Lecithin in oil-in-water emulsions

Summary A study was made to investigate the use of purified phosphatide in I.V. emulsions. Lecithin isolated from egg yolk and purified by alumina and silica chromatography was analyzed by chromatographic strip techniques as a one-component material. Highly purified lecithin was found to be an inefficient emulsifier. Moreover emulsions containing highly purified lecithin were heat-sensitive. An emulsion physical stability test was developed to evaluate emulsifier formulations containing purified phosphatides for use with small amounts of emulsions (approximately 50 g.). Using this procedure, a considerable number of substances were tested as additives to enhance the purified lecithin's emulsifying power. None were found to be as effective as natural soybean phosphatide, which was used as a control. From these observations it is indicated that pure phosphatides are inefficient emulsifiers and that those phosphatide preparations possessing good emulsifying characteristics are presumably mixtures or complexes of the phosphatides with other substances. This investigation was supported in part by funds from the Office of the Surgeon General. One of the laboratories of the Southern Utilization Research and Development Division. Agricultural Research Service, United States Department of Agriculture.     

Argan oil-in-water emulsions: Preparation and stabilization

We prepared stable oil-in-water emulsions of argan oil with two different types of mixtures of nonionic emulsifiers. Three different types of oil (Israeli argan oil, Moroccan argan oil, and soybean oil) were emulsified with mixtures of Span 80 and Tween 80. The optimum HLB value for argon oil was 11.0 (±1.0). The argan oil-in-water emulsions were stable for more than 5 mon at 25°C. Synergistic effects were found in enhancing stability of emulsions prepared with sucrose monostearate. The origin of the oil and the internal content of natural emulsifiers, such as monoglycerides and phospholipids, have a profound influence on its interfacial properties and on the stability of the argan oil-in-water emulsions.     

Kinetics of demulsification of food protein-stabilized oil-in-water emulsions

Demulsification of food protein stabilized oil-in-water emulsions was determined as a function of time. Demulsification conformed to the empirical equation q′-Q t/(B+t), where q′ is the increase in moisture content of the down layer of emulsions at time t, Q is the maximum increase in moisture content, and B is the time required to gain Q/2. Emulsions separate water according to a second order rate law, which would indicate that flocculation is the rate determining step in demulsification.     

Pyrimidinium cationic surfactants as emulsifiers for oil-in-water emulsions

Pyrimidinium cationic surfactants with 13–17 carbon atoms in the hydrophobe were used as emulsifiers for oil-inwater (heptane/water) emulsions at concentrations near the critical micelle concentrations. Interfacial tensions of the emulsifier solutions in water against heptane were measured. Drop size distributions of the emulsions were determined at different times using microscopic techniques, and the rate of coalescence was calculated. The structure having 16 carbon atoms in the alkyl chain had coalescence rates lower than the other structures, including two conventional C-16 cationics used as controls.     

Enhanced coalescence separation of oil-in-water emulsions using electrospun PVDF nanofibers

A novel and high-efficiency coalescence membrane enhanced by nano-sized polyvinylidene fluoride(PVDF) nanofibers based on polyester (PET) substrate was fabricated using electrospinning method.The properties of the electrospun nanofibers such as roughness and surface morphology greatly affected the oil droplet interception efficiency and surface wettability of the membrane.A series of coalescence units were prepared with different layers of nanofibrous membrane and the separation efficiencies at dif-ferent initial concentrations,flow rates,and oil types were tested.It is very interesting that the obtained nanofibrous membrane exhibited superoleophilicity in air but poor oleophilicity under water,which was beneficial to the coalescence process.The coalescence unit with four membrane layers had excellent per-formances under different initial concentrations and flow rates.The separation efficiency of the 4-layers unit remained above 98.2％ when the initial concentration reached up to 2000 mg·L-1.Furthermore,the unit also exhibited good performance with the increasing oil density and viscosity,which is promising for large-scale oil wastewater treatment.     

