Preparation and characterization of highly stable monodisperse argan oil‐in‐water emulsions using microchannel emulsification

Argan oil is well known for its nutraceutical properties. Its specific fatty acid composition and antioxidant content contribute to the stability of the oil and to its dietetic and culinary values. There is an increasing interest to use argan oil in cosmetics, pharmaceutics, and food products. However, the formulation of highly stable emulsions with prolonged shelf life is needed. In this study, argan oil‐in‐water (O/W) emulsions were prepared using microchannel (MC) emulsification process, stabilized by different non‐ionic emulsifiers. The effects of processing temperature on droplet size and size distribution were studied. Physical stability of argan O/W emulsions was also investigated by accelerated stability testing and during storage at room temperature (25 ± 2°C). Highly monodisperse argan O/W emulsions were produced at temperatures up to 70°C. The obtained emulsions were physically stable for several months at room temperature. Furthermore, emulsifier type, concentration, and temperature were the major determinants influencing the droplet size and size distribution. The results indicated that a suitable emulsifier should be selected by experimentation, since the interfacial tension and hydrophilic–lipophilic balance values were not suitable to predict the emulsifying efficiency. Practical applications: MC emulsification produces efficiently monodisperse droplets at wide range of temperatures. The findings of this work may be of great interest for both scientific and industrial purposes since highly stable and monodisperse argan oil‐in‐water emulsions were produced which can be incorporated into food, cosmetic, or pharmaceutical formulations.     

Preparation of monodisperse water-in-oil-in-water emulsions using microfluidization and straight-through microchannel emulsification

Water-in-soybean oil-in-water (W/O/W) emulsions with an internal water phase content of 10–30% (vol/vol) were prepared by a two-step emulsification method using microfluidization and straight-through microchannel (MC) emulsification. A straight-through MC is a silicon array of micrometer-sized through-holes running through the plate. Microfluidization produced water-in-oil (W/O) emulsions with submicron water droplets of 0.15–0.26 μm in average diameter (d _av,w/o) and 42–53% in CV (CV_w/o) using tetraglycerin monolaurate condensed ricinoleic acid esters (TGCR) and polyglycerin polycondensed ricinoleic acid esters (PGPR) as surfactants dissolved in the oil phase. The d _av,w/o and viscosity of the W/O emulsions increased with an increase in internal water phase content. Straight-through MC emulsification was performed using the W/O emulsions as the to-be-dispersed phase and polyoxyethylene (20) sorbitan monooleate (Tween^® 80) as a surfactant dissolved in the external water phase. Monodisperse W/O/W emulsions with d _av,w/o/w of 39.0–41.0 μm and CV_w/o/w below 5% were successfully formed from a straight-through MC with an oblong section (42.8×13.3 μm), using the TGCR-containing systems. The d _av,w/o/w of the monodisperse W/O/W emulsions decreased as the internal water phase content increased because of the increase in viscosity of the to-be-dispersed phase. Little leakage of the internal water droplets and no droplet coalescence or droplet break-down were observed during straight-through MC emulsification.     

Preparation of phospholipid oil‐in‐water microspheres by microchannel emulsification technique

A novel microchannel (MC) emulsification technique for producing super‐monodisperse microspheres (MS) was recently proposed. In this study, we investigated the formation of monodisperse oil‐in‐water (O/W)‐MS using lecithin and lysophosphatidylcholine (LPC) as surfactant by applying the MC emulsification technique. When we used lecithin to produce O/W‐MS, we observed coalescence of the formed MS and the continuous outflow of the oil phase through the MC. This was probably due to the insufficient interfacial activity of lecithin and the subsequent wetting of the MC surface by the oil phase during the emulsification process. The monodisperse O/W‐MS could not be produced when lecithin was used as the only surfactant. However, we successfully produced monodisperse O/W‐MS by using hydrophilic LPC dissolved in the water phase. Also, a more stable emulsification process producing monodisperse O/W‐MS was found using lecithin in the oil phase and LPC in the water phase. The monodisperse O/W‐MS production was improved by a special surface oxidation treatment of the MC plate.     

