ostwald ripening despite the low solubility of water in oil, as is shown for squalene. As is proved for the phospholipid dipalmitoylphosphatidylcholine (DPPC), concentrations below the critical aggregation concentration (CAC) form monolayers at the interfaces and smaller droplet sizes. In contrast, phospholipid concentrations above the CAC create complex multilayers at the interface with larger droplet sizes. The key factors for stable W/O emulsions in classical or innovative applications are first, the minimization of the phospholipids' capacity to form reversed micelles, and second, the adaption of the initial phospholipid concentration to the water content to enable an optimized coverage of phospholipids at the interfaces for the intended drop size.

Continuous two-phase biocatalysis using water-in-oil Pickering emulsions in a membrane reactor: Evaluation of different nanoparticles

Pickering emulsions are currently receiving increased attention as a promising alternative to dispersions or surfactant stabilized emulsions in two-phase biocatalysis. In order to design a continuous membrane reactor using water-in-oil Pickering emulsions for biocatalysis, knowledge on the filterability of the Pickering emulsion is required. This can be influenced by a number of factors, e.g. type and size of stabilizing nanoparticles, applied solvent, and used membrane. In a previous application of water-in-oil Pickering emulsions for continuous biocatalysis in a membrane reactor, spherical silica particles were used to stabilize the emulsion. This resulted in densely packed filter cakes due to unbound residual particles and decreasing flux over time. Furthermore, rather large droplet sizes with small specific interfacial areas were achieved. In this work, the use of colloidal silica nanoparticle for the stabilization of bioactive Pickering emulsions was studied. The filterability of bioactive water-in-oil Pickering emulsions stabilized by spherical or colloidal silica nanoparticles was compared. Using colloidal silica nanoparticles was found to result in smaller emulsion drop sizes, higher filterability and better reproducibility of drop size distribution and flux. An increase in water volume fraction decreased the flux level, but filtration was still possible at industrially relevant fluxes. With the selected nanoparticles, continuous biocatalysis in a membrane reactor at constant flux, i.e. constant residence time, was performed twice for 30 h. Substrate and product concentrations were constant and reproducible and the enzyme was still active after 30 h. The productivity was higher than that obtained with spherical silica nanoparticles and the process duration is the longest so far reported for continuous biocatalysis in PE at industrially relevant residence times.

Physical properties and stability evaluation of fish oil-in-water emulsions stabilized using thiol-modified β-lactoglobulin fibrils-chitosan complex

Fish oil-in-water emulsions containing fish oil, thiol-modified β-lactoglobulin (β-LG) fibrils, chitosan and maltodextrin were fabricated using a high-energy method. The results showed that chitosan coating induced charge reversal; denoting successful biopolymers complexation. A significantly (p<0.05) larger droplet size and lower polydispersity index value, attributed to the thicker chitosan coating at the oil-water interface, were observed. At high chitosan concentrations, the cationic nature of chitosan strengthened the electrostatic repulsion between the droplets, thus conferring high oxidative stability and low turbidity loss rate to the emulsions. The apparent viscosity of emulsions stabilized using thiol-modified β-LG fibrils-chitosan complex was higher than those stabilized using β-LG fibrils alone, resulting in the former's higher creaming stability. Under thermal treatments (63°C and 100°C), emulsions stabilized using thiol-modified β-LG fibrils-chitosan complex possessed higher heat stability as indicated by the consistent droplet sizes observed. Chitosan provided a thicker protective layer that protected the oil droplets against high temperature. Bridging flocculation occurred at low chitosan concentration (0.1%, w/w), as revealed through microscopic observations which indicated the presence of large flocs. All in all, this work provided us with a better understanding of the application of protein fibrils-polysaccharide complex to produce stable emulsion.