MILP synthesis of separation processes for waste oil-in-water emulsions treatment

This paper presents a novel synthesis method for designing integrated processes for oil-in-water (O/W) emulsions treatment. General superstructure involving alternative separation technologies is developed and modelled as a mixed integer linear programming (MILP) model for maximum annual profit. Separation processes in the superstructure are divided into three main sections of which the pretreatment and final treatment are limited to the selection of one alternative (or bypass) only, while within the intermediate section various combinations of different technologies in series can be selected. Integrated processes composed of selected separation techniques for given ranges of input chemical oxygen demand (COD) can be proposed by applying parametric analyses within the superstructure approach. This approach has been applied to an existing industrial case study for deriving optimal combinations of technologies for treating diverse oil-inwater emulsions within the range of input COD values between 1000 mg?L^?1 and 145000 mg?L^?1. The optimal solution represents a flexible and profitable process for reducing the COD values below maximal allowable limits for discharging effluent into surface water.

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Novel extensional device to efficiently form fine oil-in-water food emulsions

Two immiscible liquids are commonly mixed by mechanically dispersing one into the other to form emulsions. Surfactants or emulsifiers confer stability. Mechanical mixing, in practice, is an energy-intensive shear flow that is ineffective when the ratio of the dispersed-phase viscosity to the continuous-phase viscosity exceeds about four. Extensional flows are not subject to this viscosity ratio limit. This superiority of extensional flow was exploited to fabricate a novel, continuous-flow, cone-shaped device with an extensional strain of eight to make fine soybean oil-in-water emulsions. A spherical insert having a wall clearance of 25 μm was an effective design factor. Starting with ‘coarse’ 50 wt.% oil emulsions, two stretching episodes were needed for size reduction. The temperature rise was negligible, and the results were independent of the emulsifier type employed. Increasing flow rate and stretching episodes, reducing wall clearance, enhancing emulsifier concentration, and multiple passes through the device gave progressively smaller drops; the volume-averaged diameter became less than 2 μm, and the number-averaged diameter reached 0.5 μm, narrowing the size distribution. The emulsions that formed had a high viscosity and were stable. The performance of a scaled-up device was compared with other mixers. At equivalent energy density and 50 wt.% oil, drop sizes were similar for a valve homogenizer but larger for a rotor-stator mixer. At 80 wt.% oil, the rotor stator-mixer again required more energy for the same drop size, but emulsions prepared with the valve homogenizer broke. The findings of this study can help to design industrial-scale energy-efficient extensional-flow dominant devices for the formation of food emulsions.     

Effects of droplet size on the oxidative stability of oil-in-water emulsions

The effects of droplet size and emulsifiers on oxidative stability of polyunsaturated TAG in oil-in-water (o/w) emulsions with droplet sizes of 0.806±0.0690, 3.28±0.0660, or 10.7±0.106 μm (mean ± SD) were investigated. Hydroperoxide contents in the emulsion with a mean droplet size of 0.831 μm were significantly lower than those in the emulsion with a mean droplet size of 12.8 μm for up to 120 h of oxidation time. Residual oxygen contents in the headspace air of the vials containing an o/w emulsion with a mean droplet size of 0.831 μm were lower compared with those of the emulsion with a mean droplet size of 12.8 μm. Hexanal developed from soybean oil TAG o/w emulsions with smaller droplet size showed significantly lower residual oxygen contents than those of the larger droplet size emulsions. Consequently, oxidative stability of TAG in o/w emulsions could be controlled by the size of oil droplet even though the origins of TAG were different. Spin-spin relaxation time of protons of acyl residues on TAG in o/w emulsions measured by ¹H NMR suggested that motional frequency of some acyl residues was shorter in o/w emulsions with a smaller droplet size. The effect of the wedge associated with hydrophobic acyl residues of emulsifiers was proposed as a possible mechanism to explain differences in oxidative stability between o/w emulsions with different droplet sizes.     

