Preparation Methods for Monodispersed Garlic Oil Microspheres in Water Using the Microemulsion Technique and Their Potential as Antimicrobials

Garlic oil is considered as a natural broad‐spectrum antibiotic because of its well‐known antimicrobial activity. However, the characteristics of easy volatility and poor aqueous solubility limit the application of garlic oil in industry. The purpose of the present work is to develop and evaluate an oil‐free microemulsion by loading garlic oil in microemulsion system. Microemulsions were prepared with ethoxylated hydrogenated castor (Cremophor RH40) as surfactant, n‐butanol (or ethanol) as cosurfactant, oleic acid‐containing garlic oil as oil phase, and ultrapure water as water phase. The effects of the ratio of surfactant to cosurfactant and different oil concentration on the area of oil‐in‐water (O/W) microemulsion region in pseudoternary phase diagrams were investigated. The particle size and garlic oil encapsulation efficiency of the formed microemulsions with different formulations were also investigated. In addition, the antimicrobial activity in vitro against Escherichia coli and Staphylococcus aureus was assessed. The experimental results show that a stable microemulsion region can be obtained when the mass ratio of surfactant to cosurfactant is, respectively, 1:1, 2:1, and 3:1. Especially, when the mixture surfactants of RH40/n‐butanol 2/1 (w/w) is used in the microemulsion formulation, the area of O/W microemulsion region is 0.089 with the particle size 13.29 to 13.85 nm and garlic oil encapsulation efficiency 99.5%. The prepared microemulsion solution exhibits remarkable antibacterial activity against S. aureus.     

Formulation of food-grade microemulsions with glycerol monolaurate: effects of short-chain alcohols,polyols, salts and nonionic surfactants

The formulation of food-grade microemulsions with glycerol monolaurate (GML) for antimicrobial applications has been studied. The compositions included water, GML, short-chain alcohols (such as ethanol), polyols (propylene glycol and glycerol), salts (organic, such as sodium benzoate, sodium lactate and sodium propionate, and inorganic, such as NaCl) and several nonionic surfactants [such as ethoxylated sorbitan esters, sucrose esters (SEs)]. The phase behavior of these systems is discussed with respect to the influence of composition on the degree of oil solubilization in the aqueous phase. The oil solubilization was dramatically improved in the presence of the short-chain alcohols and polyols, organic salts contributed to the improvement of oil solubilization as hydrotropes. Tween 20 being the most hydrophilic surfactant in Tweens solubilized the maximum oil, but in the presence of SEs it is hard to form oil-in-water microemulsions. Viscosity measurements along selected dilution lines indicate that at a certain composition the system inverts from a water-in-oil to an oil-in-water microemulsion.     

Microemulsions: a potential delivery system for bioactives in food

Microemulsions are thermodynamically stable, transparent, low viscosity, and isotropic dispersions consisting of oil and water stabilized by an interfacial film of surfactant molecules, typically in conjunction with a cosurfactant. Microemulsions (so-called due to their small particle size; 5-100 nm) have found application in a wide variety of systems, such as pharmaceutical and oil recovery, but their application in food systems has been hindered by the types of surfactant permissible for use in food. The objective of this review is to provide an overview of the structures and phase behavior of microemulsions, methods of microemulsion formation, and techniques which may be used for characterization. A comprehensive review of previous work on both food-grade microemulsion systems, and non-food-grade systems of specific food interest is included. The application of microemulsions as reaction media, their ability to solubilize proteins and hence their use as a separation technique is also documented. In addition, attention is focused on the application of microemulsions as delivery systems for delivery of bioactive compounds, and the links between microemulsions and increased bioavailability. Future research, both applied and fundamental, should focus on surfactants which are not restricted for use in foods.     

