10-10-2014, 10:55 AM
Microencapsulation
MICROENCAPSULATION.docx (Size: 1.49 MB / Downloads: 15)
ABSTRACT
Microencapsulation is one of the quality preservation techniques of sensitive substances and a method for production of materials with new valuable properties. Microencapsulation is a process in which tiny particles or droplets are surrounded by a polymeric material to form capsules. In its simplest form, a microcapsule is a small sphere with uniform wall around it. The material inside the microcapsule is referred to as core, internal phase, or fill, whereas the wall is sometimes called a shell, coating, or membrane. Most microcapsules have diameters between a few micrometers and a few millimeters. Microcapsules offer food processer a means with which to protect sensitive food components, ensure against nutritional loss, utilize otherwise sensitive ingredients, mask or preserve flavors and aromas and transform liquids into easily handled solid ingredients.
In this seminar report, microencapsulation technique, application, advantages etc are described.
INTRODUCTION
Microencapsulation is described as a process of enclosing micron-sized particles of solids or droplets of liquids or gasses in an inert shell, which in turn isolates and protects them from the external environment. The products obtained by this process are called micro particles, microcapsules and microspheres which differentiate in morphology and internal structure. When the particle size is below 1 µm they are known as nanoparticles, nanocapsules, nanospheres, respectively, and particles having diameter between 3-800µm are known as micro particles, microcapsules or microspheres. Particles larger than 1000µm are known as macro particles.
Microencapsulation can be done (i) to protect the sensitive substances from the external environment, (ii) to mask the organoleptic properties like color, taste, odour of the substance, (iii) to obtain controlled release of the drug substance, (iv) for safe handling of the toxic materials, (v) to get targeted release of the drug and (vi) to avoid adverse effects like gastric irritation of the drug.
Micro particles or microcapsules consist of two components, namely core material and coat or shell material. Core material contains an active ingredient while coat or shell material covers or protects the core material. Generally a hydrophobic core is usually protected by a hydrophilic shell, and hydrophilic material is protected by a hydrophobic shell. The shell can consist of one or more materials. The shell of the capsule is designed to prevent diffusion of the core material into the food until the desired time. Its functions involve protecting sensitive food components such as flavors, vitamins or salts from water, oxygen or light, converting liquids that are difficult to handle into free flowing powders, and isolating specific food components from other food components during storage. Different types of materials like active pharmaceutical ingredients, proteins, peptides, volatile oils, food materials, pigments, dyes, monomers, catalysts, pesticides, etc.can be encapsulated with different types of coat or shell materials like ethyl cellulose, hydroxyl propyl methyl cellulose, sodium carboxyl methyl cellulose, sodium alginate,PLGA, gelatin, polyesters, chitosans, etc.
MICROENCAPSULATION
Microencapsulation is defined as a process in which tiny particles or droplets are surrounded by a coating or embedded in a homogeneous or heterogeneous matrix, to give small capsules with many useful properties. Microencapsulation can provide a physical barrier between the core compound and the other components of the product. It is a technique by which liquid droplets, solid particles or gas compounds are entrapped into thin films of a food grade microencapsulating agent. The core may be composed of just one or several ingredients and the wall may be single or double-layered. The retention of these cores is governed by their chemical functionality, solubility, polarity and volatility.
Six reasons for applying microencapsulation in food industry: to reduce the core reactivity with environmental factors; to decrease the transfer rate of the core material to the outside environment; to promote easier handling; to control the release of the core material; to mask the core taste and finally to dilute the core material when it is required to be used in very minute amounts. In its simplest form, a microcapsule is a small sphere with a uniform wall around it. The material inside the microcapsule is referred to as the core, internal phase or Wall, whereas the wall is sometimes called shell, coating, wall material or membrane. Practically, the core may be a crystalline material, a jagged adsorbent particle, an emulsion, a suspension of solids or a suspension of smaller microcapsules.
SPRAY DRYING
Spray drying is the most common method used for microencapsulation because it is economical. It is also one of the oldest encapsulation method. The basic steps involved in spray drying include preparation of the dispersion or emulsion to be processed, homogenization of the dispersion, and atomization of the mass into the drying chamber. The materials used for the capsule are food grade hydrocolloids such as modified starch, maltodextrin and gums (Gibbs et al., 1999). The material should have good emulsifying properties, be a good film former, have low viscosity and provide good protection to the encapsulated ingredient. The carrier is hydrated in water. The ingredient to be encapsulated is added to the carrier and homogenized. An emulsifier may also be added at this stage. The ratio of encapsulant to carrier is usually 1:4 (Gibbs et al., 1999) but this can be optimized for each individual ingredient. This mixture is then fed into the spray dryer and atomized with a nozzle or spinning wheel. Water is evaporated by the hot air (100-160 ̊ C) and the small particles are deposited to the bottom of the spray dryer where they are collected
FLUIDISED BED COATING
This process is also known as air suspension coating. It is accomplished by suspending solid particles of the core material in an upward moving stream of air, which can be heated or
cooled. Once this ‘fluid’ bed of particles has reached the required temperature, it is sprayed from the top by atomized particles of coating wall material. This wall material can be either in a molten state or dissolved in an evaporable solvent. The molten coating is hardened by solidification in cold air. The solvent-based coating is hardened by evaporation of the solvent using hot air (Risch and Reineccius, 1995). The coating can be selected from cellulose derivatives, dextrins, emulsifiers, lipids, protein derivatives and starch derivatives (Shahidi and Han, 1993). A thin layer of coating is deposited onto the core material and full coverage is achieved by multiple passes through the air stream
CONCLUSON
Microencapsulation means packaging an active ingredient inside a capsule ranging in size from one micron to several millimeters. The capsule protects the active ingredient from its surrounding environment until an appropriate time. Then, the material escapes through the capsule wall by various means, including rupture, dissolution, melting or diffusion. Microencapsulation is both an art and a science. There's no ONE way to do it, and each new application provides a fresh challenge. Solving these riddles requires experience, skill and the mastery of many different technologies
Microencapsulation system offers potential advantages over conventional drug delivery systems and also established as unique carrier systems for many pharmaceuticals (targeted drug delivery systems) and food industry. Although significant advances have been made in the field of microencapsulation, still many challenges need to be rectified during the appropriate selection of core materials, coating materials and process techniques.