一体式陶瓷外膜直接乳化法制备单分散水包油乳液

膜乳化法是靠膜两侧的压差使分散相通过微孔膜,以小液滴的形式分散在连续相中而形成乳状液的方法．与转一定体系、高压均化等传统制乳方法相比,膜乳化法所制得的乳液具有液滴尺寸均一、节能、剪应力小等特点,可应用于食品、医药、聚合物工业等领域．过去的十几年中,尽管在膜乳化方面进行了大量的工作,过程参数对乳滴尺寸的影响并未完全研究清楚．甚至在一些研究中,仅仅把平均乳滴直径作为分布参数．     

Effect of sunflower lecithins on the stability of water-in-oil and oil-in-water emulsions

Lecithins are frequently applied in the food industry as emulsifiers, viscosity regulators, and dispersing agents. The main aim of the present work was to study the emulsifying capability of diverse sunflower lecithins so as to evaluate the functionality of these by-products, which are not extensively used at present. The experimental results obtained for water-in-oil (W/O) emulsions showe that dispersions containing levels of 0.1% lecithins were more stable against coalescence than a control system, whereas those with 1% emulsifying agent exhibited the opposite behavior. On the other hand, faster sedimentation kinetics were observed at a concentration of 0.1% than at 1%. Lecithins with high phospholipid content, especially phosphatidylethanolamine and phosphatidylinositol, were found to be the best emulsifying agents for W/O dispersions. In the case of oil-in-water emulsions, it was possible to observe two processes: creaming of emulsions with the addition of 1% of lecithins, and instant creaming followed by coalescence of the cream phase in those cases corresponding to 0.1% added lecithin.     

Bio-based mesoporous sponges of chitosan conjugated with amino acid-diketopiperazine through oil-in-water emulsions

Fully bio-based chitosan derivative was synthesized using 3-benzyl-2,5-diketopiperazine-6-acetic acid (DKP) activated by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. From IR and ¹H NMR spectra, the structure of the bioconjugated chitosan and the quantitative modification were confirmed. Oil-in-water (o/w) emulsion of the obtained product was presented with the various ratios of water and benzene solution. Continuously the obtained o/w emulsions were freeze-dried to produce the mesoporous sponge, depended on the ratio of the water and benzene. These amphiphilic properties were observed by the property of the pendant DKP moieties in chitosan. The pore size in the sponges was controlled in a range from 0.1 to 0.3 μm by changing the solvent ratios.     

Influence of soybean protein isolates-phosphatidycholine interaction on the stability on oil-in-water emulsions

Soybean protein isolates and phospholipids present specific surface properties with synergistic or antagonistic effects on emulsion stability. Oil-in-water emulsions (25∶75 w/w) were prepared using native and denatured soybean isolates (NSI and DSI, respectively) with the addition of phosphatidylcholine (PC) (protein/PC ratio 100∶1 to 10∶1). The effect of ionic strength was also studied by adding sodium chloride (0–100 mM) to the aqueous phase. Analysis of NSI/PC and DSI/PC emulsions showed that the creaming rate diminished upon addition of PC, with the creamed phase showing more stability than those of the control systems. In DSI/PC systems, the coalescence process was partially controlled, as evidenced by a decrease in the size of oil droplets. Both systems were altered by the presence of sodium chloride, with an increase in the creaming rate attributable to flocculation and the coalescence of droplets. Under these conditions, DSI/PC emulsions exhibited a stronger protein-phospholipid interaction than those of NSI/PC.     

Comparison of the effects of three different phosphatidylcholines on casein-stabilized oil-in-water emulsions

Soy oil-in-water emulsions, stabilized by casein, but incorporating one of three different phosphatidylcholines (PC), namely egg-PC, di-palmitoyl phosphatidylcholine (DPPC) and di-oleyl phosphatidylcholine (DOPC), have been studied by photon correlation spectroscopy, light scattering, fast protein liquid chromatography, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Egg-PC enhanced the stability of emulsions made with low casein concentration, and it competed for space with casein at the oil-water interface during the emulsification process, but no further displacement of protein was found. DPPC had little effect on emulsion stability nor did it show a detectable competition at the interface with casein during or after emulsification. DOPC, however, not only competed with casein at the interface during emulsification, it also removed casein from the interface during storage of the emulsion. The displacement of casein caused instability of the emulsions. Adding DOPC to emulsions also led to displacement of casein from the interface and caused instability of the emulsion, but the process was much slower and occurred to a smaller extent compared to emulsions prepared with DOPC. The different behavior of egg-PC, DPPC, and DOPC on the oil-water interface was in good agreement with their relative solubility in the oil phase as measured by spectrophotometry. All three lipids modified the hydrodynamic thickness of the adsorbed casein layer corresponding to their modification of the surface concentration of casein.     