Formulation of a cosurfactant-free O/W microemulsion using nonionic surfactant mixtures

ABSTRACT:  A cosurfactant-free O/W microemulsion composed of oil, a mixture of hydrophilic and hydrophobic surfactants, and water has been developed using food-grade components as a nutrient delivery system. We started our investigation to monitor the phase behavior of this system based on a hydrophilic surfactant (Tween 80). From a phase diagram, the weight ratio of 5.4:33.8:60.8 = oil:surfactant:water was selected as a combination ratio for the O/W microemulsion system. We also investigated the combination effect of different hydrophobic surfactants to Tween 80 on microemulsion formation. Use of hydrophobic surfactants with Tween 80 produced smaller droplets than Tween 80 alone. Rheological studies showed that all microemulsions followed shear-thinning behavior. The turbidity of microemulsions did not change after accelerated stability tests, indicating that this microemulsion system was stable under the given harsh conditions. When docosahexaenoic acid (DHA) oil was applied to this microemulsion system, the particle size and the turbidity were not significantly changed. Dilution with a different aqueous medium, either water or acidic fluid, did not significantly change the microemulsion turbidity. DHA oil incorporated in microemulsion showed higher oxidation stability than free DHA oil.     

聚甘油单月桂酸酯-油酸微乳体系的构建及其性能

为构建安全高效的微乳体系,提高姜黄素的溶解度,拓展微乳液及姜黄素在食品中的应用,制备具有较高姜黄素溶解度、可无限稀释的食品级微乳液。以油酸和不同聚合度的聚甘油单月桂酸酯、不同碳链长的醇为原料,通过对拟三元相图的分析,筛选表面活性剂和助表面活性剂,研究表面活性剂与助表面活性剂质量比（Km）、水相pH值和NaCl浓度对微乳体系相行为的影响,用电导率法分析微乳液的结构,用激光粒度仪和透射电镜测定观察微乳液滴的粒径、微观形貌。结果表明,以质量比为2∶1的六聚和十聚甘油单月桂酸酯复配为表面活性剂,以乙醇为助表面活性剂,Km=1/2,制备的微乳液效果最好,微乳区域面积占比最大,微乳液滴呈均一球形,粒径在10～100?nm之间。非中性的水相、NaCl的加入均会导致微乳区域面积占比的减小和最小可稀释比的增大。当表面活性剂与油相质量比为9∶1时,能够形成可无限稀释微乳体系,该体系结构在含水量小于45%时为W/O型,继续增加含水量,体系结构逐渐转变为双连续型,含水量超过60%时为O/W型。姜黄素微乳化不影响姜黄素生物活性,且姜黄素的溶解度可达4.87?mg/mL,可有效地解决姜黄素溶解性差、稀释性差的问题,说明微乳液是姜黄素的优良载体。     

Incorporation of soybean oil improves the dilutability of essential oil microemulsions

Plant essential oils (EOs) have strong antimicrobial and antioxidant activities. However, their water insolubility and volatility limit their practical application. Microemulsions are thermodynamically stable delivery systems for hydrophobic bioactive compounds but can be destabilized after dilution by the polar phase. In the present study, soybean oil (SBO) was studied for the impacts on formation and dilutability of EO microemulsions comprised of polysorbate 80 (Tween™ 80) as a surfactant and equal mass of water and propylene glycol as the polar phase. The oil phase contained EO (cinnamon bark oil, eugenol, or thymol) and SBO at 1:0, 2:1 or 4:1 mass ratios. Pseudo-ternary phase diagrams were constructed after titrating the polar phase into Tween™ 80–oil mixture at 1:1 to 9:1 mass ratios. Blending SBO with EO expanded the regimes of microemulsions and reduced the droplet dimensions that were stable over 90 days. Viscosity and electrical conductivity data indicated the transition from W/O to O/W microemulsions as the content of polar phase increased from 10% to 90% w/w. The enhanced dilutability of microemulsions after blending with SBO can broaden the application of EOs.     

In vitro and in vivo antifungal activity of a water-dilutable cassia oil microemulsion against Geotrichum citri-aurantii

BACKGROUND: Recently, food‐grade microemulsions have been of increasing interest to researchers and have shown great potential in industrial applications. In this study a food‐grade water‐dilutable microemulsion system with cassia oil as oil, ethanol as cosurfactant, Tween 20 as surfactant and water was developed and its antifungal activity in vitro and in vivo against Geotrichum citri‐aurantii was assessed. RESULTS: The phase diagram results confirmed the feasibility of forming a water‐dilutable microemulsion based on cassia oil. One microemulsion formulation, cassia oil/ethanol/Tween 20 = 1:3:6 (w/w/w), was selected with the capability to undergo full dilution with water. The average particle size was 6.3 nm. The in vitro antifungal experiments showed that the microemulsion inhibited fungal growth on solid medium and prevented arthroconidium germination in liquid medium and that cassia oil had stronger activity when encapsulated in the microemulsion. The in vivo antifungal experiments indicated that the water‐dilutable microemulsion was effective in preventing postharvest diseases of citrus fruits caused by G. citri‐aurantii. CONCLUSION: The results of this study suggest a promising utilisation of water‐dilutable microemulsions based on essential oils for the control of postharvest diseases. Copyright © 2012 Society of Chemical Industry     

