ISSN: 2455-3751

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ASIO Journal of Microbiology, Food Science & Biotechnological Innovations (ASIO-JMFSBI)

Volume 1, Issue 1, 2015, 26-30

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A SHORT REVIEW ON PROMISING TRENDS EMPLOYED FOR PREPARATION OF NANOEMULSIONS IN FOOD APPLICATIONS

Swati Hardainiyan†

Department of Food Science and Biotechnology, Jayoti Vidyapeeth Women’s University, Jaipur, Rajasthan, India.

ARTICLE INFO

ABSTRACT

Short Review Article History

Received: 12 July, 2015 Accepted: 25 August, 2015

Corresponding Author:

†Swati Hardainiyan

Department of Food Science and

Biotechnology, Jayoti Vidyapeeth

Women’s University, Jaipur,

Rajasthan, India.

Mail Id: swati.pandithar@gmail.com

Nanoemulsions are defined as oil droplets, with particle sizes comprised between 10 and 100 nm, dispersed in aqueous media. The use of high-pressure valve homogenizers or microfluidizers often causes emulsions with droplet diameters of less than 100 to 500 nm. Nanoemulsions are thermodynamically and kinetically stable, emulsions are unstable. Emulsions are cloudy while nanoemulsions are clear and translucent. Emulsion require the large energy input while nanoemulsions are formed either with (sometime spontaneously) or without high energy input. Nanoemulsions are heterogeneous systems consisting of two immiscible liquids, with one liquid phase being dispersed as nanometric droplets into another continuous liquid phase and stabilized through an appropriate emulsifier. In particular O/W nanoemulsions, which are of prevalent interest? Nanoemulsions can be prepared with different materials depending on the desire structure and functionality by using high-energy methods (high-pressure homogenization, microfluidization, and ultrasonication) and low-energy methods (solvent diffusion). High-energy methods produce intense disruptive forces minimizing droplet size to form emulsions, while low energy methods promote spontaneous emulsification by mixing all the emulsion ingredients.Various types of nanoemulsion, including single-layer, double-layers and triple-layers nanoemulsions, could be produced, depending on the polyelectrolytes, such as alginate and chitosan. Besides the lipid and aqueous phases, the formulation of nanoemulsions requires the use of stabilizers such as emulsifiers and hydrocolloids to prevent the breakdown of the nanoemulsion structure once it is formed. Emulsions are often referred to as “nanoemulsions.”, when the use of high-pressure valve homogenizers or microfluidizers often causes emulsions with droplet diameters of less than 100 to 500 nm and functional food components can be incorporated within the droplets, the interfacial region, or the continuous phase.

Keywords: nano-emulsions, preparation techniques, food industry, food stuffs, homogenizers

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INTRODUCTION

In the last two decades, nanotechnology has rapidly emerged as one of the most promising and attractive research fields. The technology offers the potential to significantly improve the solubility and bioavailability of many functional ingredients. Nanoemulsions are defined as oil droplets, with particle sizes comprised between 10 and 100 nm, dispersed in aqueous media. The use of high-pressure valve homogenizers or microfluidizers often causes emulsions with droplet diameters of less than 100 to 500 nm [1-3]. Nanoemulsion technology is particularly suited for the fabrication of encapsulating systems for functional compounds as it prevents their degradation and improves their bioavailability. This portion focuses on nanoemulsions and provides an overview of the

production methods, materials used (solvents, emulsifiers, and functional ingredients) and of the current analytical techniques that can be used for the identification and characterization of nanoemulsions [1-5]. These systems have been thought to have several advantages over conventional emulsions as colloidal delivery systems due to their smaller particle size. Nanoemulsions constitute one of the most promising systems to improve solubility, bioavailability, and functionality of hydrophobic compounds. Food industry seeks to use these systems for the incorporation of, e.g., lipophilic functional compounds in food matrices [2-4].

