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Научни трудове на Съюза на учените в България-Пловдив Серия Г. Медицина, фармация и дентална медицина т.ХХ1. ISSN 1311-9427 (Print), ISSN 2534-9392 (On-line). 2017. Scientific works of the Union of Scientists in Bulgaria-Plovdiv, series G. Medicine, Pharmacy and Dental medicine, VoLXXI. ISSN 1311-9427 (Print), ISSN 534-9392 (On-line). 2017.
МИКРОКАПСУЛИРАНЕ НА ЕТЕРИЧНИ МАСЛА - ПОЛЗИ И ПРЕДИЗВИВАТЕЛСТВА (ОБЗОР) Веселина СтоясовтРотица Диколакова,Биссра Пиличева* Катсдра „Фармацевтсчни надки", Фармацевтич ен факуивет, Медицински УкааеавииеттПловдив, Биктария *Технологиченцеиаър за акешнамедорчиа^р. Пловдив, България
MICROENCAPSULATION OF ЕЦПЕЭТИЯА OILS - BENEFITS AND
CHALLENGES (REVIEW) VeselinaStoyanova, RositsaDikolakova, Bissera Pilicheva* Department of pharmaceailcaSsciences, kaculty of pharmacy, MedicalUnlvereity-Plovdrac Bulgaria *Technological centerOorcmergencj medtclnei Plcchiv,Bulnaria
Abstract
Essential oils (EOs) have numerous applications both in food and pharmaceutical industry, thus being widely used in aromatherapy, cosmetic products or as therapeutics in herbal medicine. A major consideration regarding EOs is their stability during processing and storage. Microencapsulation of EOs is a reliable approach to enhance stability in terms of oxidation, chemical interactions, or volatilization. In the present review, we focus on the microencapsulation of EOs as a promising and attractive application area for pharmaceutical industry. Some of the most widely used preparation techniques will be discussed; the conventional and novel coating materials will be noted. A particular attention on factors affecting microencapsulation will be drawn. Moreover, the most important characteristics and the methods for their evaluation will be thoroughly described. Prospective applications in various routes of administration of the formulated microcapsules will be pointed out.
Keywords: essential oils, microencapsulation, emulsion, stability
Introduction
Essential oils have been widely used for numerous applications both in food and pharmaceutical industry. EOs are complex liquid mixtures of volatile, lipophilic and odoriferous compounds biosynthesized by living organisms, predominantly aromatic plants. More than 300 EOs have recently gained commercial importance due to their characteristic flavour and fragrance properties, as well as various biological activities, which have been thoroughly studied and reported in the scientific literature. However, EOs have a short shelf life, as they are volatile and reactive in the presence of light, heat, moisture and oxygen. To overcome these challenges, microencapsulation has been considered as one of the most effective techniques. Furthermore, microencapsulation provides the controlled-release delivery and improves the handling of the EOs (Carvalho, 2015).
Microencapsulation of EOs
Microencapsulation is the process by which very tiny droplets or particles of liquid or solid material are surrounded or coated with a continuous film of polymeric materials. Depending on the method of microencapsulation employed, the morphology of microparticles produced can generally be divided into two main categories: matrix and reservoir types (Fig 1). Matrix-type microparticles are usually termed microspheres, while those with reservoir-type structures are commonly known as microcapsules. In a relatively simplistic form, a microcapsule is a small sphere with a uniform wall around it. The coated material is called active or core material, and the coating material is called shell, wall material, carrier or encapsulant. Microencapsulation technique allows the improvement and/or modification of the characteristics and properties of the active material, as well as its protection, stabilization and sustained release. Microencapsulation can modify the colour, shape, volume, apparent density, reactivity, durability, pressure sensitivity, heat sensitivity and photosensitivity of the encapsulated substance. Additionally, it can protect a
core substance from the effects of UV rays, moisture and oxygen and decrease the rate of evaporation or transfer of the active material from the core to the medium thus increasing the storage life of a volatile compound. Moreover,
microencapsulation may reduce agglomeration
problems of finely divided powders and improve the handling properties of sticky materials. It also enables controlled release of substances and reduces toxicity or irritancy. Microencapsulation techniques
Various techniques have been developed to microencapsulate different active materials. The method should generally be simple, reproducible, fast, effective and easy to implement on industrial scale. The choice depends on aspects such as physicochemical properties of the encapsulated and encapsulating material, the release characteristics of the encapsulated compound, purpose and cost. Some of the most important and usual microencapsulation techniques are summarized in Table 1.