Antimicrobial activity of a food-grade fully dilutable microemulsion against Escherichia coli and Staphylococcus aureus

Microemulsions are colloidal nanodispersions of oil and water stabilized by an interfacial film of surfactant molecules, typically in conjunction with a cosurfactant. There is a limited number of reports in the literature on microemulsion use for antimicrobial purposes. The physicochemical characterization of a food-grade fully dilutable microemulsion system with glycerol monolaurate (GML) as oil, organic acids as cosurfactant, Tween 80 as surfactant, and the antimicrobial activities against Escherichia coli and Staphylococcus aureus have been studied in this paper. The influence of organic acids on oil solubilization was clearly reflected in the phase behavior of these systems. Propionic acid demonstrated the greatest capability to improve the oil solubilization among the tested linear and nonlinear chain organic acids and contributed to the formation of U-type microemulsion systems. One microemulsion formulation with an average particle size of 8 nm was selected, the composition is GML/propionic acid/Tween 80/water = 3:9:8:12. The kinetics of killing experiments demonstrated that the undiluted microemulsion caused a complete loss of viability of E. coli or S. aureus cells in 1 min and still had effective bactericidal effects even when diluted, more than 99% viable E. coli cells were killed within 15 min and a complete loss of viability was achieved at 45 min while more than 99% viable S. aureus cells were killed within 30 min and a complete loss of viability was achieved at 60 min in the presence of the 10-fold diluted microemulsion. The fast killing kinetics of the ten-fold serial dilutions of microemulsions were in good agreement with the mode of action studies, indicating that the interaction between the antimicrobial microemulsions and bacterial membranes significantly decreased the bacterial cell surface hydrophobicity and induced the quick release of 260 nm absorbing materials. This work suggests the potential use of food-grade fully dilutable microemulsions for antimicrobial purposes in beverages or seafood products.     

Future developments in cosmetic formulations

In recent years, there have been a great deal of interest in applications of microemulsions, liposomes (vesicles) and multiple emulsions in cosmetic formulations. These systems will provide the cosmetic industry with new types of formulations which are easier to apply, better functional benefit and potentially safer formulations. Microemulsions are thermodynamically stable systems and hence shelf life is no problem. Many cosmetic ingredients can be adequately solubilized in the swollen micelles of the microemulsions. Such solubilized systems may enhance transport and diffusion through various barriers, eg., the skin, thus enhancing the efficacy of the formulations. However, microemulsions may cause skin irritation by disrupting the liquid crystalline structure of the stratum corneum. This problem may be overcome by formulating microemulsions, which on evaporation produce lamellar liquid crystalline structures. The problem of skin irritation is certainly reduced or eliminated using liposomes or vesicles, which offer an alternative to microemulsions. The principles for formation and stabilization of vesicles are discussed in this paper and research work is needed to produce nanocapsules from liposomes, using polymerizable surfactants. Multiple emulsions of the water/oil/water (w/o/w) or oil/water/oil (o/w/o) types are also valuable systems for formulating cosmetics. In the first place, they offer a means of sustained release of the various ingredients. Secondly, they allow one to separate the various ingredients in the formulation, thus preventing their possible interaction. The basic principles required for preparation of stable multiple emulsions are summarised. Developments of polymeric surfactants led to the formulation of stable multiple emulsions. An example of a recently formulated stable w/o/w multiple emulsion is given in this paper The stability of the system was investigated using optical microscopy. Creaming occurred on storage, particularly at high temperature (40°C) and this was significantly reduced by addition of Kelzan (a polysaccharide with high molecular weight). The final formulation was studied rheological techniques.     