Effects of addition of diacylglycerols on fat crystallization in oil‐in‐water emulsion

The effects of addition of diacylglycerols (DAGs) on the crystallization behavior of n‐hexadecane dispersed in oil‐in‐water emulsion (oil 20% and water 80%, v/v) were studied by differential scanning calorimetry (DSC) and ultrasonic velocity measurement. In an attempt to modify the crystallization rate of n‐hexadecane, five DAGs having the fatty acid moieties of behenic (DAB), stearic (DAS), palmitic (DAP), lauric (DAL) and oleic acid (DAO) were added to n‐hexadecane, which was mixed with water and Tween 20 for emulsification. The DSC study showed that the addition of DAB, DAS or DAP (1.0 wt‐% with respect to n‐hexadecane) increased the crystallization temperature (Tc) of a n‐hexadecane/water emulsion from 3 °C (without DAG) to 8 °C, whereas the addition of DAL and DAO showed no effect. The ultrasonic velocity measurement also revealed that the addition of DAGs resulted in increasing the Tc of n‐hexadecane in O/W emulsion. These effects were discussed by taking into account the formation of molecular aggregates at the interface due to the addition of DAGs, which act as a template for crystallization of n‐hexadecane. The template‐assisted crystallization depends on the structure of the fatty acid chains present in the DAG: the longer the fatty acid moiety of DAG , the more is the crystallization of n‐hexadecane in O/W emulsion accelerated.     

Preparation of micron-scale monodisperse oil-in-water microspheres by microchannel emulsification

Micron-scale monodisperse oil-in-water (O/W) micropheres (MS) were prepared using a novel microchannel (MC) emulsification technique. The characteristics of the MS preparation and the O/W-MS prepared were studied. Soybean oil and medium-chain triacyglycerol (MCT) were used as the disprrsed phase, and physiological saline was used as the continuous phase. Silicon MC with 1 to 3μm-equivalent channel diameters were employed. A novel MC module was devised to easily recover the O/W-MS prepared. The effects of the channel shape on the behavior of MS formation, on the MS size, and on the distribution were investigated. An MC with a terrace at the MC outlet stably yielded micron-scale monodisperse O/W-MS; the MS had diameters of about 5 μm, and their coefficients of variation were below 9%. Monodisperse food-grade O/W-MS with diameters of about 4 μm could be obtained by using polyglycerol fatty acid ester as the surfactant. The size and size distribution of the recovered O/W-MS remained almost constant over 60 d, demonstrating their long-term stability.     

Thixotropic Behavior of Oil‐in‐Water Emulsions Stabilized with Ethoxylated Amines at Low Shear Rates

Oil‐in‐water (O/W) emulsification is a lubricating pipeline method based on the reduction of the energy frictional loss produced during viscous flow. The flow behavior of heavy O/W emulsions formulated with nonionic surfactants is described. The effects of pH and salinity of the aqueous phase on droplet diameter, stability, and apparent viscosity of O/W emulsions were evaluated. The low‐shear Couette flow of O/W emulsions displayed intense shear‐thinning and thixotropic behavior. Thixotropy was associated to the droplet deformation energy caused by shear rate changes. The droplet deformation and alignment led to the apparent viscosity reduction compared to the fluid at rest. Thixotropic behavior is supposed to balance between the breakdown and recovery of droplet ordered structures. Emulsion formulation parameters were influenced by the aqueous phase pH, enabling to manage the emulsion properties. The droplet mean diameter of < 18 µm resulted in very stable emulsions.     

制备单分散含单体O/W乳液的SPG膜乳化过程

采用Shirasu多孔玻璃（SPG）膜乳化法制备了单分散含对苯二甲酰氯（TDC）单体的O/W乳液,系统地研究了SPG膜乳化过程的影响因素.实验结果表明,采用SPG膜乳化法制备单分散O/W乳液时,选择阴离子表面活性剂比考虑亲水亲油平衡（HLB）匹配更重要;增大分散相或连续相的黏度,能够改善乳液的单分散性和稳定性;随着单体浓度增加,乳液的单分散性变差,液滴的平均粒径逐渐变小.当SPG膜孔径大于1.0 μm左右时,可得到单分散的含TDC单体乳液;而当孔径小于1.0 μm左右时,水分子更容易扩散并溶解到油水界面甚至油相内部与TDC生成对苯二甲酸（TPA）,TPA积累到一定程度在油水界面上析出将膜孔堵塞,从而无法制得单分散乳液.随着乳化时间增长,乳液的平均直径逐渐变小、单分散性逐渐变差.     