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The major difference between emulsion and nanoemulsion are [2-8]: Nanoemulsions are thermodynamically and kinetically stable, emulsions are unstable. Emulsions are cloudy while nanoemulsions are clear and translucent. Emulsion require the large energy input while nanoemulsions are formed either with (sometime spontaneously) or without high energy input. Nanoemulsions are one of the most interesting fields of application, once they can act as carriers or delivery systems for lipophilic compounds, such as nutraceuticals, drugs, flavors, antioxidants, and antimicrobial agents. Nanoemulsions are stable colloidal systems within nanometric size (≤100 nm) formed by dispersing one liquid in another immiscible liquid using suitable emulsifiers. Compared with microemulsions, nanoemulsions are optically transparent, demonstrating better shelf stability, and the droplet size distribution remains after water dilution. Advantages[ 4-9]: Differently from microemulsions, which are thermodynamically stable systems and form spontaneously, nanoemulsions are kinetically stable and require energy to be formed. Due to their being metastable systems, nanoemulsions can be diluted with water without any change occurring in the droplet size distribution. Nanoemulsions are in fact highly stable to gravitational separation thanks to the small droplet sizes, which means that Brownian motion effects dominate over gravitational forces. In addition, nanoemulsions show a lower tendency to droplet aggregation than conventional emulsions, because the strength of the net attractive forces acting between droplets usually decreases with decreasing droplet diameters. However, coalescence phenomena due to Ostwald ripening can affect nanoemulsions stability, leading to a significant growth in droplet size over time. A number of potential advantages of using nano emulsion rather than conventional emulsions for this purpose: Carry the ingredient to the desired site of action Control the release of the ingredient (e.g., release

rate) in response an external trigger (e.g., pH, temperature, ionic strength, enzymes, etc.)

Greatly increase the bioavailability of lipophilic substances

Scatter light weakly and so can be incorporated into optically transparent products

Can be used to modulate the product texture A high stability to particle aggregation and

gravitational separation Protect the ingredient from chemical or biological

degradation Must be compatible with the food attributes (e.g.,

appearance, texture, taste/flavour) Nanoemulsions are thermodynamically and

kinetically stable therefore flocculation, aggregation, creaming and coalescence do not occur.

It is non toxic and non-irritant. Nanoemulsion is administered by various routes,

such as oral, topical, parentral and transdermal etc. Nanoemulsions can deliver both hydrophilic and

lipophilic drugs.

Droplet size are nano, so surface area is higher thus increases the rate of absorption and reduces variability, thus enhances bioavailability of drug.

Nanoemulsions are suitable for human and veterinary uses because they do not damage human or animal cell.

It protects the drug from hydrolysis and oxidation due to encapsulation in oil-droplet. It also provides taste masking.

Nanoemulsion also enhances permeation of drug through skin.

Disadvantages [6-10]: Large concentration of surfactants /co-surfactants is

required for stabilization. Its stability is affected by temperature and pH. Instability can be caused due to Oswald ripening

effect. Fabrication: Nanoemulsions are emulsions which are thermodynamically stable compared to conventional emulsions under a range of different conditions. This is due to their small size (typically 50 to 500 nm compared to 1200 nm) and mono-dispersivity. They can be diluted with water without changing the droplet size distribution. The type of surfactant used to formulate a nanoemulsion is critical to the stability of the final emulsion. Preparations of nano-emulsions can be used to encapsulate functional food components at oil/water interfaces, or throughout the continuous phase of the system. The use of multiple emulsions can create delivery systems with novel encapsulation and delivery properties. The most common examples of this are oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) emulsions. Functional food components could be encapsulated within the inner water phase, the oil phase, or the outer water phase, thereby making it possible to develop a single delivery system that contains multiple functional components [11-15]. Nanoemulsions are heterogeneous systems consisting of two immiscible liquids, with one liquid phase being dispersed as nanometric droplets into another continuous liquid phase and stabilized through an appropriate emulsifier. In particular O/W nanoemulsions, which are of prevalent interest. Various types of nanoemulsion, including single-layer, double-layers and triple-layers nanoemulsions, could be produced, depending on the polyelectrolytes, such as alginate and chitosan. Besides the lipid and aqueous phases, the formulation of nanoemulsions requires the use of stabilizers such as emulsifiers and hydrocolloids to prevent the breakdown of the nanoemulsion structure once it is formed. Emulsifiers are surface- active amphiphilic molecules; thus, the lipophilic part has affinity for non-polar media and the hydrophilic part has affinity for polar media. They are able to adsorb at the oil–water interface of droplet surfaces during emulsification, thus protecting droplets against re-coalescence or aggregation. Hydrocolloids have been exten- sively used in food formulations for their thickening properties when incorporated into aqueous phase [14-18].