Food-grade microemulsions,nanoemulsions and emulsions: Fabrication from sucrose monopalmitate & lemon oil

Sucrose monopalmitate (SMP) is a non-toxic, biodegradable, non-ionic surfactant suitable for use in foods and beverages. This study aimed to establish conditions where stable microemulsions, nanoemulsions or emulsions could be fabricated using SMP as a surfactant and lemon oil as an oil phase. Emulsions (r > 100 nm) or nanoemulsions (r < 100 nm) were formed at low surfactant-to-oil ratios (SOR < 1) depending on homogenization conditions, whereas microemulsions (r < 10 nm) were formed at higher ratios (SOR > 1). The impact of simple mixing, thermal treatment, and homogenization on the formation of the different colloidal systems was investigated. Blending/heating was needed to produce microemulsions or emulsions, whereas blending/heating/homogenization was needed to produce nanoemulsions. The impact of environmental stresses (pH, ionic strength, temperature) on the functional performance of nanoemulsions and microemulsions was examined. Relatively stable nanoemulsions could be formed at pH 6 and 7 and stable microemulsions at pH 5 and 6, but extensive particle growth/aggregation occurred at lower and higher pH values. Microemulsions were relatively stable to salt addition (0–200 mM NaCl), but nanoemulsions exhibited droplet aggregation/growth at ≥50 mM NaCl after 1 month storage at pH 7. Microemulsions formed gels at low temperatures (5 °C), were stable at ambient temperatures (23 °C), and exhibited particle growth at elevated temperatures (40 °C). Nanoemulsions were stable at refrigerator (5 °C) and ambient (23 °C) temperatures, but exhibited coalescence at elevated temperatures (40 °C). This study provides important information for optimizing the application of sucrose monoesters to form colloidal dispersions in food and beverage products.     

Lemon oil solubilization in mixed surfactant solutions: Rationalizing microemulsion & nanoemulsion formation

Lipophilic functional ingredients are usually incorporated into aqueous-based foods and beverages in the form of colloidal dispersions. In this study, we investigated the rate and extent of solubilization of emulsified lemon oil in mixed non-ionic surfactant solutions (buffer: propylene glycol = 2:1): sucrose monopalmitate (SMP) and/or Tween 80 (T80). The influence of surfactant concentration, type, and mixing ratio on lemon oil solubilization was investigated, with the aim of identifying suitable conditions for preparing stable microemulsions and nanoemulsions. Solubilization was monitored by measuring changes in light scattering by lemon oil droplets after they were dispersed in surfactant solutions (pH 7). The solubilization process was rapid (<few minutes), with the rate increasing with increasing surfactant concentration. For a particular surfactant type and concentration, lemon oil was transferred from nanoemulsion droplets into microemulsion droplets until a critical lemon oil concentration (C_sat) was reached, after which it remained as nanoemulsion droplets. The value of C_sat increased with increasing surfactant concentration and was higher for SMP than Tween 80. The impact of storage at pH 3.5 on the physical stability of microemulsions and nanoemulsions was examined. Acid stable colloidal dispersions could not be formed using SMP alone. However, relatively stable nanoemulsions and microemulsions could be formed when ≥75 or 50 wt% Tween 80 was incorporated into the surfactant phase, respectively. This study provides important information for the rational design of food-grade colloidal delivery systems for encapsulating and delivering functional lipids for food and beverage applications.     

Structural aspects of surfactant selection for the design of vegetable oil semi-synthetic metalworking fluids

This paper presents a set of surfactant-selection guidelines that can be used to design bio-based semi-synthetic metalworking fluid (MWF) microemulsions as a renewable alternative to conventional petroleum formulations. Ten surfactant classes (six anionic and four nonionic) with different head and tail structures and three vegetable base oils (canola oil, soybean oil, and a fatty acid trimethylolpropane ester) were investigated as representatives of oil and surfactant options currently under consideration in the MWF industry. All combinations of these surfactants and oils were formulated at the full range of oil to surfactant ratios and surfactant concentrations. The stability of each formulation was evaluated based on visual transparency, light transmittance, and droplet diameter. The experimental results yield the following guidelines that produce stable bio-based MWF microemulsions with minimum necessary concentrations of surfactants: (1) a combination of two surfactants, one nonionic and one water soluble co-surfactant (either nonionic or anionic) is preferred over a single surfactant; (2) the nonionic surfactant should have a carbon tail length greater than or equal to the nominal carbon chain length of the fatty acids in the oil as well as a head group that is not excessively small or large (e.g., 10-20 ethylene oxide groups for a polysorbitan ester, ethoxylated alcohol, or ethoxylated glyceryl ester); (3) the difference in tail lengths between the surfactant and the co-surfactant should be less than 6 to maximize the feasible range of oil to surfactant ratios yielding stable emulsions. These guidelines are consistent with general results of micelle solubilization theory and evidence is provided to suggest that common semi-synthetic MWF systems can be thought of as swollen micelle systems.     