Hydrophobic Modification and Regeneration of Shirasu Porous Glass Membranes on Membrane Emulsification Performance

The effect of hydrophobic modification and regeneration of Shirasu porous glass (SPG) membranes was systematically investigated on the monodispersity of emulsions. The results showed that the hydrophobic modification and regeneration of SPG membranes had little influence on the monodispersity of emulsions, no matter how many modification and regeneration runs were operated. The emulsification runs affected the emulsification performance to a certain extent when hydrophobically‐modified SPG membranes were used for preparing water‐in‐oil (W/O) emulsions repeatedly. However, they almost did not affect the emulsification performance when regenerated hydrophilic SPG membranes were used for preparing oil‐in‐water (O/W) emulsions. The SPG membranes could be used repeatedly after hydrophobic modification or regeneration with almost the same emulsification performance as fresh or freshly‐modified ones. The results provided some valuable guidance for the repetitive use of SPG membranes to prepare monodisperse O/W and W/O emulsions.     

Effect of lipid type on water‐in‐oil‐emulsions stabilized by phosphatidylcholine‐depleted lecithin and polyglycerol polyricinoleate

Water‐in‐oil (W/O, 30:70) emulsions were prepared with phosphatidylcholine‐depleted lecithin [PC/(PI,PE) = 0.16] or polyglycerol polyricinoleate (PGPR) as emulsifying agents by means of pressure homogenization. The effect of lipid type (medium‐chain triacylglycerols, sunflower, olive, butter oil, or MCT‐oil/vegetable fat blends) was investigated in relation to particle size distribution, coalescence stability and the sedimentation of the water droplets. A significant correlation (p <0.05) was observed between the interfacial pressure caused by the addition of lecithin to the pure lipids and the specific surface area of the emulsion droplets (r_s = 0.700), and between the viscosity of the lipids used as the continuous phase (reflecting the fatty acid composition) and the specific surface area of the emulsion droplets (r_s = 0.8459) on the other hand. Blends of vegetable fat and MCT‐oil led to reduced coalescence stability due to the attachment of fat crystals to the emulsion droplets. Lecithin‐stabilized W/O emulsions showed significantly higher viscosities compared to those stabilized with PGPR. It was possible to adjust the rheological properties of lecithin‐stabilized emulsions by varying the lipid phase.     

Healthier lipid combination oil‐in‐water emulsions prepared with various protein systems: an approach for development of functional meat products

Five protein‐stabilized oil‐in‐water emulsions were prepared using sodium caseinate (O/SC), soy protein isolate (O/SPI), sodium caseinate and microbial transglutaminase (O/SC + MTG), sodium caseinate, microbial transglutaminase and meat slurry (O/SC + MTG + MS) and SPI, sodium caseinate and microbial transglutaminase (O/IPS + SC + MTG); their composition (proximate analysis and fatty acid profile) and physicochemical characteristics were examined. The lipid phase was a combination of healthy fatty acids from olive, linseed and fish oils, containing low proportions (15%) of saturated fatty acids (SFA) and high proportions of monounsaturated fatty acids (MUFA, 47%) and polyunsaturated fatty acids (PUFA, 36%), with a PUFA/SFA ratio >2, and a n‐6/n‐3 PUFA ratio of 0.4. All the oil‐in‐water emulsions showed high thermal and creamy stability. Results of penetration test and dynamic rheological properties showed la existencia de different types of oil‐in‐water emulsion structures according to stabilizing system of emulsion. Those structures ranged from concentrate solution‐like (stabilized only with SC) (gel strength 0.06 mJ) to gel‐like (samples containing MTG) behaviours (gel strength ranged between 3.4 and 6.2 mJ). Morphological differences in the organization of the network structure were observed (by scanning electron microscopy) as functions of the protein system used to stabilize the oil‐in‐water emulsions.     

