August 11, 2016
Microencapsulation is one of the most promising techniques used in the pharmaceutical, agricultural, cosmetic, nutraceutical and food industries since its inception years ago. Microencapsulation is a process that produces solid particles called microcapsules with varied shapes and sizes, usually ranging between 1 µm and 1,000 µm in diameter.1,2,3 A microcapsule is a reservoir-type system with a well-defined encapsulated substance surrounded by an encapsulating material. The encapsulated substance is referred to as the core, fill or internal phase, while the encapsulating material may be called the coating, membrane, shell, carrier or external phase.4 Although used interchangeably in scientific literature, microcapsules are structurally different than microspheres. Microspheres are monolithic particulates comprised of a continuous polymeric phase in which active ingredients are dispersed throughout a matrix.4,5,6
Microcapsules are generally classified into three main categories: mononuclear, polynuclear and matrix type. Mononuclear capsules are the most common type of microcapsule, consisting of a core surrounded by the shell, whereas polynuclear capsules have many cores enclosed within a single shell. Conversely, in matrix-type microcapsules, the core material is distributed homogeneously into the shell material.7
Microencapsulation has a wide variety of applications in food and nutraceutical industries.6,8,9,10,11,12
• Protects core materials from heat, moisture, air and light
• Hinders the transfer rate or evaporation of core materials to the external environment
• Changes liquids into free-flowing solids
• Controls the release rate of core materials
• Masks the organoleptic properties of core materials
• Improves compatibility between different materials within the same microcapsule
• Extends the stability of sensitive core materials
The microencapsulation process can be divided into two distinct stages— first, the creation of small particles and second, stabilization of the particles created. Microcapsules can be tailored to a specific application by using innovative techniques such as varying the polymer ratios or changing the molecular weight of the polymer, thus providing an optimal delivery system for food ingredients.13 Several functional food and nutraceutical ingredients have been or can be encapsulated, including plant extracts, flavors, minerals, vitamins, amino acids, vegetable and marine oils, probiotics and enzymes.
Functional properties of microcapsules are not only influenced by the chosen method of microencapsulation, but also the physical characteristics of the intended core and shell materials. Ideal encapsulating agents should exhibit good rheological properties; appropriately disperse or emulsify; properly seal and hold encapsulated material; and provide protection to the core against adverse conditions such as heat, light, humidity and oxygen. Although microencapsulation materials should be soluble in commonly used solvents in the food industry, the microencapsulating agents should not exhibit reactivity with the encapsulating materials.4,11,14 Maltodextrins, cyclodextrins, starch, carboxymethyl cellulose, methyl cellulose, gum acacia, carrageenan, sodium alginate, wax and gelatin are examples of commonly used coating materials in food applications. It is common practice to use coating materials either in combination with or by adding modifiers such as oxygen scavengers, antioxidants, chelating agents and surfactants to achieve the desired functionality.
Multiple microencapsulation methods have been successfully used, including spray drying, spray cooling or chilling, solvent evaporation, polymerization, fluidized-bed coating, extrusion, lyophilization, coacervation and liposome entrapment.11,15,16,17,18,19,20 The selection of the microencapsulation method depends on the physicochemical properties of the core and coating materials, and most importantly, the intended application of the encapsulated ingredients.
Spray drying is perhaps the most widely used microencapsulation technique in the food industry; it is economical, flexible and produces high-quality microcapsules.21,22 In this process, a core material is dispersed or suspended in a coating solution, then the mixture is nebulized and subjected to a controlled stream of air.23,24 The circulating air in the chamber causes rapid vaporization of solvent and, in turn, forms a microencapsulated product. Typical equipment may include a spray dryer, heater, atomizer, spray chamber, blower or fan, cyclone and product reservoir.25 As with the food industry, this is the preferred method in the nutraceutical industry. However, there are some limitations with this technique, such as the limited availability of coating materials that can be used for applications, and it is not recommended for heat-sensitive core materials due to the high temperatures used during the drying phase of the process.
Despite the success and commonality of microencapsulation in the pharmaceutical and cosmetic industries—especially in the development of controlled and target drug delivery systems—this technology has only scratched the surface of the food and nutraceutical industries. As of now, in comparison, this technology is still far from fully developed, and has yet to become the method of choice when dealing with food and nutraceutical ingredients. Often the greatest challenge in these industries is with the selection of optimal microencapsulating techniques and encapsulating materials. Also consider possible microencapsulation challenges presented when moving from the bench scale to the manufacturing process. The development time and specific dedicated equipment required to invest in this technology can be substantial. The lower profit margins of the food industry in comparison to other market sectors become a factor when evaluating novel technologies.14,26
Although significant progress has been made in the field of microencapsulation, advancement is still required in order to further develop this technology. Improvements to existing microencapsulation methods, innovative coating materials and increased affordability will expand microencapsulation to achieve its fullest potential in the food and nutraceutical arenas.
Looking for ways to manage and reduce the risks in partnering with contract manufacturers? Join us for the Contract Manufacturing: Raising the Bar on Delivering Quality workshop on Saturday, Oct. 8, at SupplySide West 2016.
Naeem Shaikh, Ph.D., leads the formulation team and drives the research that helps inspire and propel the product momentum at National Enzyme Co (nationalenzyme.com). As an accomplished and published scientist, Shaikh leverages 28 years of renowned experience, with previous research ranging from microencapsulation to release methods for solid and liquid dosage forms.
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20Kirby CJ, Gregoriadis G. “A simple procedure for preparing liposomes capable of high encapsulation efficiency under mild conditions." Liposome Technology. CRC Press. 1984(1).
21Burgain J et al. “Encapsulation of probiotic living cells: From laboratory scale to industrial applications." J Food Eng. 2011;104(4):467-483.
22Peighambardoust SH, Tafti AG, Hesari J. “Application of spray drying for preservation of lactic acid starter cultures: A review." Trends Food Sci Technol. 2011;22(5):215-224.
23De Vos P et al. “Encapsulation for preservation of functionality and targeted delivery of bioactive food components." Int Dairy J. 2010;20(4):292-302.
24Gharsallaoui A et al. “Applications of spray-drying in microencapsulation of food ingredients: An overview." Food Research International. 2007;40(9):1107-1121.
25Lehman L et al. The Theory and Practice of Industrial Pharmacy, 3rd ed. 1976;412.
26Gouin S. “Microencapsulation: Industrial appraisal of existing technologies and trends." Trends Food Sci Technol. 2004;15(7-8):330-347.
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