Fabrication, stability and efficacy of dual-component antimicrobial nanoemulsions: Essential oil (thyme oil) and cationic surfactant (lauric arginate)

Influence of nonionic and ionic surfactants on the antifungal and mycotoxin inhibitory efficacy of cinnamon oil nanoemulsions

The influence of ionic surfactants (cationic surfactant lauric arginate and anionic surfactant lysolecithin) on the physical properties, antifungal and mycotoxin inhibitory efficacy of Tween 80 stabilized cinnamon oil-in-water nanoemulsions was investigated. Nanoemulsion droplets of similar particle diameter (∼100 nm), but variable electrical characteristics, were formed by mixing 0.1 wt% ionic surfactant with 0.9 wt% Tween 80 before homogenization. The nanoemulsions were physically stable over 28 days at 23 °C. The antifungal activity (against mycelial growth and spore germination) and mycotoxin inhibitory activity of cinnamon oil nanoemulsions bearing positive, neutral, and negative charge surface was then evaluated against two chemotypes of Fusarium graminearum. In general, the cinnamon oil played a decisive role in the resulting antifungal and mycotoxin inhibitory activities. The surfactant charge had a limited impact on the antifungal mycotoxin inhibitory activities of cinnamon oil in the nanoemulsions. Both ionic surfactant-based cinnamon oil nanoemulsions showed greater activity in inhibiting mycelial growth and mycotoxin production of F. graminearum than those based on Tween 80. Treatment of mycelium with cinnamon oil nanoemulsions resulted in the loss of cytoplasm from fungal hyphae, and accounted for the antifungal action. These results have important implications for the design of essential oil based nanoemulsions as effective antifungal delivery systems in foods.

Food Structure Development in Emulsion Systems

A number of food products exist, in part or entirely, as emulsions, while others are present in an emulsified state at some point during their production/formation. Mayonnaise, butter, margarine, salad dressing, whipped cream, and ice cream represent some of the typical examples of emulsion-based foods. Controlled by both formulation and processing aspects, the emulsion architecture that is formed ultimately determines many of the attributes of the final food product. This chapter initially provides an overview of the basic constituents of emulsions and their influence on the microstructure and stability of conventional as well as more complex systems. The available spectrum of processing routes and characterization techniques currently utilized (or emerging) within the area of emulsions is then discussed. The chapter concludes with a concise outline of the relationship between food emulsion microstructure design and its performance (textural, rheological, sensorial, etc.).

Stability of Emulsions and Nanoemulsions Stabilized with Biosurfactants, and their Antimicrobial Performance against Escherichia coli O157:H7 and Listeria monocytogenes

Two novel biosurfactants – surfactin and its variant fatty acyl glutamic acid (FA-glu) – were compared with two commercial emulsifiers – lecithin, and a mixture of Tween 80 and lauric „arginate (TLA) – for formation and stability of emulsions and nano„emulsions containing cinnamaldehyde (CM). The nano„emulsions’/emulsions’ antimicrobial performance against two common foodborne pathogens Escherichia coli O157:H7 and Listeria monocytogenes was also compared. Two emulsifier concentrations (0.5% w/w and 1% w/w) and two homogenizing pressures (62.05 MPa and 124.10 MPa) were compared for emulsions droplet stability during storage for 46 days at 4°C, 25°C, and 37°C. Surfactin, FA-glu, and TLA resulted in formation of nanoemulsions at both concentrations, but lecithin did not. Droplet sizes did not change significantly during 38 days at stored temperatures for surfactin- and TLA- stabilized nano„emulsions. However, FA-glu and lecithin stabilized emulsions coalesced after Day 13 at 37°C; also, FA-glu stabilized emulsion thickened on the 38th day at 4°C. The incorporation of CM in nanoemulsions or emulsions did not lower the minimum inhibitory concentration (MIC) for two bacteria tested in broths. However, the CM nanoemulsions and emulsions showed enhanced effects in inhibiting bacterial growths at concentrations lower than MICs compared to non-emulfied CM, with more inhibition from nanoemulsions.

