Introduction: Encapsulation is the process of enclosing or entrapping a core material (liquid, gas, solid particles, cells, dissolved active ingredients, etc.) inside a solid shell or within a solid or liquid matrix for the purpose of controlling or triggering the core material's release, immobilization, isolation, or protection. The encapsulated material is known as the core material, and the carrier material used for envelopment or entrapment is known as the shell material. Micro and nano-encapsulation are rapidly expanding to solve potential bioavailability problems, offering new solutions to the food industry 's challenges. Microparticles are particles between 3 and 800 μm in diameter, and nanoparticles are colloidal particles between 10 and 1000 nm in diameter. Microencapsulation is able to transform the liquid state into free-flowing powder form, which is readily incorporated into food products without changing the sensory quality of the food product. Ink or dye for carbonless copy papers, liquid crystals for microparticle-based displays, phase change material for smart textiles, high molecular weight gases for ultrasound contrast imaging, genetic material for in vitro compartmentalization, active food ingredients for functional food products, enzymes for biocatalytic reactors, drugs, pesticides, fragrances, antimicrobials are examples of core materials that have been encapsulated. Reservoir, matrix and the combination of reservoir and matrix systems are the main types of encapsulates. Reservoir encapsulates have an outer shell which surrounds the active agent and can be produced by one or multiple reservoir chambers. However, the active agent exists as droplets or dispersed in the wall material in the matrix system. Encapsulation technology has been used in food processing to provide an effective barrier against natural environmental parameters such as light, oxygen, and free radicals, among others. The science of encapsulation deals with the manufacture, analytical evaluation, and application of encapsulated products. Despite the passage of time, the technology that has been developed for the food industry remains relatively unsophisticated compared to many other felds of application. This is a consequence of the limitations imposed on the food industry for the use of edible, low-cost ingredients and processing Encapsulation Matrix The coating material (also known as shell, wall material, or encapsulating agent) used for encapsulating any functional food is the ‘Encapsulation Matrix’. An ideal encapsulating matrix should have the following characteristics: Good rheological properties at high concentrations Capability to disperse or emulsify the active material Nonreactivity with the material to be encapsulated Ability to seal and hold the active material Solubility in solvents acceptable by the food industry Since a single coating material cannot have all the above characteristics alone, coating materials are employed either in combination or with modifiers such as oxygen scavengers, antioxidants, chelating agents, and surfactants. Generally, the constituents for coating material are carbohydrate polymers, proteins, and lipid. Carbohydrate Polymers: The two major processes used for encapsulation of food flavorings are spray drying and extrusion, both of which depend primarily on carbohydrates used for the encapsulation matrix. The commonly used carbohydrate polymers are projected in the table below. Origin Plant Carbohydrate Polymer Modified Starch, Maltodextrins, Corn Syrup Solids, Sucrose, Cellulose and its derivatives, Agar, Exudate Gums etc. Animal/Microbial Xanthan, Dextran, Gellan, Chitosan Marine Alginate, Carrageenan Proteins: Proteins posses many properties that allow them to be an essential coating material in encapsulation. Gelatin is the most used protein for this purpose, but other proteins such as sodium caseinate, whey protein and soy concentrate, and soy protein isolates have been utilized. Protein-encapsulated tallow and vegetable oils have been applied to produce animal feed. Proteins can also be used, together with other coating materials, to form microcapsules. The table below projects different proteins used in encapsulation. Origin Protein Plant Gluten Animal/Microbial Whey protein, Gelatin, Caseins Marine - Lipid: Lipids are also somewhat used in the encapsulation of functional foods. They are: Origin Carbohydrate Polymer Plant Fatty Acids, Glycerides, Waxes, Phospholipids Animal/Microbial Fatty acids/ alcohols, Waxes, Glycerides, Phospholipids Marine - Inorganic Materials: Some inorganic materials including aluminum oxide, tripolyphosphate or silicone dioxides have been found useful in encapsulating different foods. They can be utilized alone or in combination with other materials. Encapsulated Ingredients and Their Applications Numerous kinds of food materials are encapsulated in the food industry that serve a variety of purposes. Various properties of active materials may be changed/modified by encapsulation. For example, handling and flow properties can be improved by converting a liquid to a solid encapsulated form. Hygroscopic materials can be protected from moisture. The stability of functional ingredients that are volatile or sensitive to heat, light, or oxidation can be protected, thereby extending their