Phase segregation,shear thinning and rheological behavior of crude oil-in-water emulsions

This work reports an experimental investigation of the oil segregation effect during the rheological evaluation of concentrated oil-in-water (O/W) emulsions. The results demonstrated that alkyl alcohols can significantly affect the rheological behavior of O/W emulsions. The addition of n-octanol and n-decanol to the emulsifying agent formulation produces a critical shear rate, promotes a sharp break in the flow curves and leads to a sharp viscosity drop, which was attributed to wall depletion. This phenomenon is related to the displacement of the dispersed phase away from the solid-boundary, which generates a low-viscosity oil-depleted layer that acts as a lubricating layer. The incidence of slippage depends on the alkyl-chain length and the concentration of the alcohol. The lubrication layer will promote energy savings during emulsified oil pumping and result in significant economic benefits to the petroleum industry.     

Electrochemical oxidation of hydrophobic compounds in aqueous micellar solutions and oil-in-water emulsions

The electrochemical oxidation of ferrocene (Fc) and tetrathiofulvalene (TTF) has been investigated in micelles and dodecane-in-water emulsions in order to compare the diffusional process involved in these systems. It is found that the diffusion coefficients of Fc and TTF, determined from the observed limiting currents at the rotating disc electrode, are governed by the solubilization equilibrium of the neutral substrates which are predominantly solubilized in the micelle or oil-droplet phase. In the emulsion, the cyclic voltammograms show that the current is controlled also by the rate constants of the substrate partition, which depend on the size of the emulsion droplets. The determination of the diffusion coefficients of Fc⁺ and TTF⁺, produced in situ by controlled potential electrolysis, showed that, except in SDS micellar solutions, the monocation radicals are solubilized mainly in the aqueous phase. As a result, the diffusion coefficients of the species involved in the redox system are different. In the case of TTF, the above results have a great influence upon the second oxidation step TTF⁺ → TTF²⁺. Indeed, the homogeneous solution reaction between TTF and the electrogenerated dication TTF²⁺ leads to the monocation TTF⁺ which diffuses more rapidly than its parent molecule TTF. The ratios of the two waves in cyclic and rotating disc electrode voltammetry show that the enhancement of the second wave depends mainly on the difference between the diffusion coefficients of TTF and TTF⁺ and that the nature of the solution or the size of the disperse phase has little influence upon the reaction rate of the homogeneous solution reaction.     

The role of endogenous amphiphiles on the stability of virgin olive oil-in-water emulsions

Stable virgin olive oil-in-water emulsions were prepared using total endogenous surface-active components derived from oil as emulsifying agents, and the interfacial properties of the emulsion droplets were examined. The amount of oil extracted into the aqueous buffer increased with buffer pH, with the most stable emulsions being formed at pH 7.5. Light microscopy of the emulsions revealed the presence of spherical droplets with diameters ranging from 1.5 to 3 μm. Their surface was negatively charged at pH 7.5, as confirmed by the effect of ions and polycations. Potassium chloride, Ca²⁺, and spermine induced rapid aggregation (as monitored by the turbidity change and by light microscopy), showing their maximal effect at 1 M, 4 mM, and 60 μM, respectively. Papain treatment of the emulsion particles rapidly induced particle aggregation, suggesting the destruction of stabilizing structural olive oil proteins. Unlike papain, treatment with phospholipase C did not result in an appreciable turbidity change. Treatment with soybean lipoxygenase slightly increased the turbidity of the emulsion. The interaction of linoleate-Tween 20 mixed micelles with emulsion droplets produced turbidity, which was maximal at a neutral pH, whereas interaction with proteolyzed and lipoxygenase-treated droplets induced both a significant increase in turbidity and a red shift to a different absorption maximum of the system as compared with those of the untreated emulsion.     