Impact of ripening inhibitors on molecular transport of antimicrobial components from essential oil nanoemulsions

The objective of this study was to provide insights into the mechanisms involved in the mass transport of antimicrobial compounds from essential oil nanoemulsions to bacterial cell membranes. Origanum oil-in-water nanoemulsions were produced using spontaneous emulsification by titrating a mixture of essential oil, ripening inhibitor, and surfactant (Tween 80) into 5 mM sodium citrate buffer (pH 3.5). Stable nanoemulsions containing relatively small droplets (d < 60 nm) were produced using this low-energy method. The nature of the ripening inhibitor used in the oil phase of the nanoemulsions affected the antimicrobial activity of the nanoemulsions: corn (LCT) > medium-chain triglycerides (MCT). Differences in antimicrobial activity were attributed to the differences in the rate of transfer of hydrophobic antimicrobial constituents from the nanoemulsion to the MCT emulsion, which was used to mimic the hydrophobic region of the bacterial cell membranes. Each antimicrobial nanoemulsion was separated from the MCT emulsion by a dialysis tubing. Dialysis tubing with two different pore sizes was used, one excluding nanoemulsion droplet and micelle delivery, allowing the delivery of antimicrobial compounds only through the aqueous phase and the other by both the aqueous phase and micelles. For origanum oil nanoemulsions, the delivery of all antimicrobial agents occurred more efficiently when micelles were present.

Development of a kojic monooleate-enriched oil-in-water nanoemulsion as a potential carrier for hyperpigmentation treatment

Introduction

Kojic monooleate (KMO) is an ester derived from a fungal metabolite of kojic acid with monounsaturated fatty acid, oleic acid, which contains tyrosinase inhibitor to treat skin disorders such as hyperpigmentation. In this study, KMO was formulated in an oil-in-water nanoemulsion as a carrier for better penetration into the skin.

Methods

The nanoemulsion was prepared by using high and low energy emulsification technique. D-optimal mixture experimental design was generated as a tool for optimizing the composition of nanoemulsions suitable for topical delivery systems. Effects of formulation variables including KMO (2.0%–10.0% w/w), mixture of castor oil (CO):lemon essential oil (LO; 9:1) (1.0%–5.0% w/w), Tween 80 (1.0%–4.0% w/w), xanthan gum (0.5%–1.5% w/w), and deionized water (78.8%–94.8% w/w), on droplet size as a response were determined.

Results

Analysis of variance showed that the fitness of the quadratic polynomial fits the experimental data with F-value (2,479.87), a low P-value (P<0.0001), and a nonsignificant lack of fit. The optimized formulation of KMO-enriched nanoemulsion with desirable criteria was KMO (10.0% w/w), Tween 80 (3.19% w/w), CO:LO (3.74% w/w), xanthan gum (0.70% w/w), and deionized water (81.68% w/w). This optimum formulation showed good agreement between the actual droplet size (110.01 nm) and the predicted droplet size (111.73 nm) with a residual standard error <2.0%. The optimized formulation with pH values (6.28) showed high conductivity (1,492.00 µScm⁻¹) and remained stable under accelerated stability study during storage at 4°C, 25°C, and 45°C for 90 days, centrifugal force as well as freeze–thaw cycles. Rheology measurement justified that the optimized formulation was more elastic (shear thinning and pseudo-plastic properties) rather than demonstrating viscous characteristics. In vitro cytotoxicity of the optimized KMO formulation and KMO oil showed that IC₅₀ (50% inhibition of cell viability) value was >100 µg/mL.

Conclusion

The survival rate of 3T3 cell on KMO formulation (54.76%) was found to be higher compared to KMO oil (53.37%) without any toxicity sign. This proved that the KMO formulation was less toxic and can be applied for cosmeceutical applications.