shelf life. Materials that are otherwise incompatible can be mixed and utilized safely together. Using food fortification as an example, microencapsulation can mask the undesirable taste of some nutrients (i.e., minerals) that may be imparted by the free forms, thus enabling the production of functional foods, say, a nutraceutical beverage, with desirable sensory properties. Acidulants: Acidulants facilitate the development of a wide variety of textural effects in foods because of their interaction with other macro- and micromolecules such as proteins, starches, pectins, and gum Unencapsulated food acids can react with food ingredients and cause a variety of negative effects. These include decreased shelf life of citrus-favored and starch-containing foods (e.g., pudding and pie fillings, where the acid hydrolyzes the starch), flavor loss, color degradation, and ingredient separation. Encapsulated food acids solve these and other issues by preventing oxidation and allowing for controlled release under specific conditions. Furthermore, encapsulated acids reduce hygroscopicity, dusting, and provide high flowability without clumping. Flavoring Agents: In the food industry, the development and production of artificial or natural flavors and spices is a growing field. Most favor compounds used are liquids at room temperature, and their constituents are sensitive to air, light, irradiation, and elevated temperatures. Furthermore, these favor concentrates are oily and lipophilic materials that can be challenging to work with. As a result, a process to convert these favor compounds into a more usable form is required. One of the goals of encapsulation in the food industry is to convert liquid ingredients into dry powders. Microencapsulated favors offer the convenience of a solid form over a liquid form, as well as lower volatility and oxidation. Microencapsulation has emerged as an appealing method for converting liquid food additives into stable, free-flowing powders that are easier to handle and incorporate into a dry food system. Sweeteners: Sweeteners are often subjected to the effects of moisture and/or temperature. Encapsulation of sweeteners, namely, sugars and other nutritive or artificial sweeteners, reduces their hygroscopicity, improves their flowability, and prolongs their sweetness perception. Sugar that has been encapsulated with fat and incorporated into chewing gum requires more shear and higher temperatures to release its sweetness than uncoated sugar, which dissolves more rapidly in the mouth. Colorants: Natural colors such as annatto, carotene, and turmeric have solubility issues and may produce dust clouds when used. Encapsulated colors are easier to work with and provide improved solubility, oxidation stability, and control over stratification from dry blends. Synthetic colors, like other food ingredients, can be encapsulated to improve their stability. A technique used for solubilizing oily substances in micellar solutions of protein and carbohydrates to achieve encapsulation of two oil-soluble pigments, paprika oleoresin, and carotene. Lipids: Lipids contribute to more than 30% of the dietary energy of North Americans, and similar figures apply to many other affluent societies. Use of lipids/fats are commonplace in food processing practices, but the susceptibility of lipids to oxidative degradation during processing and storage is always a concern; particular attention must be paid to foodstuffs containing higher proportions of polyunsaturated fatty acids (PUFA). One possible way to protect lipids against oxidative deterioration is via encapsulation. Early research in this area was mainly focused on production of encapsulated lipids for animal feed, but more recently, encapsulated high-fat powders or shortenings have become available in human food formulation Others: Lipids, Enzymes, Vitamins, and minerals also play a vital role in application encapsulated products in the food industry. Controlled-Release Mechanisms and their Effects Controlled Release is defined as “Modification of the rate or place at which an active substance is released.” Encapsulation allows reactive ingredients to be separated from the environment until their release is desired. Though separation is the goal of encapsulation, release mechanisms of the core material must also be considered. Controlled release technology can help a wide variety of nutritional supplements deliver their payloads more effectively while heightening produce resale frequency for brands and retailers. In essence, a well-controlled release of core material is a very important property of microcapsules. Addition of small amounts of nutrients to a food system may not affect its properties significantly, however incorporating high levels of the nutrient either to meet certain requirements or to treat an ailment will most often result in unstable and often unpalatable foods. Examples of such nutrients include fortification with calcium, vitamins, polyunsaturated fatty acids, and so on, and the associated grittiness, medicinal and oxidized taste, respectively. The two principal modes of controlled release are ‘Delayed’ and ‘Sustained’ release. Release Rate: Release rates from a single microcapsule are typically zero, half, or first order. When the core is a pure material that can be released