Encapsulation of functional lipophilic components in surfactant-based colloidal delivery systems: Vitamin E,vitamin D,and lemon oil

The fabrication and stability of surfactant-based colloidal delivery systems (microemulsions and emulsions) suitable for encapsulation of lipophilic active agents (vitamins and flavours) was investigated. An emulsion titration method was used to study the influence of surfactant type (Tween 20, 60 and 80) and oil type (Vitamin E, vitamin D₃ and lemon oil) on the incorporation of lipophilic components into surfactant micelles. Oil-in-water emulsions were formed and then different amounts were titrated into surfactant micelle solutions. The influence of surfactant-to-oil ratio (SOR) and oil type on the formation of colloidal dispersions was examined using dynamic light scattering and turbidity measurements. SOR, oil type, and surfactant type had a pronounced influence on the nature of the colloidal dispersions formed. Microemulsions could not be formed using vitamin D or E in 1% Tween solutions, due to the relatively large size of the lipophilic molecules relative to the hydrophobic interior of the surfactant micelles. On the other hand, microemulsions could be formed from lemon oil at relatively high SORs. There was not a major impact of non-ionic surfactant type (Tween 20, 60 or 80) on the formation and properties of the colloidal dispersions. However, Tween 20 micelles did appear to be able to solubilise less lemon oil than Tween 60 or 80 micelles, presumably due to their smaller dimensions. This study provides useful information for the rational design of food grade colloidal delivery systems for encapsulating flavour oils, oil-soluble vitamins, and other functional lipids for application in foods and beverages.     

Reactivity of hair cystine in microemulsion media

Reduction of keratin cystine by thioglycolic acid incorporated in microemulsions of the water/sodium dodecilsulphate/ n -pentanol/ n -dodecane system has been determined. The results obtained have been interpreted in relation to the properties of the reaction media. Microemulsions with constant oil-to-surface active mixture weight ratios ( R _o/s) and different concentrations of water were chosen as reaction media. At low water concentrations a steep increase in reactivity with the increase of water was observed at all values of R _o/s. However it was more pronounced the higher the oil content. A relation between maximum cysteine formation and percolative behaviour of the microemulsion was found at high R _o/s values.     

食品级刺五加叶黄酮微乳的制备及功能特性

黄酮类物质的溶解度低,耐碱性和抗光解能力差,化学性质很不稳定,限制了其在食品中的应用,而微乳是一种良好的载体,可解决黄酮难以利用的问题。本研究应用滴定法绘制伪三元相图来考察不同的表面活性剂、助表面活性剂、表面活性剂与助表面活性剂的质量比（Km）、油相等对微乳形成的影响,从中筛选出最佳微乳制备配方。利用透射电子显微镜和粒径分析仪研究微乳粒子的形态和粒径分布。同时以刺五加叶为原料,采用微乳化技术制备刺五加叶黄酮微乳,以超氧阴离子自由基、羟自由基及1,1-二苯基-2-三硝基苯肼自由基的清除率来考察黄酮微乳的抗氧化能力,以抑菌圈实验研究黄酮微乳的抑菌性能,以刺五加叶黄酮为对照。结果发现,以肉豆蔻酸异丙酯为油相、Tween-80为表面活性剂、无水乙醇为助表面活性剂,且Km＝2时得到的微乳区域面积最大,微乳平均粒径约18.3 nm,高速离心和长时间放置后体系均匀透明、未见分层、稳定性好。抗氧化实验表明,刺五加叶黄酮微乳的抗氧化能力优于刺五加叶黄酮对照。在抑菌圈实验中,黄酮微乳对大肠杆菌、金黄色葡萄球菌、沙门氏菌及荧光假单胞菌的抑菌效果均好于刺五加叶黄酮对照。     