Surfactant Concentration,Antioxidants, and Chelators Influencing Oxidative Stability of Water‐in‐Walnut Oil Emulsions

Effects of surfactant concentration, antioxidants with different polarities, and chelator type on the oxidative stability of water‐in‐stripped walnut oil (W/O) emulsions stabilized by polyglycerol polyricinoleate (PGPR) were evaluated. The formation of primary oxidation products (lipid hydroperoxides) and secondary oxidation products (hexanal) decreased with increasing PGPR concentrations (0.3–1.0 wt% of emulsions). Excess surfactant might solubilize lipid hydroperoxides out of the oil–water interface, resulting in the decreased lipid oxidation rates in W/O emulsions. At concentrations of 10–1000 μM, the polar Trolox demonstrated concentration‐dependent antioxidant activity according to both hydroperoxide and hexanal formation. The antioxidant efficiency of the non‐polar α‐tocopherol was slightly reduced at the higher range of 500–1000 μM based on hydroperoxide formation. Both ethylenediaminetetraacetic acid (EDTA) and deferoxamine (DFO) at concentrations of 5–100 μM reduced the rates of lipid oxidation at varying degrees, indicating that endogenous transition metals may promote lipid oxidation in W/O emulsions. EDTA was a stronger inhibitor of lipid oxidation than DFO. These results suggest that the oxidative stability of W/O emulsions could be improved by the appropriate choice of surfactant concentration, antioxidants, and chelators.     

Antioxidant activity of phenolic compounds in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose

The aim of this work was to study the evolution of oxidation and the efficiency of phenolic antioxidants in sunflower oil‐in‐water emulsions containing sodium caseinate and lactose (Cas‐Lac) or stabilized by Tween‐20 (T‐20). Two groups of phenolic antioxidants which are structurally similar were tested, i.e. (1) α‐tocopherol and its water‐soluble analogue, Trolox; and (2) gallic acid and its ester derivatives propyl gallate and dodecyl gallate. Emulsion samples were oxidized at 40 °C and the progress of oxidation was followed through quantitation of oxidized triacylglycerol monomers, dimers and oligomers. Results showed that Cas‐Lac emulsions were more stable to oxidation than T‐20 emulsions. In both types of emulsions, the most protective antioxidants were the compounds of lower polarity, namely, α‐tocopherol and dodecyl gallate. It was also found that substantial amounts of α‐tocopherol coexisted with significant polymerization, which was indicative of the heterogeneity of oxidation, i.e. differences of oxidation rate in oil droplets.     

A low‐energy emulsification batch mixer for concentrated oil‐in‐water emulsions

This work shows the formation of a high internal phase ratio oil‐in‐water (O/W) emulsion using a new type of a two‐rod batch mixer. The mixture components have sharply different viscosities [1/3400 for water‐in‐oil (W/O)], similar densities (1/0.974 for W/O), and an O/W ratio of 91% (wt/wt). The simple design of this mixer leads to a low‐energy process (10⁶ < energy density [J m^?3] < 10⁷), characterized by low rotational speed and laminar flow. The droplet size distribution during the emulsification was investigated according to different physical and formulation parameters such as stirring time (few minutes < t < 1 h), rotational speed (60 < Ω < 120 rpm), surfactant type (Triton X‐405 and X‐100), concentration (from 1 to 15.9 wt % in water), and salt addition (30 g/L). We show that all studied parameters allow a precise control of the droplet size distribution and the rheology. The resulting emulsions are unimodal and the mean droplet diameter is between 30 μm and 8 μm. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Predicting the Viscosity of Non‐Newtonian Water‐in‐Oil Emulsions Based on the Lederer Model

The accurate prediction of the viscosity of emulsions is highly important for oil well exploitation. Commonly used models for predicting the viscosity of water‐in‐oil (W/O) emulsions composed by two or three factors cannot always fit well the viscosity of W/O emulsions, especially in the case of non‐Newtonian W/O emulsions. An innovative and comprehensive method for predicting the viscosity of such emulsions was developed based on the Lederer, Arrhenius, and Einstein models, using experimental data. Compared with the commonly applied W/O emulsion viscosity models, the proposed method considers more factors, including temperature, volume fraction of water, shear rate, and viscosity of the continuous (oil) and dispersed phase (water). Numerous published data points were collected from the literature to verify the accuracy and reliability of the method. The calculation results prove the high accuracy of the model.     