Table 1. Various microencapsulation techniques (Carvalho, 2015)
Microencapsulation Particle size Advantages Drawbacks
technique ^m
Spray drying 1-50 Simple; Low process cost Easy scaling-up technique Lack of uniformity; Low oil loading Possibility of oil loss
Spray chilling 20-200 Suitable for water-soluble materials High process costs Require special handling and storage conditions
Simple coacervation 20-200 High encapsulation efficiency Expensive method
Complex coacervation 5-200 Efficient control of particle size Aggregation of particles; Hard scaling-up Evaporation of volatiles; Oxidation of product
Fluid bed spray coating >100 Low operational costs Total temperature control Long time process
Emulsification 0.1-100 Small droplets Low encapsulation efficiency; Production of high quantity residual solvent; Expensive method
Interfacial 0.5-1000 Fast Difficult to control
polymerization High encapsulation efficiency Production of high quantity residual solvent
Figure 1. Types of microparticles
Wall materials for oil encapsulation
Wall materials are major determinants of the quality and functionality of the encapsulated product. An ideal wall material should be highly water soluble, of low viscosity and should have film-forming properties; it should be inert and not react with other excipients. It should also be able to produce stable emulsions prior to microencapsulation. The wall material must be able to confer optimal protection to the encapsulated material and be capable of high loading efficiencies. On the other hand, it must be able to release the encapsulated material readily when required. Typical shell materials for microencapsulation include polysaccharides (e.g. carrageenan, gum arabic), proteins/peptides (e.g. collagen, gelatin) and lipids (e.g. lecithin, heparin) (Table 2). The most commonly used natural materials are the polysaccharides alginate and chitosan. Chitosan has many advantages such as availability, low cost, biocompatibility and biodegradability. Alginate is applied as encapsulating agent because of its low immunogenicity and biocompatibility. Additionally, alginate microparticles preparation involves mild reaction conditions. Starches that have been oxidized or incorporated with lipophilic groups were generally found to have good emulsifying and oil retentive properties with low viscosities at high solids concentration. Starches are more costly compared to some other wall materials like maltodextrins. Maltodextrins are hydrolyzed starches that are inexpensive and exhibit high solubilities with low viscosities in aqueous medium. However, they have very poor film forming and emulsifying properties and are generally unsuitable as oil encapsulates when used alone. Maltodextrins have been used in blends as matrix-forming materials to reduce the amount of the other more expensive wall material needed.
Table 2. List of shell materials used in microencapsulation
Core Shell material Microencapsulation technique
material
Lime GA and maltodextrin Spray drying
Clove Alginate Emulsion extrusion
Thyme Alginate Emulsion extrusion
Cinnamon Alginate Emulsion extrusion
Citronella Chitosan o/w emulsification
Holy basil Gelatin Simple coacervation
Rosemary Ethylcellulose Phase separation
Lavender Ethylcellulose o/w emulsification
Jasmine PMMA o/w emulsification solvent
evaporation
properties. Proteins, in particular whey protein and sodium caseinate, have been studied as oil encapsulates due to their amphiphilic properties. They have been used alone or in blends with other wall materials to encapsulate a variety of volatile and nonvolatile oils. Synthetic polymers have also been used to form microparticles. The modulation and proprieties optimization of synthetic polymers are easy, as they are available in different compositions and molecules. Nevertheless, the wide range of synthetic polymers show lack of biocompatibility. Aliphatic polyesters, such us poly(lactic acid) and copolymers of lactic and glycolic acids (e.g. PLGA), have been used as biodegradable wall synthetic polymers for controlled delivery systems. In summary, the selection of appropriate coating material should be based on the desired physical and chemical properties of the resultant microparticles. Consequently, several factors should be taken into consideration: physical and chemical properties of the core and coating materials, the stability and release characteristics of the core material, and the microencapsulation method.
Applications of microencapsulated essential oils
Microencapsulated oils have found various applications in the fields of foods, pesticides, textiles, and pharmaceuticals. Due to the wide range of essential oil applications, there has been a growing interest to encapsulate such oils to fully tap their potential benefits. Clove bud and red thyme oil
Sugars like lactose, maltose or sucrose have also been used as encapsulating agents due to their good solubility and low cost. Gum Arabic has been the conventional gum of choice for the encapsulation of flavours and oils by spray drying due to its good solubility and emulsifying
microcapsules, having acaricidal activities, were applied to fabric (Kim, 2011). In another study (Specos, 2010), citronella essential oil microcapsules applied to cotton textiles had insect-repellent activities. Such fabrics demonstrated a higher repellent effect (>90%) and long (3 wk) lasting protection from insects compared to fabrics sprayed with bulk essential oil. Microcapsules of limonene oil were successfully incorporated into perfumed textiles (Rodrigues, 2008). Medical use of textile fibers is increasing day by day. It has been found that the application of jojoba oil microcapsules onto compressive knits, developed for severe burns, preserved the initial characteristics of the knit, such as touch, flexibility, and lightness, besides playing a role in skin hydration and avoiding sebum accumulation (Jaafar, 2012). In another study, a functional textile product with aromatic oil, having good odor, moisturizing, relaxation, and anti-aging effects, was designed for use at aromatherapy and spa centers or personal care to improve the quality of life for the users. Thyme oil encapsulated in zein nanocapsules has been studied recently for its antioxidant activity and release kinetics (Wu, 2012). Chitosan microcapsules containing limomene oil were thoroughly studied for prolonged release and antibacterial activity against a wide range of species (Souza, 2014).
Conclusion
By the virtue of their biological, functional, and physicochemical properties, essential oils are being used in the preparation of safe products with a positive impact on consumer health. Microencapsulation is an effective and important tool to prepare oil-based high-quality and health-beneficial products in various industries in order to enhance their chemical, oxidative, and thermal stability. Concomitantly, the shelf-life, biological activity, functional activity, controlled release, physicochemical properties, and overall quality of oils can also be enhanced. Microencapsulated oils have been successfully applied in various food, pharmaceutical, textile, and pesticide products. Further research should be directed towards the optimization of microencapsulation technology in terms of enhancing the encapsulation efficiency.
References
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