不同类型表面活性剂微乳液热力学性质的研究

从不同种类表面活性剂／醇／硬脂酸甲酯（油相）／蔗糖水溶液所组成的微乳液体系的相图出发，研究它们所形成的微乳液的标准热力学函数，并得到标准自由能变化与醇的碳原子数和温度呈线性关系。     

Structure and rheology of semisolid o/w creams containing cetyl alcohol/non-ionic surfactant mixed emulsifier and different polymers

Oil-in-water (o/w) emulsions for cosmetic use, such as lotions and creams, are complex multiple-phase systems, which may contain a number of interacting surfactants, fatty amphiphiles, polymers and other excipients. This study investigates the influence of two synthetic cationic polymers, Polyquaternium-7 and Polyquaternium-11, and the natural anionic polymer, gum of acacia, on the rheology and microstructure of creams prepared with a non-ionic mixed emulsifier (cetyl stearyl alcohol-12EO/cetyl alcohol) using rheology (continuous shear, and viscoelastic creep and oscillation), microscopy and differential scanning calorimetry (DSC). A control cream containing no polymer was also investigated. The semisolid control cream was structured by a swollen lamellar gel network phase formed from the interaction of cetyl alcohol and the POE surfactant, in excess of that required to stabilize oil droplets, with continuous phase water. Endothermic transitions between 25 and 100 degrees C were identified as components of this phase. Incorporation of cationic polymer into the formulation caused significant loss of structure to produce a mobile semisolid containing larger oil droplets. The microscopical and thermal data implied that the cationic polymer caused the swollen lamellar gel network phase to transform into non-swollen crystals of cetyl alcohol. In contrast, incorporation of gum of acacia produced a thicker cream than the control, with smaller droplet sizes and little evidence of the gel network. Microscopical and thermal data implied that although there were also interactions between gum of acacia and both the surfactant and the swollen gel network phase, the semisolid properties were probably because of the ability of the gum of acacia to stabilize and thicken the emulsion in the absence of the swollen lamellar network.     

Stability and characterisation of phospholipid-based curcumin-encapsulated microemulsions

The ternary phase diagram of a curcumin-encapsulated O/W microemulsion system using food-acceptable components, lecithin and Tween 80 as the surfactants and ethyl oleate as the oil phase, was constructed. The stability and characterisation of curcumin in microemulsion were investigated. The results indicated that a composition of curcumin microemulsion (DI water: surfactants (the mole ratio of lecithin/Tween 80 was 0.3): EO = 10:1.7:0.4 in wt ratio) was stable for 2 months with an average diameter of 71.8 ± 2.45 nm, as detected by UV–Vis spectra and diameter distributions. The microemulsion possesses an ability to be diluted with aqueous buffer without destroying its structure for 48 h. A skin permeation study for testing the penetration effect of various curcumin loading in the microemulsions with different particle diameters was also performed and discussed in this contribution.     

食品级微乳液的研究进展

微乳液(microemulsion,简称ME)是由两种互不相溶的溶剂形成的热力学稳定体系,在医药、化妆品以及采油等领域都有广泛的应用,但在食品领域的研究还比较少。研究表明微乳液能够提高亲水性或亲脂性物质的溶解度,并能作为化学或酶法反应的有效介质,引起了广大食品领域科学工作者的关注。本文对食品级微乳液的制备、增溶作用以及作为微反应器等进行了综述。     

Optimization,characterization and in vitro evaluation of curcumin microemulsions

The purpose of this study was to improve the solubility and the stability and oral uptake of curcumin by developing an o/w microemulsion, using food grade components. Three microemulsions were developed and characterized, stabilized by non ionic surfactants Cremophor EL, Tween 20, Tween 80 or Lecitin and containing a variety of oils, namely olive oil, wheat germ oil, vitamin E. Chemical and physical stabilities of three systems was also evaluated within two months. The oral absorption of curcumin from the best microemulsion was investigated in vitro using parallel artificial membrane permeability assay (PAMPA). The optimal formulation consisted of 3.3 g/100 g of vitamin E, 53.8 g/100 g of Tween 20, 6.6 g/100 g of ethanol and water (36.3 g/100 g), with a maximum solubility of curcumin up to 14.57 mg/ml and a percentage of permeation through the artificial membrane of about 70%.