The effect of shear and oil/water ratio on the required hydrophile-lipophile balance for emulsification

Required hydrophile-lipophile balance (HLB) values were examined in terms of the nature of kerosene-water, both oil-in-water (O/W) and water-in-oil (W/O), emulsions formed using Span 80/Tween 80 surfactant blends. Both the nature of the emulsification method and the oil/water ratio were critical in determining the resulting emulsion type. Both high- and low-shear conditions were investigated. Under high shear, low internal phase emulsions formed using the surfactant mixtures that corresponded to the required HLB values for emulsification involving kerosene (6 for W/O and 14 for O/W). However, at low shear, high internal phase (concentrated) emulsions resulted. Furthermore, depending on the oil/water ratio, some of the high internal phase emulsions were opposite to the type expected, given the HLB of the surfactant blend used. From these results, it appears that the emulsification technique (applied shear and oil/water ratio) used can be of greater importance in determining the final emulsion type than the HLB values of the surfactants themselves.     

Preparation of microcapsules of W/O/W emulsions containing a polysaccharide in the outer aqueous phase by spray‐drying

A water‐in‐oil‐in‐water (W/O/W) multiple emulsion containing a hydrophilic substance, 1,3,6,8‐pyrenetetrasulfonic acid tetrasodium salt (PTSA), and a wall material in its inner and outer aqueous phases, respectively, was prepared by a two‐step emulsification using a rotor/stator homogenizer, and was further homogenized with a high‐pressure homogenizer. Maltodextrin or gum arabic were used as wall materials, and olive oil was used as the oily phase. The high encapsulation efficiency for PTSA (>0.9) was realized. The emulsion was spray‐dried to produce microcapsules of W/O/W type. The efficiencies of the microcapsules prepared with maltodextrin and gum arabic were 0.82 and 0.67, respectively. Stability of the microcapsules was examined at 37 °C and 12%, 33% and 75% relative humidity. Microcapsules prepared with maltodextrin were more stable than those prepared with gum arabic.     

Effect of triacylglycerol species on the crystallizing behavior of a model water/oil emulsion

The crystallizing behavior of a model water/oil (W/O) emulsion with different fat formulas was investigated. The model W/O emulsion was stored in a programmable oven under a temperature fluctuation cycle of 5 °C for 12 h and 20 °C for another 12 h. Crystal growth was observed using a polarization microscope, until the crystals were over 100 μm in diameter, which causes texture degradation. We examined whether the texture degradation is related to the fatty acid formula and the triglyceride formula by carbon number. We also examined the effect of the triglyceride species concentration estimated from the fatty acid formula on the texture degradation. The palmitic acid content was related with texture degradation at high concentration among the fatty acid species. The triglyceride content was not related with texture degradation. Triacylglycerol species with palmitic acid such as tripalmitate (PPP) and 1,3‐dipalmitoyl‐2‐oleoyl‐glycerol (POP) were related with texture degradation. The summed up concentration of three triglycerides [PPP, POP and 1,2‐dipalmitoyl‐3‐oleoyl‐glycerol (PPO)] was related with texture degradation.     

Interfacial Crystallization of Diacylglycerols Rich in Medium‐ and Long‐Chain Fatty Acids in Water‐in‐Oil Emulsions