Effect of oil viscosity on the rheology of oil-in-water emulsions with added solids

This paper reports an experimental study on the effect of oil viscosity on the rheology of oil-in-water (o/w) emulsions with added solids. Four oils having a viscosity range of 0.0024 to 306 Pa . s were used. The size ratio of the solids to oil droplets was varied from 2 to 16. The addition of smaller size solids to the emulsions yielded a higher viscosity than that of larger solids at the same solids volume fraction. However, when the solids were sufficiently large such that the emulsions behaved as a continuous phase towards the solids, the viscosity of the emulsion-solids mixtures tended to be independent of the solids size. The critical size ratio of the solids to oil droplets, above which the emulsions behaved as a continuous phase towards the solids, increased with the oil viscosity. The critical size ratio varied between 3 and 10.     

Optimization of the composition of low-fat oil-in-water emulsions stabilized by white lupin protein

The effect of composition (protein, xanthan gum, and oil content) of lupin protein-stabilized emulsions on their physical properties—droplet size distribution, rheological behavior, and texture—was studied. Droplet size distribution was measured by laser light-scattering experiments, rheological parameters were determined from oscillatory and steady-state flow measurements, and texture responses were obtained from texture profile analysis. Response surface methodology was used to optimize the emulsion composition using commercial mayonnaise parameters as a standard. An increase in protein, xanthan gum, or oil content produced, in the experimental range considered, an increase in the rheological and textural parameters studied, as well as a decrease in the average oil droplet diameter. It was possible to produce stable lupin protein-stabilized emulsions with physical properties similar to those of commercial mayonnaise for a wide variety of protein, xanthan gum, and oil concentration values, which may be designed to suit market specifications.     

无机盐阴阳离子对稠油水包油型乳状液稳定性的影响

考察了两性/非离子复配表面活性剂浓度、无机/有机复配碱浓度、不同价态正负离子对稠油水包油型乳状液稳定性的影响规律。实验结果表明:随着复配表面活性剂浓度的增加,乳状液的分水率先急剧降低后缓慢下降;复配碱对乳状液的稳定性存在最优浓度;无机盐对乳状液的稳定性具有双重作用,低浓度盐提高乳状液的稳定性,高浓度盐降低乳状液的稳定性;一价阳离子对乳状液的稳定性影响顺序为KCl> NaCl> LiCl;二价阳离子对乳状液稳定性的影响程度为MgCl₂> CaCl₂;一价阴离子对分水率的影响顺序为NaCl> NaBr> NaI;高价阴离子对乳状液稳定性的影响程度为Na₂SO₄> NaCl> Na₃PO₄。     

Interdroplet heterogeneous nucleation of supercooled liquid droplets by solid droplets in oil-in-water emulsions

The crystallization of oil droplets inn-hexadecane oil-inwater emulsions was monitored by pulsed nuclear magnetic resonance (NMR). The emulsions initially contained an equal mixture of solid droplets and supercooled liquid droplets at either 6 or 8°C. The degree of crystallization in the droplets was determined by measuring the NMR signal 30 μs after a 90^o radio frequency pulse was applied to the sample. The signal from the solid droplets decayed rapidly after the radio frequency pulse, allowing the measured signal to be related to the fraction of liquid droplets. No crystallization was observed in a sample that contained only supercooled liquid droplets, but crystallization was observed when solid droplets of the same material were present. This indicated that crystallization was induced in the liquid droplets by the solid droplets and was most likely caused by interactions between solid and liquid droplets-that is, by interdroplet heterogeneous nucleation. The rate of induced crystallization decreased as the viscosity of the continuous phase was increased and the size of the droplets was increased, but was independent of droplet concentration (20–40%).