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Modifying the rheology of the aqueous phase not only changes the emulsions texture and mouth-feel but also minimizes the droplets movement in the fluid so retarding gravitational separation (creaming or sedimentation) of lipid particles. In general, lipid nanoparticles can be pre- pared using two different approaches: high-energy or low-energy devices. High-energy methods consist in applying high disruptive forces with mechanical devices, capable of causing the breakup of oil droplets and disperse them into the water phase. Low- energy approaches rely on the spontaneous formation of tiny oil droplets within mixed oil–water–emulsifier systems when the solution or environmental conditions are altered, such as composition or temperature. The use of high-pressure valve homogenizers or microfluidizers often causes emulsions with droplet diameters of less than 100 to 500 nm. In modern literature such emulsions are often referred to as “nano-emulsions”. Nano emulsions are non equilibrium systems and cannot be formed spontaneously. They can be produced using two different approaches: high-energy and low energy methods. High-energy methods use intense mechanical forces to break up macroscopic phases or droplets into smaller droplets and typically involve the use of mechanical devices known as homogenizers, which may use high-shear mixing, high-pressure homogenization, or ultrasonifi cation. In contrast, low-energy methods rely on the spontaneous formation of emulsions under specifi c system compositions or environmental conditions as a result of changes in interfacial properties. The migration of the bioactive molecules from the inner oil phase to the stable surfactant layer of O/W nanoemulsions, as a consequence of more intense production conditions by high pressure homogenization (increasing number of passes and higher processing temperatures) is reported to increase the protection of bioactive molecules against chemical degradation. Nanoemulsions can be prepared with different materials depending on the desire structure and functionality by using high-energy methods (high-pressure homogenization, microfluidization, and ultrasonication) and low-energy methods (solvent diffusion). High-energy methods produce intense disruptive forces minimizing droplet size to form emulsions, while low energy methods promote spontaneous emulsification by mixing all the emulsion ingredients. Among the most used nanoemulsions are (1) the oil in water (O/W) where the oil droplets are dispersed in the aqueous phase and the interphase is stabilized by emulsifiers; (2) the multiple emulsions oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W), where, for example, nanometer size water droplets contained within large oil droplets are dispersed within an aqueous phase (W/O/W); and (3) the multilayer emulsions which consist of oil droplets surrounded by nanometric size layers of different polyelectrolytes [15-20]. A major research activity is the use of plant components (phytochemicals) as food supplements or as support for the fortified foods. Due to poor solubility in water and even oil, these phytochemicals have low bioavailability and present difficulty to be included in food. Therefore, the research in recent years was oriented towards using different methods and techniques of biocomponents encapsulation. Thus, the systems have achieved high