Essential oil based nanoemulsions to improve the microbial quality of minimally processed fruits and vegetables: A review

Due to the convenience and nutritional value, minimally processed fruits and vegetables (MPFV) are one of the rapid growing sectors in the food industry. However, their microbiological safety is a cause of great concern. Essential oils (EOs), known for potent antimicrobial efficacy have been shown to reduce microbial load in MPFV, but their low water solubility, high volatility and strong organoleptic properties limit their wide use. Encapsulating EOs to nanoemulsion offers a viable remedy for such limitations. Due to the unique properties of the EOs nanoemulsion, there has been an increasing interest in their fabrication and use in food system. The present review article encompasses the overview of the prominent microflora present in MPFV, the recent developments on the fabrication and stability of EOs based nanoemulsion, their in vitro antimicrobial activity and their application in MPFV. This review also discusses the EOs based nanoemulsions antimicrobial mechanism of action and their regulatory issues related to their use. Application of EOs based nanoemulsion either as washing disinfectant or with incorporation into edible coatings have been shown to considerably improve the microbial quality and safety of MPFV. This efficacy has been further shown to increase when combined with other hurdles. However, further studies are required on the toxicity of EOs based nanoemulsion to assure its commercial exploitation.

Thymol nanoemulsion exhibits potential antibacterial activity against bacterial pustule disease and growth promotory effect on soybean

An antibacterial and plant growth promoting nanoemulsion was formulated using thymol, an essential oil component of plant and Quillaja saponin, a glycoside surfactant of Quillaja tree. The emulsion was prepared by a sonication method. Fifty minutes of sonication delivered a long term stable thymol nanoemulsion which was characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), cryogenic-field emission scanning electron microscopy (Cryo-FESEM) and fourier transform infra-red (FTIR) spectroscopy. Creaming index, pH and dilution stability were also studied for deliberation of its practical applications. The nanoemulsion (0.01-0.06%, v/v) showed substantial in vitro growth inhibition of Xanthomonas axonopodis pv. glycine of soybean (6.7-0.0 log CFU/ml). In pot experiments, seed treatment and foliar application of the nanoemulsion (0.03-0.06%, v/v) significantly lowered the disease severity (DS) (33.3-3.3%) and increased percent efficacy of disease control (PEDC) (54.9-95.4%) of bacterial pustule in soybean caused by X. axonopodis pv. glycine. Subsequently, significant enhancements of plant growth were also recorded in plants treated with thymol nanoemulsion. This is the first report of a thymol based nanoemulsion obtained using Quillaja saponin as a surfactant. Our study claims that nano scale thymol could be a potential antimicrobial and plant growth promoting agent for agriculture.

Antibacterial activities of a cinnamon essential oil with cetylpyridinium chloride emulsion against Escherichia coli O157:H7 and Salmonella Typhimurium in basil leaves

This study examined the antibacterial activities of two different cinnamon essential oil emulsions against Escherichia coli O157:H7 and Salmonella Typhimurium on basil leaves. Cinnamon oil (0.25%) treatments containing CPC (0.05%) exhibited greater effects on the pathogenic bacteria than cinnamon oil treatment without this emulsifier (p < 0.05). Treatment with cinnamon bark and leaf oil emulsions (CBE and CLE, respectively) reduced the populations of E. coli O157:H7 by 4.10 and 5.10 log CFU/g, and S. Typhimurium by 2.71 and 2.82 log CFU/g, respectively. Scanning electron micrographs showed morphological changes in the two pathogenic bacteria following emulsion treatment. In addition, there was no difference in the color or ascorbic acid content of the basil leaves by the emulsion treatment. These results suggest that CBE or CLE treatment can be an effective way to ensure the microbial safety of minimally processed vegetables and a good alternative to chlorination treatment in the fresh produce industry.