as a pure material through the wall of a microcapsule, zeroorder release occurs. Half-order release is more common with matrix particles, whereas firstorder release is more common when the core material is a solution trapped within a solid matrix. A desired concentration of solute is reached as the solute material is released from the capsule. A microcapsule mixture will contain a variety of capsules with varying sizes and wall thicknesses. Because of the ensemble of microcapsules, the effect is to produce a release rate that is different from zero-, half-, or first-order. Release Mechanisms: The coating not only protects the core material from moisture, light, oxygen, other food ingredients, and other external agents, but it also allows/assists in controlling core material release. Thus, the release of the core material is determined by the particle type and geometry, as well as the wall material used to form the microcapsule. These factors determine the capsule's release mechanism, which may be based on solvent effects, diffusion, degradation, or particle fracture. Fracturation or Pressure-Activated Release: External forces, such as pressure, shearing, or ultrasonics, or internal forces, as in a microcapsule with a permeation-selective coating, can fracture or break open the coating. Volatile release is controlled here. Diffusion: The rate at which the core material can pass through the outer wall is determined by the kinetic relationship between the core and wall materials. It is governed strictly by the chemical properties of the micro-capsule as well as the physical properties of the wall material, such as matrix structure and pore sizes. Diffusion is a permeation process that is triggered by a concentration gradient or interchain attractive forces. In other words, it is governed by a component's solubility in the matrix (which creates a concentration gradient in the matrix to drive diffusion) and permeability through the matrix. Controlled release is frequently accomplished through a diffusion-controlled process. Melting-Activated Release: The integrity of the coating can be destroyed by thermal means. This mechanism of release involves the melting of the capsule wall (or a protective coating that has been placed on the capsule wall) to release the active material. The hydrophobic coating and core material must be immiscible with one another in order to avoid migration of the active ingredient through the wall material. This limits the usefulness of the technique for many favor applications. On the other hand, an already encapsulated favor prepared by spray drying can be coated with a hydrophobic matrix via centrifugal coating or the fluidized bed technique. In this manner, the secondary coating on the favor provides melt release properties. Solvent-Activated Release: Solvent-activated release is the most common controlledrelease mechanism used in the food industry. Since most encapsulating matrices are water-soluble, the water in the food product dissolves away the microcapsule thereby liberating its content to the food, or it causes the capsule to swell to either begin or enhance the release of the core material. However, water-insoluble coatings can also be dissolved by selecting an appropriate solvent. Encapsulated agents are often added to dry food products such as dry beverages, and cake and soup mixes. The encapsulated favors in these products are released upon rehydration. Biodegradation and pH-Sensitive Release: Solvent-activated release is the most common controlled-release mechanism used in the food industry. Since most encapsulating matrices are water-soluble, the water in the food product dissolves away the microcapsule thereby liberating its content to the food, or it causes the capsule to swell to either begin or enhance the release of the core material. However, waterinsoluble coatings can also be dissolved by selecting an appropriate solvent. Encapsulated agents are often added to dry food products such as dry beverages, and cake and soup mixes. The encapsulated favors in these products are released upon rehydration. Their release may be a sudden burst, or a continued or delayed delivery regulated by controlling the rate of wall solubility, the swelling of the wall material, pH effects, or changes in the ionic strength of the surrounding medium. Conclusion: There are various techniques available that could be used to encapsulate the functional ingredients. Different functional ingredients might require different encapsulation techniques, drying techniques and wall materials to meet the specific physicochemical and molecular requirements, as well as its desirability. Encapsulation is an effective protection method by providing a protective shell barrier on the functional ingredient with many advantages. Encapsulation of functional ingredients achieves excellent characteristics of protection, stabilization, solubility and controlled release of the active agent. Encapsulation can enhance the application in food industry by fortify the food products with specific healthy benefits and desired functionality. It can resolve the deficiencies of micronutrients worldwide. Transform the lab scale encapsulation technique into industrial scale represents the major challenge and need to further explore and overcome in the future study.