nutritional capacity. One of the solubilization methods of the phytochemicals is their inclusion in nanoemulsions [14-16]. Lemongrass oil (LO) has been encapsulated in a carnauba- shellac wax (CSW) based nanoemulsion by high pressure homogenization and alginate nanoemulsions by ultrasonication and micro fluidization. While microfluidization enhanced antimicrobial activity, ultrasounds diminished the activity. When the sunflower oil-surfactin nanoemulsion was applied to food products such as raw chicken, apple juice, milk, and mixed vegetable, a reduction in the native cultivable bacterial and fungal populations was observed [21-22]. Nanoemulsion-based delivery systems can also improve the bioavailability of the encapsulated components due the small particle size and high surface-to-volume ratio. Various methods have been developed to prepare lipophilic functional compounds with particle diameters in the nano-size range. Such methods include emulsification– evaporation, emulsification–diffusion, solvent displacement, and precipitation, and can be classified as high- or low energy approaches. Emulsions are often referred to as “nanoemulsions.”, when the use of high-pressure valve homogenizers or microfluidizers often causes emulsions with droplet diameters of less than 100 to 500 nm and functional food components can be incorporated within the droplets, the interfacial region, or the continuous phase. According to Mc Clements and Dekker (2000), the different types of nanoemulsions with more complex properties—such as nanostructured multiple emulsions or nanostructured multilayer emulsions—offer multiple encapsulating abilities from a single delivery system that can carry several functional components and these components could be released in response to a specific environmental trigger. It is possible to develop smart delivery systems by engineering the properties of the nanostructured shell around the droplets. This interfacial engineering technology would utilize food-grade ingredients (such as proteins, polysaccharides, and phospholipids) and processing operations (such as homogenization and mixing) that are already widely used in the manufacture of food emulsions [23-25]. METHODS OF PREPARATION OF NANOEMULSION Nanoemulsions have very small particle size range; they can be most effectively produced using high-pressure equipment. The most commonly used methods for producing nanoemulsions are ‘High-pressure homogenization’ and ‘Microfluidization’ used at both laboratory and industrial scale. Other methods like ‘Ultrasonification’ and ‘In-situ emulsification’ are also suitable for preparation of nanoemulsion. Factors to be considered during preparation of nanoemulsion [25-27]: a. Surfactants must be carefully chosen so that an ultra low interfacial tension (< 10-3 mN/m) can be attained at the oil / water interface which is a prime requirement to produce nanoemulsions [28-40]. b. Concentration of surfactant must be high enough to provide the number of surfactant molecules needed to stabilize the microdroplets to be produced by an ultra low interfacial tension. c. The interface must be flexible or fluid enough to promote the formation of nanoemulsions.

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HIGH-PRESSURE HOMOGENIZATION The preparation of nanoemulsions requires high-pressure homogenization. This technique makes use of high-pressure homogenizer/piston homogenizer to produce nanoemulsions of extremely low particle size (up to 1nm). The dispersion of two liquids (oily phase and aqueous phase) is achieved by forcing their mixture through a small inlet orifice at very high pressure (500 to 5000 psi), which subjects the product to intense turbulence and hydraulic shear resulting in extremely fine particles of emulsion. The particles which are formed exhibit a liquid, lipophilic core separated from the surrounding aqueous phase by a monomolecular layer of phospholipids. This technique has great efficiency, the only disadvantage being high energy consumption and increase in temperature of emulsion during processing [30-34].

MICRO FLUIDIZATION Micro fluidization is a mixing technique, which makes use of a device called microfluidizer. This device uses a high-pressure positive displacement pump (500 to 20000psi), which forces the product through the interaction chamber, which consists of small channels called ‘microchannels’. The product flows through the micro channels on to an impingement area resulting in very fine particles of sub- micron range. The two solutions (aqueous phase and oily phase) are combined together and processed in an inline homogenizer to yield a coarse emulsion. The coarse emulsion is into a microfluidizer where it is further processed to obtain a stable nanoemulsion. The coarse emulsion is passed through the interaction chamber microfluidizer repeatedly until desired particle size is obtained. The bulk emulsion is then filtered through a filter under nitrogen to remove large droplets resulting in a uniform nanoemulsion [32-34].

SPONTANEOUS EMULSIFICATION It involves three main steps a. Preparation of homogeneous organic solution composed of oil and lipophilic surfactant in water miscible solvent and hydrophilic surfactant. b. The organic phase is injected in the aqueous phase under magnetic stirring the o/w emulsion was formed. c. The water-miscible solvent is removed by evaporation under reduced pressure [33-35].

SOLVENT EVAPORATION TECHNIQUE This technique involves preparing a solution of drug followed by its emulsification in another liquid that is non-solvent for the drug. Evaporation of the solvent leads to precipitation of the drug. Crystal growth and particle aggregation can be controlled by creating high shear forces using a high-speed stirrer [36-39].

HYDROGEL METHOD It is similar to solvent evaporation method. The only difference between the two methods is that the drug solvent is miscible with the drug anti-solvent. Higher shear force prevent crystal growth and Ostwald ripening. Other method used for Nanoemulsion preparation is the phase inversion temperature technique [38-40].

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