Enhancement of physicochemical properties of nanocolloidal carrier loaded with cyclosporine for topical treatment of psoriasis: in vitro diffusion and in vivo hydrating action

Psoriasis is a chronic autoimmune disease that cannot be cured. It can however be controlled by various forms of treatment, including topical, systemic agents, and phototherapy. Topical treatment is the first-line treatment and favored by most physicians, as this form of therapy has more patient compliance. Introducing a nanoemulsion for transporting cyclosporine as an anti-inflammatory drug to an itchy site of skin disease would enhance the effectiveness of topical treatment for psoriasis. The addition of nutmeg and virgin coconut-oil mixture, with their unique properties, could improve cyclosporine loading and solubility. A high-shear homogenizer was used in formulating a cyclosporine-loaded nanoemulsion. A D-optimal mixture experimental design was used in the optimization of nanoemulsion compositions, in order to understand the relationships behind the effect of independent variables (oil, surfactant, xanthan gum, and water content) on physicochemical response (particle size and polydispersity index) and rheological response (viscosity and k-value). Investigation of these variables suggests two optimized formulations with specific oil (15% and 20%), surfactant (15%), xanthan gum (0.75%), and water content (67.55% and 62.55%), which possessed intended responses and good stability against separation over 3 months' storage at different temperatures. Optimized nanoemulsions of pH 4.5 were further studied with all types of stability analysis: physical stability, coalescence-rate analysis, Ostwald ripening, and freeze-thaw cycles. In vitro release proved the efficacy of nanosize emulsions in carrying cyclosporine across rat skin and a synthetic membrane that best fit the Korsmeyer-Peppas kinetic model. In vivo skin analysis towards healthy volunteers showed a significant improvement in the stratum corneum in skin hydration.

Preparation, characterization, and antimicrobial activity of nanoemulsions incorporating citral essential oil

Citral is a typical essential oil used in the food, cosmetic, and drug industries and has shown antimicrobial activity against microorganisms. Citral is unstable and hydrophobic under normal storage conditions, so it can easily lose its bactericide activity. Nano-emulsion technology is an excellent way to hydrophilize, microencapsulate, and protect this compound. In our studies, we used a mixed surfactant to form citral-in-water nano-emulsions, and attempted to optimize the formula for preparing nanoemulsions. Citral-in-water nanoemulsions formed at S_o 0.4 to 0.6 and ultrasonic power of 18 W for 120 seconds resulted in a droplet size of < 100 nm for nanoemulsions. The observed antimicrobial activities were significantly affected by the formulation of the nanoemulsions. The observed relationship between the formulation and activity can lead to the rational design of nanoemulsion-based delivery systems for essential oils, based on the desired function of antimicrobials in the food, cosmetics, and agrochemical industries.

Cross-Linked Polymer-Stabilized Nanocomposites for the Treatment of Bacterial Biofilms

Infections caused by bacterial biofilms are an emerging threat to human health. Conventional antibiotic therapies are ineffective against biofilms due to poor penetration of the extracellular polymeric substance secreted by colonized bacteria coupled with the rapidly growing number of antibiotic-resistant strains. Essential oils are promising natural antimicrobial agents; however, poor solubility in biological conditions limits their applications against bacteria in both dispersed (planktonic) and biofilm settings. We report here an oil-in-water cross-linked polymeric nanocomposite (∼250 nm) incorporating carvacrol oil that penetrates and eradicates multidrug-resistant (MDR) biofilms. The therapeutic potential of these materials against challenging wound biofilm infections was demonstrated through specific killing of bacteria in a mammalian cell-biofilm coculture wound model.