The effects of diacylglycerols rich in medium‐ and long‐chain fatty acids (MLCD) on the crystallization of hydrogenated palm oil (HPO) and formation of 10% water‐in‐oil (W/O) emulsion are studied, and compared with the common surfactants monostearoylglycerol (MSG) and polyglycerol polyricinoleate (PGPR). Polarized light microscopy reveals that emulsions made with MLCD form crystals around dispersed water droplets and promotes HPO crystallization at the oil‐water interface. Similar behavior is also observed in MSG‐stabilized emulsions, but is absent from emulsions made with PGPR. The large deformation yield value of the test W/O emulsion is increased four‐fold versus those stabilized via PGPR due to interfacial crystallization of HPO. However, there are no large differences in droplet size, solid fat content (SFC), thermal behavior or polymorphism to account for these substantial changes, implying that the spatial distribution of the HPO crystals within the crystal network is the driving factor responsible for the observed textural differences. MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals to enhance the rigidity of emulsion. This study provides new insights regarding the use of MLCD in W/O emulsions as template for interfacial crystallization and the possibility of tailoring their large deformation behavior. Practical Applications: MLCD is applied in preparing W/O emulsion. It is found that MLCD forms unique interfacial Pickering crystals around water droplets, which promote the surface‐inactive HPO nucleation at the oil‐water interface. Thus MLCD‐covered water droplets act as active fillers and interact with surrounding fat crystals, which can greatly enhance the rigidity of emulsion. This observation would provide a theoretical reference and practical basis for the application of the MLCD with appreciable nutritional properties in lipid‐rich products such as whipped cream, shortenings margarine, butter and ice cream, so as to substitute hydrogenated oil. MLCD‐stabilized emulsions can also be explored for the development of novel confectionery products, lipsticks, or controlled release matrices.     

A descriptive force‐balance model for droplet formation at microfluidic Y‐junctions

In a previous article, we studied the basics of emulsification in microfluidic Y‐junctions, however, without considering the effect of viscosity of the disperse phase. As it is known from investigations on many different microstructures that viscosity and viscosity ratio are governing parameters for droplet size, we here investigate whether this is also the case for microfluidic Y‐junctions and do so for a wide range of process conditions. The investigated Y‐junctions have a width of 19.9 or 12.8 μm and a depth of 5.0 μm, and the formed monodisperse droplets (CV < 1%) are between 3 and 20 μm. We varied the disperse‐phase viscosity using different oils (1–105 mPa s), and continuous‐phase viscosity using glycerol–water and ethanol–water mixtures (1.0–6.2 mPa s), which corresponds to disperse‐to‐continuous‐phase viscosity ratios from 0.4 to 105.0. Through the variation of the liquids, also a range in interfacial tensions (12–55 mN m^?1) is assessed. The disperse‐phase flow rate is varied from 0.039 to 18.0 μL h^?1, the continuous‐phase flow rate from 1.39 μL h^?1 to 0.41 mL h^?1, and this corresponds to flow rate ratios from 1.1 × 10^?3 to 0.14, which is once again based on wide range of conditions. For all these conditions, in which droplets are formed in the dripping and jetting regime, the droplet size could be described with a model based on the existing force‐balance model, but now extended to incorporate the cross‐sectional area of the droplet and the resistance with the wall. Surprisingly enough, it was found that the droplet size is not influenced by the disperse‐phase viscosity, or the viscosity ratio, but it is dominated by the resistance with the wall and the continuous‐phase properties. Because of this, emulsification with Y‐junctions is intrinsically simpler than any other shear‐based method as droplet size is only determined by the continuous phase. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Factors affecting droplet size of sodium caseinate‐stabilized O/W emulsions containing β‐carotene

This work was initiated to prepare an oil‐in‐water (O/W) emulsion containing β‐carotene by microfluidization. The β‐carotene was dissolved in triolein and microfluidized with an aqueous phase containing sodium caseinate (SC) as the emulsifier. Microfluization at 140 MPa resulted in O/W emulsions with a mean droplet diameter of ca. 120 nm, which was further confirmed by transmission electron microscopy analysis. The influences of SC concentration and microfluidization parameters on the droplet size of the emulsions were studied. The results showed that the mean droplet diameter decreased significantly (p <0.05) from 310 to 93 nm with the increase in SC concentration from 0.1 to 2 wt‐%. However, a further increase in SC concentration did not much change the droplet diameter, although the polydispersity of the emulsions was slightly improved. The droplet diameter of the emulsions was found to decrease from 200 to 120 nm with increasing microfluidization pressure, with narrower droplet size distribution. The storage study showed that the emulsions were physically stable for about 2 weeks at 4 °C in the dark. The results provide a better understanding of the performance of SC in stabilizing the O/W emulsions.