Edible Nanoemulsions as Carriers of Active Ingredients: A Review

There has been growing interest in the use of edible nanoemulsions as delivery systems for lipophilic active substances, such as oil-soluble vitamins, antimicrobials, flavors, and nutraceuticals, because of their unique physicochemical properties. Oil-in-water nanoemulsions consist of oil droplets with diameters typically between approximately 30 and 200 nm that are dispersed within an aqueous medium. The small droplet size usually leads to an improvement in stability, gravitational separation, and aggregation. Moreover, the high droplet surface area associated with the small droplet size often leads to a high reactivity with biological cells and macromolecules. As a result, lipid digestibility and bioactive bioavailability are usually higher in nanoemulsions than conventional emulsions, which is an advantage for the development of bioactive delivery systems. In this review, the most important factors affecting nanoemulsion formation and stability are highlighted, and a critical analysis of the potential benefits of using nanoemulsions in food systems is presented.

Positive charge pesticide nanoemulsions prepared by the phase inversion composition method with ionic liquids

We prepared highly stable positive charge nanoemulsions with ILs that possessed fine wetting and adhesive property on wheat leaf surfaces.

Essential oil nanoemulsions as antimicrobial agents in food

The crescent interest in the use of essential oils (EOs) as natural antimicrobials and preservatives in the food industry has been driven in the last years by the growing consumers' demand for natural products with improved microbial safety, and fresh-like organoleptic properties. Nanoemulsions efficiently contribute to support the use of EOs in foods by increasing their dispersibility in the food areas where microorganisms grow and proliferate, by reducing the impact on the quality attributes of the product, as well as by enhancing their antimicrobial activity. Understanding how nanoemulsions intervene on the mass transfer of EOs to the cell membrane and on the mechanism of antimicrobial action will support the engineering of more effective delivery systems and foster the application of EOs in real food systems. This review focuses on the enabling contribution of nanoemulsions to the use of EOs as natural preservative agents in food, (a) specifically addressing the formulation and fabrication of stable EO nanoemulsions, (b) critically analyzing the reported antimicrobial activity data, both in vitro and in product, to infer the impact of the delivery system on the mechanisms of action of EOs, as well as (c) discussing the regulatory issues associated with their use in food systems.

Latest about Spoilage by Yeasts: Focus on the Deterioration of Beverages and Other Plant-Derived Products

Food and beverage deterioration by spoilage yeasts is a serious problem that causes substantial financial losses each year. Yeasts are able to grow under harsh environmental conditions in foods with low pH, low water activity, and high sugar and/or salt content. Some of them are extremely resistant to the traditional preservatives used in the food industry. The search for new methods and agents for prevention of spoilage by yeasts is ongoing, but most of these are still at laboratory scale. This minireview gives an overview of the latest research issues relating to spoilage by yeasts, with a focus on wine and other beverages, following the interest of the research groups. It seems that a better understanding of the mechanisms to combat food-related stresses, the characteristics leading to resistance, and rapid identification of strains of yeasts in foods are the tools that can help control spoilage yeasts.

Investigation into the physical stability of a eugenol nanoemulsion in the presence of a high content of triglyceride

Schematic stability mechanism of a eugenol emulsion in the presence of a high triglyceride content.

Evidence for bactericidal activities of lipidic nanoemulsions against Pseudomonas aeruginosa

Pseudomonas aeruginosa has been implicated in a broad range of infections and shown to acquire rapid resistance to anti-microbial agents. In the present, study we have used particular amalgamation of specific lipids that hold innate antibacterial activities, which can be transformed into cationized and non-cationized nanoemulsions. The anti-Pseudomonas activities were then elucidated by transmission/scanning electron microscopy, and atomic force microscopy. The microscopic studies revealed the cell lysis due to the formation of blebs, exudation of essential cellular contents and loss of characteristics contour of the cells. The microscopic studies were then corroborated by zone of inhibition, cytoplasmic release studies, time dependent killing and MIC determination. Conclusively, it can be inferred that the delivery issues of antibiotics could be reassessed by using certain excipients that possess inherent antibacterial properties. This will not only avoid unnecessary introduction of inactive excipients in the body, but will also reduce the dose of antibiotics because of synergistic effects of excipients and drug acting together.